Fixed misspelled word 'from'

boost::core::is_same is deprecated, so use the one from Boost.TypeTraits
instead.

.drone.star

@@ -0,0 +1,36 @@
+# Use, modification, and distribution are
+# subject to the Boost Software License, Version 1.0. (See accompanying
+# file LICENSE.txt)
+#
+# Copyright Rene Rivera 2020.
+
+# For Drone CI we use the Starlark scripting language to reduce duplication.
+# As the yaml syntax for Drone CI is rather limited.
+#
+#
+globalenv={}
+linuxglobalimage="cppalliance/droneubuntu1604:1"
+windowsglobalimage="cppalliance/dronevs2019"
+
+def main(ctx):
+  return [
+  linux_cxx("TOOLSET=gcc COMPILER=g++ CXXSTD=03,11 Job 0", "g++", packages="", buildtype="boost", buildscript="drone", image=linuxglobalimage, environment={'TOOLSET': 'gcc', 'COMPILER': 'g++', 'CXXSTD': '03,11', 'DRONE_JOB_UUID': 'b6589fc6ab'}, globalenv=globalenv),
+  linux_cxx("TOOLSET=gcc COMPILER=g++-4.7 CXXSTD=03,11 Job 1", "g++-4.7", packages="g++-4.7", buildtype="boost", buildscript="drone", image=linuxglobalimage, environment={'TOOLSET': 'gcc', 'COMPILER': 'g++-4.7', 'CXXSTD': '03,11', 'DRONE_JOB_UUID': '356a192b79'}, globalenv=globalenv),
+  linux_cxx("TOOLSET=gcc COMPILER=g++-4.8 CXXSTD=03,11 Job 2", "g++-4.8", packages="g++-4.8", buildtype="boost", buildscript="drone", image=linuxglobalimage, environment={'TOOLSET': 'gcc', 'COMPILER': 'g++-4.8', 'CXXSTD': '03,11', 'DRONE_JOB_UUID': 'da4b9237ba'}, globalenv=globalenv),
+  linux_cxx("TOOLSET=gcc COMPILER=g++-4.9 CXXSTD=03,11 Job 3", "g++-4.9", packages="g++-4.9", buildtype="boost", buildscript="drone", image=linuxglobalimage, environment={'TOOLSET': 'gcc', 'COMPILER': 'g++-4.9', 'CXXSTD': '03,11', 'DRONE_JOB_UUID': '77de68daec'}, globalenv=globalenv),
+  linux_cxx("TOOLSET=gcc COMPILER=g++-5 CXXSTD=03,11,14,1z Job 4", "g++-5", packages="g++-5", buildtype="boost", buildscript="drone", image=linuxglobalimage, environment={'TOOLSET': 'gcc', 'COMPILER': 'g++-5', 'CXXSTD': '03,11,14,1z', 'DRONE_JOB_UUID': '1b64538924'}, globalenv=globalenv),
+  linux_cxx("TOOLSET=gcc COMPILER=g++-6 CXXSTD=03,11,14,1z Job 5", "g++-6", packages="g++-6", buildtype="boost", buildscript="drone", image=linuxglobalimage, environment={'TOOLSET': 'gcc', 'COMPILER': 'g++-6', 'CXXSTD': '03,11,14,1z', 'DRONE_JOB_UUID': 'ac3478d69a'}, globalenv=globalenv),
+  linux_cxx("TOOLSET=gcc COMPILER=g++-7 CXXSTD=03,11,14,17 Job 6", "g++-7", packages="g++-7", buildtype="boost", buildscript="drone", image="cppalliance/droneubuntu1404:1", environment={'TOOLSET': 'gcc', 'COMPILER': 'g++-7', 'CXXSTD': '03,11,14,17', 'DRONE_JOB_UUID': 'c1dfd96eea'}, globalenv=globalenv),
+  linux_cxx("TOOLSET=clang COMPILER=clang++ CXXSTD=03,11 Job 7", "clang++", packages="", buildtype="boost", buildscript="drone", image=linuxglobalimage, environment={'TOOLSET': 'clang', 'COMPILER': 'clang++', 'CXXSTD': '03,11', 'DRONE_JOB_UUID': '902ba3cda1'}, globalenv=globalenv),
+  linux_cxx("TOOLSET=clang COMPILER=clang++-3.5 CXXSTD=03, Job 8", "clang++-3.5", packages="clang-3.5 libstdc++-4.9-dev", llvm_os="precise", llvm_ver="3.5", buildtype="boost", buildscript="drone", image=linuxglobalimage, environment={'TOOLSET': 'clang', 'COMPILER': 'clang++-3.5', 'CXXSTD': '03,11,14,1z', 'DRONE_JOB_UUID': 'fe5dbbcea5'}, globalenv=globalenv),
+  linux_cxx("TOOLSET=clang COMPILER=clang++-3.6 CXXSTD=03, Job 9", "clang++-3.6", packages="clang-3.6", llvm_os="precise", llvm_ver="3.6", buildtype="boost", buildscript="drone", image=linuxglobalimage, environment={'TOOLSET': 'clang', 'COMPILER': 'clang++-3.6', 'CXXSTD': '03,11,14,1z', 'DRONE_JOB_UUID': '0ade7c2cf9'}, globalenv=globalenv),
+  linux_cxx("TOOLSET=clang COMPILER=clang++-3.7 CXXSTD=03, Job 10", "clang++-3.7", packages="clang-3.7", llvm_os="precise", llvm_ver="3.7", buildtype="boost", buildscript="drone", image=linuxglobalimage, environment={'TOOLSET': 'clang', 'COMPILER': 'clang++-3.7', 'CXXSTD': '03,11,14,1z', 'DRONE_JOB_UUID': 'b1d5781111'}, globalenv=globalenv),
+  linux_cxx("TOOLSET=clang COMPILER=clang++-3.8 CXXSTD=03, Job 11", "clang++-3.8", packages="clang-3.8 libstdc++-4.9-dev", llvm_os="precise", llvm_ver="3.8", buildtype="boost", buildscript="drone", image=linuxglobalimage, environment={'TOOLSET': 'clang', 'COMPILER': 'clang++-3.8', 'CXXSTD': '03,11,14,1z', 'DRONE_JOB_UUID': '17ba079149'}, globalenv=globalenv),
+  linux_cxx("TOOLSET=clang COMPILER=clang++-3.9 CXXSTD=03, Job 12", "clang++-3.9", packages="clang-3.9 libstdc++-4.9-dev", llvm_os="precise", llvm_ver="3.9", buildtype="boost", buildscript="drone", image=linuxglobalimage, environment={'TOOLSET': 'clang', 'COMPILER': 'clang++-3.9', 'CXXSTD': '03,11,14,1z', 'DRONE_JOB_UUID': '7b52009b64'}, globalenv=globalenv),
+  linux_cxx("TOOLSET=clang COMPILER=clang++-4.0 CXXSTD=03, Job 13", "clang++-4.0", packages="clang-4.0", llvm_os="trusty", llvm_ver="4.0", buildtype="boost", buildscript="drone", image="cppalliance/droneubuntu1404:1", environment={'TOOLSET': 'clang', 'COMPILER': 'clang++-4.0', 'CXXSTD': '03,11,14,1z', 'DRONE_JOB_UUID': 'bd307a3ec3'}, globalenv=globalenv),
+  linux_cxx("TOOLSET=clang COMPILER=clang++-5.0 CXXSTD=03, Job 14", "clang++-5.0", packages="clang-5.0", llvm_os="trusty", llvm_ver="5.0", buildtype="boost", buildscript="drone", image="cppalliance/droneubuntu1404:1", environment={'TOOLSET': 'clang', 'COMPILER': 'clang++-5.0', 'CXXSTD': '03,11,14,1z', 'DRONE_JOB_UUID': 'fa35e19212'}, globalenv=globalenv),
+  osx_cxx("TOOLSET=clang COMPILER=clang++ CXXSTD=03,11,1 Job 15", "clang++", packages="", buildtype="boost", buildscript="drone", environment={'TOOLSET': 'clang', 'COMPILER': 'clang++', 'CXXSTD': '03,11,14,1z', 'DRONE_JOB_UUID': 'f1abd67035'}, globalenv=globalenv),
+    ]
+
+# from https://github.com/boostorg/boost-ci
+load("@boost_ci//ci/drone/:functions.star", "linux_cxx","windows_cxx","osx_cxx","freebsd_cxx")

.drone/drone.sh

@@ -0,0 +1,37 @@
+#!/bin/bash
+
+# Copyright 2020 Rene Rivera, Sam Darwin
+# Distributed under the Boost Software License, Version 1.0.
+# (See accompanying file LICENSE.txt or copy at http://boost.org/LICENSE_1_0.txt)
+
+set -e
+export TRAVIS_BUILD_DIR=$(pwd)
+export DRONE_BUILD_DIR=$(pwd)
+export TRAVIS_BRANCH=$DRONE_BRANCH
+export VCS_COMMIT_ID=$DRONE_COMMIT
+export GIT_COMMIT=$DRONE_COMMIT
+export REPO_NAME=$DRONE_REPO
+export PATH=~/.local/bin:/usr/local/bin:$PATH
+
+if [ "$DRONE_JOB_BUILDTYPE" == "boost" ]; then
+
+echo '==================================> INSTALL'
+
+BOOST_BRANCH=develop && [ "$TRAVIS_BRANCH" == "master" ] && BOOST_BRANCH=master || true
+cd ..
+git clone -b $BOOST_BRANCH --depth 1 https://github.com/boostorg/boost.git boost-root
+cd boost-root
+git submodule update --init tools/build
+git submodule update --init libs/config
+git submodule update --init tools/boostdep
+cp -r $TRAVIS_BUILD_DIR/* libs/optional
+python tools/boostdep/depinst/depinst.py optional
+./bootstrap.sh
+./b2 headers
+
+echo '==================================> SCRIPT'
+
+echo "using $TOOLSET : : $COMPILER ;" > ~/user-config.jam
+./b2 libs/optional/test toolset=$TOOLSET cxxstd=$CXXSTD
+
+fi

.github/workflows/ci.yml

@@ -0,0 +1,396 @@
+name: GitHub Actions CI
+
+on:
+  pull_request:
+  push:
+    branches:
+      - master
+      - develop
+      - githubactions*
+      - feature/**
+      - fix/**
+      - pr/**
+
+concurrency:
+  group: ${{format('{0}:{1}', github.repository, github.ref)}}
+  cancel-in-progress: true
+
+env:
+  NET_RETRY_COUNT: 5
+
+jobs:
+  posix:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - name: "TOOLSET=gcc COMPILER=g++ CXXSTD=03,11 Job 0"
+            buildtype: "boost"
+            packages: ""
+            packages_to_remove: ""
+            os: "ubuntu-20.04"
+            container: "ubuntu:16.04"
+            cxx: "g++"
+            sources: ""
+            llvm_os: ""
+            llvm_ver: ""
+            toolset: "gcc"
+            compiler: "g++"
+            cxxstd: "03,11"
+          - name: "TOOLSET=gcc COMPILER=g++-4.7 CXXSTD=03,11 Job 1"
+            buildtype: "boost"
+            packages: "g++-4.7"
+            packages_to_remove: ""
+            os: "ubuntu-20.04"
+            container: "ubuntu:16.04"
+            cxx: "g++-4.7"
+            sources: ""
+            llvm_os: ""
+            llvm_ver: ""
+            toolset: "gcc"
+            compiler: "g++-4.7"
+            cxxstd: "03,11"
+          - name: "TOOLSET=gcc COMPILER=g++-4.8 CXXSTD=03,11 Job 2"
+            buildtype: "boost"
+            packages: "g++-4.8"
+            packages_to_remove: ""
+            os: "ubuntu-20.04"
+            container: "ubuntu:16.04"
+            cxx: "g++-4.8"
+            sources: ""
+            llvm_os: ""
+            llvm_ver: ""
+            toolset: "gcc"
+            compiler: "g++-4.8"
+            cxxstd: "03,11"
+          - name: "TOOLSET=gcc COMPILER=g++-4.9 CXXSTD=03,11 Job 3"
+            buildtype: "boost"
+            packages: "g++-4.9"
+            packages_to_remove: ""
+            os: "ubuntu-20.04"
+            container: "ubuntu:16.04"
+            cxx: "g++-4.9"
+            sources: ""
+            llvm_os: ""
+            llvm_ver: ""
+            toolset: "gcc"
+            compiler: "g++-4.9"
+            cxxstd: "03,11"
+          - name: "TOOLSET=gcc COMPILER=g++-5 CXXSTD=03,11,14,1z Job 4"
+            buildtype: "boost"
+            packages: "g++-5"
+            packages_to_remove: ""
+            os: "ubuntu-20.04"
+            container: "ubuntu:16.04"
+            cxx: "g++-5"
+            sources: ""
+            llvm_os: ""
+            llvm_ver: ""
+            toolset: "gcc"
+            compiler: "g++-5"
+            cxxstd: "03,11,14,1z"
+          - name: "TOOLSET=gcc COMPILER=g++-6 CXXSTD=03,11,14,1z Job 5"
+            buildtype: "boost"
+            packages: "g++-6"
+            packages_to_remove: ""
+            os: "ubuntu-20.04"
+            container: "ubuntu:16.04"
+            cxx: "g++-6"
+            sources: ""
+            llvm_os: ""
+            llvm_ver: ""
+            toolset: "gcc"
+            compiler: "g++-6"
+            cxxstd: "03,11,14,1z"
+          - name: "TOOLSET=gcc COMPILER=g++-7 CXXSTD=03,11,14,17 Job 6"
+            buildtype: "boost"
+            packages: "g++-7"
+            packages_to_remove: ""
+            os: "ubuntu-20.04"
+            container: "ubuntu:16.04"
+            cxx: "g++-7"
+            sources: ""
+            llvm_os: ""
+            llvm_ver: ""
+            toolset: "gcc"
+            compiler: "g++-7"
+            cxxstd: "03,11,14,17"
+          - name: "TOOLSET=clang COMPILER=clang++ CXXSTD=03,11 Job 7"
+            buildtype: "boost"
+            packages: "clang"
+            packages_to_remove: ""
+            os: "ubuntu-22.04"
+            container: "ubuntu:18.04"
+            cxx: "clang++"
+            sources: ""
+            llvm_os: ""
+            llvm_ver: ""
+            toolset: "clang"
+            compiler: "clang++"
+            cxxstd: "03,11"
+          - name: "TOOLSET=clang COMPILER=clang++-3.5 CXXSTD=03, Job 8"
+            buildtype: "boost"
+            packages: "clang-3.5 libstdc++-4.9-dev"
+            packages_to_remove: ""
+            os: "ubuntu-20.04"
+            container: "ubuntu:16.04"
+            cxx: "clang++-3.5"
+            sources: ""
+            llvm_os: "precise"
+            llvm_ver: "3.5"
+            toolset: "clang"
+            compiler: "clang++-3.5"
+            cxxstd: "03,11,14"
+          - name: "TOOLSET=clang COMPILER=clang++-3.6 CXXSTD=03, Job 9"
+            buildtype: "boost"
+            packages: "clang-3.6"
+            packages_to_remove: ""
+            os: "ubuntu-20.04"
+            container: "ubuntu:16.04"
+            cxx: "clang++-3.6"
+            sources: ""
+            llvm_os: "precise"
+            llvm_ver: "3.6"
+            toolset: "clang"
+            compiler: "clang++-3.6"
+            cxxstd: "03,11,14"
+          - name: "TOOLSET=clang COMPILER=clang++-3.7 CXXSTD=03, Job 10"
+            buildtype: "boost"
+            packages: "clang-3.7"
+            packages_to_remove: ""
+            os: "ubuntu-20.04"
+            container: "ubuntu:16.04"
+            cxx: "clang++-3.7"
+            sources: ""
+            llvm_os: "precise"
+            llvm_ver: "3.7"
+            toolset: "clang"
+            compiler: "clang++-3.7"
+            cxxstd: "03,11,14"
+          - name: "TOOLSET=clang COMPILER=clang++-3.8 CXXSTD=03, Job 11"
+            buildtype: "boost"
+            packages: "clang-3.8 libstdc++-4.9-dev"
+            packages_to_remove: ""
+            os: "ubuntu-20.04"
+            container: "ubuntu:16.04"
+            cxx: "clang++-3.8"
+            sources: ""
+            llvm_os: "precise"
+            llvm_ver: "3.8"
+            toolset: "clang"
+            compiler: "clang++-3.8"
+            cxxstd: "03,11,14"
+          - name: "TOOLSET=clang COMPILER=clang++-3.9 CXXSTD=03, Job 12"
+            buildtype: "boost"
+            packages: "clang-3.9 libstdc++-4.9-dev"
+            packages_to_remove: ""
+            os: "ubuntu-20.04"
+            container: "ubuntu:16.04"
+            cxx: "clang++-3.9"
+            sources: ""
+            llvm_os: "precise"
+            llvm_ver: "3.9"
+            toolset: "clang"
+            compiler: "clang++-3.9"
+            cxxstd: "03,11,14"
+          - name: "TOOLSET=clang COMPILER=clang++-4.0 CXXSTD=03, Job 13"
+            buildtype: "boost"
+            packages: "clang-4.0"
+            packages_to_remove: ""
+            os: "ubuntu-20.04"
+            container: "ubuntu:14.04"
+            cxx: "clang++-4.0"
+            sources: ""
+            llvm_os: "trusty"
+            llvm_ver: "4.0"
+            toolset: "clang"
+            compiler: "clang++-4.0"
+            cxxstd: "03,11,14"
+          - name: "TOOLSET=clang COMPILER=clang++-5.0 CXXSTD=03, Job 14"
+            buildtype: "boost"
+            packages: "clang-5.0"
+            packages_to_remove: ""
+            os: "ubuntu-22.04"
+            container: "ubuntu:18.04"
+            cxx: "clang++-5.0"
+            sources: ""
+            llvm_os: ""
+            llvm_ver: ""
+            toolset: "clang"
+            compiler: "clang++-5.0"
+            cxxstd: "03,11,14,1z"
+
+    runs-on: ${{ matrix.os }}
+    container: ${{ matrix.container }}
+
+    steps:
+      - name: Check if running in container
+        if: matrix.container != ''
+        run: echo "GHA_CONTAINER=${{ matrix.container }}" >> $GITHUB_ENV
+      - name: If running in container, upgrade packages
+        if: matrix.container != ''
+        run: |
+            if [ -f "/etc/debian_version" ]; then
+                echo "DEBIAN_FRONTEND=noninteractive" >> $GITHUB_ENV
+                export DEBIAN_FRONTEND=noninteractive
+                apt-get -o Acquire::Retries=$NET_RETRY_COUNT update
+                apt-get -o Acquire::Retries=$NET_RETRY_COUNT install -y sudo software-properties-common curl wget apt-transport-https ca-certificates
+                # Need (newer) git, and the older Ubuntu container may require requesting the key manually using port 80
+                curl -sSL --retry ${NET_RETRY_COUNT:-5} 'http://keyserver.ubuntu.com/pks/lookup?op=get&search=0xE1DD270288B4E6030699E45FA1715D88E1DF1F24' | sudo gpg --dearmor > /etc/apt/trusted.gpg.d/git-core_ubuntu_ppa.gpg
+                for i in {1..${NET_RETRY_COUNT:-3}}; do sudo -E add-apt-repository -y ppa:git-core/ppa && break || sleep 10; done
+                apt-get -o Acquire::Retries=$NET_RETRY_COUNT update
+                apt-get -o Acquire::Retries=$NET_RETRY_COUNT install -y g++ python libpython-dev git unzip libssl-dev build-essential libc++-helpers gcc-multilib g++-multilib pkgconf ccache
+            fi
+
+      - uses: actions/checkout@v2
+
+      - name: linux
+        shell: bash
+        env:
+          CXX: ${{ matrix.cxx }}
+          SOURCES: ${{ matrix.sources }}
+          LLVM_OS: ${{ matrix.llvm_os }}
+          LLVM_VER: ${{ matrix.llvm_ver }}
+          PACKAGES: ${{ matrix.packages }}
+          PACKAGES_TO_REMOVE: ${{ matrix.packages_to_remove }}
+          JOB_BUILDTYPE: ${{ matrix.buildtype }}
+          TOOLSET: ${{ matrix.toolset }}
+          COMPILER: ${{ matrix.compiler }}
+          CXXSTD: ${{ matrix.cxxstd }}
+          TRAVIS_BRANCH: ${{ github.base_ref }}
+          TRAVIS_OS_NAME: "linux"
+        run: |
+          echo '==================================> SETUP'
+          echo '==================================> PACKAGES'
+          set -e
+          if [ -n "$PACKAGES_TO_REMOVE" ]; then sudo apt-get purge -y $PACKAGES_TO_REMOVE; fi
+          echo ">>>>> APT: REPO.."
+          for i in {1..3}; do sudo -E apt-add-repository -y "ppa:ubuntu-toolchain-r/test" && break || sleep 2; done
+          
+          if test -n "${LLVM_OS}" ; then
+              wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | sudo apt-key add -
+              if test -n "${LLVM_VER}" ; then
+                  sudo -E apt-add-repository "deb http://apt.llvm.org/${LLVM_OS}/ llvm-toolchain-${LLVM_OS}-${LLVM_VER} main"
+              else
+                  # Snapshot (i.e. trunk) build of clang
+                  sudo -E apt-add-repository "deb http://apt.llvm.org/${LLVM_OS}/ llvm-toolchain-${LLVM_OS} main"
+              fi
+          fi
+          echo ">>>>> APT: UPDATE.."
+          sudo -E apt-get -o Acquire::Retries=3 update
+          if test -n "${SOURCES}" ; then
+              echo ">>>>> APT: INSTALL SOURCES.."
+              for SOURCE in $SOURCES; do
+                  sudo -E apt-add-repository ppa:$SOURCE
+              done
+          fi
+          echo ">>>>> APT: INSTALL ${PACKAGES}.."
+          sudo -E DEBIAN_FRONTEND=noninteractive apt-get -o Acquire::Retries=3 -y --no-install-suggests --no-install-recommends install ${PACKAGES}
+
+          echo '==================================> INSTALL AND COMPILE'
+          set -e
+          export TRAVIS_BUILD_DIR=$(pwd)
+          export TRAVIS_BRANCH=${TRAVIS_BRANCH:-$(echo $GITHUB_REF | awk 'BEGIN { FS = "/" } ; { print $3 }')}
+          export VCS_COMMIT_ID=$GITHUB_SHA
+          export GIT_COMMIT=$GITHUB_SHA
+          export REPO_NAME=$(basename $GITHUB_REPOSITORY)
+          export USER=$(whoami)
+          export CC=${CC:-gcc}
+          export PATH=~/.local/bin:/usr/local/bin:$PATH
+
+          if [ "$JOB_BUILDTYPE" == "boost" ]; then
+
+          echo '==================================> INSTALL'
+
+          BOOST_BRANCH=develop && [ "$TRAVIS_BRANCH" == "master" ] && BOOST_BRANCH=master || true
+          cd ..
+          git clone -b $BOOST_BRANCH --depth 1 https://github.com/boostorg/boost.git boost-root
+          cd boost-root
+          git submodule update --init tools/build
+          git submodule update --init libs/config
+          git submodule update --init tools/boostdep
+          cp -r $TRAVIS_BUILD_DIR/* libs/optional
+          python tools/boostdep/depinst/depinst.py optional
+          ./bootstrap.sh
+          ./b2 headers
+
+          echo '==================================> SCRIPT'
+
+          echo "using $TOOLSET : : $COMPILER ;" > ~/user-config.jam
+          ./b2 libs/optional/test toolset=$TOOLSET cxxstd=$CXXSTD
+
+          fi
+  osx:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - name: "TOOLSET=clang COMPILER=clang++ CXXSTD=03,11,1 Job 15"
+            buildtype: "boost"
+            packages: ""
+            os: "macos-11"
+            cxx: "clang++"
+            sources: ""
+            llvm_os: ""
+            llvm_ver: ""
+            toolset: "clang"
+            compiler: "clang++"
+            cxxstd: "03,11,14,17,2a"
+
+    runs-on: ${{ matrix.os }}
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: "osx"
+        shell: bash
+        env:
+          CXX: ${{ matrix.cxx }}
+          SOURCES: ${{ matrix.sources }}
+          LLVM_OS: ${{ matrix.llvm_os }}
+          LLVM_VER: ${{ matrix.llvm_ver }}
+          PACKAGES: ${{ matrix.packages }}
+          JOB_BUILDTYPE: ${{ matrix.buildtype }}
+          TOOLSET: ${{ matrix.toolset }}
+          COMPILER: ${{ matrix.compiler }}
+          CXXSTD: ${{ matrix.cxxstd }}
+          TRAVIS_BRANCH: ${{ github.base_ref }}
+          TRAVIS_OS_NAME: "osx"
+        run: |
+          echo '==================================> SETUP'
+          set -e
+          sudo mv /Library/Developer/CommandLineTools /Library/Developer/CommandLineTools.bck
+          echo '==================================> PACKAGES'
+          echo '==================================> INSTALL AND COMPILE'
+          set -e
+          export TRAVIS_BUILD_DIR=$(pwd)
+          export TRAVIS_BRANCH=${TRAVIS_BRANCH:-$(echo $GITHUB_REF | awk 'BEGIN { FS = "/" } ; { print $3 }')}
+          export VCS_COMMIT_ID=$GITHUB_SHA
+          export GIT_COMMIT=$GITHUB_SHA
+          export REPO_NAME=$(basename $GITHUB_REPOSITORY)
+          export USER=$(whoami)
+          export CC=${CC:-gcc}
+          export PATH=~/.local/bin:/usr/local/bin:$PATH
+
+          if [ "$JOB_BUILDTYPE" == "boost" ]; then
+
+          echo '==================================> INSTALL'
+
+          BOOST_BRANCH=develop && [ "$TRAVIS_BRANCH" == "master" ] && BOOST_BRANCH=master || true
+          cd ..
+          git clone -b $BOOST_BRANCH --depth 1 https://github.com/boostorg/boost.git boost-root
+          cd boost-root
+          git submodule update --init tools/build
+          git submodule update --init libs/config
+          git submodule update --init tools/boostdep
+          cp -r $TRAVIS_BUILD_DIR/* libs/optional
+          python tools/boostdep/depinst/depinst.py optional
+          ./bootstrap.sh
+          ./b2 headers
+
+          echo '==================================> SCRIPT'
+
+          echo "using $TOOLSET : : $COMPILER ;" > ~/user-config.jam
+          ./b2 libs/optional/test toolset=$TOOLSET cxxstd=$CXXSTD
+
+          fi

.travis.yml

@@ -0,0 +1,201 @@
+# Copyright 2016, 2017 Peter Dimov
+# Distributed under the Boost Software License, Version 1.0.
+# (See accompanying file LICENSE_1_0.txt or copy at http://boost.org/LICENSE_1_0.txt)
+
+language: cpp
+
+sudo: false
+
+python: "2.7"
+
+branches:
+  only:
+    - master
+    - develop
+    - /feature\/.*/
+
+env:
+  matrix:
+    - BOGUS_JOB=true
+
+matrix:
+
+  exclude:
+    - env: BOGUS_JOB=true
+
+  include:
+    - os: linux
+      compiler: g++
+      env: TOOLSET=gcc COMPILER=g++ CXXSTD=03,11
+
+    - os: linux
+      compiler: g++-4.7
+      env: TOOLSET=gcc COMPILER=g++-4.7 CXXSTD=03,11
+      addons:
+        apt:
+          packages:
+            - g++-4.7
+          sources:
+            - ubuntu-toolchain-r-test
+
+    - os: linux
+      compiler: g++-4.8
+      env: TOOLSET=gcc COMPILER=g++-4.8 CXXSTD=03,11
+      addons:
+        apt:
+          packages:
+            - g++-4.8
+          sources:
+            - ubuntu-toolchain-r-test
+    - os: linux
+      compiler: g++-4.9
+      env: TOOLSET=gcc COMPILER=g++-4.9 CXXSTD=03,11
+      addons:
+        apt:
+          packages:
+            - g++-4.9
+          sources:
+            - ubuntu-toolchain-r-test
+
+    - os: linux
+      compiler: g++-5
+      env: TOOLSET=gcc COMPILER=g++-5 CXXSTD=03,11,14,1z
+      addons:
+        apt:
+          packages:
+            - g++-5
+          sources:
+            - ubuntu-toolchain-r-test
+
+    - os: linux
+      compiler: g++-6
+      env: TOOLSET=gcc COMPILER=g++-6 CXXSTD=03,11,14,1z
+      addons:
+        apt:
+          packages:
+            - g++-6
+          sources:
+            - ubuntu-toolchain-r-test
+
+    - os: linux
+      dist: trusty
+      compiler: g++-7
+      env: TOOLSET=gcc COMPILER=g++-7 CXXSTD=03,11,14,17
+      addons:
+        apt:
+          packages:
+            - g++-7
+          sources:
+            - ubuntu-toolchain-r-test
+
+    - os: linux
+      compiler: clang++
+      env: TOOLSET=clang COMPILER=clang++ CXXSTD=03,11
+
+    - os: linux
+      compiler: clang++-3.5
+      env: TOOLSET=clang COMPILER=clang++-3.5 CXXSTD=03,11,14,1z
+      addons:
+        apt:
+          packages:
+            - clang-3.5
+            - libstdc++-4.9-dev
+          sources:
+            - ubuntu-toolchain-r-test
+            - llvm-toolchain-precise-3.5
+
+    - os: linux
+      compiler: clang++-3.6
+      env: TOOLSET=clang COMPILER=clang++-3.6 CXXSTD=03,11,14,1z
+      addons:
+        apt:
+          packages:
+            - clang-3.6
+          sources:
+            - ubuntu-toolchain-r-test
+            - llvm-toolchain-precise-3.6
+
+    - os: linux
+      compiler: clang++-3.7
+      env: TOOLSET=clang COMPILER=clang++-3.7 CXXSTD=03,11,14,1z
+      addons:
+        apt:
+          packages:
+            - clang-3.7
+          sources:
+            - ubuntu-toolchain-r-test
+            - llvm-toolchain-precise-3.7
+
+    - os: linux
+      compiler: clang++-3.8
+      env: TOOLSET=clang COMPILER=clang++-3.8 CXXSTD=03,11,14,1z
+      addons:
+        apt:
+          packages:
+            - clang-3.8
+            - libstdc++-4.9-dev
+          sources:
+            - ubuntu-toolchain-r-test
+            - llvm-toolchain-precise-3.8
+
+    - os: linux
+      compiler: clang++-3.9
+      env: TOOLSET=clang COMPILER=clang++-3.9 CXXSTD=03,11,14,1z
+      addons:
+        apt:
+          packages:
+            - clang-3.9
+            - libstdc++-4.9-dev
+          sources:
+            - ubuntu-toolchain-r-test
+            - llvm-toolchain-precise-3.9
+
+    - os: linux
+      dist: trusty
+      compiler: clang++-4.0
+      env: TOOLSET=clang COMPILER=clang++-4.0 CXXSTD=03,11,14,1z
+      addons:
+        apt:
+          packages:
+            - clang-4.0
+          sources:
+            - ubuntu-toolchain-r-test
+            - llvm-toolchain-trusty-4.0
+
+    - os: linux
+      dist: trusty
+      compiler: clang++-5.0
+      env: TOOLSET=clang COMPILER=clang++-5.0 CXXSTD=03,11,14,1z
+      addons:
+        apt:
+          packages:
+            - clang-5.0
+          sources:
+            - ubuntu-toolchain-r-test
+            - llvm-toolchain-trusty-5.0
+
+    - os: osx
+      compiler: clang++
+      env: TOOLSET=clang COMPILER=clang++ CXXSTD=03,11,14,1z
+
+install:
+  - BOOST_BRANCH=develop && [ "$TRAVIS_BRANCH" == "master" ] && BOOST_BRANCH=master || true
+  - cd ..
+  - git clone -b $BOOST_BRANCH --depth 1 https://github.com/boostorg/boost.git boost-root
+  - cd boost-root
+  - git submodule update --init tools/build
+  - git submodule update --init libs/config
+  - git submodule update --init tools/boostdep
+  - cp -r $TRAVIS_BUILD_DIR/* libs/optional
+  - python tools/boostdep/depinst/depinst.py optional
+  - ./bootstrap.sh
+  - ./b2 headers
+
+script:
+  - |-
+    echo "using $TOOLSET : : $COMPILER ;" > ~/user-config.jam
+  - ./b2 libs/optional/test toolset=$TOOLSET cxxstd=$CXXSTD
+
+notifications:
+  email:
+    on_success: always

CMakeLists.txt

@@ -0,0 +1,25 @@
+# Copyright 2019 Mike Dev
+# Distributed under the Boost Software License, Version 1.0.
+# See accompanying file LICENSE_1_0.txt or copy at https://www.boost.org/LICENSE_1_0.txt
+
+cmake_minimum_required( VERSION 3.5...3.20 )
+project( boost_optional VERSION "${BOOST_SUPERPROJECT_VERSION}" LANGUAGES CXX )
+
+add_library( boost_optional INTERFACE )
+add_library( Boost::optional ALIAS boost_optional )
+
+target_include_directories( boost_optional INTERFACE include )
+
+target_link_libraries( boost_optional
+    INTERFACE
+        Boost::assert
+        Boost::config
+        Boost::core
+        Boost::detail
+        Boost::move
+        Boost::predef
+        Boost::static_assert
+        Boost::throw_exception
+        Boost::type_traits
+        Boost::utility
+)

doc/00_optional.qbk

@@ -2,7 +2,7 @@
     [quickbook 1.4]
     [authors [Cacciola Carballal, Fernando Luis]]
     [copyright 2003-2007 Fernando Luis Cacciola Carballal]
-    [copyright 2014-2015 Andrzej Krzemieński]
+    [copyright 2014-2023 Andrzej Krzemieński]
     [category miscellaneous]
     [id optional]
     [dirname optional]
@@ -38,10 +38,10 @@ Distributed under the Boost Software License, Version 1.0.
 [/ Other web resources ]
 
 [def __HASKELL__ [@http://www.haskell.org/ Haskell]]
-[def __SGI_DEFAULT_CONSTRUCTIBLE__ [@http://www.sgi.com/tech/stl/DefaultConstructible.html `DefaultConstructible`]]
-[def __SGI_LESS_THAN_COMPARABLE__ [@http://www.sgi.com/tech/stl/LessThanComparable.html `LessThanComparable`]]
-[def __SGI_EQUALITY_COMPARABLE__ [@http://www.sgi.com/tech/stl/EqualityComparable.html `EqualityComparable`]]
-[def __SGI_GENERATOR__ [@http://www.sgi.com/tech/stl/Generator.html `Generator`]]
+[def __STD_DEFAULT_CONSTRUCTIBLE__ [@https://en.cppreference.com/w/cpp/named_req/DefaultConstructible `DefaultConstructible`]]
+[def __STD_LESS_THAN_COMPARABLE__ [@https://en.cppreference.com/w/cpp/named_req/LessThanComparable `LessThanComparable`]]
+[def __STD_EQUALITY_COMPARABLE__ [@https://en.cppreference.com/w/cpp/named_req/EqualityComparable `EqualityComparable`]]
+[def __SGI_GENERATOR__ [@http://www.rrsd.com/software_development/stl/stl/Generator.html `Generator`]]
 
 
 [/ Icons ]
@@ -61,7 +61,7 @@ Suppose we want to read a parameter form a config file which represents some int
 This is how you solve it with `boost::optional`:
 
     #include <boost/optional.hpp>
-    
+
     boost::optional<int> getConfigParam(std::string name);  // return either an int or a `not-an-int`
 
     int main()
@@ -71,7 +71,7 @@ This is how you solve it with `boost::optional`:
       else
         runWithNoMax();
     }
- 
+
 [endsect]
 
 [include 01_quick_start.qbk]
@@ -80,13 +80,14 @@ This is how you solve it with `boost::optional`:
 [include 11_development.qbk]
 [include 12_when_to_use.qbk]
 [include 13_relational_operators.qbk]
-[include 14_io.qbk]
-[include 15_optional_references.qbk]
-[include 16_in_place_factories.qbk]
-[include 17_optional_bool.qbk]
-[include 18_exception_safety.qbk]
-[include 19_type_requirements.qbk]
-[include 1A_on_performance.qbk]
+[include 14_monadic_interface.qbk]
+[include 15_io.qbk]
+[include 16_optional_references.qbk]
+[include 17_in_place_factories.qbk]
+[include 18_gotchas.qbk]
+[include 19_exception_safety.qbk]
+[include 1A_type_requirements.qbk]
+[include 1B_on_performance.qbk]
 [endsect]
 [section:reference Reference]
 [include 21_ref_none.qbk]
@@ -102,5 +103,3 @@ This is how you solve it with `boost::optional`:
 [include 90_dependencies.qbk]
 [include 91_relnotes.qbk]
 [include 92_acknowledgments.qbk]
-
-

doc/01_quick_start.qbk

@@ -25,7 +25,7 @@ All necessary functionality can be included with one header `<boost/optional.hpp
     boost::optional<int> oi = convert(text); // move-construct
     if (oi)                                  // contextual conversion to bool
       int i = *oi;                           // operator*
-    
+
 In order to test if `optional` contains a value, we use the contextual conversion to type `bool`. Because of this we can combine the initialization of the optional object and the test into one instruction:
 
     if (boost::optional<int> oi = convert(text))
@@ -34,7 +34,7 @@ In order to test if `optional` contains a value, we use the contextual conversio
 We extract the contained value with `operator*` (and with `operator->` where it makes sense). An attempt to extract the contained value of an uninitialized optional object is an ['undefined behaviour] (UB). This implementation guards the call with `BOOST_ASSERT`. Therefore you should be sure that the contained value is there before extracting. For instance, the following code is reasonably UB-safe:
 
     int i = *convert("100");
-    
+
 This is because we know that string value `"100"` converts to a valid value of `int`. If you do not like this potential UB, you can use an alternative way of extracting the contained value:
 
     try {
@@ -44,18 +44,18 @@ This is because we know that string value `"100"` converts to a valid value of `
       // deal with it
     }
 
-This version throws an exception upon an attempt to access a non-existent contained value. If your way of dealing with the missing value is to use some default, like `0`, there exists a yet another alternative:
+This version throws an exception upon an attempt to access a nonexistent contained value. If your way of dealing with the missing value is to use some default, like `0`, there exists a yet another alternative:
 
     int k = convert(text).value_or(0);
-    
+
 This uses the `atoi`-like approach to conversions: if `text` does not represent an integral number just return `0`. Finally, you can provide a callback to be called when trying to access the contained value fails:
 
     int fallback_to_default()
     {
-      cerr << "could not convert; using -1 instead" << endl; 
+      cerr << "could not convert; using -1 instead" << endl;
       return -1;
     }
-    
+
     int l = convert(text).value_or_eval(fallback_to_default);
 
 This will call the provided callback and return whatever the callback returns. The callback can have side effects: they will only be observed when the optional object does not contain a value.
@@ -63,7 +63,7 @@ This will call the provided callback and return whatever the callback returns. T
 Now, let's consider how function `convert` can be implemented.
 
     boost::optional<int> convert(const std::string& text)
-    {  
+    {
       std::stringstream s(text);
       int i;
       if ((s >> i) && s.get() == std::char_traits<char>::eof())
@@ -72,7 +72,7 @@ Now, let's consider how function `convert` can be implemented.
         return boost::none;
     }
 
-Observe the two return statements. `return i` uses the converting constructor that can create `optional<T>` from `T`. Thus constructed optional object is initialized and its value is a copy of `i`. The other return statement uses another converting constructor from a special tag `boost::none`. It is used to indicate that we want to create an uninitialized optional object. 
+Observe the two return statements. `return i` uses the converting constructor that can create `optional<T>` from `T`. Thus constructed optional object is initialized and its value is a copy of `i`. The other return statement uses another converting constructor from a special tag `boost::none`. It is used to indicate that we want to create an uninitialized optional object.
 
 [endsect]
 
@@ -91,7 +91,7 @@ We could write function `convert` in a slightly different manner, so that it has
       return ans;
     }
 
-The default constructor of `optional` creates an unitialized optional object. Unlike with `int`s you cannot have an `optional<int>` in an indeterminate state. Its state is always well defined. Instruction `ans = i` initializes the optional object. It uses the 'mixed' assignment from `int`. In general, for `optional<T>`, when an assignment from `T` is invoked, it can do two things. If the optional object is not initialized (our case here), it initializes the contained value using `T`'s copy constructor. If the optional object is already initialized, it assigns the new value to it using `T`'s copy assignment.      
+The default constructor of `optional` creates an uninitialized optional object. Unlike with `int`s you cannot have an `optional<int>` in an indeterminate state. Its state is always well defined. Instruction `ans = i` initializes the optional object. It uses the 'mixed' assignment from `int`. In general, for `optional<T>`, when an assignment from `T` is invoked, it can do two things. If the optional object is not initialized (our case here), it initializes the contained value using `T`'s copy constructor. If the optional object is already initialized, it assigns the new value to it using `T`'s copy assignment.
 [endsect]
 
 [section Optional data members]
@@ -101,20 +101,20 @@ Suppose we want to implement a ['lazy load] optimization. This is because we do
     class Widget
     {
       mutable boost::optional<const Resource> resource_;
-      
+
     public:
       Widget() {}
-      
+
       const Resource& getResource() const // not thread-safe
       {
         if (resource_ == boost::none)
             resource_.emplace("resource", "arguments");
-        
+
         return *resource_;
       }
     };
-    
-`optional`'s default constructor creates an uninitialized optional. No call to `Resource`'s default constructor is attempted. `Resource` doesn't have to be __SGI_DEFAULT_CONSTRUCTIBLE__. In function `getResource` we first check if `resource_` is initialized. This time we do not use the contextual conversion to `bool`, but a comparison with `boost::none`. These two ways are equivalent. Function `emplace` initializes the optional in-place by perfect-forwarding the arguments to the constructor of `Resource`. No copy- or move-construction is involved here. `Resource` doesn't even have to be `MoveConstructible`. 
+
+`optional`'s default constructor creates an uninitialized optional. No call to `Resource`'s default constructor is attempted. `Resource` doesn't have to be __STD_DEFAULT_CONSTRUCTIBLE__. In function `getResource` we first check if `resource_` is initialized. This time we do not use the contextual conversion to `bool`, but a comparison with `boost::none`. These two ways are equivalent. Function `emplace` initializes the optional in-place by perfect-forwarding the arguments to the constructor of `Resource`. No copy- or move-construction is involved here. `Resource` doesn't even have to be `MoveConstructible`.
 
 [note Function `emplace` is only available on compilers that support rvalue references and variadic templates. If your compiler does not support these features and you still need to avoid any move-constructions, use [link boost_optional.tutorial.in_place_factories In-Place Factories].]
 
@@ -125,17 +125,17 @@ Suppose we want to implement a ['lazy load] optimization. This is because we do
 Suppose we have class `Date`, which does not have a default constructor: there is no good candidate for a default date. We have a function that returns two dates in form of a `boost::tuple`:
 
     boost::tuple<Date, Date> getPeriod();
-    
+
 In other place we want to use the result of `getPeriod`, but want the two dates to be named: `begin` and `end`. We want to implement something like 'multiple return values':
 
     Date begin, end; // Error: no default ctor!
     boost::tie(begin, end) = getPeriod();
-    
+
 The second line works already, this is the capability of __BOOST_TUPLE__ library, but the first line won't work. We could set some invented initial dates, but it is confusing and may be an unacceptable cost, given that these values will be overwritten in the next line anyway. This is where `optional` can help:
 
     boost::optional<Date> begin, end;
     boost::tie(begin, end) = getPeriod();
-    
+
 It works because inside `boost::tie` a move-assignment from `T` is invoked on `optional<T>`, which internally calls a move-constructor of `T`.
 [endsect]
 
@@ -144,15 +144,17 @@ It works because inside `boost::tie` a move-assignment from `T` is invoked on `o
 Suppose you want to ask users to choose some number (an `int`). One of the valid responses is to choose nothing, which is represented by an uninitialized `optional<int>`. You want to make a histogram showing how many times each choice was made. You can use an `std::map`:
 
     std::map<boost::optional<int>, int> choices;
-  
+
     for (int i = 0; i < LIMIT; ++i) {
       boost::optional<int> choice = readChoice();
       ++choices[choice];
     }
-    
-This works because `optional<T>` is __SGI_LESS_THAN_COMPARABLE__ whenever `T` is __SGI_LESS_THAN_COMPARABLE__. In this case the state of being uninitialized is treated as a yet another value of `T`, which is compared less than any value of `T`.
+
+This works because `optional<T>` is __STD_LESS_THAN_COMPARABLE__ whenever `T` is __STD_LESS_THAN_COMPARABLE__.
+In this case the state of being uninitialized is treated as a yet another value of `T`,
+which is compared less than any value of `T`.
+`optional<T>` can also be stored as a key in `std::unordered_map` and `std::unordered_set`
+as it provides specializations for `std::hash`.
 [endsect]
 
 [endsect]
-
- 

doc/11_development.qbk

@@ -228,7 +228,7 @@ For value access operations `optional<>` uses operators `*` and `->` to
 lexically warn about the possibly uninitialized state appealing to the
 familiar pointer semantics w.r.t. to null pointers.
 
-[warning
+[caution
 However, it is particularly important to note that `optional<>` objects
 are not pointers. [_`optional<>` is not, and does not model, a pointer].
 ]

doc/12_when_to_use.qbk

@@ -11,7 +11,7 @@ Here, having received an empty `vec` and having no `size_t` to return is not a [
 
 Another typical situation is to indicate that we do not have a value yet, but we expect to have it later. This notion can be used in implementing solutions like lazy initialization or a two-phase initialization.
 
-`optional` can be used to take a non-__SGI_DEFAULT_CONSTRUCTIBLE__ type `T` and create a sibling type with a default constructor. This is a way to add a ['null-state] to any type that doesn't have it already.
+`optional` can be used to take a non-__STD_DEFAULT_CONSTRUCTIBLE__ type `T` and create a sibling type with a default constructor. This is a way to add a ['null-state] to any type that doesn't have it already.
 
 Sometimes type `T` already provides a built-in null-state, but it may still be useful to wrap it into `optional`. Consider `std::string`. When you read a piece of text from a GUI form or a DB table, it is hardly ever that the empty string indicates anything else but a missing text. And some data bases do not even distinguish between a null string entry and a non-null string of length 0. Still, it may be practical to use `optional<string>` to indicate in the returned type that we want to treat the empty string in a special dedicated program path:
 

doc/13_relational_operators.qbk

@@ -1,37 +1,37 @@
 
 [section Relational operators]
 
-Type `optional<T>` is __SGI_EQUALITY_COMPARABLE__ whenever `T` is __SGI_EQUALITY_COMPARABLE__. Two optional objects containing a value compare in the same way as their contained values. The uninitialized state of `optional<T>` is treated as a distinct value, equal to itself, and unequal to any value of type `T`:
+Type `optional<T>` is __STD_EQUALITY_COMPARABLE__ whenever `T` is __STD_EQUALITY_COMPARABLE__. Two optional objects containing a value compare in the same way as their contained values. The uninitialized state of `optional<T>` is treated as a distinct value, equal to itself, and unequal to any value of type `T`:
 
     boost::optional<int> oN = boost::none;
     boost::optional<int> o0 = 0;
     boost::optional<int> o1 = 1;
-    
+
     assert(oN != o0);
     assert(o1 != oN);
     assert(o0 != o1);
     assert(oN == oN);
     assert(o0 == o0);
-    
-The converting constructor from `T` as well as from `boost::none` implies the existence and semantics of the mixed comparison between `T` and `optional<T>` as well as between `none_t` and `optionl<T>`:
+
+The converting constructor from `T` as well as from `boost::none` implies the existence and semantics of the mixed comparison between `T` and `optional<T>` as well as between `none_t` and `optional<T>`:
 
     assert(oN != 0);
     assert(o1 != boost::none);
     assert(o0 != 1);
     assert(oN == boost::none);
     assert(o0 == 0);
-    
+
 This mixed comparison has a practical interpretation, which is occasionally useful:
 
     boost::optional<int> choice = ask_user();
     if (choice == 2)
         start_procedure_2();
-        
+
 In the above example, the meaning of the comparison is 'user chose number 2'. If user chose nothing, he didn't choose number 2.
 
-In case where `optional<T>` is compared to `none`, it is not required that `T` be __SGI_EQUALITY_COMPARABLE__.
+In case where `optional<T>` is compared to `none`, it is not required that `T` be __STD_EQUALITY_COMPARABLE__.
 
-In a similar manner, type `optional<T>` is __SGI_LESS_THAN_COMPARABLE__ whenever `T` is __SGI_LESS_THAN_COMPARABLE__. The optional object containing no value is compared less than any value of `T`. To illustrate this, if the default ordering of `size_t` is {`0`, `1`, `2`, ...}, the default ordering of `optional<size_t>` is {`boost::none`, `0`, `1`, `2`, ...}. This order does not have a practical interpretation. The goal is to have any semantically correct default ordering in order for `optional<T>` to be usable in ordered associative containers (wherever `T` is usable).  
+In a similar manner, type `optional<T>` is __STD_LESS_THAN_COMPARABLE__ whenever `T` is __STD_LESS_THAN_COMPARABLE__. The optional object containing no value is compared less than any value of `T`. To illustrate this, if the default ordering of `size_t` is {`0`, `1`, `2`, ...}, the default ordering of `optional<size_t>` is {`boost::none`, `0`, `1`, `2`, ...}. This order does not have a practical interpretation. The goal is to have any semantically correct default ordering in order for `optional<T>` to be usable in ordered associative containers (wherever `T` is usable).
 
 Mixed relational operators are the only case where the contained value of an optional object can be inspected without the usage of value accessing function (`operator*`, `value`, `value_or`).
 [endsect]

doc/14_monadic_interface.qbk

@@ -0,0 +1,45 @@
+[section Monadic interface]
+
+The monadic interface of `optional` allows the application of functions
+to optional values without resorting to the usage of explicit `if`-statements.
+
+Function `map` takes a function mapping type `T` onto type `U` and maps an `optional<T>`
+onto an `optional<U>` using the provided function.
+
+    int length(const string& s){ return s.size(); };
+
+    optional<string> null{}, thin{""}, word{"word"};
+    assert (null.map(length) == none);
+    assert (thin.map(length) == 0);
+    assert (word.map(length) == 4);
+
+Function `flat_map` is similar, but it requires the function to return an
+`optional<V>` for some type `V`. This `optional<V>` becomes the return type of
+`flat_map`.
+
+    optional<char> first_char(const string& s) {
+      if (s.empty()) return none;
+      else           return s[0];
+    };
+
+    optional<string> null{}, thin{""}, word{"word"};
+    assert (null.flat_map(first_char) == none);
+    assert (thin.flat_map(first_char) == none);
+    assert (word.flat_map(first_char) == 'w');
+
+These functions can be combined in one expression reflecting a chain of computations:
+
+    auto get_contents(path p) -> optional<string>;
+    auto trim(string) -> string;
+    auto length(string) -> int;
+
+    auto trimmed_size_of(optional<path> p) -> int
+    {
+      return p.flat_map(get_contents)
+              .map(trim)
+              .map(length)
+              .value_or(0);
+    }
+ 
+
+[endsect]

doc/16_optional_references.qbk

@@ -1,6 +1,8 @@
 
 [section Optional references]
 
+[section Overview]
+
 This library allows the template parameter `T` to be of reference type:
 `T&`, and to some extent, `T const&`.
 
@@ -14,14 +16,14 @@ some operations are not available in this case:
 * Value-access via pointer
 
 Also, even though `optional<T&>` treats it wrapped pseudo-object much as
-a real value, a true real reference is stored so aliasing will ocurr:
+a real value, a true real reference is stored so aliasing will occur:
 
 * Copies of `optional<T&>` will copy the references but all these references
 will nonetheless refer to the same object.
 * Value-access will actually provide access to the referenced object
 rather than the reference itself.
 
-[warning On compilers that do not conform to Standard C++ rules of reference binding, operations on optional references might give adverse results: rather than binding a reference to a designated object they may create an unexpected temporary and bind to it. For more details see [link boost_optional.dependencies_and_portability.optional_reference_binding Dependencies and Portability section].]
+[caution On compilers that do not conform to Standard C++ rules of reference binding, some operations on optional references are disabled in order to prevent subtle bugs. For more details see [link boost_optional.dependencies_and_portability.optional_reference_binding Dependencies and Portability section].]
 
 [heading Rvalue references]
 
@@ -118,3 +120,4 @@ In such a scenario, you can assign the value itself directly, as in:
     *opt=value;
 
 [endsect]
+[endsect]

doc/17_optional_bool.qbk

@@ -1,52 +0,0 @@
-
-[section A note about optional<bool>]
-
-`optional<bool>` should be used with special caution and consideration.
-
-First, it is functionally similar to a tristate boolean (false, maybe, true)
-—such as __BOOST_TRIBOOL__— except that in a tristate boolean, the maybe state
-[_represents a valid value], unlike the corresponding state of an uninitialized
-`optional<bool>`.
-It should be carefully considered if an `optional<bool>` instead of a `tribool`
-is really needed.
-
-Second, although `optional<>` provides a contextual conversion to `bool` in C++11,
- this falls back to an implicit conversion on older compilers. This conversion refers
- to the initialization state and not to the contained value. Using `optional<bool>`
- can lead to subtle errors due to the implicit `bool` conversion:
-
-    void foo ( bool v ) ;
-    void bar()
-    {
-        optional<bool> v = try();
-
-        // The following intended to pass the value of 'v' to foo():
-        foo(v);
-        // But instead, the initialization state is passed
-        // due to a typo: it should have been foo(*v).
-    }
-
-The only implicit conversion is to `bool`, and it is safe in the sense that
-typical integral promotions don't apply (i.e. if `foo()` takes an `int`
-instead, it won't compile).
-
-Third, mixed comparisons with `bool` work differently than similar mixed comparisons between pointers and `bool`, so the results might surprise you:
-
-    optional<bool> oEmpty(none), oTrue(true), oFalse(false);
-    
-    if (oEmpty == none);  // renders true
-    if (oEmpty == false); // renders false!
-    if (oEmpty == true);  // renders false!
-     
-    if (oFalse == none);  // renders false
-    if (oFalse == false); // renders true!
-    if (oFalse == true);  // renders false
-    
-    if (oTrue == none);   // renders false
-    if (oTrue == false);  // renders false
-    if (oTrue == true);   // renders true
-
-In other words, for `optional<>`, the following assertion does not hold:
-
-    assert((opt == false) == (!opt));
-[endsect]

doc/18_gotchas.qbk

@@ -0,0 +1,111 @@
+[section Gotchas]
+
+[section A note about optional<bool>]
+
+`optional<bool>` should be used with special caution and consideration.
+
+First, it is functionally similar to a tristate boolean (false, maybe, true)
+—such as __BOOST_TRIBOOL__— except that in a tristate boolean, the maybe state
+[_represents a valid value], unlike the corresponding state of an uninitialized
+`optional<bool>`.
+It should be carefully considered if an `optional<bool>` instead of a `tribool`
+is really needed.
+
+Second, although `optional<>` provides a contextual conversion to `bool` in C++11,
+ this falls back to an implicit conversion on older compilers. This conversion refers
+ to the initialization state and not to the contained value. Using `optional<bool>`
+ can lead to subtle errors due to the implicit `bool` conversion:
+
+    void foo ( bool v ) ;
+    void bar()
+    {
+        optional<bool> v = try();
+
+        // The following intended to pass the value of 'v' to foo():
+        foo(v);
+        // But instead, the initialization state is passed
+        // due to a typo: it should have been foo(*v).
+    }
+
+The only implicit conversion is to `bool`, and it is safe in the sense that
+typical integral promotions don't apply (i.e. if `foo()` takes an `int`
+instead, it won't compile).
+
+Third, mixed comparisons with `bool` work differently than similar mixed comparisons between pointers and `bool`, so the results might surprise you:
+
+    optional<bool> oEmpty(none), oTrue(true), oFalse(false);
+    
+    if (oEmpty == none);  // renders true
+    if (oEmpty == false); // renders false!
+    if (oEmpty == true);  // renders false!
+     
+    if (oFalse == none);  // renders false
+    if (oFalse == false); // renders true!
+    if (oFalse == true);  // renders false
+    
+    if (oTrue == none);   // renders false
+    if (oTrue == false);  // renders false
+    if (oTrue == true);   // renders true
+
+In other words, for `optional<>`, the following assertion does not hold:
+
+    assert((opt == false) == (!opt));
+[endsect]
+
+[section Moved-from `optional`]
+
+When an optional object that contains a value is moved from (is a source of move constructor or assignment) it still contains a value and its contained value is left in a moved-from state. This can be illustrated with the following example.
+
+    optional<std::unique_ptr<int>> opi {std::make_unique<int>(1)};
+    optional<std::unique_ptr<int>> opj = std::move(opi);
+    assert (opi);
+    assert (*opi == nullptr);
+
+Quite a lot of people expect that when an object that contains a value is moved from, its contained value should be destroyed. This is not so, for performance reasons. Current semantics allow the implementation of `boost::optional<T>` to be trivially copyable when `T` is trivial.
+[endsect]
+
+[section Mixed relational comparisons]
+
+Because `T` is convertible to `optional<T>` and because `optional<T>` is __STD_LESS_THAN_COMPARABLE__ when `T` is __STD_LESS_THAN_COMPARABLE__,
+you can sometimes get an unexpected runtime result where you would rather expect a compiler error:
+
+    optional<double> Flight_plan::weight(); // sometimes no weight can be returned
+
+    bool is_aircraft_too_heavy(Flight_plan const& p)
+    {
+       return p.weight() > p.aircraft().max_weight(); // compiles!
+    }                                                 // returns false when the optional contains no value 
+
+[endsect]
+
+[section False positive with -Wmaybe-uninitialized]
+
+Sometimes on GCC compilers below version 5.1 you may get an -Wmaybe-uninitialized warning when compiling with option -02 on a perfectly valid `boost::optional` usage. For instance in this program:
+
+    #include <boost/optional.hpp>
+
+    boost::optional<int> getitem();
+
+    int main(int argc, const char *[])
+    {
+      boost::optional<int> a = getitem();
+      boost::optional<int> b;
+
+      if (argc > 0)
+        b = argc;
+
+      if (a != b)
+        return 1;
+
+      return 0;
+    }
+    
+This is a bug in the compiler. As a workaround (provided in [@http://stackoverflow.com/questions/21755206/how-to-get-around-gcc-void-b-4-may-be-used-uninitialized-in-this-funct this Stack Overflow question]) use the following way of initializing an optional containing no value:
+
+    boost::optional<int> b = boost::make_optional(false, int());
+
+This is obviously redundant, but makes the warning disappear.
+
+[endsect]
+
+[endsect]

doc/19_exception_safety.qbk

@@ -51,7 +51,7 @@ Operation `emplace` provides basic exception safety guarantee. If it throws, the
 
 Unless `swap` on optional is customized, its primary implementation forwards calls to `T`'s `swap` or move constructor (depending on the initialization state of the optional objects). Thus, if both `T`'s `swap` and move constructor never throw, `swap` on `optional<T>` never throws. similarly, if both `T`'s `swap` and move constructor offer strong guarantee, `swap` on `optional<T>` also offers a strong guarantee.
 
-In case `swap` on optional is customized, the call to `T`'s move constructor are replaced with the calls to `T`'s default constructor followed by `swap`. (This is more useful on older compilers that do not support move semantics, when one wants to acheive stronger exception safety guarantees.) In this case the exception safety guarantees for `swap` are reliant on the guarantees of `T`'s `swap` and default constructor
+In case `swap` on optional is customized, the call to `T`'s move constructor are replaced with the calls to `T`'s default constructor followed by `swap`. (This is more useful on older compilers that do not support move semantics, when one wants to achieve stronger exception safety guarantees.) In this case the exception safety guarantees for `swap` are reliant on the guarantees of `T`'s `swap` and default constructor
 [endsect]
 
 

doc/1A_type_requirements.qbk

@@ -33,6 +33,6 @@ If `T` is `Moveable` (both __MOVE_CONSTRUCTIBLE__ and `MoveAssignable`) then `op
 
 Similarly, if `T` is `Copyable` (both __COPY_CONSTRUCTIBLE__ and `CopyAssignable`) then `optional<T>` is also `Copyable` and additionally can be constructed and assigned from an lvalue of type `T`.
 
-`T` ['is not] required to be __SGI_DEFAULT_CONSTRUCTIBLE__.
+`T` ['is not] required to be __STD_DEFAULT_CONSTRUCTIBLE__.
 
 [endsect]

doc/1B_on_performance.qbk

@@ -1,7 +1,7 @@
 
 [section Performance considerations]
 
-Technical details aside, the memory layout of `optional<T>` is more-less this:
+Technical details aside, the memory layout of `optional<T>` for a generic `T` is more-less this:
 
   template <typename T>
   class optional
@@ -9,8 +9,33 @@ Technical details aside, the memory layout of `optional<T>` is more-less this:
     bool _initialized;
     std::aligned_storage_t<sizeof(t), alignof(T)> _storage;
   };
+
+Lifetime of the `T` inside `_storage` is manually controlled with placement-`new`s and pseudo-destructor calls. However, for scalar `T`s we use a different way of storage, by simply holding a `T`:
   
-But for the purpose of this analysis, considering memory layouts, we can think of it as:
+  template <typename T>
+  class optional
+  {
+    bool _initialized;
+    T _storage;
+  };
+
+We call it a ['direct] storage. This makes `optional<T>` a trivially-copyable type for scalar `T`s. This only works for compilers that support defaulted functions (including defaulted move assignment and constructor). On compilers without defaulted functions we still use the direct storage, but `optional<T>` is no longer recognized as trivially-copyable. Apart from scalar types, we leave the programmer a way of customizing her type, so that it is recognized by `optional` as candidate for optimized storage, by specializing type trait `boost::optional_config::optional_uses_direct_storage_for`:
+
+  struct X // not trivial
+  {
+    X() {}
+  };
+
+  namespace boost { namespace optional_config {
+    
+    template <> struct optional_uses_direct_storage_for<X> : boost::true_type {};
+    
+  }}
+  
+
+[heading Controlling the size]
+  
+For the purpose of the following analysis, considering memory layouts, we can think of it as:
 
   template <typename T>
   class optional
@@ -23,7 +48,7 @@ Given type `optional<int>`, and assuming that `sizeof(int) == 4`, we will get `s
 
 [$images/opt_align1.png]
 
-This means you can fit twice as many `int`s as `optional<int>`s into the same space of memory. Therefore, if the size of the objects is critical for your application (e.g., because you want to utilize your CPU cache in order to gain performance) and you have determined you are willing to trade the code clarity, it is recommended that you simply go with type `int` and use some 'magic value' to represent ['not-an-int].
+This means you can fit twice as many `int`s as `optional<int>`s into the same space of memory. Therefore, if the size of the objects is critical for your application (e.g., because you want to utilize your CPU cache in order to gain performance) and you have determined you are willing to trade the code clarity, it is recommended that you simply go with type `int` and use some 'magic value' to represent ['not-an-int], or use something like [@https://github.com/akrzemi1/markable `markable`] library.
 
 Even if you cannot spare any value of `int` to represent ['not-an-int] (e.g., because every value is useful, or you do want to signal ['not-an-int] explicitly), at least for `Trivial` types you should consider storing the value and the `bool` flag representing the ['null-state] separately. Consider the following class:
 
@@ -61,7 +86,7 @@ Which gives us the following layout (and smaller total size):
 
 [$images/opt_align3.png]
 
-Sometimes it requires detailed consideration what data we make optional. In our case above, if we determine that both minimum and maximum value can be provided or not provided together, but one is never provided without the other, we can make only one optional memebr:
+Sometimes it requires detailed consideration what data we make optional. In our case above, if we determine that both minimum and maximum value can be provided or not provided together, but one is never provided without the other, we can make only one optional member:
 
   struct Limits
   {

doc/21_ref_none.qbk

@@ -15,14 +15,16 @@
 ```
 namespace boost {
 
-class none_t {};
+class none_t {/* see below */};
+
+inline constexpr none_t none (/* see below */);
 
-extern const none_t none; // see below
-    
 } // namespace boost
 ```
 
-Variable `none` has external linkage, however it is not required to link with any library to obtain its definition. Only by including this header file, the definition becomes available, by means of using template instantiation.
+Class `none_t` is meant to serve as a tag for selecting appropriate overloads of from `optional`'s interface. It is an empty, trivially copyable class with disabled default constructor.
+
+Constant `none` is used to indicate an optional object that does not contain a value in initialization, assignment and relational operations of `optional`.
 
 [endsect]
 

doc/23_ref_optional_io.qbk

@@ -26,11 +26,11 @@ template <class CharType, class CharTrait, class T>
   template <class CharType, class CharTrait>
   std::basic_ostream<CharType, CharTrait>&
   operator<<(std::basic_ostream<CharType, CharTrait>& out, none_t const&); ``[link reference_operator_ostream_none __GO_TO__]``
-  
+
 template<class CharType, class CharTrait, class T>
   std::basic_istream<CharType, CharTrait>&
   operator>>(std::basic_istream<CharType, CharTrait>& in, optional<T>& v); ``[link reference_operator_istream __GO_TO__]``
-  
+
 } // namespace boost
 ```
 
@@ -43,8 +43,8 @@ template<class CharType, class CharTrait, class T>
 
 
 `template <class CharType, class CharTrait, class T>` [br]
-\u00A0\u00A0\u00A0\u00A0`std::basic_ostream<CharType, CharTrait>&` [br]
-\u00A0\u00A0\u00A0\u00A0`operator<<(std::basic_ostream<CharType, CharTrait>& out, optional<T> const& v);`
+ std::basic_ostream<CharType, CharTrait>&` [br]
+ operator<<(std::basic_ostream<CharType, CharTrait>& out, optional<T> const& v);`
 
 * [*Effect:] Outputs an implementation-defined string. The output contains the information about whether the optional object contains a value or not. If `v` contains a value, the output contains result of calling `out << *v`.
 * [*Returns:] `out`.
@@ -53,8 +53,8 @@ __SPACE__
 [#reference_operator_ostream_none]
 
 `template <class CharType, class CharTrait, class T>` [br]
-\u00A0\u00A0\u00A0\u00A0`std::basic_ostream<CharType, CharTrait>&` [br]
-\u00A0\u00A0\u00A0\u00A0`operator<<(std::basic_ostream<CharType, CharTrait>& out, none_t);`
+ std::basic_ostream<CharType, CharTrait>&` [br]
+ operator<<(std::basic_ostream<CharType, CharTrait>& out, none_t);`
 
 * [*Effect:] Outputs an implementation-defined string.
 * [*Returns:] `out`.
@@ -63,11 +63,11 @@ __SPACE__
 [#reference_operator_istream]
 
 `template <class CharType, class CharTrait, class T>` [br]
-\u00A0\u00A0\u00A0\u00A0`std::basic_ostream<CharType, CharTrait>&` [br]
-\u00A0\u00A0\u00A0\u00A0`operator>>(std::basic_istream<CharType, CharTrait>& in, optional<T>& v);`
+ std::basic_ostream<CharType, CharTrait>&` [br]
+ operator>>(std::basic_istream<CharType, CharTrait>& in, optional<T>& v);`
 
-* [*Requires:] `T` is __SGI_DEFAULT_CONSTRUCTIBLE__ and __MOVE_CONSTRUCTIBLE__.
-* [*Effect:] Reads the value of optional object from `in`. If the string representation indicates that the optional object should contain a value, `v` contains a value and its contained value is obtained as if by default-constructing an object `o` of type `T` and then calling `in >> o`; otherwise `v` does not contain a value, and the previously contained value (if any) has been destroyed. 
+* [*Requires:] `T` is __STD_DEFAULT_CONSTRUCTIBLE__ and __MOVE_CONSTRUCTIBLE__.
+* [*Effect:] Reads the value of optional object from `in`. If the string representation indicates that the optional object should contain a value, `v` contains a value and its contained value is obtained as if by default-constructing an object `o` of type `T` and then calling `in >> o`; otherwise `v` does not contain a value, and the previously contained value (if any) has been destroyed.
 * [*Returns:] `out`.
 
 [endsect]

doc/27_ref_optional_synopsis.qbk

@@ -9,40 +9,142 @@
 ]
 
 
-[#ref_header_optional_optional_hpp][section:header_optional_optional Synopsis]
+[#ref_header_optional_optional_hpp] [section:header_optional_optional Synopsis]
 
     ```// In Header: <`[@boost:/boost/optional/optional.hpp boost/optional/optional.hpp]'''<phrase role="comment">&gt;</phrase>'''``
 
     namespace boost {
 
+    class in_place_init_t { /* see below */ } ; ``[link reference_in_place_init __GO_TO__]``
+    const in_place_init_t in_place_init ( /* see below */ ) ;
+
+    class in_place_init_if_t { /*see below*/ } ; ``[link reference_in_place_init_if __GO_TO__]``
+    const in_place_init_if_t in_place_init_if ( /*see below*/ ) ;
+
+    template <class T>
+    class optional ; ``[link reference_operator_template __GO_TO__]``
+
+    template <class T>
+    class optional<T&> ; ``[link reference_operator_template_spec __GO_TO__]``
+
+    template<class T> inline bool operator == ( optional<T> const& x, optional<T> const& y ) ; ``[link reference_operator_compare_equal_optional_optional __GO_TO__]``
+
+    template<class T> inline bool operator != ( optional<T> const& x, optional<T> const& y ) ; ``[link reference_operator_compare_not_equal_optional_optional __GO_TO__]``
+
+    template<class T> inline bool operator <  ( optional<T> const& x, optional<T> const& y ) ; ``[link reference_operator_compare_less_optional_optional __GO_TO__]``
+
+    template<class T> inline bool operator >  ( optional<T> const& x, optional<T> const& y ) ; ``[link reference_operator_compare_greater_optional_optional __GO_TO__]``
+
+    template<class T> inline bool operator <= ( optional<T> const& x, optional<T> const& y ) ; ``[link reference_operator_compare_less_or_equal_optional_optional __GO_TO__]``
+
+    template<class T> inline bool operator >= ( optional<T> const& x, optional<T> const& y ) ; ``[link reference_operator_compare_greater_or_equal_optional_optional __GO_TO__]``
+
+    template<class T> inline bool operator == ( optional<T> const& x, none_t ) noexcept ; ``[link reference_operator_compare_equal_optional_none __GO_TO__]``
+
+    template<class T> inline bool operator != ( optional<T> const& x, none_t ) noexcept ; ``[link reference_operator_compare_not_equal_optional_none __GO_TO__]``
+
+    template<class T> inline optional<T> make_optional ( T const& v ) ; ``[link reference_make_optional_value __GO_TO__]``
+
+    template<class T> inline optional<std::decay_t<T>> make_optional ( T && v ) ; ``[link reference_make_optional_rvalue __GO_TO__]``
+
+    template<class T> inline optional<T> make_optional ( bool condition, T const& v ) ; ``[link reference_make_optional_bool_value __GO_TO__]``
+
+    template<class T> inline optional<std::decay_t<T>> make_optional ( bool condition, T && v ) ; ``[link reference_make_optional_bool_rvalue __GO_TO__]``
+
+    template<class T> inline auto get_optional_value_or ( optional<T> const& opt, typename optional<T>::reference_const_type def ) -> typename optional<T>::reference_const_type; ``[link reference_free_get_value_or __GO_TO__]``
+
+    template<class T> inline auto get_optional_value_or ( optional<T> const& opt, typename optional<T>::reference_type def ) -> typename optional<T>::reference_type ; ``[link reference_free_get_value_or __GO_TO__]``
+
+    template<class T> inline T const& get ( optional<T> const& opt ) ; ``[link reference_optional_get __GO_TO__]``
+
+    template<class T> inline T& get ( optional<T> & opt ) ; ``[link reference_optional_get __GO_TO__]``
+
+    template<class T> inline T const* get ( optional<T> const* opt ) ; ``[link reference_optional_get __GO_TO__]``
+
+    template<class T> inline T* get ( optional<T>* opt ) ; ``[link reference_optional_get __GO_TO__]``
+
+    template<class T> inline auto get_pointer ( optional<T> const& opt ) -> ``['see below]``; ``[link reference_free_get_pointer __GO_TO__]``
+
+    template<class T> inline auto get_pointer ( optional<T> & opt ) -> ``['see below]``; ``[link reference_free_get_pointer __GO_TO__]``
+
+    template<class T> inline void swap( optional<T>& x, optional<T>& y ) ; ``[link reference_swap_optional_optional __GO_TO__]``
+
+    template<class T> inline void swap( optional<T&>& x, optional<T&>& y ) ; ``[link reference_swap_optional_reference __GO_TO__]``
+
+    } // namespace boost
+
+    namespace std {
+
+    template <typename T>
+    struct hash<boost::optional<T> > ; ``[link reference_std_hash_spec __GO_TO__]``
+
+    template <typename T>
+    struct hash<boost::optional<T&> > ; ``[link reference_std_hash_spec __GO_TO__]``
+
+    } // namespace std
+
+
+[endsect]
+
+
+[section:header_optional_in_place_init Initialization tags]
+
+[#reference_in_place_init]
+[#reference_in_place_init_if]
+
+    namespace boost {
+
+    class in_place_init_t { /* see below */ } ;
+    const in_place_init_t in_place_init ( /* see below */ ) ;
+
+    class in_place_init_if_t { /*see below*/ } ;
+    const in_place_init_if_t in_place_init_if ( /*see below*/ ) ;
+
+    }
+
+Classes `in_place_init_t` and `in_place_init_if_t` are empty classes. Their purpose is to control overload resolution in the initialization of optional objects.
+They are empty, trivially copyable classes with disabled default constructor.
+
+[endsect]
+
+[section:header_optional_optional_values Optional Values]
+
+[#reference_operator_template]
+
     template <class T>
     class optional
     {
     public :
 
-        typedef T value_type;
-        
-        // (If T is of reference type, the parameters and results by reference are by value)
+        typedef T         value_type ;
+        typedef T &       reference_type ;
+        typedef T const&  reference_const_type ;
+        typedef T &&      rval_reference_type ;
+        typedef T *       pointer_type ;
+        typedef T const*  pointer_const_type ;
 
         optional () noexcept ; ``[link reference_optional_constructor __GO_TO__]``
 
         optional ( none_t ) noexcept ; ``[link reference_optional_constructor_none_t __GO_TO__]``
 
         optional ( T const& v ) ; ``[link reference_optional_constructor_value __GO_TO__]``
-        
+
         optional ( T&& v ) ; ``[link reference_optional_constructor_move_value __GO_TO__]``
 
-        // [new in 1.34]
-        optional ( bool condition, T const& v ) ; ``[link reference_optional_constructor_bool_value __GO_TO__]`` 
+        optional ( bool condition, T const& v ) ; ``[link reference_optional_constructor_bool_value __GO_TO__]``
 
         optional ( optional const& rhs ) ; ``[link reference_optional_constructor_optional __GO_TO__]``
-        
+
         optional ( optional&& rhs ) noexcept(``['see below]``) ; ``[link reference_optional_move_constructor_optional __GO_TO__]``
 
         template<class U> explicit optional ( optional<U> const& rhs ) ; ``[link reference_optional_constructor_other_optional __GO_TO__]``
-        
+
         template<class U> explicit optional ( optional<U>&& rhs ) ; ``[link reference_optional_move_constructor_other_optional __GO_TO__]``
 
+        template<class... Args> explicit optional ( in_place_init_t, Args&&... args ) ; ``[link reference_optional_in_place_init __GO_TO__]``
+
+        template<class... Args> explicit optional ( in_place_init_if_t, bool condition, Args&&... args ) ; ``[link reference_optional_in_place_init_if __GO_TO__]``
+
         template<class InPlaceFactory> explicit optional ( InPlaceFactory const& f ) ; ``[link reference_optional_constructor_factory __GO_TO__]``
 
         template<class TypedInPlaceFactory> explicit optional ( TypedInPlaceFactory const& f ) ; ``[link reference_optional_constructor_factory __GO_TO__]``
@@ -50,18 +152,18 @@
         optional& operator = ( none_t ) noexcept ; ``[link reference_optional_operator_equal_none_t __GO_TO__]``
 
         optional& operator = ( T const& v ) ; ``[link reference_optional_operator_equal_value __GO_TO__]``
-        
+
         optional& operator = ( T&& v ) ; ``[link reference_optional_operator_move_equal_value __GO_TO__]``
 
         optional& operator = ( optional const& rhs ) ; ``[link reference_optional_operator_equal_optional __GO_TO__]``
-        
+
         optional& operator = ( optional&& rhs ) noexcept(``['see below]``) ; ``[link reference_optional_operator_move_equal_optional __GO_TO__]``
 
         template<class U> optional& operator = ( optional<U> const& rhs ) ; ``[link reference_optional_operator_equal_other_optional __GO_TO__]``
-        
+
         template<class U> optional& operator = ( optional<U>&& rhs ) ; ``[link reference_optional_operator_move_equal_other_optional __GO_TO__]``
-        
-        template<class... Args> void emplace ( Args...&& args ) ; ``[link reference_optional_emplace __GO_TO__]``
+
+        template<class... Args> void emplace ( Args&&... args ) ; ``[link reference_optional_emplace __GO_TO__]``
 
         template<class InPlaceFactory> optional& operator = ( InPlaceFactory const& f ) ; ``[link reference_optional_operator_equal_factory __GO_TO__]``
 
@@ -76,29 +178,38 @@
         T const& operator *() const& ; ``[link reference_optional_operator_asterisk __GO_TO__]``
         T&       operator *() & ; ``[link reference_optional_operator_asterisk __GO_TO__]``
         T&&      operator *() && ; ``[link reference_optional_operator_asterisk_move __GO_TO__]``
-        
+
         T const& value() const& ; ``[link reference_optional_value __GO_TO__]``
         T&       value() & ; ``[link reference_optional_value __GO_TO__]``
         T&&      value() && ; ``[link reference_optional_value_move __GO_TO__]``
-        
+
         template<class U> T value_or( U && v ) const& ; ``[link reference_optional_value_or __GO_TO__]``
         template<class U> T value_or( U && v ) && ; ``[link reference_optional_value_or_move __GO_TO__]``
-        
+
         template<class F> T value_or_eval( F f ) const& ; ``[link reference_optional_value_or_call __GO_TO__]``
         template<class F> T value_or_eval( F f ) && ; ``[link reference_optional_value_or_call_move __GO_TO__]``
 
+        template<class F> auto map( F f ) const& -> ``['see below]``; ``[link reference_optional_map __GO_TO__]``
+        template<class F> auto map( F f ) & -> ``['see below]``; ``[link reference_optional_map __GO_TO__]``
+        template<class F> auto map( F f ) && -> ``['see below]``; ``[link reference_optional_map_move __GO_TO__]``
+
+        template<class F> auto flat_map( F f ) const& -> ``['see below]``; ``[link reference_optional_flat_map __GO_TO__]``
+        template<class F> auto flat_map( F f ) & -> ``['see below]``; ``[link reference_optional_flat_map __GO_TO__]``
+        template<class F> auto flat_map( F f ) && -> ``['see below]``; ``[link reference_optional_flat_map_move __GO_TO__]``
+
         T const* get_ptr() const ; ``[link reference_optional_get_ptr __GO_TO__]``
         T*       get_ptr() ; ``[link reference_optional_get_ptr __GO_TO__]``
 
+        bool has_value() const noexcept ; ``[link reference_optional_operator_bool __GO_TO__]``
+
         explicit operator bool() const noexcept ; ``[link reference_optional_operator_bool __GO_TO__]``
 
         bool operator!() const noexcept ; ``[link reference_optional_operator_not __GO_TO__]``
 
-        // deprecated methods
-
-        // (deprecated)
         void reset() noexcept ; ``[link reference_optional_reset __GO_TO__]``
 
+        // deprecated methods
+
         // (deprecated)
         void reset ( T const& ) ; ``[link reference_optional_reset_value __GO_TO__]``
 
@@ -106,46 +217,87 @@
         bool is_initialized() const ; ``[link reference_optional_is_initialized __GO_TO__]``
 
         // (deprecated)
-        T const& get_value_or( T const& default ) const ; ``[link reference_optional_get_value_or_value __GO_TO__]`` 
+        T const& get_value_or( T const& default ) const ; ``[link reference_optional_get_value_or_value __GO_TO__]``
     };
 
-    template<class T> inline bool operator == ( optional<T> const& x, optional<T> const& y ) ; ``[link reference_operator_compare_equal_optional_optional __GO_TO__]``
-
-    template<class T> inline bool operator != ( optional<T> const& x, optional<T> const& y ) ; ``[link reference_operator_compare_not_equal_optional_optional __GO_TO__]``
-
-    template<class T> inline bool operator <  ( optional<T> const& x, optional<T> const& y ) ; ``[link reference_operator_compare_less_optional_optional __GO_TO__]``
-
-    template<class T> inline bool operator >  ( optional<T> const& x, optional<T> const& y ) ; ``[link reference_operator_compare_greater_optional_optional __GO_TO__]``
-
-    template<class T> inline bool operator <= ( optional<T> const& x, optional<T> const& y ) ; ``[link reference_operator_compare_less_or_equal_optional_optional __GO_TO__]``
-
-    template<class T> inline bool operator >= ( optional<T> const& x, optional<T> const& y ) ; ``[link reference_operator_compare_greater_or_equal_optional_optional __GO_TO__]``
-    
-    template<class T> inline bool operator == ( optional<T> const& x, none_t ) noexcept ; ``[link reference_operator_compare_equal_optional_none __GO_TO__]``
-
-    template<class T> inline bool operator != ( optional<T> const& x, none_t ) noexcept ; ``[link reference_operator_compare_not_equal_optional_none __GO_TO__]``
-
-    template<class T> inline optional<T> make_optional ( T const& v ) ; ``[link reference_make_optional_value __GO_TO__]``
-
-    template<class T> inline optional<T> make_optional ( bool condition, T const& v ) ; ``[link reference_make_optional_bool_value __GO_TO__]``
-
-    template<class T> inline T const& get_optional_value_or ( optional<T> const& opt, T const& default ) ; ``[link reference_optional_get_value_or_value __GO_TO__]`` 
-
-    template<class T> inline T const& get ( optional<T> const& opt ) ; ``[link reference_optional_get __GO_TO__]``
-
-    template<class T> inline T& get ( optional<T> & opt ) ; ``[link reference_optional_get __GO_TO__]``
-
-    template<class T> inline T const* get ( optional<T> const* opt ) ; ``[link reference_optional_get __GO_TO__]``
-
-    template<class T> inline T* get ( optional<T>* opt ) ; ``[link reference_optional_get __GO_TO__]``
-
-    template<class T> inline T const* get_pointer ( optional<T> const& opt ) ; ``[link reference_optional_get_ptr __GO_TO__]``
-
-    template<class T> inline T* get_pointer ( optional<T> & opt ) ; ``[link reference_optional_get_ptr __GO_TO__]``
-
-    template<class T> inline void swap( optional<T>& x, optional<T>& y ) ; ``[link reference_swap_optional_optional __GO_TO__]``
-
-    } // namespace boost
-
 
 [endsect]
+
+
+[section:header_optional_optional_refs Optional References]
+
+[#reference_operator_template_spec]
+    template <class T>
+    class optional<T&> // specialization for lvalue references
+    {
+    public :
+
+        typedef T& value_type;
+        typedef T& reference_type;
+        typedef T& reference_const_type; // no const propagation
+        typedef T& rval_reference_type;
+        typedef T* pointer_type;
+        typedef T* pointer_const_type;   // no const propagation
+
+        optional () noexcept ; ``[link reference_optional_ref_default_ctor __GO_TO__]``
+
+        optional ( none_t ) noexcept ; ``[link reference_optional_ref_default_ctor __GO_TO__]``
+
+        template<class R> optional(R&& r) noexcept ;  ``[link reference_optional_ref_value_ctor __GO_TO__]``
+
+        template <class R> optional(bool cond, R&& r) noexcept ; ``[link reference_optional_ref_cond_value_ctor __GO_TO__]``
+
+        optional ( optional const& rhs ) noexcept ; ``[link reference_optional_ref_copy_ctor __GO_TO__]``
+
+        template<class U> explicit optional ( optional<U&> const& rhs ) noexcept ; ``[link reference_optional_ref_ctor_from_opt_U __GO_TO__]``
+
+        optional& operator = ( none_t ) noexcept ; ``[link reference_optional_ref_assign_none_t __GO_TO__]``
+
+        optional& operator = ( optional const& rhs ) noexcept; ``[link reference_optional_ref_copy_assign __GO_TO__]``
+
+        template<class U> optional& operator = ( optional<U&> const& rhs ) noexcept ; ``[link reference_optional_ref_assign_optional_U __GO_TO__]``
+
+        template<class R> optional& operator = (R&& r) noexcept ; ``[link reference_optional_ref_assign_R __GO_TO__]``
+
+        template<class R> void emplace ( R&& r ) noexcept ; ``[link reference_optional_ref_emplace_R __GO_TO__]``
+
+        T& get() const ; ``[link reference_optional_ref_get __GO_TO__]``
+        T& operator *() const ; ``[link reference_optional_ref_get __GO_TO__]``
+
+        T* operator ->() const ; ``[link reference_optional_ref_arrow __GO_TO__]``
+
+        T& value() const& ; ``[link reference_optional_ref_value __GO_TO__]``
+
+        template<class R> T& value_or( R && r ) const noexcept ; ``[link reference_optional_ref_value_or __GO_TO__]``
+
+        template<class F> T& value_or_eval( F f ) const ; ``[link reference_optional_ref_value_or_eval __GO_TO__]``
+
+        template<class F> auto map( F f ) const -> ``['see below]``; ``[link reference_optional_ref_map __GO_TO__]``
+
+        template<class F> auto flat_map( F f ) const -> ``['see below]``; ``[link reference_optional_ref_flat_map __GO_TO__]``
+
+        T* get_ptr() const noexcept ; ``[link reference_optional_ref_get_ptr __GO_TO__]``
+
+        bool has_value() const noexcept ; ``[link reference_optional_ref_operator_bool __GO_TO__]``
+
+        explicit operator bool() const noexcept ; ``[link reference_optional_ref_operator_bool __GO_TO__]``
+
+        bool operator!() const noexcept ; ``[link reference_optional_ref_operator_not __GO_TO__]``
+
+        void reset() noexcept ; ``[link reference_optional_ref_reset __GO_TO__]``
+
+        // deprecated methods
+
+        // (deprecated)
+        template<class R> void reset ( R && r ) noexcept ; ``[link reference_optional_ref_reset_value __GO_TO__]``
+
+        // (deprecated)
+        bool is_initialized() const noexcept ; ``[link reference_optional_ref_is_initialized __GO_TO__]``
+
+        // (deprecated)
+        template<class R> T& get_value_or( R && r ) constnoexcept; ``[link reference_optional_ref_get_value_or_value __GO_TO__]``
+
+    private:
+        T* ref; // exposition only
+    };
+[endsect]

doc/90_dependencies.qbk

@@ -27,20 +27,55 @@ The implementation uses the following other Boost modules:
 
 [endsect]
 
+[section Emplace operations in older compilers][#optional_emplace_workaround]
 
-[section Optional Reference Binding]
+Certain constructors and functions in the interface of `optional` perform a 'perfect forwarding' of arguments:
 
-On compilers that do not conform to Standard C++ rules of reference binding, operations on optional references might give adverse results: rather than binding a reference to a designated object they may create an unexpected temporary and bind to it. Compilers known to have these deficiencies include GCC versions 4.2, 4.3, 4.4, 4.5; QCC 4.4.2; MSVC versions 8.0, 9.0, 10.0, 11.0, 12.0. On these compilers prefer using direct-initialization and copy assignment of optional references to copy-initialization and assignment from `T&`:
+    template<class... Args> optional(in_place_init_t, Args&&... args);
+    template<class... Args> optional(in_place_init_if_t, bool condition, Args&&... args);
+    template<class... Args> void emplace(Args&&... args);
+    
+On compilers that do not support variadic templates, each of these functions is substituted with two overloads, one forwarding a single argument, the other forwarding zero arguments. This forms the following set:
+
+    template<class Arg> optional(in_place_init_t, Arg&& arg);
+    optional(in_place_init_t);
+    
+    template<class Arg> optional(in_place_init_if_t, bool condition, Arg&& arg);
+    optional(in_place_init_if_t, bool condition);
+    
+    template<class Arg> void emplace(Arg&& arg);
+    void emplace();
+
+On compilers that do not support rvalue references, each of these functions is substituted with three overloads: taking `const` and non-`const` lvalue reference, and third forwarding zero arguments. This forms the following set:
+
+    template<class Arg> optional(in_place_init_t, const Arg& arg);
+    template<class Arg> optional(in_place_init_t, Arg& arg);
+    optional(in_place_init_t);
+    
+    template<class Arg> optional(in_place_init_if_t, bool condition, const Arg& arg);
+    template<class Arg> optional(in_place_init_if_t, bool condition, Arg& arg);
+    optional(in_place_init_if_t, bool condition);
+    
+    template<class Arg> void emplace(const Arg& arg);
+    template<class Arg> void emplace(Arg& arg);
+    void emplace();
+
+This workaround addresses about 40% of all use cases. If this is insufficient, you need to resort to using [link boost_optional.tutorial.in_place_factories In-Place Factories].    
+[endsect]
+
+[section Optional Reference Binding][#optional_reference_binding]
+
+A number of compilers incorrectly treat const lvalues of integral type as rvalues, and create an illegal temporary when binding to an lvalue reference to const in some expressions. This could result in creating an optional lvalue reference that is in fact bound to an unexpected temporary rather than to the intended object. In order to prevent hard to find run-time bugs, this library performs compile-time checks to prevent expressions that would otherwise bind an optional reference to an unexpected temporary. As a consequence, on certain compilers certain pieces of functionality in optional references are missing. In order to maintain a portability of your code across different compilers, it is recommended that you only stick to the minimum portable interface of optional references: prefer direct-initialization and copy assignment of optional references to copy-initialization and assignment from `T&`:
 
     const int i = 0;
     optional<const int&> or1;
-    optional<const int&> or2 = i;  // not portable
-    or1 = i;                       // not portable
+    optional<const int&> or2 = i;  // caution: not portable
+    or1 = i;                       // caution: not portable
     
     optional<const int&> or3(i);   // portable
     or1 = optional<const int&>(i); // portable
 
-In order to check if your compiler correctly implements reference binding use this test program. 
+Compilers known to have these deficiencies include GCC versions 4.2, 4.3, 4.4, 4.5, 5.1, 5.2; QCC 4.4.2; MSVC versions 8.0, 9.0, 10.0, 11.0, 12.0. In order to check if your compiler correctly implements reference binding use this test program. 
 
     #include <cassert>
 

doc/91_relnotes.qbk

@@ -1,7 +1,7 @@
 [/
     Boost.Optional
 
-    Copyright (c) 2015 Andrzej Krzemienski
+    Copyright (c) 2015 - 2022 Andrzej Krzemienski
 
     Distributed under the Boost Software License, Version 1.0.
     (See accompanying file LICENSE_1_0.txt or copy at
@@ -11,9 +11,97 @@
 
 [section:relnotes Release Notes]
 
+[heading Boost Release 1.83]
+
+* Deprecated support for C++03 and earlier, C++11 will be required in release 1.86.
+
+[heading Boost Release 1.80]
+
+* [*Breaking change:] Added specializations for `std::hash<boost::optional<T>>`. This fixes [@https://github.com/boostorg/optional/issues/55 issue #55]. You may get compiler errors when your program provides specializations for `std::hash<boost::optional<T>>`. If this happens, define macro `BOOST_OPTIONAL_CONFIG_DO_NOT_SPECIALIZE_STD_HASH` to suppress the specializations of `std::hash` in this library.
+
+[heading Boost Release 1.79]
+
+* Fixed [@https://github.com/boostorg/optional/issues/98 issue #98].
+* Fixed [@https://github.com/boostorg/optional/issues/92 issue #92].
+* Added support for `BOOST_NO_IOSTREAM`.
+* Now aligned storage uses `unsigned char` rather than `char` to avoid UB.
+* Now using cv-unqualified `value_type` with placement `new` to avoid UB.
+
+[heading Boost Release 1.76]
+
+* Fixed MSVC warning C4702.
+
+[heading Boost Release 1.75]
+
+* `boost::none` is `constexpr`-declared.
+
+* Fixed [@https://github.com/boostorg/optional/issues/78 issue #78].
+
+[heading Boost Release 1.73]
+
+* Fixed [@https://github.com/boostorg/optional/issues/78 issue #78].
+* `boost::none` is now declared as an inline variable (on compilers that support it): there is only one instance of `boost::none` across all translation units.
+* Fixed a number of compilation errors in GCC 4.4.7 in `optional<T>` for trivial `T`s. Thanks to Robert Leahy for the fix. For details see [@https://github.com/boostorg/optional/pull/80 pr #78].
+* Now suppressing warning `-Wweak-vtables`.
+
+[heading Boost Release 1.69]
+
+* Remove deprecation mark from `reset()` method (without arguments).
+* Fixed [@https://github.com/boostorg/optional/issues/59 issue #59].
+* Fixed bug with initialization of certain wrapper types in clang with -std=c++03. See [@https://github.com/boostorg/optional/pull/64 pr #64].
+
+[heading Boost Release 1.68]
+
+* Added member function `has_value()` for compatibility with `std::optional` ([@https://github.com/boostorg/optional/issues/52 issue #52]).
+* Added member function `map()` for transforming `optional<T>` into `optional<U>` using a function of type `T -> U`.
+* Added member function `flat_map()` for transforming `optional<T>` into `optional<U>` using a function of type `T -> optional<U>`.
+
+
+[heading Boost Release 1.67]
+
+* Fixed [@https://github.com/boostorg/optional/issues/46 issue #46].
+* Fixed `-Wzero-as-null-pointer-constant` warnings.
+
+
+[heading Boost Release 1.66]
+
+* On newer compilers `optional` is now trivially-copyable for scalar `T`s. This uses a different storage (just `T` rather than `aligned_storage`). We require the compiler to support defaulted functions.
+* Changed the implementation of `operator==` to get rid of the `-Wmaybe-uninitialized` false-positive warning from GCC.
+
+[heading Boost Release 1.63]
+* Added two new in-place constructors. They work similarly to `emplace()` functions: they initialize the contained value by perfect-forwarding the obtained arguments. One constructor always initializes the contained value, the other based on a boolean condition.
+* Syntax `o = {}` now correctly un-initializes optional, just like in `std::optional`.
+* Fixed [@https://svn.boost.org/trac/boost/ticket/12203 Trac #12203].
+* Fixed [@https://svn.boost.org/trac/boost/ticket/12563 Trac #12563].
+
+
+[heading Boost Release 1.62]
+
+* Fixed [@https://svn.boost.org/trac/boost/ticket/12179 Trac #12179].
+
+
+[heading Boost Release 1.61]
+
+* Now `boost::optional` is specialized for reference parameters. This addresses a couple of issues:
+  * the `sizeof` of optional reference is that of a pointer,
+  * some bugs connected to copying optional references are gone,
+  * all run-time bugs caused by incorrect reference binding on some compilers are now turned into compile-time errors,
+  * you can swap optional references: it is like swapping pointers: shallow, underlying objects are not affected,
+  * optional references to abstract types work.
+* Documented nested typedefs ([@https://svn.boost.org/trac/boost/ticket/5193 Trac #5193]).
+* Made the perfect-forwarding constructor SFINAE-friendly, which fixes [@https://svn.boost.org/trac/boost/ticket/12002 Trac #12002]. However, this only works in the newer platforms that correctly implement C++11 `<type_traits>`.
+* Fixed [@https://svn.boost.org/trac/boost/ticket/10445 Trac #10445].
+
+
+[heading Boost Release 1.60]
+
+* Changed the implementation of `boost::none` again. Now it is a const object with internal linkage (as any other tag). This fixes [@https://svn.boost.org/trac/boost/ticket/11203 Trac #11203].
+
+
 [heading Boost Release 1.59]
 
 * For C++03 compilers, added 0-argument overload for member function `emplace()`, and therewith removed the dependency on `<boost/utility/in_place_factory.hpp>`.
+* Fixed [@https://svn.boost.org/trac/boost/ticket/11241 Trac #11241].
 
 [heading Boost Release 1.58]
 
@@ -22,7 +110,7 @@
 * IOStream operators are now mentioned in documentation.
 * Added a way to manually disable move semantics: just define macro `BOOST_OPTIONAL_CONFIG_NO_RVALUE_REFERENCES`. This can be used to work around [@https://svn.boost.org/trac/boost/ticket/10399 Trac #10399].
 * It is no longer possible to assign `optional<U>` to `optional<T>` when `U` is not assignable or convertible to `T` ([@https://svn.boost.org/trac/boost/ticket/11087 Trac #11087]).
-* Value accessors now work correctly on rvalues of `optional<T&>` ([@https://svn.boost.org/trac/boost/ticket/10839 Trac #10839]).  
+* Value accessors now work correctly on rvalues of `optional<T&>` ([@https://svn.boost.org/trac/boost/ticket/10839 Trac #10839]).
 
 
 [heading Boost Release 1.57]

doc/Jamfile.v2

@@ -46,4 +46,8 @@ boostbook standalone
         <format>docbook:<auto-index-internal>on
     ;
 
-
+###############################################################################
+alias boostdoc ;
+explicit boostdoc ;
+alias boostrelease : standalone ;
+explicit boostrelease ;

doc/html/boost_optional/acknowledgements.html

@@ -1,9 +1,9 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Acknowledgements</title>
 <link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="../index.html" title="Boost.Optional">
 <link rel="up" href="../index.html" title="Boost.Optional">
 <link rel="prev" href="relnotes.html" title="Release Notes">
@@ -116,7 +116,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>

doc/html/boost_optional/dependencies_and_portability.html

@@ -1,13 +1,13 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Dependencies and Portability</title>
 <link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="../index.html" title="Boost.Optional">
 <link rel="up" href="../index.html" title="Boost.Optional">
 <link rel="prev" href="reference/header__boost_optional_hpp_.html" title="Header &lt;boost/optional.hpp&gt;">
-<link rel="next" href="dependencies_and_portability/optional_reference_binding.html" title="Optional Reference Binding">
+<link rel="next" href="dependencies_and_portability/emplace_operations_in_older_compilers.html" title="Emplace operations in older compilers">
 </head>
 <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
 <table cellpadding="2" width="100%"><tr>
@@ -20,7 +20,7 @@
 </tr></table>
 <hr>
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-<a accesskey="p" href="reference/header__boost_optional_hpp_.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="dependencies_and_portability/optional_reference_binding.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
+<a accesskey="p" href="reference/header__boost_optional_hpp_.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="dependencies_and_portability/emplace_operations_in_older_compilers.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
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 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
@@ -29,6 +29,8 @@
 </h2></div></div></div>
 <div class="toc"><dl class="toc">
 <dt><span class="section"><a href="dependencies_and_portability.html#boost_optional.dependencies_and_portability.dependencies">Dependencies</a></span></dt>
+<dt><span class="section"><a href="dependencies_and_portability/emplace_operations_in_older_compilers.html">Emplace
+      operations in older compilers</a></span></dt>
 <dt><span class="section"><a href="dependencies_and_portability/optional_reference_binding.html">Optional
       Reference Binding</a></span></dt>
 </dl></div>
@@ -75,7 +77,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>
@@ -83,7 +85,7 @@
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 <hr>
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+<a accesskey="p" href="reference/header__boost_optional_hpp_.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="dependencies_and_portability/emplace_operations_in_older_compilers.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
 </div>
 </body>
 </html>

doc/html/boost_optional/dependencies_and_portability/emplace_operations_in_older_compilers.html

@@ -0,0 +1,90 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
+<title>Emplace operations in older compilers</title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../index.html" title="Boost.Optional">
+<link rel="up" href="../dependencies_and_portability.html" title="Dependencies and Portability">
+<link rel="prev" href="../dependencies_and_portability.html" title="Dependencies and Portability">
+<link rel="next" href="optional_reference_binding.html" title="Optional Reference Binding">
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+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../index.html">Home</a></td>
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+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../dependencies_and_portability.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../dependencies_and_portability.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="optional_reference_binding.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.dependencies_and_portability.emplace_operations_in_older_compilers"></a><a class="link" href="emplace_operations_in_older_compilers.html" title="Emplace operations in older compilers">Emplace
+      operations in older compilers</a>
+</h3></div></div></div>
+<p>
+        <a name="optional_emplace_workaround"></a>Certain constructors and functions
+        in the interface of <code class="computeroutput"><span class="identifier">optional</span></code>
+        perform a 'perfect forwarding' of arguments:
+      </p>
+<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">&gt;</span> <span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_t</span><span class="special">,</span> <span class="identifier">Args</span><span class="special">&amp;&amp;...</span> <span class="identifier">args</span><span class="special">);</span>
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">&gt;</span> <span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_if_t</span><span class="special">,</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="identifier">Args</span><span class="special">&amp;&amp;...</span> <span class="identifier">args</span><span class="special">);</span>
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">&gt;</span> <span class="keyword">void</span> <span class="identifier">emplace</span><span class="special">(</span><span class="identifier">Args</span><span class="special">&amp;&amp;...</span> <span class="identifier">args</span><span class="special">);</span>
+</pre>
+<p>
+        On compilers that do not support variadic templates, each of these functions
+        is substituted with two overloads, one forwarding a single argument, the
+        other forwarding zero arguments. This forms the following set:
+      </p>
+<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">Arg</span><span class="special">&gt;</span> <span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_t</span><span class="special">,</span> <span class="identifier">Arg</span><span class="special">&amp;&amp;</span> <span class="identifier">arg</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_t</span><span class="special">);</span>
+
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">Arg</span><span class="special">&gt;</span> <span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_if_t</span><span class="special">,</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="identifier">Arg</span><span class="special">&amp;&amp;</span> <span class="identifier">arg</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_if_t</span><span class="special">,</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">);</span>
+
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">Arg</span><span class="special">&gt;</span> <span class="keyword">void</span> <span class="identifier">emplace</span><span class="special">(</span><span class="identifier">Arg</span><span class="special">&amp;&amp;</span> <span class="identifier">arg</span><span class="special">);</span>
+<span class="keyword">void</span> <span class="identifier">emplace</span><span class="special">();</span>
+</pre>
+<p>
+        On compilers that do not support rvalue references, each of these functions
+        is substituted with three overloads: taking <code class="computeroutput"><span class="keyword">const</span></code>
+        and non-<code class="computeroutput"><span class="keyword">const</span></code> lvalue reference,
+        and third forwarding zero arguments. This forms the following set:
+      </p>
+<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">Arg</span><span class="special">&gt;</span> <span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_t</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">Arg</span><span class="special">&amp;</span> <span class="identifier">arg</span><span class="special">);</span>
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">Arg</span><span class="special">&gt;</span> <span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_t</span><span class="special">,</span> <span class="identifier">Arg</span><span class="special">&amp;</span> <span class="identifier">arg</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_t</span><span class="special">);</span>
+
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">Arg</span><span class="special">&gt;</span> <span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_if_t</span><span class="special">,</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">Arg</span><span class="special">&amp;</span> <span class="identifier">arg</span><span class="special">);</span>
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">Arg</span><span class="special">&gt;</span> <span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_if_t</span><span class="special">,</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="identifier">Arg</span><span class="special">&amp;</span> <span class="identifier">arg</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_if_t</span><span class="special">,</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">);</span>
+
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">Arg</span><span class="special">&gt;</span> <span class="keyword">void</span> <span class="identifier">emplace</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">Arg</span><span class="special">&amp;</span> <span class="identifier">arg</span><span class="special">);</span>
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">Arg</span><span class="special">&gt;</span> <span class="keyword">void</span> <span class="identifier">emplace</span><span class="special">(</span><span class="identifier">Arg</span><span class="special">&amp;</span> <span class="identifier">arg</span><span class="special">);</span>
+<span class="keyword">void</span> <span class="identifier">emplace</span><span class="special">();</span>
+</pre>
+<p>
+        This workaround addresses about 40% of all use cases. If this is insufficient,
+        you need to resort to using <a class="link" href="../tutorial/in_place_factories.html" title="In-Place Factories">In-Place
+        Factories</a>.
+      </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+      </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../dependencies_and_portability.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../dependencies_and_portability.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="optional_reference_binding.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>

doc/html/boost_optional/dependencies_and_portability/optional_reference_binding.html

@@ -1,12 +1,12 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Optional Reference Binding</title>
 <link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="../../index.html" title="Boost.Optional">
 <link rel="up" href="../dependencies_and_portability.html" title="Dependencies and Portability">
-<link rel="prev" href="../dependencies_and_portability.html" title="Dependencies and Portability">
+<link rel="prev" href="emplace_operations_in_older_compilers.html" title="Emplace operations in older compilers">
 <link rel="next" href="../relnotes.html" title="Release Notes">
 </head>
 <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
@@ -20,7 +20,7 @@
 </tr></table>
 <hr>
 <div class="spirit-nav">
-<a accesskey="p" href="../dependencies_and_portability.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../dependencies_and_portability.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../relnotes.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+<a accesskey="p" href="emplace_operations_in_older_compilers.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../dependencies_and_portability.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../relnotes.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
 </div>
 <div class="section">
 <div class="titlepage"><div><div><h3 class="title">
@@ -28,24 +28,31 @@
       Reference Binding</a>
 </h3></div></div></div>
 <p>
-        On compilers that do not conform to Standard C++ rules of reference binding,
-        operations on optional references might give adverse results: rather than
-        binding a reference to a designated object they may create an unexpected
-        temporary and bind to it. Compilers known to have these deficiencies include
-        GCC versions 4.2, 4.3, 4.4, 4.5; QCC 4.4.2; MSVC versions 8.0, 9.0, 10.0,
-        11.0, 12.0. On these compilers prefer using direct-initialization and copy
-        assignment of optional references to copy-initialization and assignment from
-        <code class="computeroutput"><span class="identifier">T</span><span class="special">&amp;</span></code>:
+        <a name="optional_reference_binding"></a>A number of compilers incorrectly
+        treat const lvalues of integral type as rvalues, and create an illegal temporary
+        when binding to an lvalue reference to const in some expressions. This could
+        result in creating an optional lvalue reference that is in fact bound to
+        an unexpected temporary rather than to the intended object. In order to prevent
+        hard to find run-time bugs, this library performs compile-time checks to
+        prevent expressions that would otherwise bind an optional reference to an
+        unexpected temporary. As a consequence, on certain compilers certain pieces
+        of functionality in optional references are missing. In order to maintain
+        a portability of your code across different compilers, it is recommended that
+        you only stick to the minimum portable interface of optional references:
+        prefer direct-initialization and copy assignment of optional references to
+        copy-initialization and assignment from <code class="computeroutput"><span class="identifier">T</span><span class="special">&amp;</span></code>:
       </p>
 <pre class="programlisting"><span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
 <span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&amp;&gt;</span> <span class="identifier">or1</span><span class="special">;</span>
-<span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&amp;&gt;</span> <span class="identifier">or2</span> <span class="special">=</span> <span class="identifier">i</span><span class="special">;</span>  <span class="comment">// not portable</span>
-<span class="identifier">or1</span> <span class="special">=</span> <span class="identifier">i</span><span class="special">;</span>                       <span class="comment">// not portable</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&amp;&gt;</span> <span class="identifier">or2</span> <span class="special">=</span> <span class="identifier">i</span><span class="special">;</span>  <span class="comment">// caution: not portable</span>
+<span class="identifier">or1</span> <span class="special">=</span> <span class="identifier">i</span><span class="special">;</span>                       <span class="comment">// caution: not portable</span>
 
 <span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&amp;&gt;</span> <span class="identifier">or3</span><span class="special">(</span><span class="identifier">i</span><span class="special">);</span>   <span class="comment">// portable</span>
 <span class="identifier">or1</span> <span class="special">=</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&amp;&gt;(</span><span class="identifier">i</span><span class="special">);</span> <span class="comment">// portable</span>
 </pre>
 <p>
+        Compilers known to have these deficiencies include GCC versions 4.2, 4.3,
+        4.4, 4.5, 5.1, 5.2; QCC 4.4.2; MSVC versions 8.0, 9.0, 10.0, 11.0, 12.0.
         In order to check if your compiler correctly implements reference binding
         use this test program.
       </p>
@@ -86,7 +93,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>
@@ -94,7 +101,7 @@
 </tr></table>
 <hr>
 <div class="spirit-nav">
-<a accesskey="p" href="../dependencies_and_portability.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../dependencies_and_portability.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../relnotes.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+<a accesskey="p" href="emplace_operations_in_older_compilers.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../dependencies_and_portability.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../relnotes.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
 </div>
 </body>
 </html>

doc/html/boost_optional/detailed_semantics.html

@@ -422,7 +422,7 @@
 <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;&gt;</span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">uninit</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
 <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span>
 
-<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;&gt;</span> <span class="identifier">init</span><span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">uniqye_ptr</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;(</span><span class="keyword">new</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">))</span> <span class="special">);</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;&gt;</span> <span class="identifier">init</span><span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;(</span><span class="keyword">new</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">))</span> <span class="special">);</span>
 <span class="identifier">assert</span> <span class="special">(</span> <span class="special">**</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
 
 <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;&gt;</span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">init</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>

doc/html/boost_optional/development.html

@@ -293,8 +293,8 @@
       </p>
 <h5>
 <a name="boost_optional.development.the_interface.h0"></a>
-        <span class="phrase"><a name="boost_optional.development.the_interface.lexically_hinted_value_access_in_the_presence_of_possibly_untitialized_optional_objects__the_operators___and___gt_"></a></span><a class="link" href="development.html#boost_optional.development.the_interface.lexically_hinted_value_access_in_the_presence_of_possibly_untitialized_optional_objects__the_operators___and___gt_">Lexically-hinted
-        Value Access in the presence of possibly untitialized optional objects: The
+        <span class="phrase"><a name="boost_optional.development.the_interface.lexically_hinted_value_access_in_the_presence_of_possibly_uninitialized_optional_objects__the_operators___and___gt_"></a></span><a class="link" href="development.html#boost_optional.development.the_interface.lexically_hinted_value_access_in_the_presence_of_possibly_uninitialized_optional_objects__the_operators___and___gt_">Lexically-hinted
+        Value Access in the presence of possibly uninitialized optional objects: The
         operators * and -&gt;</a>
       </h5>
 <p>

doc/html/boost_optional/exception_safety_guarantees.html

@@ -148,7 +148,7 @@
       move constructor are replaced with the calls to <code class="computeroutput"><span class="identifier">T</span></code>'s
       default constructor followed by <code class="computeroutput"><span class="identifier">swap</span></code>.
       (This is more useful on older compilers that do not support move semantics,
-      when one wants to acheive stronger exception safety guarantees.) In this case
+      when one wants to achieve stronger exception safety guarantees.) In this case
       the exception safety guarantees for <code class="computeroutput"><span class="identifier">swap</span></code>
       are reliant on the guarantees of <code class="computeroutput"><span class="identifier">T</span></code>'s
       <code class="computeroutput"><span class="identifier">swap</span></code> and default constructor

doc/html/boost_optional/optional_references.html

@@ -55,7 +55,7 @@
 <p>
       Also, even though <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;</span></code>
       treats it wrapped pseudo-object much as a real value, a true real reference
-      is stored so aliasing will ocurr:
+      is stored so aliasing will occur:
     </p>
 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
 <li class="listitem">

doc/html/boost_optional/quick_start.html

@@ -1,9 +1,9 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Quick Start</title>
 <link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="../index.html" title="Boost.Optional">
 <link rel="up" href="../index.html" title="Boost.Optional">
 <link rel="prev" href="../index.html" title="Boost.Optional">
@@ -100,7 +100,7 @@
 <span class="special">}</span>
 </pre>
 <p>
-        This version throws an exception upon an attempt to access a non-existent
+        This version throws an exception upon an attempt to access a nonexistent
         contained value. If your way of dealing with the missing value is to use
         some default, like <code class="computeroutput"><span class="number">0</span></code>, there exists
         a yet another alternative:
@@ -155,7 +155,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>

doc/html/boost_optional/quick_start/bypassing_unnecessary_default_construction.html

@@ -1,9 +1,9 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Bypassing unnecessary default construction</title>
 <link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="../../index.html" title="Boost.Optional">
 <link rel="up" href="../quick_start.html" title="Quick Start">
 <link rel="prev" href="optional_data_members.html" title="Optional data members">
@@ -61,7 +61,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>

doc/html/boost_optional/quick_start/optional_automatic_variables.html

@@ -1,9 +1,9 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Optional automatic variables</title>
 <link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="../../index.html" title="Boost.Optional">
 <link rel="up" href="../quick_start.html" title="Quick Start">
 <link rel="prev" href="../quick_start.html" title="Quick Start">
@@ -44,7 +44,7 @@
 </pre>
 <p>
         The default constructor of <code class="computeroutput"><span class="identifier">optional</span></code>
-        creates an unitialized optional object. Unlike with <code class="computeroutput"><span class="keyword">int</span></code>s
+        creates an uninitialized optional object. Unlike with <code class="computeroutput"><span class="keyword">int</span></code>s
         you cannot have an <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span></code>
         in an indeterminate state. Its state is always well defined. Instruction
         <code class="computeroutput"><span class="identifier">ans</span> <span class="special">=</span>
@@ -61,7 +61,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>

doc/html/boost_optional/quick_start/optional_data_members.html

@@ -1,9 +1,9 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Optional data members</title>
 <link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="../../index.html" title="Boost.Optional">
 <link rel="up" href="../quick_start.html" title="Quick Start">
 <link rel="prev" href="optional_automatic_variables.html" title="Optional automatic variables">
@@ -80,7 +80,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>

doc/html/boost_optional/quick_start/optional_return_values.html

@@ -37,7 +37,7 @@
         is possible. A natural signature for this function can be:
       </p>
 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">optional</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
-<span class="identifier">boost</span><span class="special">::</span><span class="identifier">optionl</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">convert</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&amp;</span> <span class="identifier">text</span><span class="special">);</span>
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">convert</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&amp;</span> <span class="identifier">text</span><span class="special">);</span>
 </pre>
 <p>
         All necessary functionality can be included with one header <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">optional</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>.
@@ -49,7 +49,7 @@
         can use our function:
       </p>
 <pre class="programlisting"><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&amp;</span> <span class="identifier">text</span> <span class="special">=</span> <span class="comment">/*... */</span><span class="special">;</span>
-<span class="identifier">boost</span><span class="special">::</span><span class="identifier">optionl</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">oi</span> <span class="special">=</span> <span class="identifier">convert</span><span class="special">(</span><span class="identifier">text</span><span class="special">);</span> <span class="comment">// move-construct</span>
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">oi</span> <span class="special">=</span> <span class="identifier">convert</span><span class="special">(</span><span class="identifier">text</span><span class="special">);</span> <span class="comment">// move-construct</span>
 <span class="keyword">if</span> <span class="special">(</span><span class="identifier">oi</span><span class="special">)</span>                                 <span class="comment">// contextual conversion to bool</span>
   <span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">oi</span><span class="special">;</span>                          <span class="comment">// operator*</span>
 </pre>
@@ -58,7 +58,7 @@
         contains a value, we use the contextual conversion to type <code class="computeroutput"><span class="keyword">bool</span></code>. Because of this we can combine the initialization
         of the optional object and the test into one instruction:
       </p>
-<pre class="programlisting"><span class="keyword">if</span> <span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optionl</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">oi</span> <span class="special">=</span> <span class="identifier">convert</span><span class="special">(</span><span class="identifier">text</span><span class="special">))</span>
+<pre class="programlisting"><span class="keyword">if</span> <span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">oi</span> <span class="special">=</span> <span class="identifier">convert</span><span class="special">(</span><span class="identifier">text</span><span class="special">))</span>
   <span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">oi</span><span class="special">;</span>
 </pre>
 <p>
@@ -84,7 +84,7 @@
 <span class="special">}</span>
 </pre>
 <p>
-        This version throws an exception upon an attempt to access a non-existent
+        This version throws an exception upon an attempt to access a nonexistent
         contained value. If your way of dealing with the missing value is to use
         some default, like <code class="computeroutput"><span class="number">0</span></code>, there exists
         a yet another alternative:
@@ -98,7 +98,7 @@
         Now, let's consider how function <code class="computeroutput"><span class="identifier">convert</span></code>
         can be implemented.
       </p>
-<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optionl</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">convert</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&amp;</span> <span class="identifier">text</span><span class="special">)</span>
+<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">convert</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&amp;</span> <span class="identifier">text</span><span class="special">)</span>
 <span class="special">{</span>
   <span class="identifier">std</span><span class="special">::</span><span class="identifier">stringstream</span> <span class="identifier">s</span><span class="special">(</span><span class="identifier">text</span><span class="special">);</span>
   <span class="keyword">int</span> <span class="identifier">i</span><span class="special">;</span>

doc/html/boost_optional/quick_start/storage_in_containers.html

@@ -1,9 +1,9 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Storage in containers</title>
 <link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="../../index.html" title="Boost.Optional">
 <link rel="up" href="../quick_start.html" title="Quick Start">
 <link rel="prev" href="bypassing_unnecessary_default_construction.html" title="Bypassing unnecessary default construction">
@@ -50,7 +50,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>

doc/html/boost_optional/reference/acknowledgements.html

@@ -0,0 +1,131 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Acknowledgements</title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<link rel="home" href="../../index.html" title="Boost.Optional">
+<link rel="up" href="../../optional/reference.html" title="Reference">
+<link rel="prev" href="relnotes.html" title="Release Notes">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../index.html">Home</a></td>
+<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td>
+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="relnotes.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.reference.acknowledgements"></a><a class="link" href="acknowledgements.html" title="Acknowledgements">Acknowledgements</a>
+</h3></div></div></div>
+<h5>
+<a name="boost_optional.reference.acknowledgements.h0"></a>
+        <span class="phrase"><a name="boost_optional.reference.acknowledgements.pre_formal_review"></a></span><a class="link" href="acknowledgements.html#boost_optional.reference.acknowledgements.pre_formal_review">Pre-formal
+        review</a>
+      </h5>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+            Peter Dimov suggested the name 'optional', and was the first to point
+            out the need for aligned storage.
+          </li>
+<li class="listitem">
+            Douglas Gregor developed 'type_with_alignment', and later Eric Friedman
+            coded 'aligned_storage', which are the core of the optional class implementation.
+          </li>
+<li class="listitem">
+            Andrei Alexandrescu and Brian Parker also worked with aligned storage
+            techniques and their work influenced the current implementation.
+          </li>
+<li class="listitem">
+            Gennadiy Rozental made extensive and important comments which shaped
+            the design.
+          </li>
+<li class="listitem">
+            Vesa Karvonen and Douglas Gregor made quite useful comparisons between
+            optional, variant and any; and made other relevant comments.
+          </li>
+<li class="listitem">
+            Douglas Gregor and Peter Dimov commented on comparisons and evaluation
+            in boolean contexts.
+          </li>
+<li class="listitem">
+            Eric Friedman helped understand the issues involved with aligned storage,
+            move/copy operations and exception safety.
+          </li>
+<li class="listitem">
+            Many others have participated with useful comments: Aleksey Gurotov,
+            Kevlin Henney, David Abrahams, and others I can't recall.
+          </li>
+</ul></div>
+<h5>
+<a name="boost_optional.reference.acknowledgements.h1"></a>
+        <span class="phrase"><a name="boost_optional.reference.acknowledgements.post_formal_review"></a></span><a class="link" href="acknowledgements.html#boost_optional.reference.acknowledgements.post_formal_review">Post-formal
+        review</a>
+      </h5>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+            William Kempf carefully considered the originally proposed interface
+            and suggested the new interface which is currently used. He also started
+            and fueled the discussion about the analogy optional&lt;&gt;/smart pointer
+            and about relational operators.
+          </li>
+<li class="listitem">
+            Peter Dimov, Joel de Guzman, David Abrahams, Tanton Gibbs and Ian Hanson
+            focused on the relational semantics of optional (originally undefined);
+            concluding with the fact that the pointer-like interface doesn't make
+            it a pointer so it shall have deep relational operators.
+          </li>
+<li class="listitem">
+            Augustus Saunders also explored the different relational semantics between
+            optional&lt;&gt; and a pointer and developed the OptionalPointee concept
+            as an aid against potential conflicts on generic code.
+          </li>
+<li class="listitem">
+            Joel de Guzman noticed that optional&lt;&gt; can be seen as an API on
+            top of variant&lt;T,nil_t&gt;.
+          </li>
+<li class="listitem">
+            Dave Gomboc explained the meaning and usage of the Haskell analog to
+            optional&lt;&gt;: the Maybe type constructor (analogy originally pointed
+            out by David Sankel).
+          </li>
+<li class="listitem">
+            Other comments were posted by Vincent Finn, Anthony Williams, Ed Brey,
+            Rob Stewart, and others.
+          </li>
+<li class="listitem">
+            Joel de Guzman made the case for the support of references and helped
+            with the proper semantics.
+          </li>
+<li class="listitem">
+            Mat Marcus shown the virtues of a value-oriented interface, influencing
+            the current design, and contributed the idea of "none".
+          </li>
+<li class="listitem">
+            Vladimir Batov's design of Boost.Convert library motivated the development
+            of value accessors for <code class="computeroutput"><span class="identifier">optional</span></code>:
+            functions <code class="computeroutput"><span class="identifier">value</span></code>, <code class="computeroutput"><span class="identifier">value_or</span></code>, <code class="computeroutput"><span class="identifier">value_or_eval</span></code>.
+          </li>
+</ul></div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014-2016 Andrzej Krzemie&#324;ski<p>
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+      </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="relnotes.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a>
+</div>
+</body>
+</html>

doc/html/boost_optional/reference/dependencies_and_portability.html

@@ -0,0 +1,84 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Dependencies and Portability</title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<link rel="home" href="../../index.html" title="Boost.Optional">
+<link rel="up" href="../../optional/reference.html" title="Reference">
+<link rel="prev" href="header__boost_optional_optional_hpp_/header__boost_optional_hpp_.html" title="Header &lt;boost/optional.hpp&gt;">
+<link rel="next" href="dependencies_and_portability/optional_reference_binding.html" title="Optional Reference Binding">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../index.html">Home</a></td>
+<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td>
+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="header__boost_optional_optional_hpp_/header__boost_optional_hpp_.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="dependencies_and_portability/optional_reference_binding.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.reference.dependencies_and_portability"></a><a class="link" href="dependencies_and_portability.html" title="Dependencies and Portability">Dependencies
+      and Portability</a>
+</h3></div></div></div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.reference.dependencies_and_portability.dependencies"></a><a class="link" href="dependencies_and_portability.html#boost_optional.reference.dependencies_and_portability.dependencies" title="Dependencies">Dependencies</a>
+</h4></div></div></div>
+<p>
+          The implementation uses the following other Boost modules:
+        </p>
+<div class="orderedlist"><ol class="orderedlist" type="1">
+<li class="listitem">
+              assert
+            </li>
+<li class="listitem">
+              config
+            </li>
+<li class="listitem">
+              core
+            </li>
+<li class="listitem">
+              detail
+            </li>
+<li class="listitem">
+              move
+            </li>
+<li class="listitem">
+              mpl
+            </li>
+<li class="listitem">
+              static_assert
+            </li>
+<li class="listitem">
+              throw_exception
+            </li>
+<li class="listitem">
+              type_traits
+            </li>
+<li class="listitem">
+              utility
+            </li>
+</ol></div>
+</div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014-2016 Andrzej Krzemie&#324;ski<p>
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+      </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="header__boost_optional_optional_hpp_/header__boost_optional_hpp_.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="dependencies_and_portability/optional_reference_binding.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>

doc/html/boost_optional/reference/dependencies_and_portability/optional_reference_binding.html

@@ -0,0 +1,100 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Optional Reference Binding</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<link rel="home" href="../../../index.html" title="Boost.Optional">
+<link rel="up" href="../dependencies_and_portability.html" title="Dependencies and Portability">
+<link rel="prev" href="../dependencies_and_portability.html" title="Dependencies and Portability">
+<link rel="next" href="../relnotes.html" title="Release Notes">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../../index.html">Home</a></td>
+<td align="center"><a href="../../../../../../../libs/libraries.htm">Libraries</a></td>
+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../dependencies_and_portability.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../dependencies_and_portability.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../relnotes.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.reference.dependencies_and_portability.optional_reference_binding"></a><a class="link" href="optional_reference_binding.html" title="Optional Reference Binding">Optional
+        Reference Binding</a>
+</h4></div></div></div>
+<p>
+          On compilers that do not conform to Standard C++ rules of reference binding,
+          operations on optional references might give adverse results: rather than
+          binding a reference to a designated object they may create an unexpected
+          temporary and bind to it. Compilers known to have these deficiencies include
+          GCC versions 4.2, 4.3, 4.4, 4.5; QCC 4.4.2; MSVC versions 8.0, 9.0, 10.0,
+          11.0, 12.0. On these compilers prefer using direct-initialization and copy
+          assignment of optional references to copy-initialization and assignment
+          from <code class="computeroutput"><span class="identifier">T</span><span class="special">&amp;</span></code>:
+        </p>
+<pre class="programlisting"><span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&amp;&gt;</span> <span class="identifier">or1</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&amp;&gt;</span> <span class="identifier">or2</span> <span class="special">=</span> <span class="identifier">i</span><span class="special">;</span>  <span class="comment">// not portable</span>
+<span class="identifier">or1</span> <span class="special">=</span> <span class="identifier">i</span><span class="special">;</span>                       <span class="comment">// not portable</span>
+
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&amp;&gt;</span> <span class="identifier">or3</span><span class="special">(</span><span class="identifier">i</span><span class="special">);</span>   <span class="comment">// portable</span>
+<span class="identifier">or1</span> <span class="special">=</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&amp;&gt;(</span><span class="identifier">i</span><span class="special">);</span> <span class="comment">// portable</span>
+</pre>
+<p>
+          In order to check if your compiler correctly implements reference binding
+          use this test program.
+        </p>
+<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">cassert</span><span class="special">&gt;</span>
+
+<span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">global_i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
+
+<span class="keyword">struct</span> <span class="identifier">TestingReferenceBinding</span>
+<span class="special">{</span>
+  <span class="identifier">TestingReferenceBinding</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&amp;</span> <span class="identifier">ii</span><span class="special">)</span>
+  <span class="special">{</span>
+    <span class="identifier">assert</span><span class="special">(&amp;</span><span class="identifier">ii</span> <span class="special">==</span> <span class="special">&amp;</span><span class="identifier">global_i</span><span class="special">);</span>
+  <span class="special">}</span>
+
+  <span class="keyword">void</span> <span class="keyword">operator</span><span class="special">=(</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&amp;</span> <span class="identifier">ii</span><span class="special">)</span>
+  <span class="special">{</span>
+    <span class="identifier">assert</span><span class="special">(&amp;</span><span class="identifier">ii</span> <span class="special">==</span> <span class="special">&amp;</span><span class="identifier">global_i</span><span class="special">);</span>
+  <span class="special">}</span>
+
+  <span class="keyword">void</span> <span class="keyword">operator</span><span class="special">=(</span><span class="keyword">int</span><span class="special">&amp;&amp;)</span> <span class="comment">// remove this if your compiler doesn't have rvalue refs</span>
+  <span class="special">{</span>
+    <span class="identifier">assert</span><span class="special">(</span><span class="keyword">false</span><span class="special">);</span>
+  <span class="special">}</span>
+<span class="special">};</span>
+
+<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
+<span class="special">{</span>
+  <span class="keyword">const</span> <span class="keyword">int</span><span class="special">&amp;</span> <span class="identifier">iref</span> <span class="special">=</span> <span class="identifier">global_i</span><span class="special">;</span>
+  <span class="identifier">assert</span><span class="special">(&amp;</span><span class="identifier">iref</span> <span class="special">==</span> <span class="special">&amp;</span><span class="identifier">global_i</span><span class="special">);</span>
+
+  <span class="identifier">TestingReferenceBinding</span> <span class="identifier">ttt</span> <span class="special">=</span> <span class="identifier">global_i</span><span class="special">;</span>
+  <span class="identifier">ttt</span> <span class="special">=</span> <span class="identifier">global_i</span><span class="special">;</span>
+
+  <span class="identifier">TestingReferenceBinding</span> <span class="identifier">ttt2</span> <span class="special">=</span> <span class="identifier">iref</span><span class="special">;</span>
+  <span class="identifier">ttt2</span> <span class="special">=</span> <span class="identifier">iref</span><span class="special">;</span>
+<span class="special">}</span>
+</pre>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014-2016 Andrzej Krzemie&#324;ski<p>
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+      </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../dependencies_and_portability.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../dependencies_and_portability.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../relnotes.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>

doc/html/boost_optional/reference/header__boost_optional_bad_optional_access_hpp_.html

@@ -1,9 +1,9 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Header &lt;boost/optional/bad_optional_access.hpp&gt;</title>
 <link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
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+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="../../index.html" title="Boost.Optional">
 <link rel="up" href="../../optional/reference.html" title="Reference">
 <link rel="prev" href="../../optional/reference.html" title="Reference">
@@ -49,7 +49,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>

doc/html/boost_optional/reference/header__boost_optional_bad_optional_access_hpp_/detailed_semantics.html

@@ -1,9 +1,9 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Detailed semantics</title>
 <link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="../../../index.html" title="Boost.Optional">
 <link rel="up" href="../header__boost_optional_bad_optional_access_hpp_.html" title="Header &lt;boost/optional/bad_optional_access.hpp&gt;">
 <link rel="prev" href="../header__boost_optional_bad_optional_access_hpp_.html" title="Header &lt;boost/optional/bad_optional_access.hpp&gt;">
@@ -46,7 +46,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>

doc/html/boost_optional/reference/header__boost_optional_hpp_.html

@@ -1,12 +1,12 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Header &lt;boost/optional.hpp&gt;</title>
 <link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="../../index.html" title="Boost.Optional">
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+<link rel="prev" href="header__boost_optional_optional_hpp_/detailed_semantics___free_functions.html" title="Detailed Semantics - Free Functions">
 <link rel="next" href="../dependencies_and_portability.html" title="Dependencies and Portability">
 </head>
 <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
@@ -20,7 +20,7 @@
 </tr></table>
 <hr>
 <div class="spirit-nav">
-<a accesskey="p" href="header__boost_optional_optional_hpp_/detailed_semantics.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../dependencies_and_portability.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+<a accesskey="p" href="header__boost_optional_optional_hpp_/detailed_semantics___free_functions.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../dependencies_and_portability.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
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 <div class="section">
 <div class="titlepage"><div><div><h3 class="title">
@@ -33,7 +33,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>
@@ -41,7 +41,7 @@
 </tr></table>
 <hr>
 <div class="spirit-nav">
-<a accesskey="p" href="header__boost_optional_optional_hpp_/detailed_semantics.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../dependencies_and_portability.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+<a accesskey="p" href="header__boost_optional_optional_hpp_/detailed_semantics___free_functions.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../dependencies_and_portability.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
 </div>
 </body>
 </html>

doc/html/boost_optional/reference/header__boost_optional_optional_fwd_hpp_.html

@@ -1,9 +1,9 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
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 <link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
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 <link rel="up" href="../../optional/reference.html" title="Reference">
 <link rel="prev" href="io_header/io_semantics.html" title="Detailed semantics">
@@ -52,7 +52,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>

doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html

@@ -6,8 +6,8 @@
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+<link rel="prev" href="header_optional_optional_refs.html" title="Optional References">
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+<a accesskey="p" href="header_optional_optional_refs.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="header__boost_optional_hpp_.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
 </div>
 <div class="section">
 <div class="titlepage"><div><div><h4 class="title">
@@ -433,7 +433,7 @@
 <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;&gt;</span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">uninit</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
 <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span>
 
-<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;&gt;</span> <span class="identifier">init</span><span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">uniqye_ptr</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;(</span><span class="keyword">new</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">))</span> <span class="special">);</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;&gt;</span> <span class="identifier">init</span><span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;(</span><span class="keyword">new</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">))</span> <span class="special">);</span>
 <span class="identifier">assert</span> <span class="special">(</span> <span class="special">**</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
 
 <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;&gt;</span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">init</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
@@ -2129,7 +2129,7 @@
               is required. Other relational operations are defined in terms of this
               one. If <code class="computeroutput"><span class="identifier">T</span></code>'s <code class="computeroutput"><span class="keyword">operator</span><span class="special">&lt;</span></code>
               satisfies the axioms of <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a> (transitivity,
-              antisymmetry and irreflexivity), <code class="computeroutput"><span class="identifier">optinal</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code> is <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a>.
+              antisymmetry and irreflexivity), <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code> is <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a>.
             </li>
 <li class="listitem">
               <span class="bold"><strong>Example:</strong></span>
@@ -2368,10 +2368,48 @@
 </pre>
             </li>
 </ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_swap_optional_reference"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">swap</span>
+            <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;&amp;</span> <span class="identifier">y</span>
+            <span class="special">)</span> <span class="keyword">noexcept</span>
+            <span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="identifier">x</span></code>
+              refers to what <code class="computeroutput"><span class="identifier">y</span></code> referred
+              to before the swap (if anything). <code class="computeroutput"><span class="identifier">y</span></code>
+              refers to whatever <code class="computeroutput"><span class="identifier">x</span></code>
+              referred to before the swap.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">(</span><span class="number">12</span><span class="special">);</span>
+<span class="identifier">T</span> <span class="identifier">y</span><span class="special">(</span><span class="number">21</span><span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;</span> <span class="identifier">opt0</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;</span> <span class="identifier">optX</span> <span class="special">(</span><span class="identifier">x</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;</span> <span class="identifier">optY</span> <span class="special">(</span><span class="identifier">y</span><span class="special">);</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">optX</span><span class="special">,</span> <span class="identifier">optY</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">addressof</span><span class="special">(*</span><span class="identifier">optX</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">y</span><span class="special">));</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">addressof</span><span class="special">(*</span><span class="identifier">optY</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">x</span><span class="special">));</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">opt0</span><span class="special">,</span> <span class="identifier">optX</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt0</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">optX</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">addressof</span><span class="special">(*</span><span class="identifier">opt0</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">y</span><span class="special">));</span>
+</pre>
+              [endsect]
+            </li>
+</ul></div>
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014-2016 Andrzej Krzemie&#324;ski<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>
@@ -2379,7 +2417,7 @@
 </tr></table>
 <hr>
 <div class="spirit-nav">
-<a accesskey="p" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../header__boost_optional_hpp_.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+<a accesskey="p" href="header_optional_optional_refs.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="header__boost_optional_hpp_.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
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doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics____free_functions.html

@@ -0,0 +1,447 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Detailed Semantics -- Free Functions</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<link rel="home" href="../../../index.html" title="Boost.Optional">
+<link rel="up" href="../../../optional/reference/header__boost_optional_optional_hpp_.html" title="Header &lt;boost/optional/optional.hpp&gt;">
+<link rel="prev" href="detailed_semantics____optional_references.html" title="Detailed Semantics -- Optional References">
+<link rel="next" href="header__boost_optional_hpp_.html" title="Header &lt;boost/optional.hpp&gt;">
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+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td>
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+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="detailed_semantics____optional_references.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="header__boost_optional_hpp_.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.reference.header__boost_optional_optional_hpp_.detailed_semantics____free_functions"></a><a class="link" href="detailed_semantics____free_functions.html" title="Detailed Semantics -- Free Functions">Detailed
+        Semantics -- Free Functions</a>
+</h4></div></div></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_make_optional_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">make_optional</span><span class="special">(</span>
+            <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">v</span> <span class="special">)</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;(</span><span class="identifier">v</span><span class="special">)</span></code> for the <span class="emphasis"><em>deduced</em></span>
+              type <code class="computeroutput"><span class="identifier">T</span></code> of <code class="computeroutput"><span class="identifier">v</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">void</span> <span class="identifier">foo</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">foo</span> <span class="special">(</span> <span class="identifier">make_optional</span><span class="special">(</span><span class="number">1</span><span class="special">+</span><span class="number">1</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> <span class="comment">// Creates an optional&lt;int&gt;</span>
+</pre>
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_make_optional_bool_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">&gt;</span> <span class="identifier">make_optional</span><span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span>
+            <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">v</span> <span class="special">)</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;(</span><span class="identifier">condition</span><span class="special">,</span><span class="identifier">v</span><span class="special">)</span></code> for the <span class="emphasis"><em>deduced</em></span>
+              type <code class="computeroutput"><span class="identifier">T</span></code> of <code class="computeroutput"><span class="identifier">v</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">double</span><span class="special">&gt;</span> <span class="identifier">calculate_foo</span><span class="special">()</span>
+<span class="special">{</span>
+  <span class="keyword">double</span> <span class="identifier">val</span> <span class="special">=</span> <span class="identifier">compute_foo</span><span class="special">();</span>
+  <span class="keyword">return</span> <span class="identifier">make_optional</span><span class="special">(</span><span class="identifier">is_not_nan_and_finite</span><span class="special">(</span><span class="identifier">val</span><span class="special">),</span><span class="identifier">val</span><span class="special">);</span>
+<span class="special">}</span>
+
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">double</span><span class="special">&gt;</span> <span class="identifier">v</span> <span class="special">=</span> <span class="identifier">calculate_foo</span><span class="special">();</span>
+<span class="keyword">if</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">v</span> <span class="special">)</span>
+  <span class="identifier">error</span><span class="special">(</span><span class="string">"foo wasn't computed"</span><span class="special">);</span>
+</pre>
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_operator_compare_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+            <span class="special">==</span> <span class="special">(</span>
+            <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">y</span> <span class="special">);</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+              shall meet requirements of <a href="http://www.sgi.com/tech/stl/EqualityComparable.html" target="_top"><code class="computeroutput"><span class="identifier">EqualityComparable</span></code></a>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Returns:</strong></span> If both <code class="computeroutput"><span class="identifier">x</span></code>
+              and <code class="computeroutput"><span class="identifier">y</span></code> are initialized,
+              <code class="computeroutput"><span class="special">(*</span><span class="identifier">x</span>
+              <span class="special">==</span> <span class="special">*</span><span class="identifier">y</span><span class="special">)</span></code>.
+              If only <code class="computeroutput"><span class="identifier">x</span></code> or <code class="computeroutput"><span class="identifier">y</span></code> is initialized, <code class="computeroutput"><span class="keyword">false</span></code>.
+              If both are uninitialized, <code class="computeroutput"><span class="keyword">true</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Notes:</strong></span> This definition guarantees
+              that <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code>
+              not containing a value is compared unequal to any <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code> containing any value, and equal
+              to any other <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code> not containing a value. Pointers
+              have shallow relational operators while <code class="computeroutput"><span class="identifier">optional</span></code>
+              has deep relational operators. Do not use <code class="computeroutput"><span class="keyword">operator</span><span class="special">==</span></code> directly in generic code which expect
+              to be given either an <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code> or a pointer; use <a href="../../../../../../utility/OptionalPointee.html#equal" target="_top"><code class="computeroutput"><span class="identifier">equal_pointees</span><span class="special">()</span></code></a>
+              instead
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">oN</span><span class="special">,</span> <span class="identifier">oN_</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">o1</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">1</span><span class="special">)),</span> <span class="identifier">o1_</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">1</span><span class="special">));</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">o2</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">));</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special">==</span> <span class="identifier">oN</span> <span class="special">);</span>  <span class="comment">// Identity implies equality</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special">==</span> <span class="identifier">o1</span> <span class="special">);</span>  <span class="comment">//</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special">==</span> <span class="identifier">oN_</span> <span class="special">);</span> <span class="comment">// Both uninitialized compare equal</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special">!=</span> <span class="identifier">o1</span> <span class="special">);</span>  <span class="comment">// Initialized unequal to initialized.</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special">==</span> <span class="identifier">o1_</span> <span class="special">);</span> <span class="comment">// Both initialized compare as (*lhs == *rhs)</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special">!=</span> <span class="identifier">o2</span> <span class="special">);</span>  <span class="comment">//</span>
+</pre>
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_operator_compare_less_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+            <span class="special">&lt;</span> <span class="special">(</span>
+            <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">y</span> <span class="special">);</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Requires:</strong></span> Expression <code class="computeroutput"><span class="special">*</span><span class="identifier">x</span> <span class="special">&lt;</span> <span class="special">*</span><span class="identifier">y</span></code> shall be well-formed and its result
+              shall be convertible to <code class="computeroutput"><span class="keyword">bool</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">(!</span><span class="identifier">y</span><span class="special">)</span> <span class="special">?</span> <span class="keyword">false</span> <span class="special">:</span> <span class="special">(!</span><span class="identifier">x</span><span class="special">)</span> <span class="special">?</span> <span class="keyword">true</span> <span class="special">:</span> <span class="special">*</span><span class="identifier">x</span> <span class="special">&lt;</span>
+              <span class="special">*</span><span class="identifier">y</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Notes:</strong></span> This definition guarantees
+              that <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code>
+              not containing a value is ordered as less than any <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code> containing any value, and equivalent
+              to any other <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code> not containing a value. Pointers
+              have shallow relational operators while <code class="computeroutput"><span class="identifier">optional</span></code>
+              has deep relational operators. Do not use <code class="computeroutput"><span class="keyword">operator</span><span class="special">&lt;</span></code> directly in generic code which
+              expect to be given either an <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code> or a pointer; use <a href="../../../../../../utility/OptionalPointee.html#less" target="_top"><code class="computeroutput"><span class="identifier">less_pointees</span><span class="special">()</span></code></a>
+              instead. <code class="computeroutput"><span class="identifier">T</span></code> need not
+              be <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a>. Only
+              single <code class="computeroutput"><span class="keyword">operator</span><span class="special">&lt;</span></code>
+              is required. Other relational operations are defined in terms of this
+              one. If <code class="computeroutput"><span class="identifier">T</span></code>'s <code class="computeroutput"><span class="keyword">operator</span><span class="special">&lt;</span></code>
+              satisfies the axioms of <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a> (transitivity,
+              antisymmetry and irreflexivity), <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code> is <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">oN</span><span class="special">,</span> <span class="identifier">oN_</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">o0</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">0</span><span class="special">));</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">o1</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">1</span><span class="special">));</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">oN</span> <span class="special">&lt;</span> <span class="identifier">oN</span><span class="special">)</span> <span class="special">);</span>  <span class="comment">// Identity implies equivalence</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o1</span> <span class="special">&lt;</span> <span class="identifier">o1</span><span class="special">)</span> <span class="special">);</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">oN</span> <span class="special">&lt;</span> <span class="identifier">oN_</span><span class="special">)</span> <span class="special">);</span> <span class="comment">// Two uninitialized are equivalent</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">oN_</span> <span class="special">&lt;</span> <span class="identifier">oN</span><span class="special">)</span> <span class="special">);</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special">&lt;</span> <span class="identifier">o0</span> <span class="special">);</span>     <span class="comment">// Uninitialized is less than initialized</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o0</span> <span class="special">&lt;</span> <span class="identifier">oN</span><span class="special">)</span> <span class="special">);</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special">&lt;</span> <span class="identifier">o2</span> <span class="special">)</span> <span class="special">;</span>    <span class="comment">// Two initialized compare as (*lhs &lt; *rhs)</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o2</span> <span class="special">&lt;</span> <span class="identifier">o1</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o2</span> <span class="special">&lt;</span> <span class="identifier">o2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_operator_compare_not_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+            <span class="special">!=</span> <span class="special">(</span>
+            <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">y</span> <span class="special">);</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+              <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span>
+              <span class="identifier">x</span> <span class="special">==</span>
+              <span class="identifier">y</span> <span class="special">);</span></code>
+            </li></ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_operator_compare_greater_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+            <span class="special">&gt;</span> <span class="special">(</span>
+            <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">y</span> <span class="special">);</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+              <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">(</span>
+              <span class="identifier">y</span> <span class="special">&lt;</span>
+              <span class="identifier">x</span> <span class="special">);</span></code>
+            </li></ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_operator_compare_less_or_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+            <span class="special">&lt;=</span> <span class="special">(</span>
+            <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">y</span> <span class="special">);</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+              <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span>
+              <span class="identifier">y</span> <span class="special">&lt;</span>
+              <span class="identifier">x</span> <span class="special">);</span></code>
+            </li></ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_operator_compare_greater_or_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+            <span class="special">&gt;=</span> <span class="special">(</span>
+            <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">y</span> <span class="special">);</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+              <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span>
+              <span class="identifier">x</span> <span class="special">&lt;</span>
+              <span class="identifier">y</span> <span class="special">);</span></code>
+            </li></ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_operator_compare_equal_optional_none"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+            <span class="special">==</span> <span class="special">(</span>
+            <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">none_t</span> <span class="special">)</span>
+            <span class="keyword">noexcept</span><span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+            <span class="special">==</span> <span class="special">(</span>
+            <span class="identifier">none_t</span><span class="special">,</span>
+            <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">!</span><span class="identifier">x</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Notes:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+              need not meet requirements of <a href="http://www.sgi.com/tech/stl/EqualityComparable.html" target="_top"><code class="computeroutput"><span class="identifier">EqualityComparable</span></code></a>.
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_operator_compare_not_equal_optional_none"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+            <span class="special">!=</span> <span class="special">(</span>
+            <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">none_t</span> <span class="special">)</span>
+            <span class="keyword">noexcept</span><span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+            <span class="special">!=</span> <span class="special">(</span>
+            <span class="identifier">none_t</span><span class="special">,</span>
+            <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+              <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span>
+              <span class="identifier">x</span> <span class="special">==</span>
+              <span class="identifier">y</span> <span class="special">);</span></code>
+            </li></ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_swap_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">swap</span>
+            <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;&amp;</span> <span class="identifier">y</span>
+            <span class="special">)</span> <span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Requires:</strong></span> Lvalues of type <code class="computeroutput"><span class="identifier">T</span></code> shall be swappable and <code class="computeroutput"><span class="identifier">T</span></code> shall be <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>.
+            </li>
+<li class="listitem">
+<p class="simpara">
+              <span class="bold"><strong>Effects:</strong></span>
+            </p>
+<div class="informaltable"><table class="table">
+<colgroup>
+<col>
+<col>
+<col>
+</colgroup>
+<thead><tr></tr></thead>
+<tbody>
+<tr>
+<td>
+                    </td>
+<td>
+                      <p>
+                        <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value</strong></span>
+                      </p>
+                    </td>
+<td>
+                      <p>
+                        <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value</strong></span>
+                      </p>
+                    </td>
+</tr>
+<tr>
+<td>
+                      <p>
+                        <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+                        contains a value</strong></span>
+                      </p>
+                    </td>
+<td>
+                      <p>
+                        calls <code class="computeroutput"><span class="identifier">swap</span><span class="special">(*(*</span><span class="keyword">this</span><span class="special">),</span> <span class="special">*</span><span class="identifier">rhs</span><span class="special">)</span></code>
+                      </p>
+                    </td>
+<td>
+                      <p>
+                        initializes the contained value of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> as if direct-initializing
+                        an object of type <code class="computeroutput"><span class="identifier">T</span></code>
+                        with the expression <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code>, followed by <code class="computeroutput"><span class="identifier">rhs</span><span class="special">.</span><span class="identifier">val</span><span class="special">-&gt;</span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>,
+                        <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+                        contains a value and <code class="computeroutput"><span class="identifier">rhs</span></code>
+                        does not contain a value
+                      </p>
+                    </td>
+</tr>
+<tr>
+<td>
+                      <p>
+                        <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+                        does not contain a value</strong></span>
+                      </p>
+                    </td>
+<td>
+                      <p>
+                        initializes the contained value of <code class="computeroutput"><span class="identifier">rhs</span></code>
+                        as if direct-initializing an object of type <code class="computeroutput"><span class="identifier">T</span></code> with the expression
+                        <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*(*</span><span class="keyword">this</span><span class="special">))</span></code>,
+                        followed by <code class="computeroutput"><span class="identifier">val</span><span class="special">-&gt;</span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value
+                        and <code class="computeroutput"><span class="identifier">rhs</span></code> contains
+                        a value
+                      </p>
+                    </td>
+<td>
+                      <p>
+                        no effect
+                      </p>
+                    </td>
+</tr>
+</tbody>
+</table></div>
+</li>
+<li class="listitem">
+              <span class="bold"><strong>Postconditions:</strong></span> The states of <code class="computeroutput"><span class="identifier">x</span></code> and <code class="computeroutput"><span class="identifier">y</span></code>
+              interchanged.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Throws:</strong></span> If both are initialized, whatever
+              <code class="computeroutput"><span class="identifier">swap</span><span class="special">(</span><span class="identifier">T</span><span class="special">&amp;,</span><span class="identifier">T</span><span class="special">&amp;)</span></code>
+              throws. If only one is initialized, whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&amp;&amp;</span> <span class="special">)</span></code>
+              throws.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">(</span><span class="number">12</span><span class="special">);</span>
+<span class="identifier">T</span> <span class="identifier">y</span><span class="special">(</span><span class="number">21</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">def0</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">def1</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">optX</span><span class="special">(</span><span class="identifier">x</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">optY</span><span class="special">(</span><span class="identifier">y</span><span class="special">);</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">def0</span><span class="special">,</span><span class="identifier">def1</span><span class="special">);</span> <span class="comment">// no-op</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">def0</span><span class="special">,</span><span class="identifier">optX</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def0</span> <span class="special">==</span> <span class="identifier">x</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">optX</span> <span class="special">);</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">def0</span><span class="special">,</span><span class="identifier">optX</span><span class="special">);</span> <span class="comment">// Get back to original values</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">optX</span><span class="special">,</span><span class="identifier">optY</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">optX</span> <span class="special">==</span> <span class="identifier">y</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">optY</span> <span class="special">==</span> <span class="identifier">x</span> <span class="special">);</span>
+</pre>
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_swap_optional_reference"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">swap</span>
+            <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;&amp;</span> <span class="identifier">y</span>
+            <span class="special">)</span> <span class="keyword">noexcept</span>
+            <span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="identifier">x</span></code>
+              refers to what <code class="computeroutput"><span class="identifier">y</span></code> referred
+              to before the swap (if anything). <code class="computeroutput"><span class="identifier">y</span></code>
+              refers to whatever <code class="computeroutput"><span class="identifier">x</span></code>
+              referred to before the swap.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">(</span><span class="number">12</span><span class="special">);</span>
+<span class="identifier">T</span> <span class="identifier">y</span><span class="special">(</span><span class="number">21</span><span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;</span> <span class="identifier">opt0</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;</span> <span class="identifier">optX</span> <span class="special">(</span><span class="identifier">x</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;</span> <span class="identifier">optY</span> <span class="special">(</span><span class="identifier">y</span><span class="special">);</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">optX</span><span class="special">,</span> <span class="identifier">optY</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">addressof</span><span class="special">(*</span><span class="identifier">optX</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">y</span><span class="special">));</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">addressof</span><span class="special">(*</span><span class="identifier">optY</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">x</span><span class="special">));</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">opt0</span><span class="special">,</span> <span class="identifier">optX</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt0</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">optX</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">addressof</span><span class="special">(*</span><span class="identifier">opt0</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">y</span><span class="special">));</span>
+</pre>
+              [endsect]
+            </li>
+</ul></div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014-2016 Andrzej Krzemie&#324;ski<p>
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+      </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="detailed_semantics____optional_references.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="header__boost_optional_hpp_.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>

doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics____optional_references.html

@@ -0,0 +1,57 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Detailed Semantics -- Optional References</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<link rel="home" href="../../../index.html" title="Boost.Optional">
+<link rel="up" href="../../../optional/reference/header__boost_optional_optional_hpp_.html" title="Header &lt;boost/optional/optional.hpp&gt;">
+<link rel="prev" href="detailed_semantics____optional_values.html" title="Detailed Semantics -- Optional Values">
+<link rel="next" href="detailed_semantics____free_functions.html" title="Detailed Semantics -- Free Functions">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td>
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+<td align="center"><a href="../../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
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+<a accesskey="p" href="detailed_semantics____optional_values.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="detailed_semantics____free_functions.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.reference.header__boost_optional_optional_hpp_.detailed_semantics____optional_references"></a><a class="link" href="detailed_semantics____optional_references.html" title="Detailed Semantics -- Optional References">Detailed
+        Semantics -- Optional References</a>
+</h4></div></div></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_optional_ref_default_ctor"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;&amp;&gt;::</span><span class="identifier">optional</span><span class="special">()</span>
+            <span class="keyword">noexcept</span><span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;&amp;&gt;::</span><span class="identifier">optional</span><span class="special">(</span><span class="identifier">none_t</span><span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+              <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> refers to nothing.
+            </li></ul></div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014-2016 Andrzej Krzemie&#324;ski<p>
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+      </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="detailed_semantics____optional_values.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="detailed_semantics____free_functions.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>

doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___free_functions.html

@@ -0,0 +1,521 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
+<title>Detailed Semantics - Free Functions</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../../index.html" title="Boost.Optional">
+<link rel="up" href="../../../optional/reference/header__boost_optional_optional_hpp_.html" title="Header &lt;boost/optional/optional.hpp&gt;">
+<link rel="prev" href="detailed_semantics___optional_references.html" title="Detailed Semantics - Optional References">
+<link rel="next" href="../header__boost_optional_hpp_.html" title="Header &lt;boost/optional.hpp&gt;">
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+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../../index.html">Home</a></td>
+<td align="center"><a href="../../../../../../../libs/libraries.htm">Libraries</a></td>
+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="detailed_semantics___optional_references.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../header__boost_optional_hpp_.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.reference.header__boost_optional_optional_hpp_.detailed_semantics___free_functions"></a><a class="link" href="detailed_semantics___free_functions.html" title="Detailed Semantics - Free Functions">Detailed
+        Semantics - Free Functions</a>
+</h4></div></div></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_make_optional_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">make_optional</span><span class="special">(</span>
+            <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">v</span> <span class="special">)</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;(</span><span class="identifier">v</span><span class="special">)</span></code> for the <span class="emphasis"><em>deduced</em></span>
+              type <code class="computeroutput"><span class="identifier">T</span></code> of <code class="computeroutput"><span class="identifier">v</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">void</span> <span class="identifier">foo</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">foo</span> <span class="special">(</span> <span class="identifier">make_optional</span><span class="special">(</span><span class="number">1</span><span class="special">+</span><span class="number">1</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> <span class="comment">// Creates an optional&lt;int&gt;</span>
+</pre>
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_make_optional_rvalue"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">decay_t</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;&gt;</span>
+            <span class="identifier">make_optional</span><span class="special">(</span>
+            <span class="identifier">T</span> <span class="special">&amp;&amp;</span>
+            <span class="identifier">v</span> <span class="special">)</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+              <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">decay_t</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;&gt;(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">v</span><span class="special">))</span></code> for the <span class="emphasis"><em>deduced</em></span>
+              type <code class="computeroutput"><span class="identifier">T</span></code> of <code class="computeroutput"><span class="identifier">v</span></code>.
+            </li></ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_make_optional_bool_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">make_optional</span><span class="special">(</span>
+            <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">v</span> <span class="special">)</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;(</span><span class="identifier">condition</span><span class="special">,</span> <span class="identifier">v</span><span class="special">)</span></code> for the <span class="emphasis"><em>deduced</em></span>
+              type <code class="computeroutput"><span class="identifier">T</span></code> of <code class="computeroutput"><span class="identifier">v</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">double</span><span class="special">&gt;</span> <span class="identifier">calculate_foo</span><span class="special">()</span>
+<span class="special">{</span>
+  <span class="keyword">double</span> <span class="identifier">val</span> <span class="special">=</span> <span class="identifier">compute_foo</span><span class="special">();</span>
+  <span class="keyword">return</span> <span class="identifier">make_optional</span><span class="special">(</span><span class="identifier">is_not_nan_and_finite</span><span class="special">(</span><span class="identifier">val</span><span class="special">),</span><span class="identifier">val</span><span class="special">);</span>
+<span class="special">}</span>
+
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">double</span><span class="special">&gt;</span> <span class="identifier">v</span> <span class="special">=</span> <span class="identifier">calculate_foo</span><span class="special">();</span>
+<span class="keyword">if</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">v</span> <span class="special">)</span>
+  <span class="identifier">error</span><span class="special">(</span><span class="string">"foo wasn't computed"</span><span class="special">);</span>
+</pre>
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_make_optional_bool_rvalue"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">decay_t</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;&gt;</span>
+            <span class="identifier">make_optional</span><span class="special">(</span>
+            <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="identifier">T</span> <span class="special">&amp;&amp;</span> <span class="identifier">v</span>
+            <span class="special">)</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+              <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">decay_t</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;&gt;(</span><span class="identifier">condition</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">v</span><span class="special">))</span></code> for the <span class="emphasis"><em>deduced</em></span>
+              type <code class="computeroutput"><span class="identifier">T</span></code> of <code class="computeroutput"><span class="identifier">v</span></code>.
+            </li></ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_operator_compare_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+            <span class="special">==</span> <span class="special">(</span>
+            <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">y</span> <span class="special">);</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+              shall meet requirements of <a href="http://www.sgi.com/tech/stl/EqualityComparable.html" target="_top"><code class="computeroutput"><span class="identifier">EqualityComparable</span></code></a>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Returns:</strong></span> If both <code class="computeroutput"><span class="identifier">x</span></code>
+              and <code class="computeroutput"><span class="identifier">y</span></code> are initialized,
+              <code class="computeroutput"><span class="special">(*</span><span class="identifier">x</span>
+              <span class="special">==</span> <span class="special">*</span><span class="identifier">y</span><span class="special">)</span></code>.
+              If only <code class="computeroutput"><span class="identifier">x</span></code> or <code class="computeroutput"><span class="identifier">y</span></code> is initialized, <code class="computeroutput"><span class="keyword">false</span></code>.
+              If both are uninitialized, <code class="computeroutput"><span class="keyword">true</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Notes:</strong></span> This definition guarantees
+              that <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code>
+              not containing a value is compared unequal to any <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code> containing any value, and equal
+              to any other <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code> not containing a value. Pointers
+              have shallow relational operators while <code class="computeroutput"><span class="identifier">optional</span></code>
+              has deep relational operators. Do not use <code class="computeroutput"><span class="keyword">operator</span><span class="special">==</span></code> directly in generic code which expect
+              to be given either an <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code> or a pointer; use <a href="../../../../../../utility/OptionalPointee.html#equal" target="_top"><code class="computeroutput"><span class="identifier">equal_pointees</span><span class="special">()</span></code></a>
+              instead
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">oN</span><span class="special">,</span> <span class="identifier">oN_</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">o1</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">1</span><span class="special">)),</span> <span class="identifier">o1_</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">1</span><span class="special">));</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">o2</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">));</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special">==</span> <span class="identifier">oN</span> <span class="special">);</span>  <span class="comment">// Identity implies equality</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special">==</span> <span class="identifier">o1</span> <span class="special">);</span>  <span class="comment">//</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special">==</span> <span class="identifier">oN_</span> <span class="special">);</span> <span class="comment">// Both uninitialized compare equal</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special">!=</span> <span class="identifier">o1</span> <span class="special">);</span>  <span class="comment">// Initialized unequal to initialized.</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special">==</span> <span class="identifier">o1_</span> <span class="special">);</span> <span class="comment">// Both initialized compare as (*lhs == *rhs)</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special">!=</span> <span class="identifier">o2</span> <span class="special">);</span>  <span class="comment">//</span>
+</pre>
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_operator_compare_less_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+            <span class="special">&lt;</span> <span class="special">(</span>
+            <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">y</span> <span class="special">);</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Requires:</strong></span> Expression <code class="computeroutput"><span class="special">*</span><span class="identifier">x</span> <span class="special">&lt;</span> <span class="special">*</span><span class="identifier">y</span></code> shall be well-formed and its result
+              shall be convertible to <code class="computeroutput"><span class="keyword">bool</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">(!</span><span class="identifier">y</span><span class="special">)</span> <span class="special">?</span> <span class="keyword">false</span> <span class="special">:</span> <span class="special">(!</span><span class="identifier">x</span><span class="special">)</span> <span class="special">?</span> <span class="keyword">true</span> <span class="special">:</span> <span class="special">*</span><span class="identifier">x</span> <span class="special">&lt;</span>
+              <span class="special">*</span><span class="identifier">y</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Notes:</strong></span> This definition guarantees
+              that <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code>
+              not containing a value is ordered as less than any <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code> containing any value, and equivalent
+              to any other <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code> not containing a value. Pointers
+              have shallow relational operators while <code class="computeroutput"><span class="identifier">optional</span></code>
+              has deep relational operators. Do not use <code class="computeroutput"><span class="keyword">operator</span><span class="special">&lt;</span></code> directly in generic code which
+              expect to be given either an <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code> or a pointer; use <a href="../../../../../../utility/OptionalPointee.html#less" target="_top"><code class="computeroutput"><span class="identifier">less_pointees</span><span class="special">()</span></code></a>
+              instead. <code class="computeroutput"><span class="identifier">T</span></code> need not
+              be <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a>. Only
+              single <code class="computeroutput"><span class="keyword">operator</span><span class="special">&lt;</span></code>
+              is required. Other relational operations are defined in terms of this
+              one. If <code class="computeroutput"><span class="identifier">T</span></code>'s <code class="computeroutput"><span class="keyword">operator</span><span class="special">&lt;</span></code>
+              satisfies the axioms of <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a> (transitivity,
+              antisymmetry and irreflexivity), <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code> is <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">oN</span><span class="special">,</span> <span class="identifier">oN_</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">o0</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">0</span><span class="special">));</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">o1</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">1</span><span class="special">));</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">oN</span> <span class="special">&lt;</span> <span class="identifier">oN</span><span class="special">)</span> <span class="special">);</span>  <span class="comment">// Identity implies equivalence</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o1</span> <span class="special">&lt;</span> <span class="identifier">o1</span><span class="special">)</span> <span class="special">);</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">oN</span> <span class="special">&lt;</span> <span class="identifier">oN_</span><span class="special">)</span> <span class="special">);</span> <span class="comment">// Two uninitialized are equivalent</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">oN_</span> <span class="special">&lt;</span> <span class="identifier">oN</span><span class="special">)</span> <span class="special">);</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special">&lt;</span> <span class="identifier">o0</span> <span class="special">);</span>     <span class="comment">// Uninitialized is less than initialized</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o0</span> <span class="special">&lt;</span> <span class="identifier">oN</span><span class="special">)</span> <span class="special">);</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special">&lt;</span> <span class="identifier">o2</span> <span class="special">)</span> <span class="special">;</span>    <span class="comment">// Two initialized compare as (*lhs &lt; *rhs)</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o2</span> <span class="special">&lt;</span> <span class="identifier">o1</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o2</span> <span class="special">&lt;</span> <span class="identifier">o2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_operator_compare_not_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+            <span class="special">!=</span> <span class="special">(</span>
+            <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">y</span> <span class="special">);</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+              <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span>
+              <span class="identifier">x</span> <span class="special">==</span>
+              <span class="identifier">y</span> <span class="special">);</span></code>
+            </li></ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_operator_compare_greater_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+            <span class="special">&gt;</span> <span class="special">(</span>
+            <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">y</span> <span class="special">);</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+              <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">(</span>
+              <span class="identifier">y</span> <span class="special">&lt;</span>
+              <span class="identifier">x</span> <span class="special">);</span></code>
+            </li></ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_operator_compare_less_or_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+            <span class="special">&lt;=</span> <span class="special">(</span>
+            <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">y</span> <span class="special">);</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+              <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span>
+              <span class="identifier">y</span> <span class="special">&lt;</span>
+              <span class="identifier">x</span> <span class="special">);</span></code>
+            </li></ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_operator_compare_greater_or_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+            <span class="special">&gt;=</span> <span class="special">(</span>
+            <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">y</span> <span class="special">);</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+              <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span>
+              <span class="identifier">x</span> <span class="special">&lt;</span>
+              <span class="identifier">y</span> <span class="special">);</span></code>
+            </li></ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_operator_compare_equal_optional_none"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+            <span class="special">==</span> <span class="special">(</span>
+            <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">none_t</span> <span class="special">)</span>
+            <span class="keyword">noexcept</span><span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+            <span class="special">==</span> <span class="special">(</span>
+            <span class="identifier">none_t</span><span class="special">,</span>
+            <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">!</span><span class="identifier">x</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Notes:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+              need not meet requirements of <a href="http://www.sgi.com/tech/stl/EqualityComparable.html" target="_top"><code class="computeroutput"><span class="identifier">EqualityComparable</span></code></a>.
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_operator_compare_not_equal_optional_none"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+            <span class="special">!=</span> <span class="special">(</span>
+            <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">none_t</span> <span class="special">)</span>
+            <span class="keyword">noexcept</span><span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+            <span class="special">!=</span> <span class="special">(</span>
+            <span class="identifier">none_t</span><span class="special">,</span>
+            <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+              <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(</span><span class="identifier">x</span><span class="special">);</span></code>
+            </li></ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_free_get_pointer"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">auto</span> <span class="identifier">get_pointer</span>
+            <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;&amp;</span> <span class="identifier">o</span>
+            <span class="special">)</span> <span class="special">-&gt;</span>
+            <span class="keyword">typename</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;::</span><span class="identifier">pointer_type</span>
+            <span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">auto</span> <span class="identifier">get_pointer</span>
+            <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">o</span> <span class="special">)</span> <span class="special">-&gt;</span> <span class="keyword">typename</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;::</span><span class="identifier">pointer_const_type</span>
+            <span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="identifier">o</span><span class="special">.</span><span class="identifier">get_ptr</span><span class="special">()</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Throws:</strong></span> Nothing.
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_free_get_value_or"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">auto</span> <span class="identifier">get_optional_value_or</span>
+            <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;&amp;</span> <span class="identifier">o</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;::</span><span class="identifier">reference_type</span> <span class="identifier">def</span>
+            <span class="special">)</span> <span class="special">-&gt;</span>
+            <span class="keyword">typename</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;::</span><span class="identifier">reference_type</span>
+            <span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">auto</span> <span class="identifier">get_optional_value_or</span>
+            <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">o</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;::</span><span class="identifier">reference_const_type</span> <span class="identifier">def</span>
+            <span class="special">)</span> <span class="special">-&gt;</span>
+            <span class="keyword">typename</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;::</span><span class="identifier">reference_const_type</span>
+            <span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="identifier">o</span><span class="special">.</span><span class="identifier">get_value_or</span><span class="special">(</span><span class="identifier">def</span><span class="special">)</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Throws:</strong></span> Nothing.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Remarks:</strong></span> This function is deprecated.
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_swap_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">swap</span>
+            <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;&amp;</span> <span class="identifier">y</span>
+            <span class="special">)</span> <span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Requires:</strong></span> Lvalues of type <code class="computeroutput"><span class="identifier">T</span></code> shall be swappable and <code class="computeroutput"><span class="identifier">T</span></code> shall be <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>.
+            </li>
+<li class="listitem">
+<p class="simpara">
+              <span class="bold"><strong>Effects:</strong></span>
+            </p>
+<div class="informaltable"><table class="table">
+<colgroup>
+<col>
+<col>
+<col>
+</colgroup>
+<thead><tr></tr></thead>
+<tbody>
+<tr>
+<td>
+                    </td>
+<td>
+                      <p>
+                        <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value</strong></span>
+                      </p>
+                    </td>
+<td>
+                      <p>
+                        <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value</strong></span>
+                      </p>
+                    </td>
+</tr>
+<tr>
+<td>
+                      <p>
+                        <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+                        contains a value</strong></span>
+                      </p>
+                    </td>
+<td>
+                      <p>
+                        calls <code class="computeroutput"><span class="identifier">swap</span><span class="special">(*(*</span><span class="keyword">this</span><span class="special">),</span> <span class="special">*</span><span class="identifier">rhs</span><span class="special">)</span></code>
+                      </p>
+                    </td>
+<td>
+                      <p>
+                        initializes the contained value of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> as if direct-initializing
+                        an object of type <code class="computeroutput"><span class="identifier">T</span></code>
+                        with the expression <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code>, followed by <code class="computeroutput"><span class="identifier">rhs</span><span class="special">.</span><span class="identifier">val</span><span class="special">-&gt;</span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>,
+                        <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+                        contains a value and <code class="computeroutput"><span class="identifier">rhs</span></code>
+                        does not contain a value
+                      </p>
+                    </td>
+</tr>
+<tr>
+<td>
+                      <p>
+                        <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+                        does not contain a value</strong></span>
+                      </p>
+                    </td>
+<td>
+                      <p>
+                        initializes the contained value of <code class="computeroutput"><span class="identifier">rhs</span></code>
+                        as if direct-initializing an object of type <code class="computeroutput"><span class="identifier">T</span></code> with the expression
+                        <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*(*</span><span class="keyword">this</span><span class="special">))</span></code>,
+                        followed by <code class="computeroutput"><span class="identifier">val</span><span class="special">-&gt;</span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value
+                        and <code class="computeroutput"><span class="identifier">rhs</span></code> contains
+                        a value
+                      </p>
+                    </td>
+<td>
+                      <p>
+                        no effect
+                      </p>
+                    </td>
+</tr>
+</tbody>
+</table></div>
+</li>
+<li class="listitem">
+              <span class="bold"><strong>Postconditions:</strong></span> The states of <code class="computeroutput"><span class="identifier">x</span></code> and <code class="computeroutput"><span class="identifier">y</span></code>
+              interchanged.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Throws:</strong></span> If both are initialized, whatever
+              <code class="computeroutput"><span class="identifier">swap</span><span class="special">(</span><span class="identifier">T</span><span class="special">&amp;,</span><span class="identifier">T</span><span class="special">&amp;)</span></code>
+              throws. If only one is initialized, whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&amp;&amp;</span> <span class="special">)</span></code>
+              throws.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">(</span><span class="number">12</span><span class="special">);</span>
+<span class="identifier">T</span> <span class="identifier">y</span><span class="special">(</span><span class="number">21</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">def0</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">def1</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">optX</span><span class="special">(</span><span class="identifier">x</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">optY</span><span class="special">(</span><span class="identifier">y</span><span class="special">);</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">def0</span><span class="special">,</span><span class="identifier">def1</span><span class="special">);</span> <span class="comment">// no-op</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">def0</span><span class="special">,</span><span class="identifier">optX</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def0</span> <span class="special">==</span> <span class="identifier">x</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">optX</span> <span class="special">);</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">def0</span><span class="special">,</span><span class="identifier">optX</span><span class="special">);</span> <span class="comment">// Get back to original values</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">optX</span><span class="special">,</span><span class="identifier">optY</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">optX</span> <span class="special">==</span> <span class="identifier">y</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">optY</span> <span class="special">==</span> <span class="identifier">x</span> <span class="special">);</span>
+</pre>
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_swap_optional_reference"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">swap</span>
+            <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;&amp;</span> <span class="identifier">y</span>
+            <span class="special">)</span> <span class="keyword">noexcept</span>
+            <span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="identifier">x</span></code>
+              refers to what <code class="computeroutput"><span class="identifier">y</span></code> referred
+              to before the swap (if anything). <code class="computeroutput"><span class="identifier">y</span></code>
+              refers to whatever <code class="computeroutput"><span class="identifier">x</span></code>
+              referred to before the swap.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">(</span><span class="number">12</span><span class="special">);</span>
+<span class="identifier">T</span> <span class="identifier">y</span><span class="special">(</span><span class="number">21</span><span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;</span> <span class="identifier">opt0</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;</span> <span class="identifier">optX</span> <span class="special">(</span><span class="identifier">x</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;</span> <span class="identifier">optY</span> <span class="special">(</span><span class="identifier">y</span><span class="special">);</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">optX</span><span class="special">,</span> <span class="identifier">optY</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">addressof</span><span class="special">(*</span><span class="identifier">optX</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">y</span><span class="special">));</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">addressof</span><span class="special">(*</span><span class="identifier">optY</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">x</span><span class="special">));</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">opt0</span><span class="special">,</span> <span class="identifier">optX</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt0</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">optX</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">addressof</span><span class="special">(*</span><span class="identifier">opt0</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">y</span><span class="special">));</span>
+</pre>
+            </li>
+</ul></div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+      </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="detailed_semantics___optional_references.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../header__boost_optional_hpp_.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>

doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___optional_references.html

@@ -0,0 +1,552 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
+<title>Detailed Semantics - Optional References</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
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+<link rel="next" href="detailed_semantics___free_functions.html" title="Detailed Semantics - Free Functions">
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+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../../more/index.htm">More</a></td>
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+<a accesskey="p" href="detailed_semantics___optional_values.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="detailed_semantics___free_functions.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.reference.header__boost_optional_optional_hpp_.detailed_semantics___optional_references"></a><a class="link" href="detailed_semantics___optional_references.html" title="Detailed Semantics - Optional References">Detailed
+        Semantics - Optional References</a>
+</h4></div></div></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_optional_ref_default_ctor"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="identifier">optional</span><span class="special">()</span>
+            <span class="keyword">noexcept</span><span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="identifier">optional</span><span class="special">(</span><span class="identifier">none_t</span><span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+              <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">false</span></code>; <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> refers to nothing.
+            </li></ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_optional_ref_value_ctor"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">&gt;</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="identifier">optional</span><span class="special">(</span><span class="identifier">R</span><span class="special">&amp;&amp;</span> <span class="identifier">r</span><span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">true</span></code>; <code class="computeroutput"><span class="identifier">addressof</span><span class="special">(**</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">r</span><span class="special">)</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Remarks:</strong></span> Unless <code class="computeroutput"><span class="identifier">R</span></code>
+              is an lvalue reference, the program is ill-formed. This constructor
+              does not participate in overload resolution if <code class="computeroutput"><span class="identifier">decay</span><span class="special">&lt;</span><span class="identifier">R</span><span class="special">&gt;</span></code> is an instance of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Notes:</strong></span> This constructor is declared
+              <code class="computeroutput"><span class="keyword">explicit</span></code> on compilers
+              that do not correctly support binding to const lvalues of integral types.
+              For more details <a class="link" href="../../dependencies_and_portability/optional_reference_binding.html#optional_reference_binding">see here</a>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">vref</span> <span class="special">=</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;</span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">vref</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="special">++</span> <span class="identifier">v</span> <span class="special">;</span> <span class="comment">// mutate referee</span>
+<span class="identifier">assert</span> <span class="special">(*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span><span class="special">);</span>
+</pre>
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_optional_ref_cond_value_ctor"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">&gt;</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="identifier">optional</span><span class="special">(</span><span class="keyword">bool</span> <span class="identifier">cond</span><span class="special">,</span> <span class="identifier">R</span><span class="special">&amp;&amp;</span>
+            <span class="identifier">r</span><span class="special">)</span>
+            <span class="keyword">noexcept</span><span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Effects: </strong></span> Initializes <code class="computeroutput"><span class="identifier">ref</span></code> with expression <code class="computeroutput"><span class="identifier">cond</span> <span class="special">?</span>
+              <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">r</span><span class="special">)</span> <span class="special">:</span> <span class="keyword">nullptr</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">cond</span></code>; If <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code>, <code class="computeroutput"><span class="identifier">addressof</span><span class="special">(**</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">r</span><span class="special">)</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Remarks:</strong></span> Unless <code class="computeroutput"><span class="identifier">R</span></code>
+              is an lvalue reference, the program is ill-formed. This constructor
+              does not participate in overload resolution if <code class="computeroutput"><span class="identifier">decay</span><span class="special">&lt;</span><span class="identifier">R</span><span class="special">&gt;</span></code> is an instance of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span></code>.
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_optional_ref_copy_ctor"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="identifier">optional</span> <span class="special">(</span>
+            <span class="identifier">optional</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">rhs</span>
+            <span class="special">)</span> <span class="keyword">noexcept</span>
+            <span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Effects: </strong></span> Initializes <code class="computeroutput"><span class="identifier">ref</span></code> with expression <code class="computeroutput"><span class="identifier">rhs</span><span class="special">.</span><span class="identifier">ref</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;</span> <span class="identifier">uninit</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">uninit</span><span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;</span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">uninit</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span>
+
+<span class="identifier">T</span> <span class="identifier">v</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span> <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">ref</span> <span class="special">=</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">init</span><span class="special">(</span><span class="identifier">ref</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">init</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init2</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">v</span> <span class="special">=</span> <span class="number">3</span> <span class="special">;</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span>  <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init2</span> <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_optional_ref_ctor_from_opt_U"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">&gt;</span> <span class="keyword">explicit</span>
+            <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="identifier">optional</span> <span class="special">(</span>
+            <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">U</span><span class="special">&amp;&gt;</span>
+            <span class="keyword">const</span><span class="special">&amp;</span>
+            <span class="identifier">rhs</span> <span class="special">)</span>
+            <span class="keyword">noexcept</span> <span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_convertible</span><span class="special">&lt;</span><span class="identifier">U</span><span class="special">&amp;,</span> <span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="identifier">value</span></code>
+              is <code class="computeroutput"><span class="keyword">true</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Effects: </strong></span> Initializes <code class="computeroutput"><span class="identifier">ref</span></code> with expression <code class="computeroutput"><span class="identifier">rhs</span><span class="special">.</span><span class="identifier">ref</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span></code>.
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_optional_ref_assign_none_t"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">none_t</span>
+            <span class="special">)</span> <span class="keyword">noexcept</span>
+            <span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Effects: </strong></span> Assigns <code class="computeroutput"><span class="identifier">ref</span></code>
+              with expression <code class="computeroutput"><span class="keyword">nullptr</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">false</span></code>.
+            </li>
+</ul></div>
+<a name="reference_optional_ref_copy_assign"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="identifier">optional</span><span class="special">&amp;</span>
+            <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span>
+            <span class="keyword">const</span><span class="special">&amp;</span>
+            <span class="identifier">rhs</span> <span class="special">)</span>
+            <span class="keyword">noexcept</span> <span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Effects: </strong></span> Assigns <code class="computeroutput"><span class="identifier">ref</span></code>
+              with expression <code class="computeroutput"><span class="identifier">rhs</span><span class="special">.</span><span class="identifier">ref</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Notes:</strong></span> This behaviour is called <span class="emphasis"><em>rebinding
+              semantics</em></span>. See <a class="link" href="../../tutorial/optional_references/rebinding_semantics_for_assignment_of_optional_references.html" title="Rebinding semantics for assignment of optional references">here</a>
+              for details.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span>
+<span class="keyword">int</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span>
+<span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span>
+<span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">rb</span> <span class="special">=</span> <span class="identifier">b</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&amp;&gt;</span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&amp;&gt;</span> <span class="identifier">ora</span><span class="special">(</span><span class="identifier">ra</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&amp;&gt;</span> <span class="identifier">orb</span><span class="special">(</span><span class="identifier">rb</span><span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">def</span> <span class="special">=</span> <span class="identifier">orb</span> <span class="special">;</span> <span class="comment">// binds 'def' to 'b' through 'rb' wrapped within 'orb'</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">b</span> <span class="special">)</span> <span class="special">;</span>
+<span class="special">*</span><span class="identifier">def</span> <span class="special">=</span> <span class="identifier">ora</span> <span class="special">;</span> <span class="comment">// changes the value of 'b' to a copy of the value of 'a'</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">b</span> <span class="special">==</span> <span class="identifier">a</span> <span class="special">)</span> <span class="special">;</span>
+<span class="keyword">int</span> <span class="identifier">c</span> <span class="special">=</span> <span class="number">3</span><span class="special">;</span>
+<span class="keyword">int</span><span class="special">&amp;</span> <span class="identifier">rc</span> <span class="special">=</span> <span class="identifier">c</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&amp;&gt;</span> <span class="identifier">orc</span><span class="special">(</span><span class="identifier">rc</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">ora</span> <span class="special">=</span> <span class="identifier">orc</span> <span class="special">;</span> <span class="comment">// REBINDS ora to 'c' through 'rc'</span>
+<span class="identifier">c</span> <span class="special">=</span> <span class="number">4</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">ora</span> <span class="special">==</span> <span class="number">4</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+            </li>
+</ul></div>
+<a name="reference_optional_ref_assign_optional_U"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">&gt;</span> <span class="identifier">optional</span><span class="special">&amp;</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">U</span><span class="special">&amp;&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">rhs</span>
+            <span class="special">)</span> <span class="keyword">noexcept</span>
+            <span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_convertible</span><span class="special">&lt;</span><span class="identifier">U</span><span class="special">&amp;,</span> <span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="identifier">value</span></code>
+              is <code class="computeroutput"><span class="keyword">true</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Effects: </strong></span> Assigns <code class="computeroutput"><span class="identifier">ref</span></code>
+              with expression <code class="computeroutput"><span class="identifier">rhs</span><span class="special">.</span><span class="identifier">ref</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span></code>.
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_optional_ref_assign_R"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">&gt;</span> <span class="identifier">optional</span><span class="special">&amp;</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">R</span><span class="special">&amp;&amp;</span> <span class="identifier">r</span>
+            <span class="special">)</span> <span class="keyword">noexcept</span>
+            <span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Effects: </strong></span> Assigns <code class="computeroutput"><span class="identifier">ref</span></code>
+              with expression <code class="computeroutput"><span class="identifier">r</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">true</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Remarks:</strong></span> Unless <code class="computeroutput"><span class="identifier">R</span></code>
+              is an lvalue reference, the program is ill-formed. This function does
+              not participate in overload resolution if <code class="computeroutput"><span class="identifier">decay</span><span class="special">&lt;</span><span class="identifier">R</span><span class="special">&gt;</span></code> is an instance of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span>
+<span class="keyword">int</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span>
+<span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span>
+<span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">rb</span> <span class="special">=</span> <span class="identifier">b</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&amp;&gt;</span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&amp;&gt;</span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">ra</span><span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">def</span> <span class="special">=</span> <span class="identifier">rb</span> <span class="special">;</span> <span class="comment">// binds 'def' to 'b' through 'rb'</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">b</span> <span class="special">)</span> <span class="special">;</span>
+<span class="special">*</span><span class="identifier">def</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span> <span class="comment">// changes the value of 'b' to a copy of the value of 'a'</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">b</span> <span class="special">==</span> <span class="identifier">a</span> <span class="special">)</span> <span class="special">;</span>
+<span class="keyword">int</span> <span class="identifier">c</span> <span class="special">=</span> <span class="number">3</span><span class="special">;</span>
+<span class="keyword">int</span><span class="special">&amp;</span> <span class="identifier">rc</span> <span class="special">=</span> <span class="identifier">c</span> <span class="special">;</span>
+<span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">rc</span> <span class="special">;</span> <span class="comment">// REBINDS to 'c' through 'rc'</span>
+<span class="identifier">c</span> <span class="special">=</span> <span class="number">4</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="number">4</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_optional_ref_emplace_R"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="identifier">emplace</span><span class="special">(</span> <span class="identifier">R</span><span class="special">&amp;&amp;</span> <span class="identifier">r</span>
+            <span class="special">)</span> <span class="keyword">noexcept</span>
+            <span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Effects: </strong></span> Assigns <code class="computeroutput"><span class="identifier">ref</span></code>
+              with expression <code class="computeroutput"><span class="identifier">r</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">true</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Remarks:</strong></span> Unless <code class="computeroutput"><span class="identifier">R</span></code>
+              is an lvalue reference, the program is ill-formed. This function does
+              not participate in overload resolution if <code class="computeroutput"><span class="identifier">decay</span><span class="special">&lt;</span><span class="identifier">R</span><span class="special">&gt;</span></code> is an instance of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span></code>.
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_optional_ref_get"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="identifier">T</span><span class="special">&amp;</span>
+            <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="identifier">get</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="identifier">T</span><span class="special">&amp;</span>
+            <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="keyword">operator</span> <span class="special">*()</span>
+            <span class="keyword">const</span> <span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">true</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Effects: </strong></span> Returns <code class="computeroutput"><span class="special">*</span><span class="identifier">ref</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Throws: </strong></span> Nothing.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">vref</span> <span class="special">=</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;</span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">vref</span> <span class="special">);</span>
+<span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">vref2</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">opt</span><span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">vref2</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="special">++</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_optional_ref_arrow"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="identifier">T</span><span class="special">*</span>
+            <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="keyword">operator</span> <span class="special">-&gt;</span>
+            <span class="special">()</span> <span class="keyword">const</span>
+            <span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">true</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Effects: </strong></span> Returns <code class="computeroutput"><span class="identifier">ref</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Throws: </strong></span> Nothing.
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_optional_ref_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="identifier">T</span><span class="special">&amp;</span>
+            <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="identifier">value</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+              <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">return</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">?</span> <span class="special">*</span><span class="identifier">val</span> <span class="special">:</span> <span class="keyword">throw</span> <span class="identifier">bad_optional_access</span><span class="special">();</span></code>.
+            </li></ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_optional_ref_value_or"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">&gt;</span> <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="identifier">value_or</span><span class="special">(</span> <span class="identifier">R</span><span class="special">&amp;&amp;</span> <span class="identifier">r</span>
+            <span class="special">)</span> <span class="keyword">const</span>
+            <span class="keyword">noexcept</span><span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">if</span> <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="special">**</span><span class="keyword">this</span><span class="special">;</span> <span class="keyword">else</span> <span class="keyword">return</span>
+              <span class="identifier">r</span><span class="special">;</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Remarks:</strong></span> Unless <code class="computeroutput"><span class="identifier">R</span></code>
+              is an lvalue reference, the program is ill-formed.
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_optional_ref_value_or_eval"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">&gt;</span> <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="identifier">value_or</span><span class="special">(</span> <span class="identifier">F</span> <span class="identifier">f</span> <span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">if</span> <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="special">**</span><span class="keyword">this</span><span class="special">;</span> <span class="keyword">else</span> <span class="keyword">return</span>
+              <span class="identifier">f</span><span class="special">();</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Remarks:</strong></span> Unless <code class="computeroutput"><span class="keyword">decltype</span><span class="special">(</span><span class="identifier">f</span><span class="special">())</span></code> is an lvalue reference, the program
+              is ill-formed.
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_optional_ref_map"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">&gt;</span> <span class="keyword">auto</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="identifier">map</span><span class="special">(</span> <span class="identifier">F</span> <span class="identifier">f</span> <span class="special">)</span> <span class="keyword">const</span> <span class="special">-&gt;</span> </code><span class="emphasis"><em>see below</em></span><code class="computeroutput"><span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">if</span> <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="identifier">f</span><span class="special">(**</span><span class="keyword">this</span><span class="special">);</span> <span class="keyword">else</span> <span class="keyword">return</span> <span class="identifier">none</span><span class="special">;</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Remarks:</strong></span> The return type of this function
+              is <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">decltype</span><span class="special">(</span><span class="identifier">f</span><span class="special">(**</span><span class="keyword">this</span><span class="special">))&gt;</span></code>.
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_optional_ref_flat_map"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">&gt;</span> <span class="keyword">auto</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="identifier">flat_map</span><span class="special">(</span>
+            <span class="identifier">F</span> <span class="identifier">f</span>
+            <span class="special">)</span> <span class="keyword">const</span>
+            <span class="special">-&gt;</span> </code><span class="emphasis"><em>see below</em></span><code class="computeroutput"><span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Requires:</strong></span> The return type of expression
+              <code class="computeroutput"><span class="identifier">f</span><span class="special">(**</span><span class="keyword">this</span><span class="special">)</span></code>
+              is <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">U</span><span class="special">&gt;</span></code>
+              for some object or reference type <code class="computeroutput"><span class="identifier">U</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">if</span> <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="identifier">f</span><span class="special">(**</span><span class="keyword">this</span><span class="special">);</span> <span class="keyword">else</span> <span class="keyword">return</span> <span class="identifier">none</span><span class="special">;</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Remarks:</strong></span> The return type of this function
+              is <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">U</span><span class="special">&gt;</span></code>.
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_optional_ref_get_ptr"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="identifier">T</span><span class="special">*</span>
+            <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="identifier">get_ptr</span> <span class="special">()</span>
+            <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+              <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="identifier">ref</span></code>.
+            </li></ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_optional_ref_operator_bool"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">bool</span> <span class="identifier">has_value</span><span class="special">()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="keyword">operator</span> <span class="keyword">bool</span>
+            <span class="special">()</span> <span class="keyword">const</span>
+            <span class="keyword">noexcept</span><span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+              <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(</span><span class="identifier">ref</span><span class="special">)</span></code>.
+            </li></ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_optional_ref_operator_not"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="keyword">operator</span> <span class="special">!</span> <span class="special">()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+              <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">!</span><span class="keyword">bool</span><span class="special">(</span><span class="identifier">ref</span><span class="special">)</span></code>.
+            </li></ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_optional_ref_reset"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="identifier">reset</span><span class="special">()</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+              <span class="bold"><strong>Effects:</strong></span> Same as <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span> <span class="special">=</span> <span class="identifier">none</span></code>.
+            </li></ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_optional_ref_reset_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">&gt;</span> <span class="keyword">void</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="identifier">reset</span> <span class="special">(</span> <span class="identifier">R</span><span class="special">&amp;&amp;</span>
+            <span class="identifier">r</span><span class="special">)</span>
+            <span class="keyword">noexcept</span><span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special">&lt;</span><span class="identifier">R</span><span class="special">&gt;(</span><span class="identifier">r</span><span class="special">)</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Remarks:</strong></span> This function is deprecated.
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_optional_ref_is_initialized"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">bool</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="identifier">is_initialized</span><span class="special">()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">return</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Remarks:</strong></span> This function is deprecated.
+            </li>
+</ul></div>
+<p>
+          <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+        </p>
+<a name="reference_optional_ref_get_value_or_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+            <code class="computeroutput"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">&gt;</span> <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="identifier">get_value_or</span><span class="special">(</span> <span class="identifier">R</span><span class="special">&amp;&amp;</span> <span class="identifier">r</span>
+            <span class="special">)</span> <span class="keyword">const</span>
+            <span class="keyword">noexcept</span><span class="special">;</span></code>
+          </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+              <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">return</span> <span class="identifier">value_or</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special">&lt;</span><span class="identifier">R</span><span class="special">&gt;(</span><span class="identifier">r</span><span class="special">);</span></code>.
+            </li>
+<li class="listitem">
+              <span class="bold"><strong>Remarks:</strong></span> This function is deprecated.
+            </li>
+</ul></div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+      </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="detailed_semantics___optional_values.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="detailed_semantics___free_functions.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>

doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/header__boost_optional_hpp_.html

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+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Header &lt;boost/optional.hpp&gt;</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<link rel="home" href="../../../index.html" title="Boost.Optional">
+<link rel="up" href="../../../optional/reference/header__boost_optional_optional_hpp_.html" title="Header &lt;boost/optional/optional.hpp&gt;">
+<link rel="prev" href="../../../optional/reference/header__boost_optional_optional_hpp_.html" title="Header &lt;boost/optional/optional.hpp&gt;">
+<link rel="next" href="../dependencies_and_portability.html" title="Dependencies and Portability">
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+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
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+<a accesskey="p" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../dependencies_and_portability.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.reference.header__boost_optional_optional_hpp_.header__boost_optional_hpp_"></a><a class="link" href="header__boost_optional_hpp_.html" title="Header &lt;boost/optional.hpp&gt;">Header
+        &lt;boost/optional.hpp&gt;</a>
+</h4></div></div></div>
+<p>
+          This is an alias for header <a class="link" href="../../../optional/reference/header__boost_optional_optional_hpp_.html#boost_optional.reference.header__boost_optional_optional_hpp_.header_optional_optional" title="Synopsis"><code class="computeroutput"><span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">optional</span><span class="special">/</span><span class="identifier">optional</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code></a>.
+        </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014-2016 Andrzej Krzemie&#324;ski<p>
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+      </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../dependencies_and_portability.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>

doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/header_optional_in_place_init.html

@@ -0,0 +1,61 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
+<title>Initialization tags</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../../index.html" title="Boost.Optional">
+<link rel="up" href="../../../optional/reference/header__boost_optional_optional_hpp_.html" title="Header &lt;boost/optional/optional.hpp&gt;">
+<link rel="prev" href="../../../optional/reference/header__boost_optional_optional_hpp_.html" title="Header &lt;boost/optional/optional.hpp&gt;">
+<link rel="next" href="header_optional_optional_values.html" title="Optional Values">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../../index.html">Home</a></td>
+<td align="center"><a href="../../../../../../../libs/libraries.htm">Libraries</a></td>
+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="header_optional_optional_values.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.reference.header__boost_optional_optional_hpp_.header_optional_in_place_init"></a><a class="link" href="header_optional_in_place_init.html" title="Initialization tags">Initialization
+        tags</a>
+</h4></div></div></div>
+<a name="reference_in_place_init"></a><a name="reference_in_place_init_if"></a><pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span>
+
+<span class="keyword">class</span> <span class="identifier">in_place_init_t</span> <span class="special">{</span> <span class="comment">/* see below */</span> <span class="special">}</span> <span class="special">;</span>
+<span class="keyword">const</span> <span class="identifier">in_place_init_t</span> <span class="identifier">in_place_init</span> <span class="special">(</span> <span class="comment">/* see below */</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="keyword">class</span> <span class="identifier">in_place_init_if_t</span> <span class="special">{</span> <span class="comment">/*see below*/</span> <span class="special">}</span> <span class="special">;</span>
+<span class="keyword">const</span> <span class="identifier">in_place_init_if_t</span> <span class="identifier">in_place_init_if</span> <span class="special">(</span> <span class="comment">/*see below*/</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="special">}</span>
+</pre>
+<p>
+          Classes <code class="computeroutput"><span class="identifier">in_place_init_t</span></code>
+          and <code class="computeroutput"><span class="identifier">in_place_init_if_t</span></code>
+          are empty classes. Their purpose is to control overload resolution in the
+          initialization of optional objects. They are empty, trivially copyable
+          classes with disabled default constructor.
+        </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+      </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="header_optional_optional_values.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>

doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/header_optional_optional_refs.html

@@ -0,0 +1,118 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
+<title>Optional References</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../../index.html" title="Boost.Optional">
+<link rel="up" href="../../../optional/reference/header__boost_optional_optional_hpp_.html" title="Header &lt;boost/optional/optional.hpp&gt;">
+<link rel="prev" href="header_optional_optional_values.html" title="Optional Values">
+<link rel="next" href="detailed_semantics___optional_values.html" title="Detailed Semantics - Optional Values">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../../index.html">Home</a></td>
+<td align="center"><a href="../../../../../../../libs/libraries.htm">Libraries</a></td>
+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="header_optional_optional_values.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="detailed_semantics___optional_values.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.reference.header__boost_optional_optional_hpp_.header_optional_optional_refs"></a><a class="link" href="header_optional_optional_refs.html" title="Optional References">Optional
+        References</a>
+</h4></div></div></div>
+<a name="reference_operator_template_spec"></a><pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
+<span class="keyword">class</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;</span> <span class="comment">// specialization for lvalue references</span>
+<span class="special">{</span>
+<span class="keyword">public</span> <span class="special">:</span>
+
+    <span class="keyword">typedef</span> <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">value_type</span><span class="special">;</span>
+    <span class="keyword">typedef</span> <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">reference_type</span><span class="special">;</span>
+    <span class="keyword">typedef</span> <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">reference_const_type</span><span class="special">;</span> <span class="comment">// no const propagation</span>
+    <span class="keyword">typedef</span> <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">rval_reference_type</span><span class="special">;</span>
+    <span class="keyword">typedef</span> <span class="identifier">T</span><span class="special">*</span> <span class="identifier">pointer_type</span><span class="special">;</span>
+    <span class="keyword">typedef</span> <span class="identifier">T</span><span class="special">*</span> <span class="identifier">pointer_const_type</span><span class="special">;</span>   <span class="comment">// no const propagation</span>
+
+    <span class="identifier">optional</span> <span class="special">()</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_default_ctor"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">none_t</span> <span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_default_ctor"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">&gt;</span> <span class="identifier">optional</span><span class="special">(</span><span class="identifier">R</span><span class="special">&amp;&amp;</span> <span class="identifier">r</span><span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span>  <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_value_ctor"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">&gt;</span> <span class="identifier">optional</span><span class="special">(</span><span class="keyword">bool</span> <span class="identifier">cond</span><span class="special">,</span> <span class="identifier">R</span><span class="special">&amp;&amp;</span> <span class="identifier">r</span><span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_cond_value_ctor"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">optional</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_copy_ctor"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">&gt;</span> <span class="keyword">explicit</span> <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">U</span><span class="special">&amp;&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_ctor_from_opt_U"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="identifier">optional</span><span class="special">&amp;</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">none_t</span> <span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_assign_none_t"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="identifier">optional</span><span class="special">&amp;</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_copy_assign"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">&gt;</span> <span class="identifier">optional</span><span class="special">&amp;</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">U</span><span class="special">&amp;&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_assign_optional_U"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">&gt;</span> <span class="identifier">optional</span><span class="special">&amp;</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span><span class="identifier">R</span><span class="special">&amp;&amp;</span> <span class="identifier">r</span><span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_assign_R"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">&gt;</span> <span class="keyword">void</span> <span class="identifier">emplace</span> <span class="special">(</span> <span class="identifier">R</span><span class="special">&amp;&amp;</span> <span class="identifier">r</span> <span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_emplace_R"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">get</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_get"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+    <span class="identifier">T</span><span class="special">&amp;</span> <span class="keyword">operator</span> <span class="special">*()</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_get"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="identifier">T</span><span class="special">*</span> <span class="keyword">operator</span> <span class="special">-&gt;()</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_arrow"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">value</span><span class="special">()</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_value"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">&gt;</span> <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">value_or</span><span class="special">(</span> <span class="identifier">R</span> <span class="special">&amp;&amp;</span> <span class="identifier">r</span> <span class="special">)</span> <span class="keyword">const</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_value_or"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">&gt;</span> <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">value_or_eval</span><span class="special">(</span> <span class="identifier">F</span> <span class="identifier">f</span> <span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_value_or_eval"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">&gt;</span> <span class="keyword">auto</span> <span class="identifier">map</span><span class="special">(</span> <span class="identifier">F</span> <span class="identifier">f</span> <span class="special">)</span> <span class="keyword">const</span> <span class="special">-&gt;</span> <span class="emphasis"><em>see below</em></span><span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_map"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">&gt;</span> <span class="keyword">auto</span> <span class="identifier">flat_map</span><span class="special">(</span> <span class="identifier">F</span> <span class="identifier">f</span> <span class="special">)</span> <span class="keyword">const</span> <span class="special">-&gt;</span> <span class="emphasis"><em>see below</em></span><span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_flat_map"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="identifier">T</span><span class="special">*</span> <span class="identifier">get_ptr</span><span class="special">()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_get_ptr"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">bool</span> <span class="identifier">has_value</span><span class="special">()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_operator_bool"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">explicit</span> <span class="keyword">operator</span> <span class="keyword">bool</span><span class="special">()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_operator_bool"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">!()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_operator_not"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">void</span> <span class="identifier">reset</span><span class="special">()</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_reset"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="comment">// deprecated methods</span>
+
+    <span class="comment">// (deprecated)</span>
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">&gt;</span> <span class="keyword">void</span> <span class="identifier">reset</span> <span class="special">(</span> <span class="identifier">R</span> <span class="special">&amp;&amp;</span> <span class="identifier">r</span> <span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_reset_value"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="comment">// (deprecated)</span>
+    <span class="keyword">bool</span> <span class="identifier">is_initialized</span><span class="special">()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_is_initialized"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="comment">// (deprecated)</span>
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">&gt;</span> <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">get_value_or</span><span class="special">(</span> <span class="identifier">R</span> <span class="special">&amp;&amp;</span> <span class="identifier">r</span> <span class="special">)</span> <span class="identifier">constnoexcept</span><span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_get_value_or_value"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+<span class="keyword">private</span><span class="special">:</span>
+    <span class="identifier">T</span><span class="special">*</span> <span class="identifier">ref</span><span class="special">;</span> <span class="comment">// exposition only</span>
+<span class="special">};</span>
+</pre>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+      </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="header_optional_optional_values.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="detailed_semantics___optional_values.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>

doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/header_optional_optional_values.html

@@ -0,0 +1,153 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
+<title>Optional Values</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../../index.html" title="Boost.Optional">
+<link rel="up" href="../../../optional/reference/header__boost_optional_optional_hpp_.html" title="Header &lt;boost/optional/optional.hpp&gt;">
+<link rel="prev" href="header_optional_in_place_init.html" title="Initialization tags">
+<link rel="next" href="header_optional_optional_refs.html" title="Optional References">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td>
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+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../../more/index.htm">More</a></td>
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+<a accesskey="p" href="header_optional_in_place_init.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="header_optional_optional_refs.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.reference.header__boost_optional_optional_hpp_.header_optional_optional_values"></a><a class="link" href="header_optional_optional_values.html" title="Optional Values">Optional
+        Values</a>
+</h4></div></div></div>
+<a name="reference_operator_template"></a><pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
+<span class="keyword">class</span> <span class="identifier">optional</span>
+<span class="special">{</span>
+<span class="keyword">public</span> <span class="special">:</span>
+
+    <span class="keyword">typedef</span> <span class="identifier">T</span>         <span class="identifier">value_type</span> <span class="special">;</span>
+    <span class="keyword">typedef</span> <span class="identifier">T</span> <span class="special">&amp;</span>       <span class="identifier">reference_type</span> <span class="special">;</span>
+    <span class="keyword">typedef</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span>  <span class="identifier">reference_const_type</span> <span class="special">;</span>
+    <span class="keyword">typedef</span> <span class="identifier">T</span> <span class="special">&amp;&amp;</span>      <span class="identifier">rval_reference_type</span> <span class="special">;</span>
+    <span class="keyword">typedef</span> <span class="identifier">T</span> <span class="special">*</span>       <span class="identifier">pointer_type</span> <span class="special">;</span>
+    <span class="keyword">typedef</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span>  <span class="identifier">pointer_const_type</span> <span class="special">;</span>
+
+    <span class="identifier">optional</span> <span class="special">()</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_constructor"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">none_t</span> <span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_constructor_none_t"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_constructor_value"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&amp;&amp;</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_constructor_move_value"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="identifier">optional</span> <span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_constructor_bool_value"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">optional</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_constructor_optional"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&amp;&amp;</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">(</span><span class="emphasis"><em>see below</em></span><span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_move_constructor_optional"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">&gt;</span> <span class="keyword">explicit</span> <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">U</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_constructor_other_optional"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">&gt;</span> <span class="keyword">explicit</span> <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">U</span><span class="special">&gt;&amp;&amp;</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_move_constructor_other_optional"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">&gt;</span> <span class="keyword">explicit</span> <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">in_place_init_t</span><span class="special">,</span> <span class="identifier">Args</span><span class="special">&amp;&amp;...</span> <span class="identifier">args</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_in_place_init"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">&gt;</span> <span class="keyword">explicit</span> <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">in_place_init_if_t</span><span class="special">,</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="identifier">Args</span><span class="special">&amp;&amp;...</span> <span class="identifier">args</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_in_place_init_if"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">InPlaceFactory</span><span class="special">&gt;</span> <span class="keyword">explicit</span> <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">InPlaceFactory</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">f</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_constructor_factory"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">TypedInPlaceFactory</span><span class="special">&gt;</span> <span class="keyword">explicit</span> <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">TypedInPlaceFactory</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">f</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_constructor_factory"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="identifier">optional</span><span class="special">&amp;</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">none_t</span> <span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_equal_none_t"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="identifier">optional</span><span class="special">&amp;</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_equal_value"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="identifier">optional</span><span class="special">&amp;</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&amp;&amp;</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_move_equal_value"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="identifier">optional</span><span class="special">&amp;</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_equal_optional"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="identifier">optional</span><span class="special">&amp;</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&amp;&amp;</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">(</span><span class="emphasis"><em>see below</em></span><span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_move_equal_optional"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">&gt;</span> <span class="identifier">optional</span><span class="special">&amp;</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">U</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_equal_other_optional"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">&gt;</span> <span class="identifier">optional</span><span class="special">&amp;</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">U</span><span class="special">&gt;&amp;&amp;</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_move_equal_other_optional"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">&gt;</span> <span class="keyword">void</span> <span class="identifier">emplace</span> <span class="special">(</span> <span class="identifier">Args</span><span class="special">&amp;&amp;...</span> <span class="identifier">args</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_emplace"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">InPlaceFactory</span><span class="special">&gt;</span> <span class="identifier">optional</span><span class="special">&amp;</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">InPlaceFactory</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">f</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_equal_factory"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">TypedInPlaceFactory</span><span class="special">&gt;</span> <span class="identifier">optional</span><span class="special">&amp;</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">TypedInPlaceFactory</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">f</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_equal_factory"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">get</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_get"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+    <span class="identifier">T</span><span class="special">&amp;</span>       <span class="identifier">get</span><span class="special">()</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_get"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="keyword">operator</span> <span class="special">-&gt;()</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_arrow"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+    <span class="identifier">T</span><span class="special">*</span>       <span class="keyword">operator</span> <span class="special">-&gt;()</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_arrow"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="keyword">operator</span> <span class="special">*()</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_asterisk"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+    <span class="identifier">T</span><span class="special">&amp;</span>       <span class="keyword">operator</span> <span class="special">*()</span> <span class="special">&amp;</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_asterisk"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+    <span class="identifier">T</span><span class="special">&amp;&amp;</span>      <span class="keyword">operator</span> <span class="special">*()</span> <span class="special">&amp;&amp;</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_asterisk_move"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">value</span><span class="special">()</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_value"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+    <span class="identifier">T</span><span class="special">&amp;</span>       <span class="identifier">value</span><span class="special">()</span> <span class="special">&amp;</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_value"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+    <span class="identifier">T</span><span class="special">&amp;&amp;</span>      <span class="identifier">value</span><span class="special">()</span> <span class="special">&amp;&amp;</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_value_move"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">&gt;</span> <span class="identifier">T</span> <span class="identifier">value_or</span><span class="special">(</span> <span class="identifier">U</span> <span class="special">&amp;&amp;</span> <span class="identifier">v</span> <span class="special">)</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_value_or"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">&gt;</span> <span class="identifier">T</span> <span class="identifier">value_or</span><span class="special">(</span> <span class="identifier">U</span> <span class="special">&amp;&amp;</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">&amp;&amp;</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_value_or_move"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">&gt;</span> <span class="identifier">T</span> <span class="identifier">value_or_eval</span><span class="special">(</span> <span class="identifier">F</span> <span class="identifier">f</span> <span class="special">)</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_value_or_call"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">&gt;</span> <span class="identifier">T</span> <span class="identifier">value_or_eval</span><span class="special">(</span> <span class="identifier">F</span> <span class="identifier">f</span> <span class="special">)</span> <span class="special">&amp;&amp;</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_value_or_call_move"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">&gt;</span> <span class="keyword">auto</span> <span class="identifier">map</span><span class="special">(</span> <span class="identifier">F</span> <span class="identifier">f</span> <span class="special">)</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="special">-&gt;</span> <span class="emphasis"><em>see below</em></span><span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_map"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">&gt;</span> <span class="keyword">auto</span> <span class="identifier">map</span><span class="special">(</span> <span class="identifier">F</span> <span class="identifier">f</span> <span class="special">)</span> <span class="special">&amp;</span> <span class="special">-&gt;</span> <span class="emphasis"><em>see below</em></span><span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_map"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">&gt;</span> <span class="keyword">auto</span> <span class="identifier">map</span><span class="special">(</span> <span class="identifier">F</span> <span class="identifier">f</span> <span class="special">)</span> <span class="special">&amp;&amp;</span> <span class="special">-&gt;</span> <span class="emphasis"><em>see below</em></span><span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_map_move"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">&gt;</span> <span class="keyword">auto</span> <span class="identifier">flat_map</span><span class="special">(</span> <span class="identifier">F</span> <span class="identifier">f</span> <span class="special">)</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="special">-&gt;</span> <span class="emphasis"><em>see below</em></span><span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_flat_map"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">&gt;</span> <span class="keyword">auto</span> <span class="identifier">flat_map</span><span class="special">(</span> <span class="identifier">F</span> <span class="identifier">f</span> <span class="special">)</span> <span class="special">&amp;</span> <span class="special">-&gt;</span> <span class="emphasis"><em>see below</em></span><span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_flat_map"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">&gt;</span> <span class="keyword">auto</span> <span class="identifier">flat_map</span><span class="special">(</span> <span class="identifier">F</span> <span class="identifier">f</span> <span class="special">)</span> <span class="special">&amp;&amp;</span> <span class="special">-&gt;</span> <span class="emphasis"><em>see below</em></span><span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_flat_map_move"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">get_ptr</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_get_ptr"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+    <span class="identifier">T</span><span class="special">*</span>       <span class="identifier">get_ptr</span><span class="special">()</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_get_ptr"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">bool</span> <span class="identifier">has_value</span><span class="special">()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_bool"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">explicit</span> <span class="keyword">operator</span> <span class="keyword">bool</span><span class="special">()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_bool"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">!()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_not"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="keyword">void</span> <span class="identifier">reset</span><span class="special">()</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_reset"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="comment">// deprecated methods</span>
+
+    <span class="comment">// (deprecated)</span>
+    <span class="keyword">void</span> <span class="identifier">reset</span> <span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_reset_value"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="comment">// (deprecated)</span>
+    <span class="keyword">bool</span> <span class="identifier">is_initialized</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_is_initialized"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+    <span class="comment">// (deprecated)</span>
+    <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">get_value_or</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="keyword">default</span> <span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_get_value_or_value"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+<span class="special">};</span>
+</pre>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+      </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="header_optional_in_place_init.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="header_optional_optional_refs.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>

doc/html/boost_optional/reference/io_header.html

@@ -1,9 +1,9 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Header &lt;boost/optional/optional_io.hpp&gt;</title>
 <link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="../../index.html" title="Boost.Optional">
 <link rel="up" href="../../optional/reference.html" title="Reference">
 <link rel="prev" href="header__boost_optional_bad_optional_access_hpp_/detailed_semantics.html" title="Detailed semantics">
@@ -58,7 +58,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>

doc/html/boost_optional/reference/io_header/io_semantics.html

@@ -1,9 +1,9 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Detailed semantics</title>
 <link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="../../../index.html" title="Boost.Optional">
 <link rel="up" href="../io_header.html" title="Header &lt;boost/optional/optional_io.hpp&gt;">
 <link rel="prev" href="../io_header.html" title="Header &lt;boost/optional/optional_io.hpp&gt;">
@@ -32,7 +32,7 @@
           <span class="special">&lt;</span><span class="keyword">class</span>
           <span class="identifier">CharType</span><span class="special">,</span>
           <span class="keyword">class</span> <span class="identifier">CharTrait</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span></code>
-          <br> &#160;&#160;&#160;&#160;<code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_ostream</span><span class="special">&lt;</span><span class="identifier">CharType</span><span class="special">,</span> <span class="identifier">CharTrait</span><span class="special">&gt;&amp;</span></code> <br> &#160;&#160;&#160;&#160;<code class="computeroutput"><span class="keyword">operator</span><span class="special">&lt;&lt;(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_ostream</span><span class="special">&lt;</span><span class="identifier">CharType</span><span class="special">,</span> <span class="identifier">CharTrait</span><span class="special">&gt;&amp;</span>
+          <br>     <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_ostream</span><span class="special">&lt;</span><span class="identifier">CharType</span><span class="special">,</span> <span class="identifier">CharTrait</span><span class="special">&gt;&amp;</span></code> <br>     <code class="computeroutput"><span class="keyword">operator</span><span class="special">&lt;&lt;(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_ostream</span><span class="special">&lt;</span><span class="identifier">CharType</span><span class="special">,</span> <span class="identifier">CharTrait</span><span class="special">&gt;&amp;</span>
           <span class="identifier">out</span><span class="special">,</span>
           <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">v</span><span class="special">);</span></code>
         </p>
@@ -53,8 +53,8 @@
         </p>
 <p>
           <code class="computeroutput"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">CharType</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">CharTrait</span><span class="special">,</span>
-          <span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span></code> <br> &#160;&#160;&#160;&#160;<code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_ostream</span><span class="special">&lt;</span><span class="identifier">CharType</span><span class="special">,</span> <span class="identifier">CharTrait</span><span class="special">&gt;&amp;</span></code>
-          <br> &#160;&#160;&#160;&#160;<code class="computeroutput"><span class="keyword">operator</span><span class="special">&lt;&lt;(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_ostream</span><span class="special">&lt;</span><span class="identifier">CharType</span><span class="special">,</span> <span class="identifier">CharTrait</span><span class="special">&gt;&amp;</span> <span class="identifier">out</span><span class="special">,</span> <span class="identifier">none_t</span><span class="special">);</span></code>
+          <span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span></code> <br>     <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_ostream</span><span class="special">&lt;</span><span class="identifier">CharType</span><span class="special">,</span> <span class="identifier">CharTrait</span><span class="special">&gt;&amp;</span></code>
+          <br>     <code class="computeroutput"><span class="keyword">operator</span><span class="special">&lt;&lt;(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_ostream</span><span class="special">&lt;</span><span class="identifier">CharType</span><span class="special">,</span> <span class="identifier">CharTrait</span><span class="special">&gt;&amp;</span> <span class="identifier">out</span><span class="special">,</span> <span class="identifier">none_t</span><span class="special">);</span></code>
         </p>
 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
 <li class="listitem">
@@ -70,8 +70,8 @@
         </p>
 <p>
           <code class="computeroutput"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">CharType</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">CharTrait</span><span class="special">,</span>
-          <span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span></code> <br> &#160;&#160;&#160;&#160;<code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_ostream</span><span class="special">&lt;</span><span class="identifier">CharType</span><span class="special">,</span> <span class="identifier">CharTrait</span><span class="special">&gt;&amp;</span></code>
-          <br> &#160;&#160;&#160;&#160;<code class="computeroutput"><span class="keyword">operator</span><span class="special">&gt;&gt;(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_istream</span><span class="special">&lt;</span><span class="identifier">CharType</span><span class="special">,</span> <span class="identifier">CharTrait</span><span class="special">&gt;&amp;</span> <span class="identifier">in</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;&amp;</span> <span class="identifier">v</span><span class="special">);</span></code>
+          <span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span></code> <br>     <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_ostream</span><span class="special">&lt;</span><span class="identifier">CharType</span><span class="special">,</span> <span class="identifier">CharTrait</span><span class="special">&gt;&amp;</span></code>
+          <br>     <code class="computeroutput"><span class="keyword">operator</span><span class="special">&gt;&gt;(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_istream</span><span class="special">&lt;</span><span class="identifier">CharType</span><span class="special">,</span> <span class="identifier">CharTrait</span><span class="special">&gt;&amp;</span> <span class="identifier">in</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;&amp;</span> <span class="identifier">v</span><span class="special">);</span></code>
         </p>
 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
 <li class="listitem">
@@ -98,7 +98,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>

doc/html/boost_optional/reference/relnotes.html

@@ -0,0 +1,183 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Release Notes</title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<link rel="home" href="../../index.html" title="Boost.Optional">
+<link rel="up" href="../../optional/reference.html" title="Reference">
+<link rel="prev" href="dependencies_and_portability/optional_reference_binding.html" title="Optional Reference Binding">
+<link rel="next" href="acknowledgements.html" title="Acknowledgements">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../index.html">Home</a></td>
+<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td>
+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="dependencies_and_portability/optional_reference_binding.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="acknowledgements.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.reference.relnotes"></a><a class="link" href="relnotes.html" title="Release Notes">Release Notes</a>
+</h3></div></div></div>
+<h5>
+<a name="boost_optional.reference.relnotes.h0"></a>
+        <span class="phrase"><a name="boost_optional.reference.relnotes.boost_release_x_xx"></a></span><a class="link" href="relnotes.html#boost_optional.reference.relnotes.boost_release_x_xx">Boost Release
+        X.XX</a>
+      </h5>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+            Now <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span></code> is specialized for reference
+            parameters. This way the <code class="computeroutput"><span class="keyword">sizeof</span></code>
+            of optional reference is that of a pointer, and a number of bugs is avoided.
+          </li></ul></div>
+<h5>
+<a name="boost_optional.reference.relnotes.h1"></a>
+        <span class="phrase"><a name="boost_optional.reference.relnotes.boost_release_1_60"></a></span><a class="link" href="relnotes.html#boost_optional.reference.relnotes.boost_release_1_60">Boost Release
+        1.60</a>
+      </h5>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+            Changed the implementation of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span></code>
+            again. Now it is a const object with internal linkage (as any other tag).
+            This fixes <a href="https://svn.boost.org/trac/boost/ticket/11203" target="_top">Trac
+            #11203</a>.
+          </li></ul></div>
+<h5>
+<a name="boost_optional.reference.relnotes.h2"></a>
+        <span class="phrase"><a name="boost_optional.reference.relnotes.boost_release_1_59"></a></span><a class="link" href="relnotes.html#boost_optional.reference.relnotes.boost_release_1_59">Boost Release
+        1.59</a>
+      </h5>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+            For C++03 compilers, added 0-argument overload for member function <code class="computeroutput"><span class="identifier">emplace</span><span class="special">()</span></code>,
+            and therewith removed the dependency on <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">utility</span><span class="special">/</span><span class="identifier">in_place_factory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>.
+          </li>
+<li class="listitem">
+            Fixed <a href="https://svn.boost.org/trac/boost/ticket/11241" target="_top">Trac
+            #11241</a>.
+          </li>
+</ul></div>
+<h5>
+<a name="boost_optional.reference.relnotes.h3"></a>
+        <span class="phrase"><a name="boost_optional.reference.relnotes.boost_release_1_58"></a></span><a class="link" href="relnotes.html#boost_optional.reference.relnotes.boost_release_1_58">Boost Release
+        1.58</a>
+      </h5>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+            <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none_t</span></code> is no longer convertible from
+            literal <code class="computeroutput"><span class="number">0</span></code>. This avoids a
+            bug where <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">rational</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;&gt;</span>
+            <span class="identifier">oi</span> <span class="special">=</span>
+            <span class="number">0</span><span class="special">;</span></code>
+            would initialize an optional object with no contained value.
+          </li>
+<li class="listitem">
+            Improved the trick that prevents streaming out <code class="computeroutput"><span class="identifier">optional</span></code>
+            without header <code class="computeroutput"><span class="identifier">optional_io</span><span class="special">.</span><span class="identifier">hpp</span></code>
+            by using safe-bool idiom. This addresses <a href="https://svn.boost.org/trac/boost/ticket/10825" target="_top">Trac
+            #10825</a>.
+          </li>
+<li class="listitem">
+            IOStream operators are now mentioned in documentation.
+          </li>
+<li class="listitem">
+            Added a way to manually disable move semantics: just define macro <code class="computeroutput"><span class="identifier">BOOST_OPTIONAL_CONFIG_NO_RVALUE_REFERENCES</span></code>.
+            This can be used to work around <a href="https://svn.boost.org/trac/boost/ticket/10399" target="_top">Trac
+            #10399</a>.
+          </li>
+<li class="listitem">
+            It is no longer possible to assign <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">U</span><span class="special">&gt;</span></code> to <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code> when <code class="computeroutput"><span class="identifier">U</span></code>
+            is not assignable or convertible to <code class="computeroutput"><span class="identifier">T</span></code>
+            (<a href="https://svn.boost.org/trac/boost/ticket/11087" target="_top">Trac #11087</a>).
+          </li>
+<li class="listitem">
+            Value accessors now work correctly on rvalues of <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;</span></code> (<a href="https://svn.boost.org/trac/boost/ticket/10839" target="_top">Trac
+            #10839</a>).
+          </li>
+</ul></div>
+<h5>
+<a name="boost_optional.reference.relnotes.h4"></a>
+        <span class="phrase"><a name="boost_optional.reference.relnotes.boost_release_1_57"></a></span><a class="link" href="relnotes.html#boost_optional.reference.relnotes.boost_release_1_57">Boost Release
+        1.57</a>
+      </h5>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+            <a href="https://github.com/boostorg/optional/pull/9" target="_top">Git pull #9</a>:
+            <span class="emphasis"><em>"Supply <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">string</span><span class="special">&gt;</span></code>
+            to fix C++03 compile error on <code class="computeroutput"><span class="identifier">logic_error</span><span class="special">(</span><span class="string">"..."</span><span class="special">)</span></code>"</em></span>.
+          </li></ul></div>
+<h5>
+<a name="boost_optional.reference.relnotes.h5"></a>
+        <span class="phrase"><a name="boost_optional.reference.relnotes.boost_release_1_56"></a></span><a class="link" href="relnotes.html#boost_optional.reference.relnotes.boost_release_1_56">Boost Release
+        1.56</a>
+      </h5>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+            Added support for rvalue references. Now <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code> works with moveable but non-copyable
+            <code class="computeroutput"><span class="identifier">T</span></code>'s,
+          </li>
+<li class="listitem">
+            Improved <code class="computeroutput"><span class="identifier">swap</span></code> (now uses
+            move operations),
+          </li>
+<li class="listitem">
+            Added function <code class="computeroutput"><span class="identifier">emplace</span><span class="special">()</span></code>. This is the last of the requests from
+            <a href="https://svn.boost.org/trac/boost/ticket/1841" target="_top">Trac #1841</a>,
+          </li>
+<li class="listitem">
+            <code class="computeroutput"><span class="identifier">optional</span></code> is moveable,
+            including conditional <code class="computeroutput"><span class="keyword">noexcept</span></code>
+            specifications, which make it <code class="computeroutput"><span class="identifier">move_if_noexcept</span></code>-friendly,
+          </li>
+<li class="listitem">
+            Using explicit operator bool() on platforms that support it (<a href="https://svn.boost.org/trac/boost/ticket/4227" target="_top">Trac
+            #4227</a>) (breaking change),
+          </li>
+<li class="listitem">
+            Forward declaration of <code class="computeroutput"><span class="keyword">operator</span><span class="special">&lt;&lt;(</span><span class="identifier">ostream</span><span class="special">&amp;,</span> <span class="identifier">optional</span>
+            <span class="keyword">const</span><span class="special">&amp;)</span></code>
+            to prevent inadvertent incorrect serialization of optional objects,
+          </li>
+<li class="listitem">
+            Removed deprecated function <code class="computeroutput"><span class="identifier">reset</span><span class="special">()</span></code> from examples (<a href="https://svn.boost.org/trac/boost/ticket/9005" target="_top">Trac
+            #9005</a>),
+          </li>
+<li class="listitem">
+            Equality comparison with <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span></code>
+            does not require that <code class="computeroutput"><span class="identifier">T</span></code>
+            be EqualityComparable,
+          </li>
+<li class="listitem">
+            Optional rvalue references are explicitly disallowed,
+          </li>
+<li class="listitem">
+            Binding temporaries to optional references is explicitly disallowed (breaking
+            change),
+          </li>
+<li class="listitem">
+            More ways to access the contained value, functions <code class="computeroutput"><span class="identifier">value</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">value_or</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">value_or_eval</span><span class="special">()</span></code>,
+          </li>
+<li class="listitem">
+            Updated and reorganized documentation, added tutorial and quick guide
+            sections.
+          </li>
+</ul></div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014-2016 Andrzej Krzemie&#324;ski<p>
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+      </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="dependencies_and_portability/optional_reference_binding.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="acknowledgements.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>

doc/html/boost_optional/relnotes.html

@@ -1,9 +1,9 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Release Notes</title>
 <link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="../index.html" title="Boost.Optional">
 <link rel="up" href="../index.html" title="Boost.Optional">
 <link rel="prev" href="dependencies_and_portability/optional_reference_binding.html" title="Optional Reference Binding">
@@ -28,15 +28,246 @@
 </h2></div></div></div>
 <h4>
 <a name="boost_optional.relnotes.h0"></a>
+      <span class="phrase"><a name="boost_optional.relnotes.boost_release_1_79"></a></span><a class="link" href="relnotes.html#boost_optional.relnotes.boost_release_1_79">Boost
+      Release 1.79</a>
+    </h4>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+          Fixed <a href="https://github.com/boostorg/optional/issues/98" target="_top">issue
+          #98</a>.
+        </li>
+<li class="listitem">
+          Fixed <a href="https://github.com/boostorg/optional/issues/92" target="_top">issue
+          #92</a>.
+        </li>
+<li class="listitem">
+          Added support for <code class="computeroutput"><span class="identifier">BOOST_NO_IOSTREAM</span></code>.
+        </li>
+<li class="listitem">
+          Now aligned storage uses <code class="computeroutput"><span class="keyword">unsigned</span>
+          <span class="keyword">char</span></code> rather than <code class="computeroutput"><span class="keyword">char</span></code>
+          to avoid UB.
+        </li>
+<li class="listitem">
+          Now using cv-unqualified <code class="computeroutput"><span class="identifier">value_type</span></code>
+          with placement <code class="computeroutput"><span class="keyword">new</span></code> to avoid
+          UB.
+        </li>
+</ul></div>
+<h4>
+<a name="boost_optional.relnotes.h1"></a>
+      <span class="phrase"><a name="boost_optional.relnotes.boost_release_1_76"></a></span><a class="link" href="relnotes.html#boost_optional.relnotes.boost_release_1_76">Boost
+      Release 1.76</a>
+    </h4>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+          Fixed MSVC warning C4702.
+        </li></ul></div>
+<h4>
+<a name="boost_optional.relnotes.h2"></a>
+      <span class="phrase"><a name="boost_optional.relnotes.boost_release_1_75"></a></span><a class="link" href="relnotes.html#boost_optional.relnotes.boost_release_1_75">Boost
+      Release 1.75</a>
+    </h4>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+          <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span></code> is <code class="computeroutput"><span class="keyword">constexpr</span></code>-declared.
+        </li>
+<li class="listitem">
+          Fixed <a href="https://github.com/boostorg/optional/issues/78" target="_top">issue
+          #78</a>.
+        </li>
+</ul></div>
+<h4>
+<a name="boost_optional.relnotes.h3"></a>
+      <span class="phrase"><a name="boost_optional.relnotes.boost_release_1_73"></a></span><a class="link" href="relnotes.html#boost_optional.relnotes.boost_release_1_73">Boost
+      Release 1.73</a>
+    </h4>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+          Fixed <a href="https://github.com/boostorg/optional/issues/78" target="_top">issue
+          #78</a>.
+        </li>
+<li class="listitem">
+          <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span></code> is now declared as an inline variable
+          (on compilers that support it): there is only one instance of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span></code> across all translation units.
+        </li>
+<li class="listitem">
+          Fixed a number of compilation errors in GCC 4.4.7 in <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code> for trivial <code class="computeroutput"><span class="identifier">T</span></code>s.
+          Thanks to Robert Leahy for the fix. For details see <a href="https://github.com/boostorg/optional/pull/80" target="_top">pr
+          #78</a>.
+        </li>
+<li class="listitem">
+          Now suppressing warning <code class="computeroutput"><span class="special">-</span><span class="identifier">Wweak</span><span class="special">-</span><span class="identifier">vtables</span></code>.
+        </li>
+</ul></div>
+<h4>
+<a name="boost_optional.relnotes.h4"></a>
+      <span class="phrase"><a name="boost_optional.relnotes.boost_release_1_69"></a></span><a class="link" href="relnotes.html#boost_optional.relnotes.boost_release_1_69">Boost
+      Release 1.69</a>
+    </h4>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+          Remove deprecation mark from <code class="computeroutput"><span class="identifier">reset</span><span class="special">()</span></code> method (without arguments).
+        </li>
+<li class="listitem">
+          Fixed <a href="https://github.com/boostorg/optional/issues/59" target="_top">issue
+          #59</a>.
+        </li>
+<li class="listitem">
+          Fixed bug with initialization of certain wrapper types in clang with -std=c++03.
+          See <a href="https://github.com/boostorg/optional/pull/64" target="_top">pr #64</a>.
+        </li>
+</ul></div>
+<h4>
+<a name="boost_optional.relnotes.h5"></a>
+      <span class="phrase"><a name="boost_optional.relnotes.boost_release_1_68"></a></span><a class="link" href="relnotes.html#boost_optional.relnotes.boost_release_1_68">Boost
+      Release 1.68</a>
+    </h4>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+          Added member function <code class="computeroutput"><span class="identifier">has_value</span><span class="special">()</span></code> for compatibility with <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">optional</span></code> (<a href="https://github.com/boostorg/optional/issues/52" target="_top">issue
+          #52</a>).
+        </li>
+<li class="listitem">
+          Added member function <code class="computeroutput"><span class="identifier">map</span><span class="special">()</span></code> for transforming <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code> into <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">U</span><span class="special">&gt;</span></code> using a function of type <code class="computeroutput"><span class="identifier">T</span> <span class="special">-&gt;</span> <span class="identifier">U</span></code>.
+        </li>
+<li class="listitem">
+          Added member function <code class="computeroutput"><span class="identifier">flat_map</span><span class="special">()</span></code> for transforming <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code> into <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">U</span><span class="special">&gt;</span></code> using a function of type <code class="computeroutput"><span class="identifier">T</span> <span class="special">-&gt;</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">U</span><span class="special">&gt;</span></code>.
+        </li>
+</ul></div>
+<h4>
+<a name="boost_optional.relnotes.h6"></a>
+      <span class="phrase"><a name="boost_optional.relnotes.boost_release_1_67"></a></span><a class="link" href="relnotes.html#boost_optional.relnotes.boost_release_1_67">Boost
+      Release 1.67</a>
+    </h4>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+          Fixed <a href="https://github.com/boostorg/optional/issues/46" target="_top">issue
+          #46</a>.
+        </li>
+<li class="listitem">
+          Fixed <code class="computeroutput"><span class="special">-</span><span class="identifier">Wzero</span><span class="special">-</span><span class="identifier">as</span><span class="special">-</span><span class="identifier">null</span><span class="special">-</span><span class="identifier">pointer</span><span class="special">-</span><span class="identifier">constant</span></code> warnings.
+        </li>
+</ul></div>
+<h4>
+<a name="boost_optional.relnotes.h7"></a>
+      <span class="phrase"><a name="boost_optional.relnotes.boost_release_1_66"></a></span><a class="link" href="relnotes.html#boost_optional.relnotes.boost_release_1_66">Boost
+      Release 1.66</a>
+    </h4>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+          On newer compilers <code class="computeroutput"><span class="identifier">optional</span></code>
+          is now trivially-copyable for scalar <code class="computeroutput"><span class="identifier">T</span></code>s.
+          This uses a different storage (just <code class="computeroutput"><span class="identifier">T</span></code>
+          rather than <code class="computeroutput"><span class="identifier">aligned_storage</span></code>).
+          We require the compiler to support defaulted functions.
+        </li>
+<li class="listitem">
+          Changed the implementation of <code class="computeroutput"><span class="keyword">operator</span><span class="special">==</span></code> to get rid of the <code class="computeroutput"><span class="special">-</span><span class="identifier">Wmaybe</span><span class="special">-</span><span class="identifier">uninitialized</span></code> false-positive warning
+          from GCC.
+        </li>
+</ul></div>
+<h4>
+<a name="boost_optional.relnotes.h8"></a>
+      <span class="phrase"><a name="boost_optional.relnotes.boost_release_1_63"></a></span><a class="link" href="relnotes.html#boost_optional.relnotes.boost_release_1_63">Boost
+      Release 1.63</a>
+    </h4>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+          Added two new in-place constructors. They work similarly to <code class="computeroutput"><span class="identifier">emplace</span><span class="special">()</span></code>
+          functions: they initialize the contained value by perfect-forwarding the
+          obtained arguments. One constructor always initializes the contained value,
+          the other based on a boolean condition.
+        </li>
+<li class="listitem">
+          Syntax <code class="computeroutput"><span class="identifier">o</span> <span class="special">=</span>
+          <span class="special">{}</span></code> now correctly un-initializes
+          optional, just like in <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">optional</span></code>.
+        </li>
+<li class="listitem">
+          Fixed <a href="https://svn.boost.org/trac/boost/ticket/12203" target="_top">Trac #12203</a>.
+        </li>
+<li class="listitem">
+          Fixed <a href="https://svn.boost.org/trac/boost/ticket/12563" target="_top">Trac #12563</a>.
+        </li>
+</ul></div>
+<h4>
+<a name="boost_optional.relnotes.h9"></a>
+      <span class="phrase"><a name="boost_optional.relnotes.boost_release_1_62"></a></span><a class="link" href="relnotes.html#boost_optional.relnotes.boost_release_1_62">Boost
+      Release 1.62</a>
+    </h4>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+          Fixed <a href="https://svn.boost.org/trac/boost/ticket/12179" target="_top">Trac #12179</a>.
+        </li></ul></div>
+<h4>
+<a name="boost_optional.relnotes.h10"></a>
+      <span class="phrase"><a name="boost_optional.relnotes.boost_release_1_61"></a></span><a class="link" href="relnotes.html#boost_optional.relnotes.boost_release_1_61">Boost
+      Release 1.61</a>
+    </h4>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+          Now <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span></code> is specialized for reference
+          parameters. This addresses a couple of issues:
+          <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
+<li class="listitem">
+                the <code class="computeroutput"><span class="keyword">sizeof</span></code> of optional
+                reference is that of a pointer,
+              </li>
+<li class="listitem">
+                some bugs connected to copying optional references are gone,
+              </li>
+<li class="listitem">
+                all run-time bugs caused by incorrect reference binding on some compilers
+                are now turned into compile-time errors,
+              </li>
+<li class="listitem">
+                you can swap optional references: it is like swapping pointers: shallow,
+                underlying objects are not affected,
+              </li>
+<li class="listitem">
+                optional references to abstract types work.
+              </li>
+</ul></div>
+        </li>
+<li class="listitem">
+          Documented nested typedefs (<a href="https://svn.boost.org/trac/boost/ticket/5193" target="_top">Trac
+          #5193</a>).
+        </li>
+<li class="listitem">
+          Made the perfect-forwarding constructor SFINAE-friendly, which fixes <a href="https://svn.boost.org/trac/boost/ticket/12002" target="_top">Trac #12002</a>.
+          However, this only works in the newer platforms that correctly implement
+          C++11 <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">type_traits</span><span class="special">&gt;</span></code>.
+        </li>
+<li class="listitem">
+          Fixed <a href="https://svn.boost.org/trac/boost/ticket/10445" target="_top">Trac #10445</a>.
+        </li>
+</ul></div>
+<h4>
+<a name="boost_optional.relnotes.h11"></a>
+      <span class="phrase"><a name="boost_optional.relnotes.boost_release_1_60"></a></span><a class="link" href="relnotes.html#boost_optional.relnotes.boost_release_1_60">Boost
+      Release 1.60</a>
+    </h4>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+          Changed the implementation of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span></code>
+          again. Now it is a const object with internal linkage (as any other tag).
+          This fixes <a href="https://svn.boost.org/trac/boost/ticket/11203" target="_top">Trac
+          #11203</a>.
+        </li></ul></div>
+<h4>
+<a name="boost_optional.relnotes.h12"></a>
       <span class="phrase"><a name="boost_optional.relnotes.boost_release_1_59"></a></span><a class="link" href="relnotes.html#boost_optional.relnotes.boost_release_1_59">Boost
       Release 1.59</a>
     </h4>
-<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
           For C++03 compilers, added 0-argument overload for member function <code class="computeroutput"><span class="identifier">emplace</span><span class="special">()</span></code>,
           and therewith removed the dependency on <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">utility</span><span class="special">/</span><span class="identifier">in_place_factory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>.
-        </li></ul></div>
+        </li>
+<li class="listitem">
+          Fixed <a href="https://svn.boost.org/trac/boost/ticket/11241" target="_top">Trac #11241</a>.
+        </li>
+</ul></div>
 <h4>
-<a name="boost_optional.relnotes.h1"></a>
+<a name="boost_optional.relnotes.h13"></a>
       <span class="phrase"><a name="boost_optional.relnotes.boost_release_1_58"></a></span><a class="link" href="relnotes.html#boost_optional.relnotes.boost_release_1_58">Boost
       Release 1.58</a>
     </h4>
@@ -72,7 +303,7 @@
         </li>
 </ul></div>
 <h4>
-<a name="boost_optional.relnotes.h2"></a>
+<a name="boost_optional.relnotes.h14"></a>
       <span class="phrase"><a name="boost_optional.relnotes.boost_release_1_57"></a></span><a class="link" href="relnotes.html#boost_optional.relnotes.boost_release_1_57">Boost
       Release 1.57</a>
     </h4>
@@ -82,7 +313,7 @@
           to fix C++03 compile error on <code class="computeroutput"><span class="identifier">logic_error</span><span class="special">(</span><span class="string">"..."</span><span class="special">)</span></code>"</em></span>.
         </li></ul></div>
 <h4>
-<a name="boost_optional.relnotes.h3"></a>
+<a name="boost_optional.relnotes.h15"></a>
       <span class="phrase"><a name="boost_optional.relnotes.boost_release_1_56"></a></span><a class="link" href="relnotes.html#boost_optional.relnotes.boost_release_1_56">Boost
       Release 1.56</a>
     </h4>
@@ -139,7 +370,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>

doc/html/boost_optional/tutorial.html

@@ -398,8 +398,8 @@
         </p>
 <h6>
 <a name="boost_optional.tutorial.design_overview.the_interface.h0"></a>
-          <span class="phrase"><a name="boost_optional.tutorial.design_overview.the_interface.lexically_hinted_value_access_in_the_presence_of_possibly_untitialized_optional_objects__the_operators___and___gt_"></a></span><a class="link" href="tutorial.html#boost_optional.tutorial.design_overview.the_interface.lexically_hinted_value_access_in_the_presence_of_possibly_untitialized_optional_objects__the_operators___and___gt_">Lexically-hinted
-          Value Access in the presence of possibly untitialized optional objects:
+          <span class="phrase"><a name="boost_optional.tutorial.design_overview.the_interface.lexically_hinted_value_access_in_the_presence_of_possibly_uninitialized_optional_objects__the_operators___and___gt_"></a></span><a class="link" href="tutorial.html#boost_optional.tutorial.design_overview.the_interface.lexically_hinted_value_access_in_the_presence_of_possibly_uninitialized_optional_objects__the_operators___and___gt_">Lexically-hinted
+          Value Access in the presence of possibly uninitialized optional objects:
           The operators * and -&gt;</a>
         </h6>
 <p>

doc/html/boost_optional/tutorial/a_note_about_optional_bool_.html

@@ -94,7 +94,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014-2016 Andrzej Krzemie&#324;ski<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>

doc/html/boost_optional/tutorial/design_overview.html

@@ -1,9 +1,9 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Design Overview</title>
 <link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="../../index.html" title="Boost.Optional">
 <link rel="up" href="../../optional/tutorial.html" title="Tutorial">
 <link rel="prev" href="../../optional/tutorial.html" title="Tutorial">
@@ -65,8 +65,8 @@
           <code class="computeroutput"><span class="identifier">npos</span></code>, -1, etc... This is
           equivalent to adding the special value to the set of possible values of
           a given type. This super set of <code class="computeroutput"><span class="identifier">T</span></code>
-          plus some <span class="emphasis"><em>nil_t</em></span>&#8212;where <code class="computeroutput"><span class="identifier">nil_t</span></code>
-          is some stateless POD&#8212;can be modeled in modern languages as a <span class="bold"><strong>discriminated union</strong></span> of T and nil_t. Discriminated
+          plus some <span class="emphasis"><em>nil_t</em></span>—where <code class="computeroutput"><span class="identifier">nil_t</span></code>
+          is some stateless POD—can be modeled in modern languages as a <span class="bold"><strong>discriminated union</strong></span> of T and nil_t. Discriminated
           unions are often called <span class="emphasis"><em>variants</em></span>. A variant has a
           <span class="emphasis"><em>current type</em></span>, which in our case is either <code class="computeroutput"><span class="identifier">T</span></code> or <code class="computeroutput"><span class="identifier">nil_t</span></code>.
           Using the <a href="../../../../../variant/index.html" target="_top">Boost.Variant</a>
@@ -100,8 +100,8 @@
         </p>
 <p>
           In any event, both the discriminated-union or the single-element container
-          models serve as a conceptual ground for a class representing optional&#8212;i.e.
-          possibly uninitialized&#8212;objects. For instance, these models show the
+          models serve as a conceptual ground for a class representing optional—i.e.
+          possibly uninitialized—objects. For instance, these models show the
           <span class="emphasis"><em>exact</em></span> semantics required for a wrapper of optional
           values:
         </p>
@@ -170,7 +170,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>

doc/html/boost_optional/tutorial/design_overview/the_interface.html

@@ -1,9 +1,9 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>The Interface</title>
 <link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="../../../index.html" title="Boost.Optional">
 <link rel="up" href="../design_overview.html" title="Design Overview">
 <link rel="prev" href="the_semantics.html" title="The semantics">
@@ -79,7 +79,7 @@
           facto</em></span> standard for handling optional objects because all you
           have to do to refer to a value which you don't really have is to use a
           null pointer value of the appropriate type. Pointers have been used for
-          decades&#8212;from the days of C APIs to modern C++ libraries&#8212;to <span class="emphasis"><em>refer</em></span>
+          decades—from the days of C APIs to modern C++ libraries—to <span class="emphasis"><em>refer</em></span>
           to optional (that is, possibly nonexistent) objects; particularly as optional
           arguments to a function, but also quite often as optional data members.
         </p>
@@ -93,7 +93,7 @@
           and this information is tied to the <span class="emphasis"><em>syntax</em></span> of the
           expressions. That is, the presence of operators <code class="computeroutput"><span class="special">*</span></code>
           and <code class="computeroutput"><span class="special">-&gt;</span></code> tell by themselves
-          &#8212;without any additional context&#8212; that the expression will be undefined
+          —without any additional context— that the expression will be undefined
           unless the implied pointee actually exist.
         </p>
 <p>
@@ -142,10 +142,10 @@
           about the possibly uninitialized state appealing to the familiar pointer
           semantics w.r.t. to null pointers.
         </p>
-<div class="warning"><table border="0" summary="Warning">
+<div class="caution"><table border="0" summary="Caution">
 <tr>
-<td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../../../../../doc/src/images/warning.png"></td>
-<th align="left">Warning</th>
+<td rowspan="2" align="center" valign="top" width="25"><img alt="[Caution]" src="../../../../../../../doc/src/images/caution.png"></td>
+<th align="left">Caution</th>
 </tr>
 <tr><td align="left" valign="top"><p>
             However, it is particularly important to note that <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;&gt;</span></code> objects are not pointers. <span class="underline"><code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;&gt;</span></code> is not, and does not model, a
@@ -173,7 +173,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>

doc/html/boost_optional/tutorial/design_overview/the_semantics.html

@@ -1,9 +1,9 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>The semantics</title>
 <link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="../../../index.html" title="Boost.Optional">
 <link rel="up" href="../design_overview.html" title="Design Overview">
 <link rel="prev" href="../design_overview.html" title="Design Overview">
@@ -107,7 +107,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>

doc/html/boost_optional/tutorial/exception_safety_guarantees.html

@@ -1,12 +1,12 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Exception Safety Guarantees</title>
 <link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="../../index.html" title="Boost.Optional">
 <link rel="up" href="../../optional/tutorial.html" title="Tutorial">
-<link rel="prev" href="a_note_about_optional_bool_.html" title="A note about optional&lt;bool&gt;">
+<link rel="prev" href="gotchas/false_positive_with__wmaybe_uninitialized.html" title="False positive with -Wmaybe-uninitialized">
 <link rel="next" href="type_requirements.html" title="Type requirements">
 </head>
 <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
@@ -20,7 +20,7 @@
 </tr></table>
 <hr>
 <div class="spirit-nav">
-<a accesskey="p" href="a_note_about_optional_bool_.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="type_requirements.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+<a accesskey="p" href="gotchas/false_positive_with__wmaybe_uninitialized.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="type_requirements.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
 </div>
 <div class="section">
 <div class="titlepage"><div><div><h3 class="title">
@@ -153,7 +153,7 @@
         move constructor are replaced with the calls to <code class="computeroutput"><span class="identifier">T</span></code>'s
         default constructor followed by <code class="computeroutput"><span class="identifier">swap</span></code>.
         (This is more useful on older compilers that do not support move semantics,
-        when one wants to acheive stronger exception safety guarantees.) In this
+        when one wants to achieve stronger exception safety guarantees.) In this
         case the exception safety guarantees for <code class="computeroutput"><span class="identifier">swap</span></code>
         are reliant on the guarantees of <code class="computeroutput"><span class="identifier">T</span></code>'s
         <code class="computeroutput"><span class="identifier">swap</span></code> and default constructor
@@ -161,7 +161,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>
@@ -169,7 +169,7 @@
 </tr></table>
 <hr>
 <div class="spirit-nav">
-<a accesskey="p" href="a_note_about_optional_bool_.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="type_requirements.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+<a accesskey="p" href="gotchas/false_positive_with__wmaybe_uninitialized.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="type_requirements.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
 </div>
 </body>
 </html>

doc/html/boost_optional/tutorial/gotchas.html

@@ -0,0 +1,112 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
+<title>Gotchas</title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../index.html" title="Boost.Optional">
+<link rel="up" href="../../optional/tutorial.html" title="Tutorial">
+<link rel="prev" href="in_place_factories.html" title="In-Place Factories">
+<link rel="next" href="gotchas/moved_from__optional_.html" title="Moved-from optional">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../index.html">Home</a></td>
+<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td>
+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="in_place_factories.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="gotchas/moved_from__optional_.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.tutorial.gotchas"></a><a class="link" href="gotchas.html" title="Gotchas">Gotchas</a>
+</h3></div></div></div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.tutorial.gotchas.a_note_about_optional_bool_"></a><a class="link" href="gotchas.html#boost_optional.tutorial.gotchas.a_note_about_optional_bool_" title="A note about optional&lt;bool&gt;">A
+        note about optional&lt;bool&gt;</a>
+</h4></div></div></div>
+<p>
+          <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">bool</span><span class="special">&gt;</span></code>
+          should be used with special caution and consideration.
+        </p>
+<p>
+          First, it is functionally similar to a tristate boolean (false, maybe,
+          true) —such as <a href="../../../../../../doc/html/tribool.html" target="_top">boost::tribool</a>—
+          except that in a tristate boolean, the maybe state <span class="underline">represents
+          a valid value</span>, unlike the corresponding state of an uninitialized
+          <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">bool</span><span class="special">&gt;</span></code>.
+          It should be carefully considered if an <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">bool</span><span class="special">&gt;</span></code> instead of a <code class="computeroutput"><span class="identifier">tribool</span></code>
+          is really needed.
+        </p>
+<p>
+          Second, although <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;&gt;</span></code> provides a contextual conversion
+          to <code class="computeroutput"><span class="keyword">bool</span></code> in C++11, this falls
+          back to an implicit conversion on older compilers. This conversion refers
+          to the initialization state and not to the contained value. Using <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">bool</span><span class="special">&gt;</span></code>
+          can lead to subtle errors due to the implicit <code class="computeroutput"><span class="keyword">bool</span></code>
+          conversion:
+        </p>
+<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">foo</span> <span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="keyword">void</span> <span class="identifier">bar</span><span class="special">()</span>
+<span class="special">{</span>
+    <span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">bool</span><span class="special">&gt;</span> <span class="identifier">v</span> <span class="special">=</span> <span class="keyword">try</span><span class="special">();</span>
+
+    <span class="comment">// The following intended to pass the value of 'v' to foo():</span>
+    <span class="identifier">foo</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+    <span class="comment">// But instead, the initialization state is passed</span>
+    <span class="comment">// due to a typo: it should have been foo(*v).</span>
+<span class="special">}</span>
+</pre>
+<p>
+          The only implicit conversion is to <code class="computeroutput"><span class="keyword">bool</span></code>,
+          and it is safe in the sense that typical integral promotions don't apply
+          (i.e. if <code class="computeroutput"><span class="identifier">foo</span><span class="special">()</span></code>
+          takes an <code class="computeroutput"><span class="keyword">int</span></code> instead, it won't
+          compile).
+        </p>
+<p>
+          Third, mixed comparisons with <code class="computeroutput"><span class="keyword">bool</span></code>
+          work differently than similar mixed comparisons between pointers and <code class="computeroutput"><span class="keyword">bool</span></code>, so the results might surprise you:
+        </p>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">bool</span><span class="special">&gt;</span> <span class="identifier">oEmpty</span><span class="special">(</span><span class="identifier">none</span><span class="special">),</span> <span class="identifier">oTrue</span><span class="special">(</span><span class="keyword">true</span><span class="special">),</span> <span class="identifier">oFalse</span><span class="special">(</span><span class="keyword">false</span><span class="special">);</span>
+
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oEmpty</span> <span class="special">==</span> <span class="identifier">none</span><span class="special">);</span>  <span class="comment">// renders true</span>
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oEmpty</span> <span class="special">==</span> <span class="keyword">false</span><span class="special">);</span> <span class="comment">// renders false!</span>
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oEmpty</span> <span class="special">==</span> <span class="keyword">true</span><span class="special">);</span>  <span class="comment">// renders false!</span>
+
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oFalse</span> <span class="special">==</span> <span class="identifier">none</span><span class="special">);</span>  <span class="comment">// renders false</span>
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oFalse</span> <span class="special">==</span> <span class="keyword">false</span><span class="special">);</span> <span class="comment">// renders true!</span>
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oFalse</span> <span class="special">==</span> <span class="keyword">true</span><span class="special">);</span>  <span class="comment">// renders false</span>
+
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oTrue</span> <span class="special">==</span> <span class="identifier">none</span><span class="special">);</span>   <span class="comment">// renders false</span>
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oTrue</span> <span class="special">==</span> <span class="keyword">false</span><span class="special">);</span>  <span class="comment">// renders false</span>
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oTrue</span> <span class="special">==</span> <span class="keyword">true</span><span class="special">);</span>   <span class="comment">// renders true</span>
+</pre>
+<p>
+          In other words, for <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;&gt;</span></code>, the following assertion does not
+          hold:
+        </p>
+<pre class="programlisting"><span class="identifier">assert</span><span class="special">((</span><span class="identifier">opt</span> <span class="special">==</span> <span class="keyword">false</span><span class="special">)</span> <span class="special">==</span> <span class="special">(!</span><span class="identifier">opt</span><span class="special">));</span>
+</pre>
+</div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+      </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="in_place_factories.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="gotchas/moved_from__optional_.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
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doc/html/boost_optional/tutorial/gotchas/false_positive_with__wmaybe_uninitialized.html

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+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
+<title>False positive with -Wmaybe-uninitialized</title>
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+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.tutorial.gotchas.false_positive_with__wmaybe_uninitialized"></a><a class="link" href="false_positive_with__wmaybe_uninitialized.html" title="False positive with -Wmaybe-uninitialized">False
+        positive with -Wmaybe-uninitialized</a>
+</h4></div></div></div>
+<p>
+          Sometimes on GCC compilers below version 5.1 you may get an -Wmaybe-uninitialized
+          warning when compiling with option -02 on a perfectly valid <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span></code> usage. For instance in this
+          program:
+        </p>
+<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">optional</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">getitem</span><span class="special">();</span>
+
+<span class="keyword">int</span> <span class="identifier">main</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">argc</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*[])</span>
+<span class="special">{</span>
+  <span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">a</span> <span class="special">=</span> <span class="identifier">getitem</span><span class="special">();</span>
+  <span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">b</span><span class="special">;</span>
+
+  <span class="keyword">if</span> <span class="special">(</span><span class="identifier">argc</span> <span class="special">&gt;</span> <span class="number">0</span><span class="special">)</span>
+    <span class="identifier">b</span> <span class="special">=</span> <span class="identifier">argc</span><span class="special">;</span>
+
+  <span class="keyword">if</span> <span class="special">(</span><span class="identifier">a</span> <span class="special">!=</span> <span class="identifier">b</span><span class="special">)</span>
+    <span class="keyword">return</span> <span class="number">1</span><span class="special">;</span>
+
+  <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
+<span class="special">}</span>
+</pre>
+<p>
+          This is a bug in the compiler. As a workaround (provided in <a href="http://stackoverflow.com/questions/21755206/how-to-get-around-gcc-void-b-4-may-be-used-uninitialized-in-this-funct" target="_top">this
+          Stack Overflow question</a>) use the following way of initializing
+          an optional containing no value:
+        </p>
+<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">b</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">make_optional</span><span class="special">(</span><span class="keyword">false</span><span class="special">,</span> <span class="keyword">int</span><span class="special">());</span>
+</pre>
+<p>
+          This is obviously redundant, but makes the warning disappear.
+        </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+      </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="mixed_relational_comparisons.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../gotchas.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../exception_safety_guarantees.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
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+</html>

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+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
+<title>Mixed relational comparisons</title>
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+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.tutorial.gotchas.mixed_relational_comparisons"></a><a class="link" href="mixed_relational_comparisons.html" title="Mixed relational comparisons">Mixed
+        relational comparisons</a>
+</h4></div></div></div>
+<p>
+          Because <code class="computeroutput"><span class="identifier">T</span></code> is convertible
+          to <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code>
+          and because <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code>
+          is <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a> when <code class="computeroutput"><span class="identifier">T</span></code> is <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a>, you can sometimes
+          get an unexpected runtime result where you would rather expect a compiler
+          error:
+        </p>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">double</span><span class="special">&gt;</span> <span class="identifier">Flight_plan</span><span class="special">::</span><span class="identifier">weight</span><span class="special">();</span> <span class="comment">// sometimes no weight can be returned</span>
+
+<span class="keyword">bool</span> <span class="identifier">is_aircraft_too_heavy</span><span class="special">(</span><span class="identifier">Flight_plan</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">p</span><span class="special">)</span>
+<span class="special">{</span>
+   <span class="keyword">return</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">weight</span><span class="special">()</span> <span class="special">&gt;</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">aircraft</span><span class="special">().</span><span class="identifier">max_weight</span><span class="special">();</span> <span class="comment">// compiles!</span>
+<span class="special">}</span>                                                 <span class="comment">// returns false when the optional contains no value </span>
+</pre>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+      </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="moved_from__optional_.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../gotchas.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="false_positive_with__wmaybe_uninitialized.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
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doc/html/boost_optional/tutorial/gotchas/moved_from__optional_.html

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+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
+<title>Moved-from optional</title>
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+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../gotchas.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../gotchas.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="mixed_relational_comparisons.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.tutorial.gotchas.moved_from__optional_"></a><a class="link" href="moved_from__optional_.html" title="Moved-from optional">Moved-from
+        <code class="computeroutput"><span class="identifier">optional</span></code></a>
+</h4></div></div></div>
+<p>
+          When an optional object that contains a value is moved from (is a source
+          of move constructor or assignment) it still contains a value and its contained
+          value is left in a moved-from state. This can be illustrated with the following
+          example.
+        </p>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;&gt;</span> <span class="identifier">opi</span> <span class="special">{</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">make_unique</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;(</span><span class="number">1</span><span class="special">)};</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;&gt;</span> <span class="identifier">opj</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">opi</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">opi</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(*</span><span class="identifier">opi</span> <span class="special">==</span> <span class="keyword">nullptr</span><span class="special">);</span>
+</pre>
+<p>
+          Quite a lot of people expect that when an object that contains a value
+          is moved from, its contained value should be destroyed. This is not so,
+          for performance reasons. Current semantics allow the implementation of
+          <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code>
+          to be trivially copyable when <code class="computeroutput"><span class="identifier">T</span></code>
+          is trivial.
+        </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+      </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../gotchas.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../gotchas.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="mixed_relational_comparisons.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>

doc/html/boost_optional/tutorial/in_place_factories.html

@@ -1,13 +1,13 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>In-Place Factories</title>
 <link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="../../index.html" title="Boost.Optional">
 <link rel="up" href="../../optional/tutorial.html" title="Tutorial">
-<link rel="prev" href="rebinding_semantics_for_assignment_of_optional_references.html" title="Rebinding semantics for assignment of optional references">
-<link rel="next" href="a_note_about_optional_bool_.html" title="A note about optional&lt;bool&gt;">
+<link rel="prev" href="optional_references/rebinding_semantics_for_assignment_of_optional_references.html" title="Rebinding semantics for assignment of optional references">
+<link rel="next" href="gotchas.html" title="Gotchas">
 </head>
 <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
 <table cellpadding="2" width="100%"><tr>
@@ -20,7 +20,7 @@
 </tr></table>
 <hr>
 <div class="spirit-nav">
-<a accesskey="p" href="rebinding_semantics_for_assignment_of_optional_references.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="a_note_about_optional_bool_.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+<a accesskey="p" href="optional_references/rebinding_semantics_for_assignment_of_optional_references.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="gotchas.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
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 <div class="titlepage"><div><div><h3 class="title">
@@ -183,7 +183,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>
@@ -191,7 +191,7 @@
 </tr></table>
 <hr>
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+<a accesskey="p" href="optional_references/rebinding_semantics_for_assignment_of_optional_references.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="gotchas.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
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doc/html/boost_optional/tutorial/io_operators.html

@@ -1,9 +1,9 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>IO operators</title>
 <link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="../../index.html" title="Boost.Optional">
 <link rel="up" href="../../optional/tutorial.html" title="Tutorial">
 <link rel="prev" href="relational_operators.html" title="Relational operators">
@@ -73,7 +73,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>

doc/html/boost_optional/tutorial/optional_references.html

@@ -1,13 +1,13 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Optional references</title>
 <link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="../../index.html" title="Boost.Optional">
 <link rel="up" href="../../optional/tutorial.html" title="Tutorial">
 <link rel="prev" href="io_operators.html" title="IO operators">
-<link rel="next" href="rebinding_semantics_for_assignment_of_optional_references.html" title="Rebinding semantics for assignment of optional references">
+<link rel="next" href="optional_references/rebinding_semantics_for_assignment_of_optional_references.html" title="Rebinding semantics for assignment of optional references">
 </head>
 <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
 <table cellpadding="2" width="100%"><tr>
@@ -20,88 +20,90 @@
 </tr></table>
 <hr>
 <div class="spirit-nav">
-<a accesskey="p" href="io_operators.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="rebinding_semantics_for_assignment_of_optional_references.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+<a accesskey="p" href="io_operators.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="optional_references/rebinding_semantics_for_assignment_of_optional_references.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
 </div>
 <div class="section">
 <div class="titlepage"><div><div><h3 class="title">
 <a name="boost_optional.tutorial.optional_references"></a><a class="link" href="optional_references.html" title="Optional references">Optional
       references</a>
 </h3></div></div></div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.tutorial.optional_references.overview"></a><a class="link" href="optional_references.html#boost_optional.tutorial.optional_references.overview" title="Overview">Overview</a>
+</h4></div></div></div>
 <p>
-        This library allows the template parameter <code class="computeroutput"><span class="identifier">T</span></code>
-        to be of reference type: <code class="computeroutput"><span class="identifier">T</span><span class="special">&amp;</span></code>, and to some extent, <code class="computeroutput"><span class="identifier">T</span>
-        <span class="keyword">const</span><span class="special">&amp;</span></code>.
-      </p>
+          This library allows the template parameter <code class="computeroutput"><span class="identifier">T</span></code>
+          to be of reference type: <code class="computeroutput"><span class="identifier">T</span><span class="special">&amp;</span></code>, and to some extent, <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span></code>.
+        </p>
 <p>
-        However, since references are not real objects some restrictions apply and
-        some operations are not available in this case:
-      </p>
+          However, since references are not real objects some restrictions apply
+          and some operations are not available in this case:
+        </p>
 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
 <li class="listitem">
-            Converting constructors
-          </li>
+              Converting constructors
+            </li>
 <li class="listitem">
-            Converting assignment
-          </li>
+              Converting assignment
+            </li>
 <li class="listitem">
-            InPlace construction
-          </li>
+              InPlace construction
+            </li>
 <li class="listitem">
-            InPlace assignment
-          </li>
+              InPlace assignment
+            </li>
 <li class="listitem">
-            Value-access via pointer
-          </li>
+              Value-access via pointer
+            </li>
 </ul></div>
 <p>
-        Also, even though <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;</span></code>
-        treats it wrapped pseudo-object much as a real value, a true real reference
-        is stored so aliasing will ocurr:
-      </p>
+          Also, even though <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;</span></code> treats it wrapped pseudo-object
+          much as a real value, a true real reference is stored so aliasing will
+          occur:
+        </p>
 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
 <li class="listitem">
-            Copies of <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;</span></code>
-            will copy the references but all these references will nonetheless refer
-            to the same object.
-          </li>
+              Copies of <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;</span></code> will copy the references but
+              all these references will nonetheless refer to the same object.
+            </li>
 <li class="listitem">
-            Value-access will actually provide access to the referenced object rather
-            than the reference itself.
-          </li>
+              Value-access will actually provide access to the referenced object
+              rather than the reference itself.
+            </li>
 </ul></div>
-<div class="warning"><table border="0" summary="Warning">
+<div class="caution"><table border="0" summary="Caution">
 <tr>
-<td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../../../../doc/src/images/warning.png"></td>
-<th align="left">Warning</th>
+<td rowspan="2" align="center" valign="top" width="25"><img alt="[Caution]" src="../../../../../../doc/src/images/caution.png"></td>
+<th align="left">Caution</th>
 </tr>
 <tr><td align="left" valign="top"><p>
-          On compilers that do not conform to Standard C++ rules of reference binding,
-          operations on optional references might give adverse results: rather than
-          binding a reference to a designated object they may create an unexpected
-          temporary and bind to it. For more details see <a class="link" href="../dependencies_and_portability/optional_reference_binding.html" title="Optional Reference Binding">Dependencies
-          and Portability section</a>.
-        </p></td></tr>
+            On compilers that do not conform to Standard C++ rules of reference binding,
+            some operations on optional references are disabled in order to prevent
+            subtle bugs. For more details see <a class="link" href="../dependencies_and_portability/optional_reference_binding.html" title="Optional Reference Binding">Dependencies
+            and Portability section</a>.
+          </p></td></tr>
 </table></div>
-<h5>
-<a name="boost_optional.tutorial.optional_references.h0"></a>
-        <span class="phrase"><a name="boost_optional.tutorial.optional_references.rvalue_references"></a></span><a class="link" href="optional_references.html#boost_optional.tutorial.optional_references.rvalue_references">Rvalue
-        references</a>
-      </h5>
+<h6>
+<a name="boost_optional.tutorial.optional_references.overview.h0"></a>
+          <span class="phrase"><a name="boost_optional.tutorial.optional_references.overview.rvalue_references"></a></span><a class="link" href="optional_references.html#boost_optional.tutorial.optional_references.overview.rvalue_references">Rvalue
+          references</a>
+        </h6>
 <p>
-        Rvalue references and lvalue references to const have the ability in C++
-        to extend the life time of a temporary they bind to. Optional references
-        do not have this capability, therefore to avoid surprising effects it is
-        not possible to initialize an optional references from a temporary. Optional
-        rvalue references are disabled altogether. Also, the initialization and assignment
-        of an optional reference to const from rvalue reference is disabled.
-      </p>
+          Rvalue references and lvalue references to const have the ability in C++
+          to extend the life time of a temporary they bind to. Optional references
+          do not have this capability, therefore to avoid surprising effects it is
+          not possible to initialize an optional references from a temporary. Optional
+          rvalue references are disabled altogether. Also, the initialization and
+          assignment of an optional reference to const from rvalue reference is disabled.
+        </p>
 <pre class="programlisting"><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&amp;</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">1</span><span class="special">;</span>            <span class="comment">// legal</span>
 <span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&amp;&gt;</span> <span class="identifier">oi</span> <span class="special">=</span> <span class="number">1</span><span class="special">;</span> <span class="comment">// illegal</span>
 </pre>
 </div>
+</div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>
@@ -109,7 +111,7 @@
 </tr></table>
 <hr>
 <div class="spirit-nav">
-<a accesskey="p" href="io_operators.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="rebinding_semantics_for_assignment_of_optional_references.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+<a accesskey="p" href="io_operators.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="optional_references/rebinding_semantics_for_assignment_of_optional_references.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
 </div>
 </body>
 </html>

doc/html/boost_optional/tutorial/optional_references/rebinding_semantics_for_assignment_of_optional_references.html

@@ -0,0 +1,147 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
+<title>Rebinding semantics for assignment of optional references</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../../index.html" title="Boost.Optional">
+<link rel="up" href="../optional_references.html" title="Optional references">
+<link rel="prev" href="../optional_references.html" title="Optional references">
+<link rel="next" href="../in_place_factories.html" title="In-Place Factories">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../../index.html">Home</a></td>
+<td align="center"><a href="../../../../../../../libs/libraries.htm">Libraries</a></td>
+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../optional_references.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../optional_references.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../in_place_factories.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.tutorial.optional_references.rebinding_semantics_for_assignment_of_optional_references"></a><a class="link" href="rebinding_semantics_for_assignment_of_optional_references.html" title="Rebinding semantics for assignment of optional references">Rebinding
+        semantics for assignment of optional references</a>
+</h4></div></div></div>
+<p>
+          If you assign to an <span class="emphasis"><em>uninitialized </em></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;</span></code> the effect is to bind (for the
+          first time) to the object. Clearly, there is no other choice.
+        </p>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">x</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span>
+<span class="keyword">int</span><span class="special">&amp;</span> <span class="identifier">rx</span> <span class="special">=</span> <span class="identifier">x</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&amp;&gt;</span> <span class="identifier">ora</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&amp;&gt;</span> <span class="identifier">orb</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">ora</span> <span class="special">=</span> <span class="identifier">orb</span> <span class="special">;</span> <span class="comment">// now 'ora' is bound to 'x' through 'rx'</span>
+<span class="special">*</span><span class="identifier">ora</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span> <span class="comment">// Changes value of 'x' through 'ora'</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">x</span><span class="special">==</span><span class="number">2</span><span class="special">);</span>
+</pre>
+<p>
+          If you assign to a bare C++ reference, the assignment is forwarded to the
+          referenced object; its value changes but the reference is never rebound.
+        </p>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span>
+<span class="keyword">int</span><span class="special">&amp;</span> <span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span>
+<span class="keyword">int</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span>
+<span class="keyword">int</span><span class="special">&amp;</span> <span class="identifier">rb</span> <span class="special">=</span> <span class="identifier">b</span> <span class="special">;</span>
+<span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">rb</span> <span class="special">;</span> <span class="comment">// Changes the value of 'a' to 'b'</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">a</span><span class="special">==</span><span class="identifier">b</span><span class="special">);</span>
+<span class="identifier">b</span> <span class="special">=</span> <span class="number">3</span> <span class="special">;</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">ra</span><span class="special">!=</span><span class="identifier">b</span><span class="special">);</span> <span class="comment">// 'ra' is not rebound to 'b'</span>
+</pre>
+<p>
+          Now, if you assign to an <span class="emphasis"><em>initialized </em></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;</span></code>,
+          the effect is to <span class="bold"><strong>rebind</strong></span> to the new object
+          instead of assigning the referee. This is unlike bare C++ references.
+        </p>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span>
+<span class="keyword">int</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span>
+<span class="keyword">int</span><span class="special">&amp;</span> <span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span>
+<span class="keyword">int</span><span class="special">&amp;</span> <span class="identifier">rb</span> <span class="special">=</span> <span class="identifier">b</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&amp;&gt;</span> <span class="identifier">ora</span><span class="special">(</span><span class="identifier">ra</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&amp;&gt;</span> <span class="identifier">orb</span><span class="special">(</span><span class="identifier">rb</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">ora</span> <span class="special">=</span> <span class="identifier">orb</span> <span class="special">;</span> <span class="comment">// 'ora' is rebound to 'b'</span>
+<span class="special">*</span><span class="identifier">ora</span> <span class="special">=</span> <span class="number">3</span> <span class="special">;</span> <span class="comment">// Changes value of 'b' (not 'a')</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">a</span><span class="special">==</span><span class="number">1</span><span class="special">);</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">b</span><span class="special">==</span><span class="number">3</span><span class="special">);</span>
+</pre>
+<h6>
+<a name="boost_optional.tutorial.optional_references.rebinding_semantics_for_assignment_of_optional_references.h0"></a>
+          <span class="phrase"><a name="boost_optional.tutorial.optional_references.rebinding_semantics_for_assignment_of_optional_references.rationale"></a></span><a class="link" href="rebinding_semantics_for_assignment_of_optional_references.html#boost_optional.tutorial.optional_references.rebinding_semantics_for_assignment_of_optional_references.rationale">Rationale</a>
+        </h6>
+<p>
+          Rebinding semantics for the assignment of <span class="emphasis"><em>initialized </em></span>
+          <code class="computeroutput"><span class="identifier">optional</span></code> references has
+          been chosen to provide <span class="bold"><strong>consistency among initialization
+          states</strong></span> even at the expense of lack of consistency with the semantics
+          of bare C++ references. It is true that <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">U</span><span class="special">&gt;</span></code> strives to behave as much as possible
+          as <code class="computeroutput"><span class="identifier">U</span></code> does whenever it is
+          initialized; but in the case when <code class="computeroutput"><span class="identifier">U</span></code>
+          is <code class="computeroutput"><span class="identifier">T</span><span class="special">&amp;</span></code>,
+          doing so would result in inconsistent behavior w.r.t to the lvalue initialization
+          state.
+        </p>
+<p>
+          Imagine <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;</span></code>
+          forwarding assignment to the referenced object (thus changing the referenced
+          object value but not rebinding), and consider the following code:
+        </p>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&amp;&gt;</span> <span class="identifier">a</span> <span class="special">=</span> <span class="identifier">get</span><span class="special">();</span>
+<span class="keyword">int</span> <span class="identifier">x</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span>
+<span class="keyword">int</span><span class="special">&amp;</span> <span class="identifier">rx</span> <span class="special">=</span> <span class="identifier">x</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&amp;&gt;</span> <span class="identifier">b</span><span class="special">(</span><span class="identifier">rx</span><span class="special">);</span>
+<span class="identifier">a</span> <span class="special">=</span> <span class="identifier">b</span> <span class="special">;</span>
+</pre>
+<p>
+          What does the assignment do?
+        </p>
+<p>
+          If <code class="computeroutput"><span class="identifier">a</span></code> is <span class="emphasis"><em>uninitialized</em></span>,
+          the answer is clear: it binds to <code class="computeroutput"><span class="identifier">x</span></code>
+          (we now have another reference to <code class="computeroutput"><span class="identifier">x</span></code>).
+          But what if <code class="computeroutput"><span class="identifier">a</span></code> is already
+          <span class="emphasis"><em>initialized</em></span>? it would change the value of the referenced
+          object (whatever that is); which is inconsistent with the other possible
+          case.
+        </p>
+<p>
+          If <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;</span></code>
+          would assign just like <code class="computeroutput"><span class="identifier">T</span><span class="special">&amp;</span></code> does, you would never be able to use
+          Optional's assignment without explicitly handling the previous initialization
+          state unless your code is capable of functioning whether after the assignment,
+          <code class="computeroutput"><span class="identifier">a</span></code> aliases the same object
+          as <code class="computeroutput"><span class="identifier">b</span></code> or not.
+        </p>
+<p>
+          That is, you would have to discriminate in order to be consistent.
+        </p>
+<p>
+          If in your code rebinding to another object is not an option, then it is
+          very likely that binding for the first time isn't either. In such case,
+          assignment to an <span class="emphasis"><em>uninitialized </em></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;</span></code> shall be prohibited. It is quite
+          possible that in such a scenario it is a precondition that the lvalue must
+          be already initialized. If it isn't, then binding for the first time is
+          OK while rebinding is not which is IMO very unlikely. In such a scenario,
+          you can assign the value itself directly, as in:
+        </p>
+<pre class="programlisting"><span class="identifier">assert</span><span class="special">(!!</span><span class="identifier">opt</span><span class="special">);</span>
+<span class="special">*</span><span class="identifier">opt</span><span class="special">=</span><span class="identifier">value</span><span class="special">;</span>
+</pre>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+      </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../optional_references.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../optional_references.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../in_place_factories.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>

doc/html/boost_optional/tutorial/performance_considerations.html

@@ -1,9 +1,9 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Performance considerations</title>
 <link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="../../index.html" title="Boost.Optional">
 <link rel="up" href="../../optional/tutorial.html" title="Tutorial">
 <link rel="prev" href="type_requirements.html" title="Type requirements">
@@ -29,7 +29,8 @@
 </h3></div></div></div>
 <p>
         Technical details aside, the memory layout of <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code>
-        is more-less this:
+        for a generic <code class="computeroutput"><span class="identifier">T</span></code> is more-less
+        this:
       </p>
 <pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">&gt;</span>
 <span class="keyword">class</span> <span class="identifier">optional</span>
@@ -39,8 +40,49 @@
 <span class="special">};</span>
 </pre>
 <p>
-        But for the purpose of this analysis, considering memory layouts, we can
-        think of it as:
+        Lifetime of the <code class="computeroutput"><span class="identifier">T</span></code> inside
+        <code class="computeroutput"><span class="identifier">_storage</span></code> is manually controlled
+        with placement-<code class="computeroutput"><span class="keyword">new</span></code>s and pseudo-destructor
+        calls. However, for scalar <code class="computeroutput"><span class="identifier">T</span></code>s
+        we use a different way of storage, by simply holding a <code class="computeroutput"><span class="identifier">T</span></code>:
+      </p>
+<pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">&gt;</span>
+<span class="keyword">class</span> <span class="identifier">optional</span>
+<span class="special">{</span>
+  <span class="keyword">bool</span> <span class="identifier">_initialized</span><span class="special">;</span>
+  <span class="identifier">T</span> <span class="identifier">_storage</span><span class="special">;</span>
+<span class="special">};</span>
+</pre>
+<p>
+        We call it a <span class="emphasis"><em>direct</em></span> storage. This makes <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code> a
+        trivially-copyable type for scalar <code class="computeroutput"><span class="identifier">T</span></code>s.
+        This only works for compilers that support defaulted functions (including
+        defaulted move assignment and constructor). On compilers without defaulted
+        functions we still use the direct storage, but <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code>
+        is no longer recognized as trivially-copyable. Apart from scalar types, we
+        leave the programmer a way of customizing her type, so that it is recognized
+        by <code class="computeroutput"><span class="identifier">optional</span></code> as candidate
+        for optimized storage, by specializing type trait <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional_config</span><span class="special">::</span><span class="identifier">optional_uses_direct_storage_for</span></code>:
+      </p>
+<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">X</span> <span class="comment">// not trivial</span>
+<span class="special">{</span>
+  <span class="identifier">X</span><span class="special">()</span> <span class="special">{}</span>
+<span class="special">};</span>
+
+<span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">optional_config</span> <span class="special">{</span>
+
+  <span class="keyword">template</span> <span class="special">&lt;&gt;</span> <span class="keyword">struct</span> <span class="identifier">optional_uses_direct_storage_for</span><span class="special">&lt;</span><span class="identifier">X</span><span class="special">&gt;</span> <span class="special">:</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">true_type</span> <span class="special">{};</span>
+
+<span class="special">}}</span>
+</pre>
+<h5>
+<a name="boost_optional.tutorial.performance_considerations.h0"></a>
+        <span class="phrase"><a name="boost_optional.tutorial.performance_considerations.controlling_the_size"></a></span><a class="link" href="performance_considerations.html#boost_optional.tutorial.performance_considerations.controlling_the_size">Controlling
+        the size</a>
+      </h5>
+<p>
+        For the purpose of the following analysis, considering memory layouts, we
+        can think of it as:
       </p>
 <pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">&gt;</span>
 <span class="keyword">class</span> <span class="identifier">optional</span>
@@ -67,7 +109,7 @@
         for your application (e.g., because you want to utilize your CPU cache in
         order to gain performance) and you have determined you are willing to trade
         the code clarity, it is recommended that you simply go with type <code class="computeroutput"><span class="keyword">int</span></code> and use some 'magic value' to represent
-        <span class="emphasis"><em>not-an-int</em></span>.
+        <span class="emphasis"><em>not-an-int</em></span>, or use something like <a href="https://github.com/akrzemi1/markable" target="_top"><code class="computeroutput"><span class="identifier">markable</span></code></a> library.
       </p>
 <p>
         Even if you cannot spare any value of <code class="computeroutput"><span class="keyword">int</span></code>
@@ -123,7 +165,7 @@
         Sometimes it requires detailed consideration what data we make optional.
         In our case above, if we determine that both minimum and maximum value can
         be provided or not provided together, but one is never provided without the
-        other, we can make only one optional memebr:
+        other, we can make only one optional member:
       </p>
 <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">Limits</span>
 <span class="special">{</span>
@@ -143,7 +185,7 @@
         <span class="inlinemediaobject"><img src="../../images/opt_align4.png" alt="opt_align4"></span>
       </p>
 <h5>
-<a name="boost_optional.tutorial.performance_considerations.h0"></a>
+<a name="boost_optional.tutorial.performance_considerations.h1"></a>
         <span class="phrase"><a name="boost_optional.tutorial.performance_considerations.optional_function_parameters"></a></span><a class="link" href="performance_considerations.html#boost_optional.tutorial.performance_considerations.optional_function_parameters">Optional
         function parameters</a>
       </h5>
@@ -209,7 +251,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>

doc/html/boost_optional/tutorial/rebinding_semantics_for_assignment_of_optional_references.html

@@ -135,7 +135,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014-2016 Andrzej Krzemie&#324;ski<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>

doc/html/boost_optional/tutorial/relational_operators.html

@@ -1,9 +1,9 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Relational operators</title>
 <link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="../../index.html" title="Boost.Optional">
 <link rel="up" href="../../optional/tutorial.html" title="Tutorial">
 <link rel="prev" href="when_to_use_optional.html" title="When to use Optional">
@@ -51,7 +51,7 @@
         of the mixed comparison between <code class="computeroutput"><span class="identifier">T</span></code>
         and <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code> as
         well as between <code class="computeroutput"><span class="identifier">none_t</span></code> and
-        <code class="computeroutput"><span class="identifier">optionl</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code>:
+        <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code>:
       </p>
 <pre class="programlisting"><span class="identifier">assert</span><span class="special">(</span><span class="identifier">oN</span> <span class="special">!=</span> <span class="number">0</span><span class="special">);</span>
 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">o1</span> <span class="special">!=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span><span class="special">);</span>
@@ -99,7 +99,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>

doc/html/boost_optional/tutorial/type_requirements.html

@@ -1,9 +1,9 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Type requirements</title>
 <link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="../../index.html" title="Boost.Optional">
 <link rel="up" href="../../optional/tutorial.html" title="Tutorial">
 <link rel="prev" href="exception_safety_guarantees.html" title="Exception Safety Guarantees">
@@ -95,7 +95,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>

doc/html/boost_optional/tutorial/when_to_use_optional.html

@@ -1,9 +1,9 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>When to use Optional</title>
 <link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="../../index.html" title="Boost.Optional">
 <link rel="up" href="../../optional/tutorial.html" title="Tutorial">
 <link rel="prev" href="design_overview/the_interface.html" title="The Interface">
@@ -128,7 +128,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>

doc/html/index.html

@@ -1,9 +1,9 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Boost.Optional</title>
 <link rel="stylesheet" href="../../../../doc/src/boostbook.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="index.html" title="Boost.Optional">
 <link rel="next" href="boost_optional/quick_start.html" title="Quick Start">
 </head>
@@ -25,8 +25,8 @@
 <div><div class="author"><h3 class="author">
 <span class="firstname">Fernando Luis</span> <span class="surname">Cacciola Carballal</span>
 </h3></div></div>
-<div><p class="copyright">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal</p></div>
-<div><p class="copyright">Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski</p></div>
+<div><p class="copyright">Copyright © 2003-2007 Fernando Luis Cacciola Carballal</p></div>
+<div><p class="copyright">Copyright © 2014-2021 Andrzej Krzemieński</p></div>
 <div><div class="legalnotice">
 <a name="optional.legal"></a><p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
@@ -62,12 +62,9 @@
 <dt><span class="section"><a href="boost_optional/tutorial/io_operators.html">IO operators</a></span></dt>
 <dt><span class="section"><a href="boost_optional/tutorial/optional_references.html">Optional
       references</a></span></dt>
-<dt><span class="section"><a href="boost_optional/tutorial/rebinding_semantics_for_assignment_of_optional_references.html">Rebinding
-      semantics for assignment of optional references</a></span></dt>
 <dt><span class="section"><a href="boost_optional/tutorial/in_place_factories.html">In-Place
       Factories</a></span></dt>
-<dt><span class="section"><a href="boost_optional/tutorial/a_note_about_optional_bool_.html">A
-      note about optional&lt;bool&gt;</a></span></dt>
+<dt><span class="section"><a href="boost_optional/tutorial/gotchas.html">Gotchas</a></span></dt>
 <dt><span class="section"><a href="boost_optional/tutorial/exception_safety_guarantees.html">Exception
       Safety Guarantees</a></span></dt>
 <dt><span class="section"><a href="boost_optional/tutorial/type_requirements.html">Type requirements</a></span></dt>
@@ -92,6 +89,8 @@
     and Portability</a></span></dt>
 <dd><dl>
 <dt><span class="section"><a href="boost_optional/dependencies_and_portability.html#boost_optional.dependencies_and_portability.dependencies">Dependencies</a></span></dt>
+<dt><span class="section"><a href="boost_optional/dependencies_and_portability/emplace_operations_in_older_compilers.html">Emplace
+      operations in older compilers</a></span></dt>
 <dt><span class="section"><a href="boost_optional/dependencies_and_portability/optional_reference_binding.html">Optional
       Reference Binding</a></span></dt>
 </dl></dd>
@@ -115,7 +114,7 @@
       <span class="phrase"><a name="optional.introduction.problem"></a></span><a class="link" href="index.html#optional.introduction.problem">Problem</a>
     </h4>
 <p>
-      Suppose we want to read a parameter form a config file which represents some
+      Suppose we want to read a parameter from a config file which represents some
       integral value, let's call it <code class="computeroutput"><span class="string">"MaxValue"</span></code>.
       It is possible that this parameter is not specified; such situation is no error.
       It is valid to not specify the parameter and in that case the program is supposed
@@ -146,7 +145,7 @@
 </div>
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
-<td align="left"><p><small>Last revised: July 08, 2015 at 21:39:55 GMT</small></p></td>
+<td align="left"><p><small>Last revised: March 26, 2022 at 22:47:53 GMT</small></p></td>
 <td align="right"><div class="copyright-footer"></div></td>
 </tr></table>
 <hr>

doc/html/optional/reference.html

@@ -1,9 +1,9 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Reference</title>
 <link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="../index.html" title="Boost.Optional">
 <link rel="up" href="../index.html" title="Boost.Optional">
 <link rel="prev" href="../boost_optional/tutorial/performance_considerations.html" title="Performance considerations">
@@ -52,26 +52,30 @@
 </p>
 <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span>
 
-<span class="keyword">class</span> <span class="identifier">none_t</span> <span class="special">{};</span>
+<span class="keyword">class</span> <span class="identifier">none_t</span> <span class="special">{/*</span> <span class="identifier">see</span> <span class="identifier">below</span> <span class="special">*/};</span>
 
-<span class="keyword">extern</span> <span class="keyword">const</span> <span class="identifier">none_t</span> <span class="identifier">none</span><span class="special">;</span> <span class="comment">// see below</span>
+<span class="keyword">inline</span> <span class="keyword">constexpr</span> <span class="identifier">none_t</span> <span class="identifier">none</span> <span class="special">(/*</span> <span class="identifier">see</span> <span class="identifier">below</span> <span class="special">*/);</span>
 
 <span class="special">}</span> <span class="comment">// namespace boost</span>
 </pre>
 <p>
         </p>
 <p>
-          Variable <code class="computeroutput"><span class="identifier">none</span></code> has external
-          linkage, however it is not required to link with any library to obtain
-          its definition. Only by including this header file, the definition becomes
-          available, by means of using template instantiation.
+          Class <code class="computeroutput"><span class="identifier">none_t</span></code> is meant to
+          serve as a tag for selecting appropriate overloads of from <code class="computeroutput"><span class="identifier">optional</span></code>'s interface. It is an empty,
+          trivially copyable class with disabled default constructor.
+        </p>
+<p>
+          Constant <code class="computeroutput"><span class="identifier">none</span></code> is used to
+          indicate an optional object that does not contain a value in initialization,
+          assignment and relational operations of <code class="computeroutput"><span class="identifier">optional</span></code>.
         </p>
 </div>
 </div>
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>

doc/html/optional/reference/header__boost_optional_optional_hpp_.html

@@ -1,13 +1,13 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Header &lt;boost/optional/optional.hpp&gt;</title>
 <link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="../../index.html" title="Boost.Optional">
 <link rel="up" href="../reference.html" title="Reference">
 <link rel="prev" href="../../boost_optional/reference/header__boost_optional_optional_fwd_hpp_.html" title="Header &lt;boost/optional/optional_fwd.hpp&gt;">
-<link rel="next" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html" title="Detailed Semantics">
+<link rel="next" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/header_optional_in_place_init.html" title="Initialization tags">
 </head>
 <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
 <table cellpadding="2" width="100%"><tr>
@@ -20,7 +20,7 @@
 </tr></table>
 <hr>
 <div class="spirit-nav">
-<a accesskey="p" href="../../boost_optional/reference/header__boost_optional_optional_fwd_hpp_.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+<a accesskey="p" href="../../boost_optional/reference/header__boost_optional_optional_fwd_hpp_.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/header_optional_in_place_init.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
 </div>
 <div class="section">
 <div class="titlepage"><div><div><h3 class="title">
@@ -35,135 +35,61 @@
 
 <span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span>
 
+<span class="keyword">class</span> <span class="identifier">in_place_init_t</span> <span class="special">{</span> <span class="comment">/* see below */</span> <span class="special">}</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/header_optional_in_place_init.html#reference_in_place_init"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
+<span class="keyword">const</span> <span class="identifier">in_place_init_t</span> <span class="identifier">in_place_init</span> <span class="special">(</span> <span class="comment">/* see below */</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="keyword">class</span> <span class="identifier">in_place_init_if_t</span> <span class="special">{</span> <span class="comment">/*see below*/</span> <span class="special">}</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/header_optional_in_place_init.html#reference_in_place_init_if"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
+<span class="keyword">const</span> <span class="identifier">in_place_init_if_t</span> <span class="identifier">in_place_init_if</span> <span class="special">(</span> <span class="comment">/*see below*/</span> <span class="special">)</span> <span class="special">;</span>
+
 <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
-<span class="keyword">class</span> <span class="identifier">optional</span>
-<span class="special">{</span>
-<span class="keyword">public</span> <span class="special">:</span>
+<span class="keyword">class</span> <span class="identifier">optional</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/header_optional_optional_values.html#reference_operator_template"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
 
-    <span class="keyword">typedef</span> <span class="identifier">T</span> <span class="identifier">value_type</span><span class="special">;</span>
+<span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
+<span class="keyword">class</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/header_optional_optional_refs.html#reference_operator_template_spec"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
 
-    <span class="comment">// (If T is of reference type, the parameters and results by reference are by value)</span>
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special">==</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___free_functions.html#reference_operator_compare_equal_optional_optional"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
 
-    <span class="identifier">optional</span> <span class="special">()</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_constructor"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special">!=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___free_functions.html#reference_operator_compare_not_equal_optional_optional"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
 
-    <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">none_t</span> <span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_constructor_none_t"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special">&lt;</span>  <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___free_functions.html#reference_operator_compare_less_optional_optional"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
 
-    <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_constructor_value"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special">&gt;</span>  <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___free_functions.html#reference_operator_compare_greater_optional_optional"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
 
-    <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&amp;&amp;</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_constructor_move_value"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special">&lt;=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___free_functions.html#reference_operator_compare_less_or_equal_optional_optional"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
 
-    <span class="comment">// [new in 1.34]</span>
-    <span class="identifier">optional</span> <span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_constructor_bool_value"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special">&gt;=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___free_functions.html#reference_operator_compare_greater_or_equal_optional_optional"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
 
-    <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">optional</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_constructor_optional"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special">==</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">none_t</span> <span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___free_functions.html#reference_operator_compare_equal_optional_none"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
 
-    <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&amp;&amp;</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">(</span><span class="emphasis"><em>see below</em></span><span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_move_constructor_optional"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special">!=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">none_t</span> <span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___free_functions.html#reference_operator_compare_not_equal_optional_none"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
 
-    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">&gt;</span> <span class="keyword">explicit</span> <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">U</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_constructor_other_optional"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">make_optional</span> <span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___free_functions.html#reference_make_optional_value"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
 
-    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">&gt;</span> <span class="keyword">explicit</span> <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">U</span><span class="special">&gt;&amp;&amp;</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_move_constructor_other_optional"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">decay_t</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;&gt;</span> <span class="identifier">make_optional</span> <span class="special">(</span> <span class="identifier">T</span> <span class="special">&amp;&amp;</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___free_functions.html#reference_make_optional_rvalue"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
 
-    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">InPlaceFactory</span><span class="special">&gt;</span> <span class="keyword">explicit</span> <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">InPlaceFactory</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">f</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_constructor_factory"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">make_optional</span> <span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___free_functions.html#reference_make_optional_bool_value"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
 
-    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">TypedInPlaceFactory</span><span class="special">&gt;</span> <span class="keyword">explicit</span> <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">TypedInPlaceFactory</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">f</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_constructor_factory"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">decay_t</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;&gt;</span> <span class="identifier">make_optional</span> <span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="identifier">T</span> <span class="special">&amp;&amp;</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___free_functions.html#reference_make_optional_bool_rvalue"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
 
-    <span class="identifier">optional</span><span class="special">&amp;</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">none_t</span> <span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_operator_equal_none_t"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="keyword">auto</span> <span class="identifier">get_optional_value_or</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">opt</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;::</span><span class="identifier">reference_const_type</span> <span class="identifier">def</span> <span class="special">)</span> <span class="special">-&gt;</span> <span class="keyword">typename</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;::</span><span class="identifier">reference_const_type</span><span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___free_functions.html#reference_free_get_value_or"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
 
-    <span class="identifier">optional</span><span class="special">&amp;</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_operator_equal_value"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="keyword">auto</span> <span class="identifier">get_optional_value_or</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">opt</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;::</span><span class="identifier">reference_type</span> <span class="identifier">def</span> <span class="special">)</span> <span class="special">-&gt;</span> <span class="keyword">typename</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;::</span><span class="identifier">reference_type</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___free_functions.html#reference_free_get_value_or"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
 
-    <span class="identifier">optional</span><span class="special">&amp;</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&amp;&amp;</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_operator_move_equal_value"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">get</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___optional_values.html#reference_optional_get"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
 
-    <span class="identifier">optional</span><span class="special">&amp;</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_operator_equal_optional"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">get</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="special">&amp;</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___optional_values.html#reference_optional_get"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
 
-    <span class="identifier">optional</span><span class="special">&amp;</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&amp;&amp;</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">(</span><span class="emphasis"><em>see below</em></span><span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_operator_move_equal_optional"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">get</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___optional_values.html#reference_optional_get"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
 
-    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">&gt;</span> <span class="identifier">optional</span><span class="special">&amp;</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">U</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_operator_equal_other_optional"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="identifier">T</span><span class="special">*</span> <span class="identifier">get</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;*</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___optional_values.html#reference_optional_get"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
 
-    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">&gt;</span> <span class="identifier">optional</span><span class="special">&amp;</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">U</span><span class="special">&gt;&amp;&amp;</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_operator_move_equal_other_optional"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="keyword">auto</span> <span class="identifier">get_pointer</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">-&gt;</span> <span class="emphasis"><em>see below</em></span><span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___free_functions.html#reference_free_get_pointer"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
 
-    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">&gt;</span> <span class="keyword">void</span> <span class="identifier">emplace</span> <span class="special">(</span> <span class="identifier">Args</span><span class="special">...&amp;&amp;</span> <span class="identifier">args</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_emplace"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="keyword">auto</span> <span class="identifier">get_pointer</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="special">&amp;</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">-&gt;</span> <span class="emphasis"><em>see below</em></span><span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___free_functions.html#reference_free_get_pointer"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
 
-    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">InPlaceFactory</span><span class="special">&gt;</span> <span class="identifier">optional</span><span class="special">&amp;</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">InPlaceFactory</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">f</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_operator_equal_factory"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="keyword">void</span> <span class="identifier">swap</span><span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;&amp;</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___free_functions.html#reference_swap_optional_optional"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
 
-    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">TypedInPlaceFactory</span><span class="special">&gt;</span> <span class="identifier">optional</span><span class="special">&amp;</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">TypedInPlaceFactory</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">f</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_operator_equal_factory"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-    <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">get</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_get"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-    <span class="identifier">T</span><span class="special">&amp;</span>       <span class="identifier">get</span><span class="special">()</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_get"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-    <span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="keyword">operator</span> <span class="special">-&gt;()</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_operator_arrow"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-    <span class="identifier">T</span><span class="special">*</span>       <span class="keyword">operator</span> <span class="special">-&gt;()</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_operator_arrow"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-    <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="keyword">operator</span> <span class="special">*()</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_operator_asterisk"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-    <span class="identifier">T</span><span class="special">&amp;</span>       <span class="keyword">operator</span> <span class="special">*()</span> <span class="special">&amp;</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_operator_asterisk"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-    <span class="identifier">T</span><span class="special">&amp;&amp;</span>      <span class="keyword">operator</span> <span class="special">*()</span> <span class="special">&amp;&amp;</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_operator_asterisk_move"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-    <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">value</span><span class="special">()</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_value"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-    <span class="identifier">T</span><span class="special">&amp;</span>       <span class="identifier">value</span><span class="special">()</span> <span class="special">&amp;</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_value"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-    <span class="identifier">T</span><span class="special">&amp;&amp;</span>      <span class="identifier">value</span><span class="special">()</span> <span class="special">&amp;&amp;</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_value_move"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">&gt;</span> <span class="identifier">T</span> <span class="identifier">value_or</span><span class="special">(</span> <span class="identifier">U</span> <span class="special">&amp;&amp;</span> <span class="identifier">v</span> <span class="special">)</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_value_or"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">&gt;</span> <span class="identifier">T</span> <span class="identifier">value_or</span><span class="special">(</span> <span class="identifier">U</span> <span class="special">&amp;&amp;</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">&amp;&amp;</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_value_or_move"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">&gt;</span> <span class="identifier">T</span> <span class="identifier">value_or_eval</span><span class="special">(</span> <span class="identifier">F</span> <span class="identifier">f</span> <span class="special">)</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_value_or_call"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-    <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">&gt;</span> <span class="identifier">T</span> <span class="identifier">value_or_eval</span><span class="special">(</span> <span class="identifier">F</span> <span class="identifier">f</span> <span class="special">)</span> <span class="special">&amp;&amp;</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_value_or_call_move"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-    <span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">get_ptr</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_get_ptr"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-    <span class="identifier">T</span><span class="special">*</span>       <span class="identifier">get_ptr</span><span class="special">()</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_get_ptr"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-    <span class="keyword">explicit</span> <span class="keyword">operator</span> <span class="keyword">bool</span><span class="special">()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_operator_bool"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-    <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">!()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_operator_not"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-    <span class="comment">// deprecated methods</span>
-
-    <span class="comment">// (deprecated)</span>
-    <span class="keyword">void</span> <span class="identifier">reset</span><span class="special">()</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_reset"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-    <span class="comment">// (deprecated)</span>
-    <span class="keyword">void</span> <span class="identifier">reset</span> <span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_reset_value"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-    <span class="comment">// (deprecated)</span>
-    <span class="keyword">bool</span> <span class="identifier">is_initialized</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_is_initialized"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-    <span class="comment">// (deprecated)</span>
-    <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">get_value_or</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="keyword">default</span> <span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_get_value_or_value"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-<span class="special">};</span>
-
-<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special">==</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_operator_compare_equal_optional_optional"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special">!=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_operator_compare_not_equal_optional_optional"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special">&lt;</span>  <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_operator_compare_less_optional_optional"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special">&gt;</span>  <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_operator_compare_greater_optional_optional"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special">&lt;=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_operator_compare_less_or_equal_optional_optional"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special">&gt;=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_operator_compare_greater_or_equal_optional_optional"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special">==</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">none_t</span> <span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_operator_compare_equal_optional_none"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special">!=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">none_t</span> <span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_operator_compare_not_equal_optional_none"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">make_optional</span> <span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_make_optional_value"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">make_optional</span> <span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_make_optional_bool_value"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">get_optional_value_or</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">opt</span><span class="special">,</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="keyword">default</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_get_value_or_value"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">get</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_get"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">get</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="special">&amp;</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_get"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">get</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_get"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="identifier">T</span><span class="special">*</span> <span class="identifier">get</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;*</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_get"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">get_pointer</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_get_ptr"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="identifier">T</span><span class="special">*</span> <span class="identifier">get_pointer</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="special">&amp;</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_optional_get_ptr"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
-
-<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="keyword">void</span> <span class="identifier">swap</span><span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;&amp;</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html#reference_swap_optional_optional"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
+<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="keyword">inline</span> <span class="keyword">void</span> <span class="identifier">swap</span><span class="special">(</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&amp;&gt;&amp;</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___free_functions.html#reference_swap_optional_reference"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
 
 <span class="special">}</span> <span class="comment">// namespace boost</span>
 </pre>
@@ -171,7 +97,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>
@@ -179,7 +105,7 @@
 </tr></table>
 <hr>
 <div class="spirit-nav">
-<a accesskey="p" href="../../boost_optional/reference/header__boost_optional_optional_fwd_hpp_.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+<a accesskey="p" href="../../boost_optional/reference/header__boost_optional_optional_fwd_hpp_.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../../boost_optional/reference/header__boost_optional_optional_hpp_/header_optional_in_place_init.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
 </div>
 </body>
 </html>

doc/html/optional/tutorial.html

@@ -1,9 +1,9 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Tutorial</title>
 <link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
 <link rel="home" href="../index.html" title="Boost.Optional">
 <link rel="up" href="../index.html" title="Boost.Optional">
 <link rel="prev" href="../boost_optional/quick_start/storage_in_containers.html" title="Storage in containers">
@@ -36,12 +36,9 @@
 <dt><span class="section"><a href="../boost_optional/tutorial/io_operators.html">IO operators</a></span></dt>
 <dt><span class="section"><a href="../boost_optional/tutorial/optional_references.html">Optional
       references</a></span></dt>
-<dt><span class="section"><a href="../boost_optional/tutorial/rebinding_semantics_for_assignment_of_optional_references.html">Rebinding
-      semantics for assignment of optional references</a></span></dt>
 <dt><span class="section"><a href="../boost_optional/tutorial/in_place_factories.html">In-Place
       Factories</a></span></dt>
-<dt><span class="section"><a href="../boost_optional/tutorial/a_note_about_optional_bool_.html">A
-      note about optional&lt;bool&gt;</a></span></dt>
+<dt><span class="section"><a href="../boost_optional/tutorial/gotchas.html">Gotchas</a></span></dt>
 <dt><span class="section"><a href="../boost_optional/tutorial/exception_safety_guarantees.html">Exception
       Safety Guarantees</a></span></dt>
 <dt><span class="section"><a href="../boost_optional/tutorial/type_requirements.html">Type requirements</a></span></dt>
@@ -142,7 +139,7 @@
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"></td>
-<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014, 2015 Andrzej Krzemie&#324;ski<p>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2021 Andrzej Krzemieński<p>
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
       </p>

include/boost/none.hpp

@@ -1,5 +1,5 @@
 // Copyright (C) 2003, Fernando Luis Cacciola Carballal.
-// Copyright (C) 2014 Andrzej Krzemienski.
+// Copyright (C) 2014, 2015 Andrzej Krzemienski.
 //
 // Distributed under the Boost Software License, Version 1.0.
 // (See accompanying file LICENSE_1_0.txt or copy at
@@ -13,6 +13,7 @@
 #ifndef BOOST_NONE_17SEP2003_HPP
 #define BOOST_NONE_17SEP2003_HPP
 
+#include "boost/config.hpp"
 #include "boost/none_t.hpp"
 
 // NOTE: Borland users have to include this header outside any precompiled headers
@@ -22,8 +23,10 @@
 namespace boost {
 
 #ifdef BOOST_OPTIONAL_USE_OLD_DEFINITION_OF_NONE
-none_t const none = (static_cast<none_t>(0)) ;
-#else
+
+BOOST_INLINE_VARIABLE none_t BOOST_CONSTEXPR_OR_CONST none = (static_cast<none_t>(0)) ;
+
+#elif defined BOOST_OPTIONAL_USE_SINGLETON_DEFINITION_OF_NONE
 
 namespace detail { namespace optional_detail {
 
@@ -33,7 +36,7 @@ namespace detail { namespace optional_detail {
   {
     static const T instance;
   };
-  
+
   template <typename T>
   const T none_instance<T>::instance = T(); // global, but because 'tis a template, no cpp file required
 
@@ -42,12 +45,15 @@ namespace detail { namespace optional_detail {
 
 namespace {
   // TU-local
-  const none_t& none = detail::optional_detail::none_instance<none_t>::instance; 
+  const none_t& none = detail::optional_detail::none_instance<none_t>::instance;
 }
 
-#endif
+#else
+
+BOOST_INLINE_VARIABLE BOOST_CONSTEXPR_OR_CONST none_t none ((none_t::init_tag()));
+
+#endif // older definitions
 
 } // namespace boost
 
-#endif
-
+#endif // header guard

include/boost/none_t.hpp

@@ -1,5 +1,5 @@
 // Copyright (C) 2003, Fernando Luis Cacciola Carballal.
-// Copyright (C) 2014 Andrzej Krzemienski.
+// Copyright (C) 2014, 2015 Andrzej Krzemienski.
 //
 // Use, modification, and distribution is subject to the Boost Software
 // License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
@@ -13,16 +13,37 @@
 #ifndef BOOST_NONE_T_17SEP2003_HPP
 #define BOOST_NONE_T_17SEP2003_HPP
 
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if defined (BOOST_NO_CXX11_RVALUE_REFERENCES) || defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) || defined(BOOST_NO_CXX11_REF_QUALIFIERS) \
+|| defined(BOOST_NO_CXX11_LAMBDAS) || defined(BOOST_NO_CXX11_DECLTYPE_N3276) || defined(BOOST_NO_CXX11_NOEXCEPT) || defined(BOOST_NO_CXX11_DELETED_FUNCTIONS) || defined(BOOST_NO_CXX11_DEFAULTED_FUNCTIONS) || defined(BOOST_NO_CXX11_DEFAULTED_MOVES) || defined(BOOST_NO_CXX11_EXPLICIT_CONVERSION_OPERATORS)
+
+BOOST_PRAGMA_MESSAGE("C++03 support is deprecated in Boost.Optional 1.83 and will be removed in Boost.Optional 1.86.")
+
+#endif
+
 namespace boost {
 
 #ifdef BOOST_OPTIONAL_USE_OLD_DEFINITION_OF_NONE
+
 namespace detail { struct none_helper{}; }
 typedef int detail::none_helper::*none_t ;
-#else
+
+#elif defined BOOST_OPTIONAL_USE_SINGLETON_DEFINITION_OF_NONE
+
 class none_t {};
-#endif
+
+#else
+
+struct none_t
+{
+  struct init_tag{};
+  explicit BOOST_CONSTEXPR none_t(init_tag){} // to disable default constructor
+};
+
+#endif // old implementation workarounds
 
 } // namespace boost
 
-#endif
-
+#endif // header guard

include/boost/optional/bad_optional_access.hpp

@@ -19,6 +19,11 @@
 
 namespace boost {
 
+#if defined(__clang__)
+# pragma clang diagnostic push
+# pragma clang diagnostic ignored "-Wweak-vtables"
+#endif
+
 class bad_optional_access : public std::logic_error
 {
 public:
@@ -27,6 +32,10 @@ public:
     {}
 };
 
+#if defined(__clang__)
+# pragma clang diagnostic pop
+#endif
+
 } // namespace boost
 
 #endif

include/boost/optional/detail/experimental_traits.hpp

@@ -0,0 +1,104 @@
+// Copyright (C) 2017 Andrzej Krzemienski.
+//
+// Use, modification, and distribution is subject to the Boost Software
+// License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//
+// See http://www.boost.org/libs/optional for documentation.
+//
+// You are welcome to contact the author at:
+//  akrzemi1@gmail.com
+
+#ifndef BOOST_OPTIONAL_DETAIL_EXPERIMENTAL_TRAITS_04NOV2017_HPP
+#define BOOST_OPTIONAL_DETAIL_EXPERIMENTAL_TRAITS_04NOV2017_HPP
+
+#include <boost/config.hpp>
+#include <boost/detail/workaround.hpp>
+#include <boost/predef.h>
+#include <boost/type_traits.hpp>
+  
+// The condition to use POD implementation
+
+#ifdef BOOST_OPTIONAL_CONFIG_NO_POD_SPEC
+# define BOOST_OPTIONAL_DETAIL_NO_SPEC_FOR_TRIVIAL_TYPES
+#elif defined BOOST_OPTIONAL_CONFIG_NO_SPEC_FOR_TRIVIAL_TYPES
+# define BOOST_OPTIONAL_DETAIL_NO_SPEC_FOR_TRIVIAL_TYPES
+#elif !defined BOOST_HAS_TRIVIAL_CONSTRUCTOR
+# define BOOST_OPTIONAL_DETAIL_NO_SPEC_FOR_TRIVIAL_TYPES
+#elif !defined BOOST_HAS_TRIVIAL_MOVE_ASSIGN
+# define BOOST_OPTIONAL_DETAIL_NO_SPEC_FOR_TRIVIAL_TYPES
+#elif !defined BOOST_HAS_TRIVIAL_MOVE_CONSTRUCTOR
+# define BOOST_OPTIONAL_DETAIL_NO_SPEC_FOR_TRIVIAL_TYPES
+#elif !defined BOOST_HAS_TRIVIAL_COPY
+# define BOOST_OPTIONAL_DETAIL_NO_SPEC_FOR_TRIVIAL_TYPES
+#elif !defined BOOST_HAS_TRIVIAL_ASSIGN
+# define BOOST_OPTIONAL_DETAIL_NO_SPEC_FOR_TRIVIAL_TYPES
+#elif !defined BOOST_HAS_TRIVIAL_DESTRUCTOR
+# define BOOST_OPTIONAL_DETAIL_NO_SPEC_FOR_TRIVIAL_TYPES
+#elif BOOST_WORKAROUND(BOOST_GCC, < 50000)
+# define BOOST_OPTIONAL_DETAIL_NO_SPEC_FOR_TRIVIAL_TYPES
+#endif
+
+// GCC 5 or higher, or clang with libc++ or clang with libstdc++ 5 or higher
+#if __cplusplus >= 201103L
+#  if BOOST_WORKAROUND(BOOST_GCC, >= 50000)
+#    define BOOST_OPTIONAL_DETAIL_USE_STD_TYPE_TRAITS
+#  elif (defined BOOST_CLANG)
+#    if BOOST_LIB_STD_CXX > 0
+#      define BOOST_OPTIONAL_DETAIL_USE_STD_TYPE_TRAITS
+#    elif BOOST_LIB_STD_GNU >= 441200023 && BOOST_LIB_STD_GNU != 450600023 && BOOST_LIB_STD_GNU != 450600026 && BOOST_LIB_STD_GNU != 460800003 && BOOST_LIB_STD_GNU != 450400026 && BOOST_LIB_STD_GNU != 460700026
+#      define BOOST_OPTIONAL_DETAIL_USE_STD_TYPE_TRAITS
+#    endif
+#  endif
+#endif  
+
+
+#ifndef BOOST_OPTIONAL_DETAIL_USE_STD_TYPE_TRAITS
+#  define BOOST_OPTIONAL_DETAIL_HAS_TRIVIAL_CTOR(T) BOOST_HAS_TRIVIAL_CONSTRUCTOR(T)
+#else
+#  include <type_traits>
+#  define BOOST_OPTIONAL_DETAIL_HAS_TRIVIAL_CTOR(T) std::is_trivially_default_constructible<T>::value
+#endif
+  
+  
+namespace boost { namespace optional_detail {
+  
+#ifndef BOOST_OPTIONAL_DETAIL_NO_SPEC_FOR_TRIVIAL_TYPES
+template <typename T>
+struct is_type_trivially_copyable
+  : boost::conditional<(boost::has_trivial_copy_constructor<T>::value &&
+                        boost::has_trivial_move_constructor<T>::value &&
+                        boost::has_trivial_destructor<T>::value &&
+                        boost::has_trivial_move_assign<T>::value &&
+                        boost::has_trivial_assign<T>::value),
+                        boost::true_type, boost::false_type>::type
+{};
+#else
+template <typename T>
+struct is_type_trivially_copyable
+: boost::conditional<(boost::is_scalar<T>::value && !boost::is_const<T>::value && !boost::is_volatile<T>::value),
+                     boost::true_type, boost::false_type>::type
+{};
+#endif
+
+
+
+#ifndef BOOST_OPTIONAL_DETAIL_NO_SPEC_FOR_TRIVIAL_TYPES  
+template <typename T>
+struct optional_uses_direct_storage_for_
+  : boost::conditional< (is_type_trivially_copyable<T>::value && BOOST_OPTIONAL_DETAIL_HAS_TRIVIAL_CTOR(T)) ||
+                        (boost::is_scalar<T>::value && !boost::is_const<T>::value && !boost::is_volatile<T>::value)
+                      , boost::true_type, boost::false_type>::type
+{};
+#else
+template <typename T>
+struct optional_uses_direct_storage_for_
+  : boost::conditional<(boost::is_scalar<T>::value && !boost::is_const<T>::value && !boost::is_volatile<T>::value)
+                      , boost::true_type, boost::false_type>::type
+{};
+#endif
+
+
+}} // boost::optional_detail
+
+#endif

include/boost/optional/detail/optional_aligned_storage.hpp

@@ -0,0 +1,71 @@
+// Copyright (C) 2003, 2008 Fernando Luis Cacciola Carballal.
+// Copyright (C) 2016 Andrzej Krzemienski.
+//
+// Use, modification, and distribution is subject to the Boost Software
+// License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//
+// See http://www.boost.org/libs/optional for documentation.
+//
+// You are welcome to contact the author at:
+//  fernando_cacciola@hotmail.com
+//  akrzemi1@gmail.com
+
+#ifndef BOOST_OPTIONAL_OPTIONAL_DETAIL_OPTIONAL_ALIGNED_STORAGE_AJK_12FEB2016_HPP
+#define BOOST_OPTIONAL_OPTIONAL_DETAIL_OPTIONAL_ALIGNED_STORAGE_AJK_12FEB2016_HPP
+
+namespace boost {
+
+namespace optional_detail {
+// This local class is used instead of that in "aligned_storage.hpp"
+// because I've found the 'official' class to ICE BCB5.5
+// when some types are used with optional<>
+// (due to sizeof() passed down as a non-type template parameter)
+template <class T>
+class aligned_storage
+{
+    // Borland ICEs if unnamed unions are used for this!
+    // BOOST_MAY_ALIAS works around GCC warnings about breaking strict aliasing rules when casting storage address to T*
+    union BOOST_MAY_ALIAS dummy_u
+    {
+        unsigned char data[ sizeof(T) ];
+        BOOST_DEDUCED_TYPENAME type_with_alignment<
+          ::boost::alignment_of<T>::value >::type aligner_;
+    } dummy_ ;
+
+  public:
+
+#if defined(BOOST_OPTIONAL_DETAIL_USE_ATTRIBUTE_MAY_ALIAS)
+    void const* address() const { return &dummy_; }
+    void      * address()       { return &dummy_; }
+#else
+    void const* address() const { return dummy_.data; }
+    void      * address()       { return dummy_.data; }
+#endif
+
+#if defined(BOOST_OPTIONAL_DETAIL_USE_ATTRIBUTE_MAY_ALIAS)
+    // This workaround is supposed to silence GCC warnings about broken strict aliasing rules
+    T const* ptr_ref() const
+    {
+        union { void const* ap_pvoid; T const* as_ptype; } caster = { address() };
+        return caster.as_ptype;
+    }
+    T *      ptr_ref()
+    {
+        union { void* ap_pvoid; T* as_ptype; } caster = { address() };
+        return caster.as_ptype;
+    }
+#else
+    T const* ptr_ref() const { return static_cast<T const*>(address()); }
+    T *      ptr_ref()       { return static_cast<T *>     (address()); }
+#endif
+
+    T const& ref() const { return *ptr_ref(); }
+    T &      ref()       { return *ptr_ref(); }
+  
+} ;
+
+} // namespace optional_detail
+} // namespace boost
+
+#endif // header guard

include/boost/optional/detail/optional_config.hpp

@@ -0,0 +1,135 @@
+// Copyright (C) 2003, 2008 Fernando Luis Cacciola Carballal.
+// Copyright (C) 2015 - 2017 Andrzej Krzemienski.
+//
+// Use, modification, and distribution is subject to the Boost Software
+// License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//
+// See http://www.boost.org/libs/optional for documentation.
+//
+// You are welcome to contact the author at:
+//  akrzemi1@gmail.com
+
+#ifndef BOOST_OPTIONAL_DETAIL_OPTIONAL_CONFIG_AJK_28JAN2015_HPP
+#define BOOST_OPTIONAL_DETAIL_OPTIONAL_CONFIG_AJK_28JAN2015_HPP
+
+#include <boost/config.hpp>
+#include <boost/detail/workaround.hpp>
+
+#if (defined BOOST_NO_CXX11_RVALUE_REFERENCES) || (defined BOOST_OPTIONAL_CONFIG_NO_RVALUE_REFERENCES)
+# define BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
+#endif
+
+#if BOOST_WORKAROUND(BOOST_INTEL_CXX_VERSION,<=700)
+// AFAICT only Intel 7 correctly resolves the overload set
+// that includes the in-place factory taking functions,
+// so for the other icc versions, in-place factory support
+// is disabled
+# define BOOST_OPTIONAL_NO_INPLACE_FACTORY_SUPPORT
+#endif
+
+#if BOOST_WORKAROUND(BOOST_BORLANDC, <= 0x551)
+// BCB (5.5.1) cannot parse the nested template struct in an inplace factory.
+# define BOOST_OPTIONAL_NO_INPLACE_FACTORY_SUPPORT
+#endif
+
+#if !defined(BOOST_OPTIONAL_NO_INPLACE_FACTORY_SUPPORT) \
+    && defined BOOST_BCB_PARTIAL_SPECIALIZATION_BUG
+// BCB (up to 5.64) has the following bug:
+//   If there is a member function/operator template of the form
+//     template<class Expr> mfunc( Expr expr ) ;
+//   some calls are resolved to this even if there are other better matches.
+//   The effect of this bug is that calls to converting ctors and assignments
+//   are incorrectly sink to this general catch-all member function template as shown above.
+# define BOOST_OPTIONAL_WEAK_OVERLOAD_RESOLUTION
+#endif
+
+#if !defined(BOOST_NO_MAY_ALIAS)
+// GCC since 3.3 and some other compilers have may_alias attribute that helps to alleviate
+// optimizer issues with regard to violation of the strict aliasing rules. The optional< T >
+// storage type is marked with this attribute in order to let the compiler know that it will
+// alias objects of type T and silence compilation warnings.
+# define BOOST_OPTIONAL_DETAIL_USE_ATTRIBUTE_MAY_ALIAS
+#endif
+
+#if (defined(_MSC_VER) && _MSC_VER <= 1800)
+// on MSVC 2013 and earlier an unwanted temporary is created when you assign from
+// a const lvalue of integral type. Thus we bind not to the original address but
+// to a temporary. 
+# define BOOST_OPTIONAL_CONFIG_NO_PROPER_ASSIGN_FROM_CONST_INT
+#endif
+
+#if (defined __GNUC__) && (!defined BOOST_INTEL_CXX_VERSION) && (!defined __clang__)
+// On some GCC versions an unwanted temporary is created when you copy-initialize
+// from a const lvalue of integral type. Thus we bind not to the original address but
+// to a temporary.
+
+# if (__GNUC__ < 4)
+#  define BOOST_OPTIONAL_CONFIG_NO_PROPER_CONVERT_FROM_CONST_INT
+# endif
+
+# if (__GNUC__ == 4 && __GNUC_MINOR__ <= 5)
+#  define BOOST_OPTIONAL_CONFIG_NO_PROPER_CONVERT_FROM_CONST_INT
+# endif
+
+# if (__GNUC__ == 5 && __GNUC_MINOR__ < 2)
+#  define BOOST_OPTIONAL_CONFIG_NO_PROPER_CONVERT_FROM_CONST_INT
+# endif
+
+# if (__GNUC__ == 5 && __GNUC_MINOR__ == 2 && __GNUC_PATCHLEVEL__ == 0)
+#  define BOOST_OPTIONAL_CONFIG_NO_PROPER_CONVERT_FROM_CONST_INT
+# endif
+
+#endif // defined(__GNUC__)
+
+#if (defined __GNUC__) && (!defined BOOST_NO_CXX11_RVALUE_REFERENCES)
+// On some initial rvalue reference implementations GCC does it in a strange way,
+// preferring perfect-forwarding constructor to implicit copy constructor.
+
+# if (__GNUC__ == 4 && __GNUC_MINOR__ == 4)
+#  define BOOST_OPTIONAL_CONFIG_NO_LEGAL_CONVERT_FROM_REF
+# endif
+
+# if (__GNUC__ == 4 && __GNUC_MINOR__ == 5)
+#  define BOOST_OPTIONAL_CONFIG_NO_LEGAL_CONVERT_FROM_REF
+# endif
+
+#endif // defined(__GNUC__)
+
+#if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) && !defined(BOOST_NO_CXX11_DECLTYPE) && !BOOST_WORKAROUND(BOOST_MSVC, < 1800) && !BOOST_WORKAROUND(BOOST_GCC_VERSION, < 40500) && !defined(__SUNPRO_CC)
+  // this condition is a copy paste from is_constructible.hpp
+  // I also disable SUNPRO, as it seems not to support type_traits correctly
+#else
+# define BOOST_OPTIONAL_DETAIL_NO_IS_CONSTRUCTIBLE_TRAIT
+#endif
+
+#if defined __SUNPRO_CC
+# define BOOST_OPTIONAL_DETAIL_NO_SFINAE_FRIENDLY_CONSTRUCTORS
+#elif (defined _MSC_FULL_VER) && (_MSC_FULL_VER < 190023026)
+# define BOOST_OPTIONAL_DETAIL_NO_SFINAE_FRIENDLY_CONSTRUCTORS
+#elif defined BOOST_GCC && !defined BOOST_GCC_CXX11
+# define BOOST_OPTIONAL_DETAIL_NO_SFINAE_FRIENDLY_CONSTRUCTORS
+#elif defined BOOST_GCC_VERSION && BOOST_GCC_VERSION < 40800
+# define BOOST_OPTIONAL_DETAIL_NO_SFINAE_FRIENDLY_CONSTRUCTORS
+#endif
+
+
+// Detect support for defaulting move operations
+// (some older compilers implement rvalue references,
+// defaulted functions but move operations are not special members and cannot be defaulted)
+
+#ifdef BOOST_NO_CXX11_DEFAULTED_FUNCTIONS
+# define BOOST_OPTIONAL_DETAIL_NO_DEFAULTED_MOVE_FUNCTIONS
+#elif BOOST_WORKAROUND(BOOST_MSVC, < 1900)
+# define BOOST_OPTIONAL_DETAIL_NO_DEFAULTED_MOVE_FUNCTIONS
+#elif BOOST_WORKAROUND(BOOST_GCC_VERSION, < 40600)
+# define BOOST_OPTIONAL_DETAIL_NO_DEFAULTED_MOVE_FUNCTIONS
+#endif
+
+
+#ifdef BOOST_OPTIONAL_CONFIG_NO_DIRECT_STORAGE_SPEC
+# define BOOST_OPTIONAL_DETAIL_NO_DIRECT_STORAGE_SPEC
+#endif
+
+
+#endif // header guard

include/boost/optional/detail/optional_factory_support.hpp

@@ -0,0 +1,36 @@
+// Copyright (C) 2003, 2008 Fernando Luis Cacciola Carballal.
+// Copyright (C) 2016 Andrzej Krzemienski.
+//
+// Use, modification, and distribution is subject to the Boost Software
+// License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//
+// See http://www.boost.org/libs/optional for documentation.
+//
+// You are welcome to contact the author at:
+//  fernando_cacciola@hotmail.com
+//  akrzemi1@gmail.com
+
+#ifndef BOOST_OPTIONAL_OPTIONAL_DETAIL_OPTIONAL_FACTORY_SUPPORT_AJK_12FEB2016_HPP
+#define BOOST_OPTIONAL_OPTIONAL_DETAIL_OPTIONAL_FACTORY_SUPPORT_AJK_12FEB2016_HPP
+
+// Daniel Wallin discovered that bind/apply.hpp badly interacts with the apply<>
+// member template of a factory as used in the optional<> implementation.
+// He proposed this simple fix which is to move the call to apply<> outside
+// namespace boost.
+namespace boost_optional_detail
+{
+  template <class T, class Factory>
+  inline void construct(Factory const& factory, void* address)
+  {
+    factory.BOOST_NESTED_TEMPLATE apply<T>(address);
+  }
+}
+
+namespace boost
+{
+  class in_place_factory_base ;
+  class typed_in_place_factory_base ;
+}
+
+#endif // header guard

include/boost/optional/detail/optional_hash.hpp

@@ -0,0 +1,49 @@
+// Copyright (C) 2022 Andrzej Krzemienski.
+//
+// Use, modification, and distribution is subject to the Boost Software
+// License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//
+// See http://www.boost.org/libs/optional for documentation.
+//
+// You are welcome to contact the author at:
+//  akrzemi1@gmail.com
+
+#ifndef BOOST_OPTIONAL_DETAIL_OPTIONAL_HASH_AJK_20MAY2022_HPP
+#define BOOST_OPTIONAL_DETAIL_OPTIONAL_HASH_AJK_20MAY2022_HPP
+
+#include <boost/optional/optional_fwd.hpp>
+#include <boost/config.hpp>
+
+#if !defined(BOOST_OPTIONAL_CONFIG_DO_NOT_SPECIALIZE_STD_HASH) && !defined(BOOST_NO_CXX11_HDR_FUNCTIONAL)
+
+#include <functional>
+
+namespace std
+{
+  template <typename T>
+  struct hash<boost::optional<T> >
+  {
+    typedef std::size_t result_type;
+    typedef boost::optional<T> argument_type;
+
+    BOOST_CONSTEXPR result_type operator()(const argument_type& arg) const {
+      return arg ? std::hash<T>()(*arg) : result_type();
+    }
+  };
+
+  template <typename T>
+  struct hash<boost::optional<T&> >
+  {
+    typedef std::size_t result_type;
+    typedef boost::optional<T&> argument_type;
+
+    BOOST_CONSTEXPR result_type operator()(const argument_type& arg) const {
+      return arg ? std::hash<T>()(*arg) : result_type();
+    }
+  };
+}
+
+#endif // !defined(BOOST_OPTIONAL_CONFIG_DO_NOT_SPECIALIZE_STD_HASH) && !defined(BOOST_NO_CXX11_HDR_FUNCTIONAL)
+
+#endif // header guard

include/boost/optional/detail/optional_reference_spec.hpp

@@ -0,0 +1,279 @@
+// Copyright (C) 2015-2018 Andrzej Krzemienski.
+//
+// Use, modification, and distribution is subject to the Boost Software
+// License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//
+// See http://www.boost.org/libs/optional for documentation.
+//
+// You are welcome to contact the author at:
+//  akrzemi1@gmail.com
+
+#ifndef BOOST_OPTIONAL_DETAIL_OPTIONAL_REFERENCE_SPEC_AJK_03OCT2015_HPP
+#define BOOST_OPTIONAL_DETAIL_OPTIONAL_REFERENCE_SPEC_AJK_03OCT2015_HPP
+
+#ifdef BOOST_OPTIONAL_CONFIG_NO_PROPER_ASSIGN_FROM_CONST_INT
+#include <boost/type_traits/is_integral.hpp>
+#include <boost/type_traits/is_const.hpp>
+#endif
+
+# if 1
+
+namespace boost {
+
+namespace detail {
+
+#ifndef BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
+
+template <class From>
+void prevent_binding_rvalue()
+{
+#ifndef BOOST_OPTIONAL_CONFIG_ALLOW_BINDING_TO_RVALUES
+    BOOST_STATIC_ASSERT_MSG(boost::is_lvalue_reference<From>::value, 
+                            "binding rvalue references to optional lvalue references is disallowed");
+#endif    
+}
+
+template <class T>
+BOOST_DEDUCED_TYPENAME boost::remove_reference<T>::type& forward_reference(T&& r)
+{
+    BOOST_STATIC_ASSERT_MSG(boost::is_lvalue_reference<T>::value, 
+                            "binding rvalue references to optional lvalue references is disallowed");
+    return boost::forward<T>(r);
+}
+
+#endif // BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
+
+
+template <class T>
+struct is_const_integral
+{
+  static const bool value = boost::is_const<T>::value && boost::is_integral<T>::value;
+};
+
+template <class T>
+struct is_const_integral_bad_for_conversion
+{
+#if (!defined BOOST_OPTIONAL_CONFIG_ALLOW_BINDING_TO_RVALUES) && (defined BOOST_OPTIONAL_CONFIG_NO_PROPER_CONVERT_FROM_CONST_INT)
+  static const bool value = boost::is_const<T>::value && boost::is_integral<T>::value;
+#else
+  static const bool value = false;
+#endif
+};
+
+template <class From>
+void prevent_assignment_from_false_const_integral()
+{
+#ifndef BOOST_OPTIONAL_CONFIG_ALLOW_BINDING_TO_RVALUES
+#ifdef BOOST_OPTIONAL_CONFIG_NO_PROPER_ASSIGN_FROM_CONST_INT
+    // MSVC compiler without rvalue references: we need to disable the assignment from
+    // const integral lvalue reference, as it may be an invalid temporary
+    BOOST_STATIC_ASSERT_MSG(!is_const_integral<From>::value, 
+                            "binding const lvalue references to integral types is disabled in this compiler");
+#endif
+#endif   
+}
+
+
+template <class T>
+struct is_optional_
+{
+  static const bool value = false;
+};
+
+template <class U>
+struct is_optional_< ::boost::optional<U> >
+{
+  static const bool value = true;
+};
+
+template <class T>
+struct is_no_optional
+{
+  static const bool value = !is_optional_<BOOST_DEDUCED_TYPENAME boost::decay<T>::type>::value;
+};
+
+
+template <class T, class U>
+  struct is_same_decayed
+  {
+    static const bool value = ::boost::is_same<T, BOOST_DEDUCED_TYPENAME ::boost::remove_reference<U>::type>::value
+                           || ::boost::is_same<T, const BOOST_DEDUCED_TYPENAME ::boost::remove_reference<U>::type>::value;
+  };
+
+template <class T, class U>
+struct no_unboxing_cond
+{
+  static const bool value = is_no_optional<U>::value && !is_same_decayed<T, U>::value;
+};
+
+
+} // namespace detail
+
+template <class T>
+class optional<T&> : public optional_detail::optional_tag
+{
+    T* ptr_;
+    
+public:
+    typedef T& value_type;
+    typedef T& reference_type;
+    typedef T& reference_const_type;
+    typedef T& rval_reference_type;
+    typedef T* pointer_type;
+    typedef T* pointer_const_type;
+    
+    optional() BOOST_NOEXCEPT : ptr_() {}
+    optional(none_t) BOOST_NOEXCEPT : ptr_() {}  
+
+    template <class U>
+        explicit optional(const optional<U&>& rhs) BOOST_NOEXCEPT : ptr_(rhs.get_ptr()) {}
+    optional(const optional& rhs) BOOST_NOEXCEPT : ptr_(rhs.get_ptr()) {}
+    
+    // the following two implement a 'conditionally explicit' constructor: condition is a hack for buggy compilers with screwed conversion construction from const int
+    template <class U>
+      explicit optional(U& rhs, BOOST_DEDUCED_TYPENAME boost::enable_if_c<detail::is_same_decayed<T, U>::value && detail::is_const_integral_bad_for_conversion<U>::value, bool>::type = true) BOOST_NOEXCEPT
+      : ptr_(boost::addressof(rhs)) {}
+      
+    template <class U>
+      optional(U& rhs, BOOST_DEDUCED_TYPENAME boost::enable_if_c<detail::is_same_decayed<T, U>::value && !detail::is_const_integral_bad_for_conversion<U>::value, bool>::type = true) BOOST_NOEXCEPT
+      : ptr_(boost::addressof(rhs)) {}
+
+    optional& operator=(const optional& rhs) BOOST_NOEXCEPT { ptr_ = rhs.get_ptr(); return *this; }
+    template <class U>
+        optional& operator=(const optional<U&>& rhs) BOOST_NOEXCEPT { ptr_ = rhs.get_ptr(); return *this; }
+    optional& operator=(none_t) BOOST_NOEXCEPT { ptr_ = 0; return *this; }
+    
+    
+    void swap(optional& rhs) BOOST_NOEXCEPT { std::swap(ptr_, rhs.ptr_); }
+    T& get() const { BOOST_ASSERT(ptr_); return   *ptr_; }
+
+    T* get_ptr() const BOOST_NOEXCEPT { return ptr_; }
+    T* operator->() const { BOOST_ASSERT(ptr_); return ptr_; }
+    T& operator*() const { BOOST_ASSERT(ptr_); return *ptr_; }
+    
+    T& value() const
+    {
+      if (this->is_initialized())
+        return this->get();
+      else
+        throw_exception(bad_optional_access());
+    }
+    
+    bool operator!() const BOOST_NOEXCEPT { return ptr_ == 0; }  
+    BOOST_EXPLICIT_OPERATOR_BOOL_NOEXCEPT()
+      
+    void reset() BOOST_NOEXCEPT { ptr_ = 0; }
+
+    bool is_initialized() const BOOST_NOEXCEPT { return ptr_ != 0; }
+    bool has_value() const BOOST_NOEXCEPT { return ptr_ != 0; }
+    
+    template <typename F>
+    optional<typename boost::result_of<F(T&)>::type> map(F f) const
+    {
+      if (this->has_value())
+        return f(this->get());
+      else
+        return none;
+    }
+
+    template <typename F>
+    optional<typename optional_detail::optional_value_type<typename boost::result_of<F(T&)>::type>::type> flat_map(F f) const
+      {
+        if (this->has_value())
+          return f(get());
+        else
+          return none;
+      }
+    
+#ifndef BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES   
+ 
+    optional(T&& /* rhs */) BOOST_NOEXCEPT { detail::prevent_binding_rvalue<T&&>(); }
+    
+    template <class R>
+        optional(R&& r, BOOST_DEDUCED_TYPENAME boost::enable_if<detail::no_unboxing_cond<T, R>, bool>::type = true) BOOST_NOEXCEPT
+        : ptr_(boost::addressof(r)) { detail::prevent_binding_rvalue<R>(); }
+        
+    template <class R>
+        optional(bool cond, R&& r, BOOST_DEDUCED_TYPENAME boost::enable_if<detail::is_no_optional<R>, bool>::type = true) BOOST_NOEXCEPT
+        : ptr_(cond ? boost::addressof(r) : 0) { detail::prevent_binding_rvalue<R>(); }
+        
+    template <class R>
+        BOOST_DEDUCED_TYPENAME boost::enable_if<detail::is_no_optional<R>, optional<T&>&>::type
+        operator=(R&& r) BOOST_NOEXCEPT { detail::prevent_binding_rvalue<R>(); ptr_ = boost::addressof(r); return *this; }
+        
+    template <class R>
+        void emplace(R&& r, BOOST_DEDUCED_TYPENAME boost::enable_if<detail::is_no_optional<R>, bool>::type = true) BOOST_NOEXCEPT
+        { detail::prevent_binding_rvalue<R>(); ptr_ = boost::addressof(r); }
+        
+    template <class R>
+      T& get_value_or(R&& r, BOOST_DEDUCED_TYPENAME boost::enable_if<detail::is_no_optional<R>, bool>::type = true) const BOOST_NOEXCEPT
+      { detail::prevent_binding_rvalue<R>(); return ptr_ ? *ptr_ : r; }
+      
+    template <class R>
+        T& value_or(R&& r, BOOST_DEDUCED_TYPENAME boost::enable_if<detail::is_no_optional<R>, bool>::type = true) const BOOST_NOEXCEPT
+        { detail::prevent_binding_rvalue<R>(); return ptr_ ? *ptr_ : r; }
+        
+    template <class R>
+      void reset(R&& r, BOOST_DEDUCED_TYPENAME boost::enable_if<detail::is_no_optional<R>, bool>::type = true) BOOST_NOEXCEPT
+      { detail::prevent_binding_rvalue<R>(); ptr_ = boost::addressof(r); }
+      
+    template <class F>
+        T& value_or_eval(F f) const { return ptr_ ? *ptr_ : detail::forward_reference(f()); }
+      
+#else  // BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
+
+    
+    // the following two implement a 'conditionally explicit' constructor
+    template <class U>
+      explicit optional(U& v, BOOST_DEDUCED_TYPENAME boost::enable_if_c<detail::no_unboxing_cond<T, U>::value && detail::is_const_integral_bad_for_conversion<U>::value, bool>::type = true) BOOST_NOEXCEPT
+      : ptr_(boost::addressof(v)) { }
+      
+    template <class U>
+      optional(U& v, BOOST_DEDUCED_TYPENAME boost::enable_if_c<detail::no_unboxing_cond<T, U>::value && !detail::is_const_integral_bad_for_conversion<U>::value, bool>::type = true) BOOST_NOEXCEPT
+      : ptr_(boost::addressof(v)) { }
+        
+    template <class U>
+      optional(bool cond, U& v, BOOST_DEDUCED_TYPENAME boost::enable_if<detail::is_no_optional<U>, bool>::type = true) BOOST_NOEXCEPT : ptr_(cond ? boost::addressof(v) : 0) {}
+
+    template <class U>
+      BOOST_DEDUCED_TYPENAME boost::enable_if<detail::is_no_optional<U>, optional<T&>&>::type
+      operator=(U& v) BOOST_NOEXCEPT
+      {
+        detail::prevent_assignment_from_false_const_integral<U>();
+        ptr_ = boost::addressof(v); return *this;
+      }
+
+    template <class U>
+        void emplace(U& v, BOOST_DEDUCED_TYPENAME boost::enable_if<detail::is_no_optional<U>, bool>::type = true) BOOST_NOEXCEPT
+        { ptr_ = boost::addressof(v); }
+        
+    template <class U>
+      T& get_value_or(U& v, BOOST_DEDUCED_TYPENAME boost::enable_if<detail::is_no_optional<U>, bool>::type = true) const BOOST_NOEXCEPT
+      { return ptr_ ? *ptr_ : v; }
+      
+    template <class U>
+        T& value_or(U& v, BOOST_DEDUCED_TYPENAME boost::enable_if<detail::is_no_optional<U>, bool>::type = true) const BOOST_NOEXCEPT
+        { return ptr_ ? *ptr_ : v; }
+        
+    template <class U>
+      void reset(U& v, BOOST_DEDUCED_TYPENAME boost::enable_if<detail::is_no_optional<U>, bool>::type = true) BOOST_NOEXCEPT
+      { ptr_ = boost::addressof(v); }
+      
+    template <class F>
+      T& value_or_eval(F f) const { return ptr_ ? *ptr_ : f(); }
+      
+#endif // BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
+};
+
+template <class T> 
+  void swap ( optional<T&>& x, optional<T&>& y) BOOST_NOEXCEPT
+{
+  x.swap(y);
+}
+
+} // namespace boost
+
+#endif // 1/0
+
+#endif // header guard

include/boost/optional/detail/optional_relops.hpp

@@ -0,0 +1,196 @@
+// Copyright (C) 2003, 2008 Fernando Luis Cacciola Carballal.
+// Copyright (C) 2015 Andrzej Krzemienski.
+//
+// Use, modification, and distribution is subject to the Boost Software
+// License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//
+// See http://www.boost.org/libs/optional for documentation.
+//
+// You are welcome to contact the author at:
+//  akrzemi1@gmail.com
+
+#ifndef BOOST_OPTIONAL_DETAIL_OPTIONAL_RELOPS_AJK_03OCT2015_HPP
+#define BOOST_OPTIONAL_DETAIL_OPTIONAL_RELOPS_AJK_03OCT2015_HPP
+
+namespace boost {
+
+// optional's relational operators ( ==, !=, <, >, <=, >= ) have deep-semantics (compare values).
+// WARNING: This is UNLIKE pointers. Use equal_pointees()/less_pointees() in generic code instead.
+
+
+//
+// optional<T> vs optional<T> cases
+//
+
+template<class T>
+inline
+bool operator == ( optional<T> const& x, optional<T> const& y )
+{ return bool(x) && bool(y) ? *x == *y : bool(x) == bool(y); }
+
+template<class T>
+inline
+bool operator < ( optional<T> const& x, optional<T> const& y )
+{ return less_pointees(x,y); }
+
+template<class T>
+inline
+bool operator != ( optional<T> const& x, optional<T> const& y )
+{ return !( x == y ) ; }
+
+template<class T>
+inline
+bool operator > ( optional<T> const& x, optional<T> const& y )
+{ return y < x ; }
+
+template<class T>
+inline
+bool operator <= ( optional<T> const& x, optional<T> const& y )
+{ return !( y < x ) ; }
+
+template<class T>
+inline
+bool operator >= ( optional<T> const& x, optional<T> const& y )
+{ return !( x < y ) ; }
+
+
+//
+// optional<T> vs T cases
+//
+template<class T>
+inline
+bool operator == ( optional<T> const& x, T const& y )
+{ return equal_pointees(x, optional<T>(y)); }
+
+template<class T>
+inline
+bool operator < ( optional<T> const& x, T const& y )
+{ return less_pointees(x, optional<T>(y)); }
+
+template<class T>
+inline
+bool operator != ( optional<T> const& x, T const& y )
+{ return !( x == y ) ; }
+
+template<class T>
+inline
+bool operator > ( optional<T> const& x, T const& y )
+{ return y < x ; }
+
+template<class T>
+inline
+bool operator <= ( optional<T> const& x, T const& y )
+{ return !( y < x ) ; }
+
+template<class T>
+inline
+bool operator >= ( optional<T> const& x, T const& y )
+{ return !( x < y ) ; }
+
+//
+// T vs optional<T> cases
+//
+
+template<class T>
+inline
+bool operator == ( T const& x, optional<T> const& y )
+{ return equal_pointees( optional<T>(x), y ); }
+
+template<class T>
+inline
+bool operator < ( T const& x, optional<T> const& y )
+{ return less_pointees( optional<T>(x), y ); }
+
+template<class T>
+inline
+bool operator != ( T const& x, optional<T> const& y )
+{ return !( x == y ) ; }
+
+template<class T>
+inline
+bool operator > ( T const& x, optional<T> const& y )
+{ return y < x ; }
+
+template<class T>
+inline
+bool operator <= ( T const& x, optional<T> const& y )
+{ return !( y < x ) ; }
+
+template<class T>
+inline
+bool operator >= ( T const& x, optional<T> const& y )
+{ return !( x < y ) ; }
+
+
+//
+// optional<T> vs none cases
+//
+
+template<class T>
+inline
+bool operator == ( optional<T> const& x, none_t ) BOOST_NOEXCEPT
+{ return !x; }
+
+template<class T>
+inline
+bool operator < ( optional<T> const& x, none_t )
+{ return less_pointees(x,optional<T>() ); }
+
+template<class T>
+inline
+bool operator != ( optional<T> const& x, none_t ) BOOST_NOEXCEPT
+{ return bool(x); }
+
+template<class T>
+inline
+bool operator > ( optional<T> const& x, none_t y )
+{ return y < x ; }
+
+template<class T>
+inline
+bool operator <= ( optional<T> const& x, none_t y )
+{ return !( y < x ) ; }
+
+template<class T>
+inline
+bool operator >= ( optional<T> const& x, none_t y )
+{ return !( x < y ) ; }
+
+//
+// none vs optional<T> cases
+//
+
+template<class T>
+inline
+bool operator == ( none_t , optional<T> const& y ) BOOST_NOEXCEPT
+{ return !y; }
+
+template<class T>
+inline
+bool operator < ( none_t , optional<T> const& y )
+{ return less_pointees(optional<T>() ,y); }
+
+template<class T>
+inline
+bool operator != ( none_t, optional<T> const& y ) BOOST_NOEXCEPT
+{ return bool(y); }
+
+template<class T>
+inline
+bool operator > ( none_t x, optional<T> const& y )
+{ return y < x ; }
+
+template<class T>
+inline
+bool operator <= ( none_t x, optional<T> const& y )
+{ return !( y < x ) ; }
+
+template<class T>
+inline
+bool operator >= ( none_t x, optional<T> const& y )
+{ return !( x < y ) ; }
+
+} // namespace boost
+
+#endif // header guard
+

include/boost/optional/detail/optional_swap.hpp

@@ -0,0 +1,117 @@
+// Copyright (C) 2003, 2008 Fernando Luis Cacciola Carballal.
+// Copyright (C) 2015 Andrzej Krzemienski.
+//
+// Use, modification, and distribution is subject to the Boost Software
+// License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//
+// See http://www.boost.org/libs/optional for documentation.
+//
+// You are welcome to contact the author at:
+//  akrzemi1@gmail.com
+
+#ifndef BOOST_OPTIONAL_DETAIL_OPTIONAL_SWAP_AJK_28JAN2015_HPP
+#define BOOST_OPTIONAL_DETAIL_OPTIONAL_SWAP_AJK_28JAN2015_HPP
+
+#include <boost/core/invoke_swap.hpp>
+#include <boost/optional/optional_fwd.hpp>
+
+namespace boost {
+
+namespace optional_detail {
+
+template <bool use_default_constructor> struct swap_selector;
+
+template <>
+struct swap_selector<true>
+{
+    template <class T>
+    static void optional_swap ( optional<T>& x, optional<T>& y )
+    {
+        const bool hasX = !!x;
+        const bool hasY = !!y;
+
+        if ( !hasX && !hasY )
+            return;
+
+        if( !hasX )
+            x.emplace();
+        else if ( !hasY )
+            y.emplace();
+
+        // Boost.Core.Swap will take care of ADL and workarounds for broken compilers
+        boost::core::invoke_swap(x.get(), y.get());
+
+        if( !hasX )
+            y = boost::none ;
+        else if( !hasY )
+            x = boost::none ;
+    }
+};
+
+#ifdef BOOST_OPTIONAL_DETAIL_MOVE
+# undef BOOST_OPTIONAL_DETAIL_MOVE
+#endif
+
+#ifndef BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
+# define BOOST_OPTIONAL_DETAIL_MOVE(EXPR_) boost::move(EXPR_)
+#else
+# define BOOST_OPTIONAL_DETAIL_MOVE(EXPR_) EXPR_
+#endif
+
+template <>
+struct swap_selector<false>
+{
+    template <class T>
+    static void optional_swap ( optional<T>& x, optional<T>& y ) 
+    //BOOST_NOEXCEPT_IF(::boost::is_nothrow_move_constructible<T>::value && BOOST_NOEXCEPT_EXPR(boost::core::invoke_swap(*x, *y)))
+    {
+        if (x)
+        {
+            if (y)
+            {
+                boost::core::invoke_swap(*x, *y);
+            }
+            else
+            {
+                y = BOOST_OPTIONAL_DETAIL_MOVE(*x);
+                x = boost::none;
+            }
+        }
+        else
+        {
+            if (y)
+            {
+                x = BOOST_OPTIONAL_DETAIL_MOVE(*y);
+                y = boost::none;
+            }
+        }
+    }
+};
+
+} // namespace optional_detail
+
+#if (!defined BOOST_NO_CXX11_RVALUE_REFERENCES) && (!defined BOOST_CONFIG_RESTORE_OBSOLETE_SWAP_IMPLEMENTATION)
+
+template<class T>
+struct optional_swap_should_use_default_constructor : boost::false_type {} ;
+
+#else
+
+template<class T>
+struct optional_swap_should_use_default_constructor : has_nothrow_default_constructor<T> {} ;
+
+#endif
+
+template <class T>
+inline void swap ( optional<T>& x, optional<T>& y )
+//BOOST_NOEXCEPT_IF(::boost::is_nothrow_move_constructible<T>::value && BOOST_NOEXCEPT_EXPR(boost::core::invoke_swap(*x, *y)))
+{
+    optional_detail::swap_selector<optional_swap_should_use_default_constructor<T>::value>::optional_swap(x, y);
+}
+
+} // namespace boost
+
+#undef BOOST_OPTIONAL_DETAIL_MOVE
+
+#endif // header guard

include/boost/optional/detail/optional_trivially_copyable_base.hpp

@@ -0,0 +1,510 @@
+// Copyright (C) 2017 Andrzej Krzemienski.
+//
+// Use, modification, and distribution is subject to the Boost Software
+// License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//
+// See http://www.boost.org/libs/optional for documentation.
+//
+// You are welcome to contact the author at:
+//  akrzemi1@gmail.com
+
+// trivially-copyable version of the storage
+
+template<class T>
+class tc_optional_base : public optional_tag
+{
+  private :
+
+    typedef tc_optional_base<T> this_type ;
+
+  protected :
+
+    typedef T value_type ;
+
+  protected:
+    typedef T &       reference_type ;
+    typedef T const&  reference_const_type ;
+#ifndef  BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
+    typedef T &&  rval_reference_type ;
+    typedef T &&  reference_type_of_temporary_wrapper ;
+#endif
+    typedef T *         pointer_type ;
+    typedef T const*    pointer_const_type ;
+    typedef T const&    argument_type ;
+
+    tc_optional_base()
+      :
+      m_initialized(false) {}
+
+    tc_optional_base ( none_t )
+      :
+      m_initialized(false) {}
+
+    tc_optional_base ( init_value_tag, argument_type val )
+      :
+      m_initialized(true), m_storage(val) {}
+
+    tc_optional_base ( bool cond, argument_type val )
+      :
+      m_initialized(cond), m_storage(val) {}
+
+    // tc_optional_base ( tc_optional_base const& ) = default;
+
+
+#ifndef  BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
+
+    template<class Expr, class PtrExpr>
+    explicit tc_optional_base ( Expr&& expr, PtrExpr const* tag )
+      :
+      m_initialized(false)
+    {
+      construct(boost::forward<Expr>(expr),tag);
+    }
+
+#else
+    // This is used for both converting and in-place constructions.
+    // Derived classes use the 'tag' to select the appropriate
+    // implementation (the correct 'construct()' overload)
+    template<class Expr>
+    explicit tc_optional_base ( Expr const& expr, Expr const* tag )
+      :
+      m_initialized(false)
+    {
+      construct(expr,tag);
+    }
+
+#endif
+
+    // tc_optional_base& operator= ( tc_optional_base const& ) = default;
+    // ~tc_optional_base() = default;
+
+    // Assigns from another optional<T> (deep-copies the rhs value)
+    void assign ( tc_optional_base const& rhs )
+    {
+      *this = rhs;
+    }
+
+    // Assigns from another _convertible_ optional<U> (deep-copies the rhs value)
+    template<class U>
+    void assign ( optional<U> const& rhs )
+    {
+      if ( rhs.is_initialized() )
+#ifndef BOOST_OPTIONAL_CONFIG_RESTORE_ASSIGNMENT_OF_NONCONVERTIBLE_TYPES
+        m_storage = rhs.get();
+#else
+        m_storage = static_cast<value_type>(rhs.get());
+#endif
+
+      m_initialized = rhs.is_initialized();
+    }
+
+#ifndef BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
+    // move-assigns from another _convertible_ optional<U> (deep-moves from the rhs value)
+    template<class U>
+    void assign ( optional<U>&& rhs )
+    {
+      typedef BOOST_DEDUCED_TYPENAME optional<U>::rval_reference_type ref_type;
+      if ( rhs.is_initialized() )
+        m_storage = static_cast<ref_type>(rhs.get());
+      m_initialized = rhs.is_initialized();
+    }
+#endif
+
+    void assign ( argument_type val )
+    {
+      construct(val);
+    }
+
+    void assign ( none_t ) { destroy(); }
+
+#ifndef BOOST_OPTIONAL_NO_INPLACE_FACTORY_SUPPORT
+
+#ifndef BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
+    template<class Expr, class ExprPtr>
+    void assign_expr ( Expr&& expr, ExprPtr const* tag )
+    {
+       construct(boost::forward<Expr>(expr),tag);
+    }
+#else
+    template<class Expr>
+    void assign_expr ( Expr const& expr, Expr const* tag )
+    {
+      construct(expr,tag);
+    }
+#endif
+
+#endif
+
+  public :
+
+    // Destroys the current value, if any, leaving this UNINITIALIZED
+    // No-throw (assuming T::~T() doesn't)
+    void reset() BOOST_NOEXCEPT { destroy(); }
+
+    // **DEPRECATED** Replaces the current value -if any- with 'val'
+    void reset ( argument_type val ) BOOST_NOEXCEPT { assign(val); }
+
+    // Returns a pointer to the value if this is initialized, otherwise,
+    // returns NULL.
+    // No-throw
+    pointer_const_type get_ptr() const { return m_initialized ? get_ptr_impl() : 0 ; }
+    pointer_type       get_ptr()       { return m_initialized ? get_ptr_impl() : 0 ; }
+
+    bool is_initialized() const { return m_initialized ; }
+
+  protected :
+
+    void construct ( argument_type val )
+     {
+       m_storage = val ;
+       m_initialized = true ;
+     }
+
+
+#if (!defined BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES) && (!defined BOOST_NO_CXX11_VARIADIC_TEMPLATES)
+    // Constructs in-place
+    // upon exception *this is always uninitialized
+    template<class... Args>
+    void construct ( in_place_init_t, Args&&... args )
+    {
+      m_storage = value_type( boost::forward<Args>(args)... ) ;
+      m_initialized = true ;
+    }
+
+    template<class... Args>
+    void emplace_assign ( Args&&... args )
+    {
+      construct(in_place_init, boost::forward<Args>(args)...);
+    }
+
+    template<class... Args>
+    explicit tc_optional_base ( in_place_init_t, Args&&... args )
+      :
+      m_initialized(false)
+    {
+      construct(in_place_init, boost::forward<Args>(args)...);
+    }
+
+    template<class... Args>
+    explicit tc_optional_base ( in_place_init_if_t, bool cond, Args&&... args )
+      :
+      m_initialized(false)
+    {
+      if ( cond )
+        construct(in_place_init, boost::forward<Args>(args)...);
+    }
+#elif (!defined BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES)
+    template<class Arg>
+    void construct ( in_place_init_t, Arg&& arg )
+     {
+       m_storage = value_type( boost::forward<Arg>(arg) );
+       m_initialized = true ;
+     }
+
+    void construct ( in_place_init_t )
+     {
+       m_storage = value_type();
+       m_initialized = true ;
+     }
+
+    template<class Arg>
+    void emplace_assign ( Arg&& arg )
+     {
+       construct(in_place_init, boost::forward<Arg>(arg)) ;
+     }
+
+    void emplace_assign ()
+     {
+       construct(in_place_init) ;
+     }
+
+    template<class Arg>
+    explicit tc_optional_base ( in_place_init_t, Arg&& arg )
+      :
+      m_initialized(false)
+    {
+      construct(in_place_init, boost::forward<Arg>(arg));
+    }
+
+    explicit tc_optional_base ( in_place_init_t )
+      :
+      m_initialized(false), m_storage() {}
+
+    template<class Arg>
+    explicit tc_optional_base ( in_place_init_if_t, bool cond, Arg&& arg )
+      :
+      m_initialized(false)
+    {
+      if ( cond )
+        construct(in_place_init, boost::forward<Arg>(arg));
+    }
+
+    explicit tc_optional_base ( in_place_init_if_t, bool cond )
+      :
+      m_initialized(false)
+    {
+      if ( cond )
+        construct(in_place_init);
+    }
+
+#else
+
+    template<class Arg>
+    void construct ( in_place_init_t, const Arg& arg )
+     {
+       m_storage = value_type( arg );
+       m_initialized = true ;
+     }
+
+    template<class Arg>
+    void construct ( in_place_init_t, Arg& arg )
+     {
+       m_storage = value_type( arg );
+       m_initialized = true ;
+     }
+
+    void construct ( in_place_init_t )
+     {
+       m_storage = value_type();
+       m_initialized = true ;
+     }
+
+    template<class Arg>
+    void emplace_assign ( const Arg& arg )
+    {
+      construct(in_place_init, arg);
+    }
+
+    template<class Arg>
+    void emplace_assign ( Arg& arg )
+    {
+      construct(in_place_init, arg);
+    }
+
+    void emplace_assign ()
+    {
+      construct(in_place_init);
+    }
+
+    template<class Arg>
+    explicit tc_optional_base ( in_place_init_t, const Arg& arg )
+      : m_initialized(false)
+    {
+      construct(in_place_init, arg);
+    }
+
+    template<class Arg>
+    explicit tc_optional_base ( in_place_init_t, Arg& arg )
+      : m_initialized(false)
+    {
+      construct(in_place_init, arg);
+    }
+
+    explicit tc_optional_base ( in_place_init_t )
+      : m_initialized(false)
+    {
+      construct(in_place_init);
+    }
+
+    template<class Arg>
+    explicit tc_optional_base ( in_place_init_if_t, bool cond, const Arg& arg )
+      : m_initialized(false)
+    {
+      if ( cond )
+        construct(in_place_init, arg);
+    }
+
+    template<class Arg>
+    explicit tc_optional_base ( in_place_init_if_t, bool cond, Arg& arg )
+      : m_initialized(false)
+    {
+      if ( cond )
+        construct(in_place_init, arg);
+    }
+
+    explicit tc_optional_base ( in_place_init_if_t, bool cond )
+      : m_initialized(false)
+    {
+      if ( cond )
+        construct(in_place_init);
+    }
+#endif
+
+#ifndef BOOST_OPTIONAL_NO_INPLACE_FACTORY_SUPPORT
+
+#ifndef BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
+    // Constructs in-place using the given factory
+    template<class Expr>
+    void construct ( Expr&& factory, in_place_factory_base const* )
+     {
+       boost_optional_detail::construct<value_type>(factory, boost::addressof(m_storage));
+       m_initialized = true ;
+     }
+
+    // Constructs in-place using the given typed factory
+    template<class Expr>
+    void construct ( Expr&& factory, typed_in_place_factory_base const* )
+     {
+       factory.apply(boost::addressof(m_storage)) ;
+       m_initialized = true ;
+     }
+
+    template<class Expr>
+    void assign_expr_to_initialized ( Expr&& factory, in_place_factory_base const* tag )
+     {
+       destroy();
+       construct(factory,tag);
+     }
+
+    // Constructs in-place using the given typed factory
+    template<class Expr>
+    void assign_expr_to_initialized ( Expr&& factory, typed_in_place_factory_base const* tag )
+     {
+       destroy();
+       construct(factory,tag);
+     }
+
+#else
+    // Constructs in-place using the given factory
+    template<class Expr>
+    void construct ( Expr const& factory, in_place_factory_base const* )
+     {
+       boost_optional_detail::construct<value_type>(factory, boost::addressof(m_storage));
+       m_initialized = true ;
+     }
+
+    // Constructs in-place using the given typed factory
+    template<class Expr>
+    void construct ( Expr const& factory, typed_in_place_factory_base const* )
+     {
+       factory.apply(boost::addressof(m_storage)) ;
+       m_initialized = true ;
+     }
+
+    template<class Expr>
+    void assign_expr_to_initialized ( Expr const& factory, in_place_factory_base const* tag )
+     {
+       destroy();
+       construct(factory,tag);
+     }
+
+    // Constructs in-place using the given typed factory
+    template<class Expr>
+    void assign_expr_to_initialized ( Expr const& factory, typed_in_place_factory_base const* tag )
+     {
+       destroy();
+       construct(factory,tag);
+     }
+#endif
+
+#endif
+
+#ifndef BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
+    // Constructs using any expression implicitly convertible to the single argument
+    // of a one-argument T constructor.
+    // Converting constructions of optional<T> from optional<U> uses this function with
+    // 'Expr' being of type 'U' and relying on a converting constructor of T from U.
+    template<class Expr>
+    void construct ( Expr&& expr, void const* )
+    {
+      m_storage = value_type(boost::forward<Expr>(expr)) ;
+      m_initialized = true ;
+    }
+
+    // Assigns using a form any expression implicitly convertible to the single argument
+    // of a T's assignment operator.
+    // Converting assignments of optional<T> from optional<U> uses this function with
+    // 'Expr' being of type 'U' and relying on a converting assignment of T from U.
+    template<class Expr>
+    void assign_expr_to_initialized ( Expr&& expr, void const* )
+    {
+      assign_value( boost::forward<Expr>(expr) );
+    }
+#else
+    // Constructs using any expression implicitly convertible to the single argument
+    // of a one-argument T constructor.
+    // Converting constructions of optional<T> from optional<U> uses this function with
+    // 'Expr' being of type 'U' and relying on a converting constructor of T from U.
+    template<class Expr>
+    void construct ( Expr const& expr, void const* )
+     {
+       m_storage = value_type(expr) ;
+       m_initialized = true ;
+     }
+
+    // Assigns using a form any expression implicitly convertible to the single argument
+    // of a T's assignment operator.
+    // Converting assignments of optional<T> from optional<U> uses this function with
+    // 'Expr' being of type 'U' and relying on a converting assignment of T from U.
+    template<class Expr>
+    void assign_expr_to_initialized ( Expr const& expr, void const* )
+     {
+       assign_value(expr);
+     }
+
+#endif
+
+#ifdef BOOST_OPTIONAL_WEAK_OVERLOAD_RESOLUTION
+    // BCB5.64 (and probably lower versions) workaround.
+    //   The in-place factories are supported by means of catch-all constructors
+    //   and assignment operators (the functions are parameterized in terms of
+    //   an arbitrary 'Expr' type)
+    //   This compiler incorrectly resolves the overload set and sinks optional<T> and optional<U>
+    //   to the 'Expr'-taking functions even though explicit overloads are present for them.
+    //   Thus, the following overload is needed to properly handle the case when the 'lhs'
+    //   is another optional.
+    //
+    // For VC<=70 compilers this workaround doesn't work because the compiler issues and error
+    // instead of choosing the wrong overload
+    //
+#ifndef  BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
+    // Notice that 'Expr' will be optional<T> or optional<U> (but not tc_optional_base<..>)
+    template<class Expr>
+    void construct ( Expr&& expr, optional_tag const* )
+     {
+       if ( expr.is_initialized() )
+       {
+         // An exception can be thrown here.
+         // It it happens, THIS will be left uninitialized.
+         m_storage = value_type(boost::move(expr.get())) ;
+         m_initialized = true ;
+       }
+     }
+#else
+    // Notice that 'Expr' will be optional<T> or optional<U> (but not tc_optional_base<..>)
+    template<class Expr>
+    void construct ( Expr const& expr, optional_tag const* )
+     {
+       if ( expr.is_initialized() )
+       {
+         // An exception can be thrown here.
+         // It it happens, THIS will be left uninitialized.
+         m_storage = value_type(expr.get()) ;
+         m_initialized = true ;
+       }
+     }
+#endif
+#endif // defined BOOST_OPTIONAL_WEAK_OVERLOAD_RESOLUTION
+
+    void assign_value ( argument_type val ) { m_storage = val; }
+#ifndef  BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
+    void assign_value ( rval_reference_type val ) { m_storage = static_cast<rval_reference_type>(val); }
+#endif
+
+    void destroy()
+    {
+      m_initialized = false;
+    }
+
+    reference_const_type get_impl() const { return m_storage ; }
+    reference_type       get_impl()       { return m_storage ; }
+
+    pointer_const_type get_ptr_impl() const { return boost::addressof(m_storage); }
+    pointer_type       get_ptr_impl()       { return boost::addressof(m_storage); }
+
+  private :
+
+    bool m_initialized ;
+    T    m_storage ;
+} ;

include/boost/optional/optional_fwd.hpp

@@ -1,4 +1,5 @@
 // Copyright (C) 2003, 2008 Fernando Luis Cacciola Carballal.
+// Copyright (C) 2016 Andrzej Krzemienski
 //
 // Use, modification, and distribution is subject to the Boost Software
 // License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
@@ -15,15 +16,25 @@
 #ifndef BOOST_OPTIONAL_OPTIONAL_FWD_FLC_19NOV2002_HPP
 #define BOOST_OPTIONAL_OPTIONAL_FWD_FLC_19NOV2002_HPP
 
+#include <boost/config.hpp>
 
 namespace boost {
 
 template<class T> class optional ;
 
-template<class T> void swap ( optional<T>& , optional<T>& );
+// This forward is needed to refer to namespace scope swap from the member swap
+template<class T> void swap ( optional<T>& , optional<T>& ) ;
 
 template<class T> struct optional_swap_should_use_default_constructor ;
 
+#ifndef BOOST_OPTIONAL_CONFIG_DONT_SPECIALIZE_OPTIONAL_REFS
+
+template<class T> class optional<T&> ;
+
+template<class T> void swap ( optional<T&>& , optional<T&>& ) BOOST_NOEXCEPT;
+
+#endif
+
 } // namespace boost
 
 #endif