Parameter List Features

function_type

Header

#include <boost/callable_traits/function_type.hpp>

Definition

template<typename T>
using function_type_t = //see below

template<typename T>
struct function_type {
    using type = function_type_t<T>;
};

Constraints

T must be one of the following:
- function
- function pointer
- function reference
- member function pointer
- member data pointer
- user-defined type with a non-overloaded operator()
- type of a non-generic lambda

Behavior

When the constraints are violated, a substitution failure occurs.
When T is a function, the aliased type is identical to T, except that the aliased function type will not have member qualifiers or the transaction_safe specifier.
When T is a function pointer, the aliased type is equivalent to std::remove_pointer_t<T>.
When T is a function reference, the aliased type is equivalent to std::remove_reference_t<T>.
When T is a function object, the aliased type is a function type with the same return type and parameter list as T's operator().
When T is a member function pointer, the aliased type is a function type with the same return type as T, and the first parameter is a reference to the parent class of T, qualified according to the member qualifiers on T. The subsequent parameters, if any, are the parameter types of T.
When T is a member data pointer, the aliased type is a function type returning the underlying member type of T, taking a single parameter, which is a const reference to the parent type of T.
In all cases, the aliased function type will not have member qualifiers, and will not have the transaction_safe specifier.

Compatibility Notes

Full support on GCC 4.7.4+, Clang 3.5+, Visual Studio 2015, and XCode 6.4+.

Input/Output Examples

`T`	`function_type_t<T>`
`void(int)`	`void(int)`
`void(int) const`	`void(int)`
`void(int) transaction_safe`	`void(int)`
`void(*)(int)`	`void(int)`
`void(&)(int)`	`void(int)`
`void(*)()`	`void()`
`int(foo::*)(int)`	`int(foo&, int)`
`int(foo::*)(int) const`	`int(const foo&, int)`
`void(foo::*)() volatile &&`	`void(volatile foo&&)`
`int foo::*`	`int(const foo&)`
`const int foo::*`	`int(const foo&)`
`int`	(substitution failure)
`int (*const)()`	(substitution failure)

Example Program

#include <type_traits>
#include <boost/callable_traits.hpp>

namespace ct = boost::callable_traits;

template<typename T>
void test(){

    // this example shows how boost::callable_traits::function_type_t
    // bevaves consistently for many different types
    using type = ct::function_type_t<T>;
    using expect = void(int, float&, const char*);
    static_assert(std::is_same<expect, type>{}, "");
}

int main() {

    auto lamda = [](int, float&, const char*){};
    using lam = decltype(lamda);
    test<lam>();

    using function_ptr = void(*)(int, float&, const char*);
    test<function_ptr>();

    using function_ref = void(&)(int, float&, const char*);
    test<function_ref>();

    using function = void(int, float&, const char*);
    test<function>();

    using abominable = void(int, float&, const char*) const;
    test<abominable>();
}

args

Header

#include <boost/callable_traits/args.hpp>

Definition

template<typename T>
using args_t = //see below

template<typename T>
struct args {
    using type = args_t<T>;
};

Constraints

T must be one of the following:
- function
- function pointer
- function reference
- member function pointer
- member data pointer
- user-defined type with a non-overloaded operator()
- type of a non-generic lambda

Behavior

When the constraints are violated, a substitution failure occurs.
When T is a function, function pointer, or function reference, the aliased type is a std::tuple whose element types match those of the function's parameter list.
When T is a function object, the aliased type is a std::tuple whose element types match those of the function object's operator() parameter list.
When T is a member function pointer, the aliased type is a std::tuple instantiation, where the first tuple element is a reference to the parent class of T, qualified according to the member qualifiers on T, such that this first tuple element type is equivalent to boost::callable_traits::qualified_class_of_t<T>. The subsequent template type arguments, if any, are the parameter types of the member function.
When T is a member data pointer, the aliased type is a std::tuple with a single element, which is a const reference to the parent class of T.

Compatibility Notes

Full support on GCC 4.7.4+, Clang 3.5+, Visual Studio 2015, and XCode 6.4+.

Input/Output Examples

`T`	`args_t<T>`
`void(float, char, int)`	`std::tuple<float, char, int>`
`void(*)(float, char, int)`	`std::tuple<float, char, int`
`void(&)(float, char, int)`	`std::tuple<float, char, int`
`void(float, char, int) const &&`	`std::tuple<float, char, int>`
`void(*)()`	`std::tuple<>`
`void(foo::*)(float, char, int)`	`std::tuple<foo&, float, char, int>`
`int(foo::*)(int) const`	`std::tuple<const foo&, int>`
`void(foo::*)() volatile &&`	`std::tuple<volatile foo &&>`
`int foo::*`	`std::tuple<const foo&>`
`const int foo::*`	`std::tuple<const foo&>`
`int`	(substitution failure)
`int (*const)()`	(substitution failure)

Example Program

#include <type_traits>
#include <memory>
#include <boost/callable_traits.hpp>

namespace ct = boost::callable_traits;

template<typename T, typename Expect>
void test(){
    using args_t = ct::args_t<T>;
    static_assert(std::is_same<args_t, Expect>::value, "");
}

int main() {

    {
        auto lamda = [](int, float&, const char*){};
        using lam = decltype(lamda);
        using expect = std::tuple<int, float&, const char*>;

        test<lam, expect>();
    }

    {
        struct foo;
        using pmf = void(foo::*)(int, float&, const char*);
        using expect = std::tuple<foo&, int, float&, const char*>;

        test<pmf, expect>();
    }

    {
        using function_ptr = void(*)(int, float&, const char*);
        using expect = std::tuple<int, float&, const char*>;
        test<function_ptr, expect>();
    }

    {
        using function_ref = void(&)(int, float&, const char*);
        using expect = std::tuple<int, float&, const char*>;
        test<function_ref, expect>();
    }

    {
        using function = void(int, float&, const char*);
        using expect = std::tuple<int, float&, const char*>;
        test<function, expect>();
    }

    {
        using abominable = void(int, float&, const char*) const;
        using expect = std::tuple<int, float&, const char*>;
        test<abominable, expect>();
    }
}

arg_at

Header

#include <boost/callable_traits/arg_at.hpp>

Definition

BOOST_CLBL_TRTS_NAMESPACE_BEGIN



template<std::size_t I, typename T>
using arg_at_t = //see below

template<std::size_t I, typename T>
struct arg_at {
    using type = arg_at_t<I, T>;
};

Constraints

T must be one of the following:
- function
- function pointer
- function reference
- member function pointer
- member data pointer
- user-defined type with non-overloaded operator()
- type of a non-generic lambda
I must be less than std::tuple_size<boost::callable_traits::args_t<T>>::value

Behavior

If any constraints are violated, a substitution failure occurs.
Otherwise, arg_at_t<Index, T> is equivalent to std::tuple_element_t<Index, boost::callable_traits::args_t<T>>.

Compatibility Notes

Full support on GCC 4.7.4+, Clang 3.5+, Visual Studio 2015, and XCode 6.4+.

Example Program

#include <type_traits>
#include <boost/callable_traits/arg_at.hpp>

namespace ct = boost::callable_traits;

int main() {

    auto lambda = [](int, char, float){};
    using lt = decltype(lambda);

    using second_param = ct::arg_at_t<1, lt>;
    static_assert(std::is_same<second_param, char>::value, "");

    // With pointer-to-member functions, the implicit "this" pointer
    // is treated as the first parameter, in the form of a reference.
    using pmf = decltype(&lt::operator());
    using object_ref = ct::arg_at_t<0, pmf>;
    static_assert(std::is_same<object_ref, lt const &>::value, "");
}

clear_args

Header

#include <boost/callable_traits/clear_args.hpp>

Definition

template<typename T>
using clear_args_t = //see below

template<typename T>
struct clear_args {
    using type = clear_args_t<T>;
};

Constraints

T must be one of the following:
- function
- function pointer
- function reference
- member function pointer

Behavior

When the constraints are violated, a substitution failure occurs.
The aliased type has an empty parameter list, but is otherwise identical to T.

Compatibility Notes

Full support on GCC 4.7.4+, Clang 3.5+, Visual Studio 2015, and XCode 6.4+.

Input/Output Examples

`T`	`clear_args_t<T>`
`void(float, char, int)`	`void()`
`void(*)(float, char, int)`	`void(*)()`
`void(&)(float, char, int)`	`void(&)()`
`void(float, char, int) const &&`	`void() const &&`
`void(*)()`	`void(*)()`
`void(foo::*)(float, char, int)`	`void(foo::*)()`
`int(foo::*)(int) const`	`int(foo::*)() const`
`void(foo::*)() volatile &&`	`void(foo::*)() volatile &&`
`int foo::*`	(substitution failure)
`int`	(substitution failure)
`int (*const)()`	(substitution failure)

Example Program

#include <boost/callable_traits/clear_args.hpp>

namespace ct = boost::callable_traits;

int main() {

    using f = void(int, char);
    using cleared = ct::clear_args_t<f>;
    using expect = void();
    static_assert(std::is_same<cleared, expect>::value, "");
}

pop_front_args

Header

#include <boost/callable_traits/pop_front_args.hpp>

Definition

template<typename T, std::size_t Count = 1>
using pop_front_args_t = //see below

template<typename T, std::size_t Count = 1>
struct pop_front_args {
    using type = pop_front_args_t<T, Count>;
};

Constraints

T must be one of the following:
- function type
- function pointer type
- function reference type
- member function pointer type

Behavior

A substitution failure occurs if the constraints are violated.
The aliased type is identical to T, except that Count number of parameters are removed from the front of the parameter list.
If Count is greater than or equal to the number of parameters in T, then the aliased type will have an empty parameter list.

Compatibility Notes

Full support on GCC 4.7.4+, Clang 3.5+, Visual Studio 2015, and XCode 6.4+.

Input/Output Examples

`T`	`pop_front_args_t<T, 2>`
`int(char, short, int) const &&`	`int(int) const &&`
`int(*)(char, short, int)`	`int(*)(int)`
`int(&)(char, short, int)`	`int(&)(int)`
`int(foo::*)(char, short, int)`	`int(foo::*)(int)`

Example Program

#include <boost/callable_traits/pop_front_args.hpp>

namespace ct = boost::callable_traits;

static_assert(std::is_same<
    ct::pop_front_args_t<int(char, short, int)>,
    int(short, int)
>::value, "");

struct foo;

static_assert(std::is_same<
    ct::pop_front_args_t<int(foo::*)(char, short, int) const, 2>,
    int(foo::*)(int) const
>::value, "");

static_assert(std::is_same<
    ct::pop_front_args_t<int(*)(char, short, int), 3>,
    int(*)()
>::value, "");

static_assert(std::is_same<
    //overflow is handled
    ct::pop_front_args_t<int(&)(char, short, int), 27>,
    int(&)()
>::value, "");

int main() {}

push_front_args

Header

#include <boost/callable_traits/push_front_args.hpp>

Definition

template<typename T, typename... Args>
using push_front_args_t = //see below

template<typename T, typename... Args>
struct push_front_args {
    using type = push_front_args_t<T, Args...>;
};

Constraints

T must be one of the following:
- function type
- function pointer type
- function reference type
- member function pointer type

Behavior

A substitution failure occurs if the constraints are violated.
The aliased type is identical to T, except that Args... types have been added to the front of the parameter list.

Compatibility Notes

Full support on GCC 4.7.4+, Clang 3.5+, Visual Studio 2015, and XCode 6.4+.

Input/Output Examples

`T`	`push_front_args_t<T, float, double>`
`int(char)`	`int(float, double, char)`
`int(*)(char)`	`int(*)(float, double, char)`
`int(&)(char)`	`int(&)(float, double, char)`
`int(foo::*)(char) volatile`	`int(foo::*)(float, double, char) volatile`

Example Program

#include <boost/callable_traits/push_front_args.hpp>

namespace ct = boost::callable_traits;

int main() {

    using f = void(int, char);
    using test = ct::push_front_args_t<f, long, void*>;
    using expect = void(long, void*, int, char);
    static_assert(std::is_same<test, expect>::value, "");
}

expand_args

Header

#include <boost/callable_traits/expand_args.hpp>

Definition

template<typename T, template<class...> class Container>
using expand_args_t = //see below

template<typename T, template<class...> class Container>
struct expand_args {
    using type = expand_args_t<T, Container>;
};

Constraints

T must be one of the following:
- function
- function pointer
- function reference
- member function pointer
- member data pointer
- user-defined type with a non-overloaded operator()
- type of a non-generic lambda

Behavior

When the constraints are violated, a substitution failure occurs.
When T is a function, function pointer, or function reference, the aliased type is the Container template instantiated with the types from the parameter list of T.
When T is a function object, the aliased type is the Container template instantiated with the types from the parameter list of T's operator().
When T is a member function pointer, the aliased type is a Container template instantiation, where the first template type argument is a reference to the parent class of T, qualified according to the member qualifiers on T, such that this type is equivalent to boost::callable_traits::qualified_class_of_t<T>. The subsequent template type arguments are the parameter list of the member function.
When T is a member data pointer, the aliased type is the Container template instantiated with a const reference to the parent class of T.

Compatibility Notes

Full support on GCC 4.7.4+, Clang 3.5+, Visual Studio 2015, and XCode 6.4+.

Input/Output Examples

`T`	`expand_args_t<T, std::tuple>`
`void(float, char, int)`	`std::tuple<float, char, int>`
`void(*)(float, char, int)`	`std::tuple<float, char, int>`
`void(&)(float, char, int)`	`std::tuple<float, char, int>`
`void(float, char, int) const &&`	`std::tuple<float, char, int>`
`void(*)()`	`std::tuple<>`
`void(*)() transaction_safe`	`std::tuple<>`
`void(foo::*)(float, char, int)`	`std::tuple<foo&, float, char, int>`
`int(foo::*)(int) const`	`std::tuple<const foo&, float, char, int>`
`void(foo::*)() volatile &&`	`std::tuple<volatile foo &&>`
`int foo::*`	`std::tuple<const foo&>`
`int`	(substitution failure)
`int (*const)()`	(substitution failure)

Example Program

#include <boost/callable_traits/expand_args.hpp>

namespace ct = boost::callable_traits;

void f(int, char);

template<typename, typename> struct foo{};

int main() {

    using args = ct::expand_args_t<decltype(f), foo>;
    static_assert(std::is_same<args, foo<int, char>>::value, "");
}

expand_args_left

Header

#include <boost/callable_traits/expand_args_left.hpp>

Definition

template<typename T, template<class...> class Container, typename... RightArgs>
using expand_args_left_t = //see below

template<typename T, template<class...> class Container, typename... RightArgs>
struct expand_args_left {
    using type = expand_args_left_t<T, Container, RightArgs...>;
};

Constraints

T must be one of the following:
- function
- function pointer
- function reference
- member function pointer
- member data pointer
- user-defined type with a non-overloaded operator()
- type of a non-generic lambda

Behavior

When the constraints are violated, a substitution failure occurs.
expand_args_left is identical to expand_args, except that additional type arguments for Container may be supplied. the types determined by T are expanded first (on the left), followed by the supplied RightArgs....

Compatibility Notes

Full support on GCC 4.7.4+, Clang 3.5+, Visual Studio 2015, and XCode 6.4+.

Input/Output Examples

`T`	`expand_args_left_t<T, std::tuple, short, void*>`
`void(float, char, int)`	`std::tuple<float, char, int, short, void*>`
`void(*)(float, char, int)`	`std::tuple<float, char, int, short, void*>`
`void(&)(float, char, int)`	`std::tuple<float, char, int, short, void*>`
`void(float, char, int) const &&`	`std::tuple<float, char, int, short, void*>`
`void(*)()`	`std::tuple<short, void*>`
`void(*)() transaction_safe`	`std::tuple<short, void*>`
`void(foo::*)(float, char, int)`	`std::tuple<foo&, float, char, int, short, void*>`
`int(foo::*)(int) const`	`std::tuple<const foo&, float, char, int, short, void*>`
`void(foo::*)() volatile &&`	`std::tuple<volatile foo &&, short, void*>`
`int foo::*`	`std::tuple<const foo&, short, void*>`
`int`	(substitution failure)
`int (*const)()`	(substitution failure)

Example Program

#include <boost/callable_traits/expand_args_left.hpp>

namespace ct = boost::callable_traits;

void f(int, char);

template<typename...> struct foo{};

int main() {

    using args = ct::expand_args_left_t<decltype(f), foo, void*>;
    static_assert(std::is_same<args, foo<int, char, void*>>::value, "");
}

expand_args_right

Header

#include <boost/callable_traits/expand_args_right.hpp>

Definition

template<typename T, template<class...> class Container, typename... LeftArgs>
using expand_args_right_t = //see below

template<typename T, template<class...> class Container, typename... LeftArgs>
struct expand_args_right {
    using type = expand_args_right_t<T, Container, LeftArgs...>;
};

Constraints

T must be one of the following:
- function
- function pointer
- function reference
- member function pointer
- member data pointer
- user-defined type with a non-overloaded operator()
- type of a non-generic lambda

Behavior

When the constraints are violated, a substitution failure occurs.
expand_args_right is identical to expand_args, except that additional type arguments for Container may be supplied, which are expanded into the Container template first. The types determined by T are expanded last (to the right of the supplied LeftArgs...).

Compatibility Notes

Full support on GCC 4.7.4+, Clang 3.5+, Visual Studio 2015, and XCode 6.4+.

Input/Output Examples

`T`	`expand_args_right_t<T, std::tuple, short, void*>`
`void(float, char, int)`	`std::tuple<short, void*, float, char, int>`
`void(*)(float, char, int)`	`std::tuple<short, void*, float, char, int>`
`void(&)(float, char, int)`	`std::tuple<short, void*, float, char, int>`
`void(float, char, int) const &&`	`std::tuple<short, void*, float, char, int>`
`void(*)()`	`std::tuple<short, void*>`
`void(*)() transaction_safe`	`std::tuple<short, void*>`
`void(foo::*)(float, char, int)`	`std::tuple<short, void*, foo&, float, char, int>`
`int(foo::*)(int) const`	`std::tuple<short, void*, const foo&, float, char, int>`
`void(foo::*)() volatile &&`	`std::tuple<short, void*, volatile foo &&>`
`int foo::*`	`std::tuple<short, void*, const foo&>`
`int`	(substitution failure)
`int (*const)()`	(substitution failure)

Example Program

#include <boost/callable_traits/expand_args_right.hpp>

namespace ct = boost::callable_traits;

void f(int, char);

template<typename...> struct foo{};

int main() {

    using args = ct::expand_args_right_t<decltype(f), foo, void*>;
    static_assert(std::is_same<args, foo<void*, int, char>>::value, "");
}

add_varargs

Header

#include <boost/callable_traits/add_varargs.hpp>

Definition

template<typename T>
using add_varargs_t = //see below

template<typename T>
struct add_varargs {
    using type = add_varargs_t<T>;
};

Constraints

T must be one of the following:
- function type
- function pointer type
- function reference type
- member function pointer type

Behavior

A substitution failure occurs if the constraints are violated.
Adds C-style variadics (...) to the signature of T, if not already present.

Compatibility Notes

Full support on GCC 4.7.4+, Clang 3.5+, Visual Studio 2015, and XCode 6.4+.

Input/Output Examples

`T`	`add_varargs_t<T>`
`int()`	`int(...)`
`int(int)`	`int(int, ...)`
`int (&)()`	`int(&)(...)`
`int (*)()`	`int(*)(...)`
`int (*)(...)`	`int(*)(...)`
`int(foo::*)()`	`int(foo::*)(...)`
`int(foo::*)() &`	`int(foo::*)(...) &`
`int(foo::*)() &&`	`int(foo::*)(...) &&`
`int(foo::*)() const`	`int(foo::*)(...) const`
`int(foo::*)() transaction_safe`	`int(foo::*)(...) transaction_safe`
`int`	(substitution failure)
`int foo::*`	(substitution failure)
`int (*&)()`	(substitution failure)

Example Program

#include <type_traits>
#include <boost/callable_traits/add_varargs.hpp>

namespace ct = boost::callable_traits;

struct foo {};

int main() {

    {
        using f = void(int);
        using expect = void(int, ...);
        using test = ct::add_varargs_t<f>;
        static_assert(std::is_same<test, expect>::value, "");
    } {
        using fp = void(*)();
        using expect = void(*)(...);
        using test = ct::add_varargs_t<fp>;
        static_assert(std::is_same<test, expect>::value, "");
    } {
        using fr = void(&)(const char*);
        using expect = void(&)(const char*, ...);
        using test = ct::add_varargs_t<fr>;
        static_assert(std::is_same<test, expect>::value, "");
    } {
        using pmf = void(foo::*)() const;
        using expect = void(foo::*)(...) const;
        using test = ct::add_varargs_t<pmf>;
        static_assert(std::is_same<test, expect>::value, "");

        // add_varargs_t doesn't change anything when
        // the type already has varargs.
        using twice = ct::add_varargs_t<test>;
        static_assert(std::is_same<test, twice>::value, "");
    }
}

remove_varargs

Header

#include <boost/callable_traits/remove_varargs.hpp>

Definition

template<typename T>
using remove_varargs_t = //see below

template<typename T>
struct remove_varargs {
    using type = remove_varargs_t<T>;
};

Constraints

T must be one of the following:
- function type
- function pointer type
- function reference type
- member function pointer type

Behavior

A substitution failure occurs if the constraints are violated.
Removes C-style variadics (...) from the signature of T, if present.

Compatibility Notes

Full support on GCC 4.7.4+, Clang 3.5+, Visual Studio 2015, and XCode 6.4+.

Input/Output Examples

`T`	`remove_varargs_t<T>`
`int(...)`	`int()`
`int(int, ...)`	`int(int)`
`int (&)(...)`	`int(&)()`
`int (*)()`	`int(*)()`
`int(foo::*)(...)`	`int(foo::*)()`
`int(foo::*)(...) &`	`int(foo::*)() &`
`int(foo::*)(...) &&`	`int(foo::*)() &&`
`int(foo::*)(...) const`	`int(foo::*)() const`
`int(foo::*)(...) transaction_safe`	`int(foo::*)() transaction_safe`
`int`	(substitution failure)
`int foo::*`	(substitution failure)
`int (* const)()`	(substitution failure)

Example Program

#include <type_traits>
#include <boost/callable_traits/remove_varargs.hpp>

namespace ct = boost::callable_traits;

struct foo {};

int main() {

    {
        using f = void(int, ...);
        using expect = void(int);
        using test = ct::remove_varargs_t<f>;
        static_assert(std::is_same<test, expect>::value, "");
    } {
        using fp = void(*)(...);
        using expect = void(*)();
        using test = ct::remove_varargs_t<fp>;
        static_assert(std::is_same<test, expect>::value, "");
    } {
        using fr = void(&)(const char*, ...);
        using expect = void(&)(const char*);
        using test = ct::remove_varargs_t<fr>;
        static_assert(std::is_same<test, expect>::value, "");
    } {
        using pmf = void(foo::*)(...) const;
        using expect = void(foo::*)() const;
        using test = ct::remove_varargs_t<pmf>;
        static_assert(std::is_same<test, expect>::value, "");
    }
}

has_varargs

Header

#include <boost/callable_traits/has_varargs.hpp>

Definition

template<typename T>
struct has_varargs; //see below


#ifdef BOOST_CLBL_TRTS_DISABLE_VARIABLE_TEMPLATES

template<typename T>
struct has_varargs_v {
    static_assert(std::is_same<T, detail::dummy>::value,
        "Variable templates not supported on this compiler.");
};

#else

template<typename T>
constexpr bool has_varargs_v = //see below
#endif

Constraints

none

Behavior

std::false_type is inherited by has_varargs<T> and is aliased by typename has_varargs<T>::type, except when one of the following criteria is met, in which case std::true_type would be similarly inherited and aliased:
- T is a function, function pointer, or function reference where the function's parameter list includes C-style variadics.
- T is a pointer to a member function with C-style variadics in the parameter list.
- T is a function object with a non-overloaded operator(), which has C-style variadics in the parameter list of its operator().
On compilers that support variable templates, has_varargs_v<T> is equivalent to has_varargs<T>::value.

Compatibility Notes

Full support on GCC 4.7.4+, Clang 3.5+, Visual Studio 2015, and XCode 6.4+.

Input/Output Examples

`T`	`has_varargs_v<T>`
`void(...)`	`true`
`void(int, ...) const`	`true`
`void(*)(...)`	`true`
`void(&)(...)`	`true`
`void(foo::*)(...) const`	`true`
`void(*)()`	`false`
`void(*&)()`	`false`
`int`	`false`
`const int`	`false`
`int foo::*`	`false`

Example Program

#include <type_traits>
#include <boost/callable_traits/has_varargs.hpp>

namespace ct = boost::callable_traits;

static_assert(ct::has_varargs<int(...)>::value, "");
static_assert(!ct::has_varargs<int()>::value, "");

int main() {}