singleton.hpp

См. документацию.

#pragma once
#include "multi_index.hpp"
#include "system.hpp"
 
namespace  eosio {
 
   template<name::raw SingletonName, typename T>
   class singleton
   {
      constexpr static uint64_t pk_value = static_cast<uint64_t>(SingletonName);
 
      struct row {
         T value;
 
         uint64_t primary_key() const { return pk_value; }
 
         EOSLIB_SERIALIZE( row, (value) )
      };
 
      typedef eosio::multi_index<SingletonName, row> table;
 
      public:
 
         singleton( name code, uint64_t scope ) : _t( code, scope ) {}
 
         bool exists() {
            return _t.find( pk_value ) != _t.end();
         }
 
         T get() {
            auto itr = _t.find( pk_value );
            eosio::check( itr != _t.end(), "singleton does not exist" );
            return itr->value;
         }
 
         T get_or_default( const T& def = T() ) {
            auto itr = _t.find( pk_value );
            return itr != _t.end() ? itr->value : def;
         }
 
         T get_or_create( name bill_to_account, const T& def = T() ) {
            auto itr = _t.find( pk_value );
            return itr != _t.end() ? itr->value
               : _t.emplace(bill_to_account, [&](row& r) { r.value = def; })->value;
         }
 
         void set( const T& value, name bill_to_account ) {
            auto itr = _t.find( pk_value );
            if( itr != _t.end() ) {
               _t.modify(itr, bill_to_account, [&](row& r) { r.value = value; });
            } else {
               _t.emplace(bill_to_account, [&](row& r) { r.value = value; });
            }
         }
 
         void remove( ) {
            auto itr = _t.find( pk_value );
            if( itr != _t.end() ) {
               _t.erase(itr);
            }
         }
 
      private:
         table _t;
   };
}