daw_json_default_constuctor_fwd.h

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// Copyright (c) Darrell Wright
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE or copy at http://www.boost.org/LICENSE_1_0.txt)
//
// Official repository: https://github.com/beached/daw_json_link
//
 
#pragma once
 
#include "daw/json/impl/version.h"
 
#include "daw/json/concepts/daw_nullable_value.h"
 
#include <daw/cpp_17.h>
#include <daw/daw_attributes.h>
#include <daw/daw_cpp20_concept.h>
#include <daw/daw_enable_requires.h>
#include <daw/daw_move.h>
#include <daw/daw_traits.h>
 
#include <memory>
#include <type_traits>
 
/***
 * Customization point traits
 *
 */
namespace daw::json {
  inline namespace DAW_JSON_VER {
    namespace json_details {
      template<typename T, typename... Args>
      DAW_CPP20_CONCEPT should_list_construct_v =
        not std::is_constructible_v<T, Args...> and
        daw::traits::is_list_constructible_v<T, Args...>;
    }
    template<typename T, typename = void>
    struct default_constructor {
      using i_am_the_default_default_constructor_type = void;
 
      template<
        typename... Args DAW_ENABLEIF( std::is_constructible_v<T, Args...> )>
      DAW_REQUIRES( std::is_constructible_v<T, Args...> )
      [[nodiscard]] DAW_ATTRIB_INLINE DAW_JSON_CPP23_STATIC_CALL_OP constexpr T
      operator( )( Args &&...args ) DAW_JSON_CPP23_STATIC_CALL_OP_CONST {
 
        return T( DAW_FWD( args )... );
      }
 
      template<typename... Args DAW_ENABLEIF(
        json_details::should_list_construct_v<T, Args...> )>
      DAW_REQUIRES( json_details::should_list_construct_v<T, Args...> )
      [[nodiscard]] DAW_ATTRIB_INLINE DAW_JSON_CPP23_STATIC_CALL_OP constexpr T
      operator( )( Args &&...args ) DAW_JSON_CPP23_STATIC_CALL_OP_CONST
        noexcept( std::is_nothrow_constructible_v<T, Args...> ) {
        return T{ DAW_FWD( args )... };
      }
    };
 
    template<typename T, typename = void>
    struct nullable_constructor : default_constructor<T> {
      using default_constructor<T>::operator( );
    };
 
    template<typename T>
    DAW_REQUIRES( concepts::nullable_impl::is_list_constructible_v<T> and
                  not concepts::is_nullable_value_v<T> )
    struct nullable_constructor<T DAW_ENABLEIF_S(
      concepts::nullable_impl::is_list_constructible_v<T> and
      not concepts::is_nullable_value_v<T> )> : default_constructor<T> {
      using default_constructor<T>::operator( );
      [[nodiscard]] DAW_ATTRIB_INLINE DAW_JSON_CPP23_STATIC_CALL_OP constexpr T
      operator( )( ) DAW_JSON_CPP23_STATIC_CALL_OP_CONST {
        return T{ };
      }
    };
  } // namespace DAW_JSON_VER
} // namespace daw::json