daw_nullable_value_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/daw_callable.h"
 
#include <daw/daw_cpp_feature_check.h>
#include <daw/daw_enable_requires.h>
#include <daw/daw_is_detected.h>
 
#include <cstddef>
#include <type_traits>
 
namespace daw::json {
  inline namespace DAW_JSON_VER {
    namespace concepts {
      namespace nullable_impl {
#if not defined( DAW_HAS_GCC ) or DAW_HAS_GCC_VER_GTE( 12, 0 )
        template<typename T, typename... Args>
        using is_list_constructible_test =
          decltype( T{ std::declval<Args>( )... } );
#else
        template<typename T, typename... Args>
        using is_list_constructible_test =
          decltype( std::declval<void ( * )( T )>( )(
            { std::declval<Args>( )... } ) );
#endif
        template<typename T, typename... Args>
        DAW_CPP20_CONCEPT is_list_constructible_v =
          daw::is_detected_v<is_list_constructible_test, T, Args...>;
 
        template<typename T, typename... Args>
        DAW_CPP20_CONCEPT is_nullable_value_type_constructible_v =
          std::is_constructible_v<T, Args...> or
          is_list_constructible_v<T, Args...>;
      } // namespace nullable_impl
 
      struct construct_nullable_with_value_t {
        explicit construct_nullable_with_value_t( ) = default;
      };
      inline constexpr auto construct_nullable_with_value =
        construct_nullable_with_value_t{ };
 
      struct construct_nullable_with_pointer_t {
        explicit construct_nullable_with_pointer_t( ) = default;
      };
      inline constexpr auto construct_nullable_with_pointer =
        construct_nullable_with_pointer_t{ };
 
      struct construct_nullable_with_empty_t {
        explicit construct_nullable_with_empty_t( ) = default;
      };
      inline constexpr auto construct_nullable_with_empty =
        construct_nullable_with_empty_t{ };
 
      DAW_JSON_CPP23_STATIC_CALL_OP_DISABLE_WARNING
      template<typename T, typename...>
      struct nullable_value_traits {
 
        using value_type = T;
 
        using nullable_type = T;
 
        static constexpr bool is_nullable = false;
 
        constexpr value_type read( T const &v ) const noexcept {
          return v;
        }
        DAW_JSON_CPP23_STATIC_CALL_OP constexpr nullable_type operator( )(
          construct_nullable_with_value_t ) DAW_JSON_CPP23_STATIC_CALL_OP_CONST
          noexcept( std::is_nothrow_default_constructible_v<value_type> ) {
          return value_type{ };
        }
        template<typename... Args DAW_ENABLEIF(
          nullable_impl::is_nullable_value_type_constructible_v<nullable_type,
                                                                Args...> )>
        DAW_REQUIRES( nullable_impl::is_nullable_value_type_constructible_v<
                      nullable_type, Args...> )
        DAW_JSON_CPP23_STATIC_CALL_OP constexpr nullable_type
        operator( )( construct_nullable_with_empty_t,
                     Args &&...args ) DAW_JSON_CPP23_STATIC_CALL_OP_CONST
          noexcept( std::is_nothrow_constructible_v<nullable_type, Args...> ) {
          if constexpr( std::is_constructible_v<nullable_type, Args...> ) {
            return T( DAW_FWD( args )... );
          } else {
            return T{ DAW_FWD( args )... };
          }
        }
        static constexpr bool has_value( T const & ) noexcept {
          return true;
        }
      };
      DAW_JSON_CPP23_STATIC_CALL_OP_ENABLE_WARNING
 
      template<typename T>
      using nullable_value_type_t =
        typename nullable_value_traits<T>::value_type;
 
      template<typename T>
      DAW_CPP20_CONCEPT is_nullable_value_v =
        nullable_value_traits<T>::is_nullable;
 
      template<typename T>
      constexpr bool nullable_value_has_value( T const &opt ) {
        return nullable_value_traits<T>::has_value( opt );
      }
 
      template<typename T>
      constexpr auto const &nullable_value_read( T const &opt ) {
        return nullable_value_traits<T>::read( opt );
      }
 
      template<typename T, typename... Args>
      DAW_CPP20_CONCEPT is_nullable_value_constructible_v =
        is_nullable_value_v<T> and
        daw::is_callable_v<nullable_value_traits<T>,
                           construct_nullable_with_value_t, Args...>;
 
      template<typename T, typename... Args>
      DAW_CPP20_CONCEPT is_nullable_pointer_constructible_v =
        is_nullable_value_v<T> and
        daw::is_callable_v<nullable_value_traits<T>,
                           construct_nullable_with_pointer_t, Args...>;
 
      template<typename T, typename... Args>
      DAW_CPP20_CONCEPT is_nullable_value_nothrow_constructible_v =
        is_nullable_value_constructible_v<T, Args...> and
        daw::is_nothrow_callable_v<nullable_value_traits<T>,
                                   construct_nullable_with_value_t, Args...>;
 
      template<typename T>
      DAW_CPP20_CONCEPT is_nullable_empty_constructible_v =
        is_nullable_value_v<T> and
        daw::is_callable_v<nullable_value_traits<T>,
                           construct_nullable_with_empty_t>;
 
      template<typename T>
      DAW_CPP20_CONCEPT is_nullable_empty_nothrow_constructible_v =
        is_nullable_empty_constructible_v<T> and
        daw::is_nothrow_callable_v<nullable_value_traits<T>,
                                   construct_nullable_with_empty_t>;
 
    } // namespace concepts
  } // namespace DAW_JSON_VER
} // namespace daw::json