daw_json_link_describe.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_describe
//
 
#pragma once
 
#include <daw/json/daw_json_link.h>
 
#include <daw/daw_enable_requires.h>
#include <daw/daw_traits.h>
 
#if not __has_include( <boost/describe.hpp> ) and __has_include( <boost/mp11.hpp> )
#error \
  "In order to use daw_json_link_describe.h Boost.Describe and Boost.Mp11 must be available"
#endif
 
#include <boost/describe.hpp>
#include <boost/mp11.hpp>
#include <cstddef>
#include <tuple>
#include <utility>
 
namespace daw::json {
  template<typename, typename = void>
  inline constexpr bool use_boost_describe_v = true;
 
  namespace describe_impl {
    template<typename, typename>
    struct describe_member_impl;
 
    template<typename T, std::size_t... Is>
    struct describe_member_impl<T, std::index_sequence<Is...>> {
      static constexpr char const name[sizeof...( Is )]{ T::name[Is]... };
      using type =
        json_link<name,
                  daw::traits::member_type_of_t<DAW_TYPEOF( T::pointer )>>;
    };
 
    template<typename T>
    using describe_member =
      describe_member_impl<T, std::make_index_sequence<
                                std::char_traits<char>::length( T::name ) + 1>>;
 
    template<typename>
    struct member_list;
 
    template<template<typename...> typename List, typename... Ts>
    struct member_list<List<Ts...>> {
      template<typename U>
      using desc_t = typename describe_member<U>::type;
 
      using type = json_member_list<desc_t<Ts>...>;
    };
  } // namespace describe_impl
 
  template<typename T>
  DAW_REQUIRES( boost::describe::has_describe_members<T>::value
                  and use_boost_describe_v<T> )
  struct json_data_contract<T> {
  private:
    using pub_desc_t =
      boost::describe::describe_members<T, boost::describe::mod_public>;
    using pri_desc_t =
      boost::describe::describe_members<T, boost::describe::mod_private>;
    using pro_desc_t =
      boost::describe::describe_members<T, boost::describe::mod_protected>;
    static_assert( boost::mp11::mp_empty<pri_desc_t>::value,
                   "Classes with private member variables are not supported. "
                   "Must use a manual mapping." );
    static_assert( boost::mp11::mp_empty<pro_desc_t>::value,
                   "Classes with protected member variables are not supported. "
                   "Must use a manual mapping." );
 
    template<typename U>
    using desc_t = typename describe_impl::describe_member<U>::type;
 
    template<template<typename...> typename List, typename... Ts>
    static constexpr auto to_json_data_impl( T const &value,
                                             List<Ts...> const & ) noexcept {
      return std::forward_as_tuple( value.*Ts::pointer... );
    }
 
  public:
    using type = typename describe_impl::member_list<pub_desc_t>::type;
 
    static constexpr auto to_json_data( T const &value ) noexcept {
      return to_json_data_impl( value, pub_desc_t{ } );
    }
  };
} // namespace daw::json