daw_json_container_appender.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.h
//
 
#pragma once
 
#include "version.h"
 
#include <daw/cpp_17.h>
#include <daw/daw_attributes.h>
#include <daw/daw_move.h>
 
#include <cstddef>
#include <iterator>
#include <memory>
#include <type_traits>
 
namespace daw::json {
  inline namespace DAW_JSON_VER {
    namespace json_details {
      DAW_MAKE_REQ_TRAIT2(
        has_push_back_v, std::declval<T &>( ).push_back( std::declval<U>( ) ) );
 
      template<typename, typename, typename = void>
      inline constexpr bool has_insert_end_v = false;
 
      template<typename Container, typename Value>
      inline constexpr bool has_insert_end_v<
        Container, Value,
        std::void_t<decltype( std::declval<Container &>( ).insert(
          std::end( std::declval<Container &>( ) ),
          std::declval<Value>( ) ) )>> = true;
    } // namespace json_details
    /***
     * @brief A generic output iterator that can push_back or insert depending
     * on what the type supports. This is like std::back_inserter
     * @tparam Container Container object to append to
     */
    template<typename Container>
    struct basic_appender {
      using value_type = typename Container::value_type;
      using reference = value_type;
      using pointer = value_type const *;
      using difference_type = std::ptrdiff_t;
      using iterator_category = std::output_iterator_tag;
 
    private:
      Container *m_container;
 
    public:
      explicit inline constexpr basic_appender( Container &container )
        : m_container( &container ) {}
 
      template<typename Value>
      DAW_ATTRIB_FLATINLINE inline constexpr void operator( )( Value &&value ) {
        if constexpr( json_details::has_push_back_v<
                        Container, daw::remove_cvref_t<Value>> ) {
          m_container->push_back( DAW_FWD( value ) );
        } else if constexpr( json_details::has_insert_end_v<
                               Container, daw::remove_cvref_t<Value>> ) {
          m_container->insert( std::end( *m_container ), DAW_FWD( value ) );
        } else {
          static_assert(
            json_details::has_push_back_v<Container,
                                          daw::remove_cvref_t<Value>> or
              json_details::has_insert_end_v<Container,
                                             daw::remove_cvref_t<Value>>,
            "basic_appender requires a Container that either has push_back "
            "or "
            "insert with the end iterator as first argument" );
        }
      }
 
      template<typename Value DAW_JSON_ENABLEIF(
        not std::is_same_v<basic_appender, daw::remove_cvref_t<Value>> )>
      DAW_JSON_REQUIRES(
        not std::is_same_v<basic_appender, daw::remove_cvref_t<Value>> )
      DAW_ATTRIB_INLINE constexpr basic_appender &
      operator=( Value &&v ) {
        operator( )( DAW_FWD( v ) );
        return *this;
      }
 
      DAW_ATTRIB_INLINE constexpr basic_appender &operator++( ) {
        return *this;
      }
 
      DAW_ATTRIB_INLINE constexpr basic_appender operator++( int ) & {
        return *this;
      }
 
      DAW_ATTRIB_INLINE constexpr basic_appender &operator*( ) {
        return *this;
      }
    };
  } // namespace DAW_JSON_VER
} // namespace daw::json