json.hpp

/*
    __ _____ _____ _____
 __|  |   __|     |   | |  JSON for Modern C++
|  |  |__   |  |  | | | |  version 2.0.0
|_____|_____|_____|_|___|  https://github.com/nlohmann/json

Licensed under the MIT License <http://opensource.org/licenses/MIT>.
Copyright (c) 2013-2016 Niels Lohmann <http://nlohmann.me>.

Permission is hereby  granted, free of charge, to any  person obtaining a copy
of this software and associated  documentation files (the "Software"), to deal
in the Software  without restriction, including without  limitation the rights
to  use, copy,  modify, merge,  publish, distribute,  sublicense, and/or  sell
copies  of  the Software,  and  to  permit persons  to  whom  the Software  is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE  IS PROVIDED "AS  IS", WITHOUT WARRANTY  OF ANY KIND,  EXPRESS OR
IMPLIED,  INCLUDING BUT  NOT  LIMITED TO  THE  WARRANTIES OF  MERCHANTABILITY,
FITNESS FOR  A PARTICULAR PURPOSE AND  NONINFRINGEMENT. IN NO EVENT  SHALL THE
AUTHORS  OR COPYRIGHT  HOLDERS  BE  LIABLE FOR  ANY  CLAIM,  DAMAGES OR  OTHER
LIABILITY, WHETHER IN AN ACTION OF  CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE  OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/

#ifndef NLOHMANN_JSON_HPP
#define NLOHMANN_JSON_HPP

#include <algorithm>
#include <array>
#include <cassert>
#include <cerrno>
#include <ciso646>
#include <cmath>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <functional>
#include <initializer_list>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <limits>
#include <map>
#include <memory>
#include <sstream>
#include <stdexcept>
#include <string>
#include <type_traits>
#include <utility>
#include <vector>

// disable float-equal warnings on GCC/clang
#if defined(__clang__) || defined(__GNUC__) || defined(__GNUG__)
    #pragma GCC diagnostic push
    #pragma GCC diagnostic ignored "-Wfloat-equal"
#endif

namespace nlohmann
{


namespace
{
template<typename T>
struct has_mapped_type
{
  private:
    template<typename C> static char test(typename C::mapped_type*);
    template<typename C> static char (&test(...))[2];
  public:
    static constexpr bool value = sizeof(test<T>(0)) == 1;
};

}

template <
    template<typename U, typename V, typename... Args> class ObjectType = std::map,
    template<typename U, typename... Args> class ArrayType = std::vector,
    class StringType = std::string,
    class BooleanType = bool,
    class NumberIntegerType = std::int64_t,
    class NumberUnsignedType = std::uint64_t,
    class NumberFloatType = double,
    template<typename U> class AllocatorType = std::allocator
    >
class basic_json
{
  private:
    using basic_json_t = basic_json<ObjectType,
          ArrayType,
          StringType,
          BooleanType,
          NumberIntegerType,
          NumberUnsignedType,
          NumberFloatType,
          AllocatorType>;

  public:

    // container types //


    using value_type = basic_json;

    using reference = value_type&;
    using const_reference = const value_type&;

    using difference_type = std::ptrdiff_t;
    using size_type = std::size_t;

    using allocator_type = AllocatorType<basic_json>;

    using pointer = typename std::allocator_traits<allocator_type>::pointer;
    using const_pointer = typename std::allocator_traits<allocator_type>::const_pointer;

    // forward declaration
    template<typename Base> class json_reverse_iterator;

    class iterator;
    class const_iterator;
    using reverse_iterator = json_reverse_iterator<typename basic_json::iterator>;
    using const_reverse_iterator = json_reverse_iterator<typename basic_json::const_iterator>;



    static allocator_type get_allocator()
    {
        return allocator_type();
    }


    // JSON value data types //


    using object_t = ObjectType<StringType,
          basic_json,
          std::less<StringType>,
          AllocatorType<std::pair<const StringType,
          basic_json>>>;

    using array_t = ArrayType<basic_json, AllocatorType<basic_json>>;

    using string_t = StringType;

    using boolean_t = BooleanType;

    using number_integer_t = NumberIntegerType;

    using number_unsigned_t = NumberUnsignedType;

    using number_float_t = NumberFloatType;



    // JSON type enumeration //

    enum class value_t : uint8_t
    {
        null,            
        object,          
        array,           
        string,          
        boolean,         
        number_integer,  
        number_unsigned, 
        number_float,    
        discarded        
    };


  private:
    template<typename T, typename... Args>
    static T* create(Args&& ... args)
    {
        AllocatorType<T> alloc;
        auto deleter = [&](T * object)
        {
            alloc.deallocate(object, 1);
        };
        std::unique_ptr<T, decltype(deleter)> object(alloc.allocate(1), deleter);
        alloc.construct(object.get(), std::forward<Args>(args)...);
        return object.release();
    }

    // JSON value storage //

    union json_value
    {
        object_t* object;
        array_t* array;
        string_t* string;
        boolean_t boolean;
        number_integer_t number_integer;
        number_unsigned_t number_unsigned;
        number_float_t number_float;

        json_value() = default;
        json_value(boolean_t v) noexcept : boolean(v) {}
        json_value(number_integer_t v) noexcept : number_integer(v) {}
        json_value(number_unsigned_t v) noexcept : number_unsigned(v) {}
        json_value(number_float_t v) noexcept : number_float(v) {}
        json_value(value_t t)
        {
            switch (t)
            {
                case value_t::object:
                {
                    object = create<object_t>();
                    break;
                }

                case value_t::array:
                {
                    array = create<array_t>();
                    break;
                }

                case value_t::string:
                {
                    string = create<string_t>("");
                    break;
                }

                case value_t::boolean:
                {
                    boolean = boolean_t(false);
                    break;
                }

                case value_t::number_integer:
                {
                    number_integer = number_integer_t(0);
                    break;
                }

                case value_t::number_unsigned:
                {
                    number_unsigned = number_unsigned_t(0);
                    break;
                }

                case value_t::number_float:
                {
                    number_float = number_float_t(0.0);
                    break;
                }

                default:
                {
                    break;
                }
            }
        }

        json_value(const string_t& value)
        {
            string = create<string_t>(value);
        }

        json_value(const object_t& value)
        {
            object = create<object_t>(value);
        }

        json_value(const array_t& value)
        {
            array = create<array_t>(value);
        }
    };


  public:
    // JSON parser callback //

    enum class parse_event_t : uint8_t
    {
        object_start,
        object_end,
        array_start,
        array_end,
        key,
        value
    };

    using parser_callback_t = std::function<bool(int depth, parse_event_t event, basic_json& parsed)>;


    // constructors //


    basic_json(const value_t value_type)
        : m_type(value_type), m_value(value_type)
    {}

    basic_json() = default;

    basic_json(std::nullptr_t) noexcept
        : basic_json(value_t::null)
    {}

    basic_json(const object_t& val)
        : m_type(value_t::object), m_value(val)
    {}

    template <class CompatibleObjectType, typename
              std::enable_if<
                  std::is_constructible<typename object_t::key_type, typename CompatibleObjectType::key_type>::value and
                  std::is_constructible<basic_json, typename CompatibleObjectType::mapped_type>::value, int>::type
              = 0>
    basic_json(const CompatibleObjectType& val)
        : m_type(value_t::object)
    {
        using std::begin;
        using std::end;
        m_value.object = create<object_t>(begin(val), end(val));
    }

    basic_json(const array_t& val)
        : m_type(value_t::array), m_value(val)
    {}

    template <class CompatibleArrayType, typename
              std::enable_if<
                  not std::is_same<CompatibleArrayType, typename basic_json_t::iterator>::value and
                  not std::is_same<CompatibleArrayType, typename basic_json_t::const_iterator>::value and
                  not std::is_same<CompatibleArrayType, typename basic_json_t::reverse_iterator>::value and
                  not std::is_same<CompatibleArrayType, typename basic_json_t::const_reverse_iterator>::value and
                  not std::is_same<CompatibleArrayType, typename array_t::iterator>::value and
                  not std::is_same<CompatibleArrayType, typename array_t::const_iterator>::value and
                  std::is_constructible<basic_json, typename CompatibleArrayType::value_type>::value, int>::type
              = 0>
    basic_json(const CompatibleArrayType& val)
        : m_type(value_t::array)
    {
        using std::begin;
        using std::end;
        m_value.array = create<array_t>(begin(val), end(val));
    }

    basic_json(const string_t& val)
        : m_type(value_t::string), m_value(val)
    {}

    basic_json(const typename string_t::value_type* val)
        : basic_json(string_t(val))
    {}

    template <class CompatibleStringType, typename
              std::enable_if<
                  std::is_constructible<string_t, CompatibleStringType>::value, int>::type
              = 0>
    basic_json(const CompatibleStringType& val)
        : basic_json(string_t(val))
    {}

    basic_json(boolean_t val) noexcept
        : m_type(value_t::boolean), m_value(val)
    {}

    template<typename T,
             typename std::enable_if<
                 not (std::is_same<T, int>::value)
                 and std::is_same<T, number_integer_t>::value
                 , int>::type
             = 0>
    basic_json(const number_integer_t val) noexcept
        : m_type(value_t::number_integer), m_value(val)
    {}

    basic_json(const int val) noexcept
        : m_type(value_t::number_integer),
          m_value(static_cast<number_integer_t>(val))
    {}

    template<typename CompatibleNumberIntegerType, typename
             std::enable_if<
                 std::is_constructible<number_integer_t, CompatibleNumberIntegerType>::value and
                 std::numeric_limits<CompatibleNumberIntegerType>::is_integer and
                 std::numeric_limits<CompatibleNumberIntegerType>::is_signed,
                 CompatibleNumberIntegerType>::type
             = 0>
    basic_json(const CompatibleNumberIntegerType val) noexcept
        : m_type(value_t::number_integer),
          m_value(static_cast<number_integer_t>(val))
    {}

    template<typename T,
             typename std::enable_if<
                 not (std::is_same<T, int>::value)
                 and std::is_same<T, number_unsigned_t>::value
                 , int>::type
             = 0>
    basic_json(const number_unsigned_t val) noexcept
        : m_type(value_t::number_unsigned), m_value(val)
    {}

    template < typename CompatibleNumberUnsignedType, typename
               std::enable_if <
                   std::is_constructible<number_unsigned_t, CompatibleNumberUnsignedType>::value and
                   std::numeric_limits<CompatibleNumberUnsignedType>::is_integer and
                   !std::numeric_limits<CompatibleNumberUnsignedType>::is_signed,
                   CompatibleNumberUnsignedType >::type
               = 0 >
    basic_json(const CompatibleNumberUnsignedType val) noexcept
        : m_type(value_t::number_unsigned),
          m_value(static_cast<number_unsigned_t>(val))
    {}

    basic_json(const number_float_t val) noexcept
        : m_type(value_t::number_float), m_value(val)
    {
        // replace infinity and NAN by null
        if (not std::isfinite(val))
        {
            m_type = value_t::null;
            m_value = json_value();
        }
    }

    template<typename CompatibleNumberFloatType, typename = typename
             std::enable_if<
                 std::is_constructible<number_float_t, CompatibleNumberFloatType>::value and
                 std::is_floating_point<CompatibleNumberFloatType>::value>::type
             >
    basic_json(const CompatibleNumberFloatType val) noexcept
        : basic_json(number_float_t(val))
    {}

    basic_json(std::initializer_list<basic_json> init,
               bool type_deduction = true,
               value_t manual_type = value_t::array)
    {
        // the initializer list could describe an object
        bool is_an_object = true;

        // check if each element is an array with two elements whose first
        // element is a string
        for (const auto& element : init)
        {
            if (not element.is_array() or element.size() != 2
                    or not element[0].is_string())
            {
                // we found an element that makes it impossible to use the
                // initializer list as object
                is_an_object = false;
                break;
            }
        }

        // adjust type if type deduction is not wanted
        if (not type_deduction)
        {
            // if array is wanted, do not create an object though possible
            if (manual_type == value_t::array)
            {
                is_an_object = false;
            }

            // if object is wanted but impossible, throw an exception
            if (manual_type == value_t::object and not is_an_object)
            {
                throw std::domain_error("cannot create object from initializer list");
            }
        }

        if (is_an_object)
        {
            // the initializer list is a list of pairs -> create object
            m_type = value_t::object;
            m_value = value_t::object;

            assert(m_value.object != nullptr);

            for (auto& element : init)
            {
                m_value.object->emplace(*(element[0].m_value.string), element[1]);
            }
        }
        else
        {
            // the initializer list describes an array -> create array
            m_type = value_t::array;
            m_value.array = create<array_t>(init);
        }
    }

    static basic_json array(std::initializer_list<basic_json> init =
                                std::initializer_list<basic_json>())
    {
        return basic_json(init, false, value_t::array);
    }

    static basic_json object(std::initializer_list<basic_json> init =
                                 std::initializer_list<basic_json>())
    {
        return basic_json(init, false, value_t::object);
    }

    basic_json(size_type cnt, const basic_json& val)
        : m_type(value_t::array)
    {
        m_value.array = create<array_t>(cnt, val);
    }

    template <class InputIT, typename
              std::enable_if<
                  std::is_same<InputIT, typename basic_json_t::iterator>::value or
                  std::is_same<InputIT, typename basic_json_t::const_iterator>::value
                  , int>::type
              = 0>
    basic_json(InputIT first, InputIT last) : m_type(first.m_object->m_type)
    {
        // make sure iterator fits the current value
        if (first.m_object != last.m_object)
        {
            throw std::domain_error("iterators are not compatible");
        }

        // check if iterator range is complete for primitive values
        switch (m_type)
        {
            case value_t::boolean:
            case value_t::number_float:
            case value_t::number_integer:
            case value_t::number_unsigned:
            case value_t::string:
            {
                if (not first.m_it.primitive_iterator.is_begin() or not last.m_it.primitive_iterator.is_end())
                {
                    throw std::out_of_range("iterators out of range");
                }
                break;
            }

            default:
            {
                break;
            }
        }

        switch (m_type)
        {
            case value_t::number_integer:
            {
                assert(first.m_object != nullptr);
                m_value.number_integer = first.m_object->m_value.number_integer;
                break;
            }

            case value_t::number_unsigned:
            {
                assert(first.m_object != nullptr);
                m_value.number_unsigned = first.m_object->m_value.number_unsigned;
                break;
            }

            case value_t::number_float:
            {
                assert(first.m_object != nullptr);
                m_value.number_float = first.m_object->m_value.number_float;
                break;
            }

            case value_t::boolean:
            {
                assert(first.m_object != nullptr);
                m_value.boolean = first.m_object->m_value.boolean;
                break;
            }

            case value_t::string:
            {
                assert(first.m_object != nullptr);
                m_value = *first.m_object->m_value.string;
                break;
            }

            case value_t::object:
            {
                m_value.object = create<object_t>(first.m_it.object_iterator, last.m_it.object_iterator);
                break;
            }

            case value_t::array:
            {
                m_value.array = create<array_t>(first.m_it.array_iterator, last.m_it.array_iterator);
                break;
            }

            default:
            {
                assert(first.m_object != nullptr);
                throw std::domain_error("cannot use construct with iterators from " + first.m_object->type_name());
            }
        }
    }

    explicit basic_json(std::istream& i, parser_callback_t cb = nullptr)
    {
        *this = parser(i, cb).parse();
    }

    // other constructors and destructor //

    basic_json(const basic_json& other)
        : m_type(other.m_type)
    {
        switch (m_type)
        {
            case value_t::object:
            {
                assert(other.m_value.object != nullptr);
                m_value = *other.m_value.object;
                break;
            }

            case value_t::array:
            {
                assert(other.m_value.array != nullptr);
                m_value = *other.m_value.array;
                break;
            }

            case value_t::string:
            {
                assert(other.m_value.string != nullptr);
                m_value = *other.m_value.string;
                break;
            }

            case value_t::boolean:
            {
                m_value = other.m_value.boolean;
                break;
            }

            case value_t::number_integer:
            {
                m_value = other.m_value.number_integer;
                break;
            }

            case value_t::number_unsigned:
            {
                m_value = other.m_value.number_unsigned;
                break;
            }

            case value_t::number_float:
            {
                m_value = other.m_value.number_float;
                break;
            }

            default:
            {
                break;
            }
        }
    }

    basic_json(basic_json&& other) noexcept
        : m_type(std::move(other.m_type)),
          m_value(std::move(other.m_value))
    {
        // invalidate payload
        other.m_type = value_t::null;
        other.m_value = {};
    }

    reference& operator=(basic_json other) noexcept (
        std::is_nothrow_move_constructible<value_t>::value and
        std::is_nothrow_move_assignable<value_t>::value and
        std::is_nothrow_move_constructible<json_value>::value and
        std::is_nothrow_move_assignable<json_value>::value
    )
    {
        using std::swap;
        swap(m_type, other.m_type);
        swap(m_value, other.m_value);
        return *this;
    }

    ~basic_json()
    {
        switch (m_type)
        {
            case value_t::object:
            {
                AllocatorType<object_t> alloc;
                alloc.destroy(m_value.object);
                alloc.deallocate(m_value.object, 1);
                break;
            }

            case value_t::array:
            {
                AllocatorType<array_t> alloc;
                alloc.destroy(m_value.array);
                alloc.deallocate(m_value.array, 1);
                break;
            }

            case value_t::string:
            {
                AllocatorType<string_t> alloc;
                alloc.destroy(m_value.string);
                alloc.deallocate(m_value.string, 1);
                break;
            }

            default:
            {
                // all other types need no specific destructor
                break;
            }
        }
    }


  public:
    // object inspection //


    string_t dump(const int indent = -1) const
    {
        std::stringstream ss;

        if (indent >= 0)
        {
            dump(ss, true, static_cast<unsigned int>(indent));
        }
        else
        {
            dump(ss, false, 0);
        }

        return ss.str();
    }

    constexpr value_t type() const noexcept
    {
        return m_type;
    }

    constexpr bool is_primitive() const noexcept
    {
        return is_null() or is_string() or is_boolean() or is_number();
    }

    constexpr bool is_structured() const noexcept
    {
        return is_array() or is_object();
    }

    constexpr bool is_null() const noexcept
    {
        return m_type == value_t::null;
    }

    constexpr bool is_boolean() const noexcept
    {
        return m_type == value_t::boolean;
    }

    constexpr bool is_number() const noexcept
    {
        return is_number_integer() or is_number_float();
    }

    constexpr bool is_number_integer() const noexcept
    {
        return m_type == value_t::number_integer or m_type == value_t::number_unsigned;
    }

    constexpr bool is_number_unsigned() const noexcept
    {
        return m_type == value_t::number_unsigned;
    }

    constexpr bool is_number_float() const noexcept
    {
        return m_type == value_t::number_float;
    }

    constexpr bool is_object() const noexcept
    {
        return m_type == value_t::object;
    }

    constexpr bool is_array() const noexcept
    {
        return m_type == value_t::array;
    }

    constexpr bool is_string() const noexcept
    {
        return m_type == value_t::string;
    }

    constexpr bool is_discarded() const noexcept
    {
        return m_type == value_t::discarded;
    }

    constexpr operator value_t() const noexcept
    {
        return m_type;
    }


  private:
    // value access //

    template <class T, typename
              std::enable_if<
                  std::is_convertible<typename object_t::key_type, typename T::key_type>::value and
                  std::is_convertible<basic_json_t, typename T::mapped_type>::value
                  , int>::type = 0>
    T get_impl(T*) const
    {
        if (is_object())
        {
            assert(m_value.object != nullptr);
            return T(m_value.object->begin(), m_value.object->end());
        }
        else
        {
            throw std::domain_error("type must be object, but is " + type_name());
        }
    }

    object_t get_impl(object_t*) const
    {
        if (is_object())
        {
            assert(m_value.object != nullptr);
            return *(m_value.object);
        }
        else
        {
            throw std::domain_error("type must be object, but is " + type_name());
        }
    }

    template <class T, typename
              std::enable_if<
                  std::is_convertible<basic_json_t, typename T::value_type>::value and
                  not std::is_same<basic_json_t, typename T::value_type>::value and
                  not std::is_arithmetic<T>::value and
                  not std::is_convertible<std::string, T>::value and
                  not has_mapped_type<T>::value
                  , int>::type = 0>
    T get_impl(T*) const
    {
        if (is_array())
        {
            T to_vector;
            assert(m_value.array != nullptr);
            std::transform(m_value.array->begin(), m_value.array->end(),
                           std::inserter(to_vector, to_vector.end()), [](basic_json i)
            {
                return i.get<typename T::value_type>();
            });
            return to_vector;
        }
        else
        {
            throw std::domain_error("type must be array, but is " + type_name());
        }
    }

    template <class T, typename
              std::enable_if<
                  std::is_convertible<basic_json_t, T>::value and
                  not std::is_same<basic_json_t, T>::value
                  , int>::type = 0>
    std::vector<T> get_impl(std::vector<T>*) const
    {
        if (is_array())
        {
            std::vector<T> to_vector;
            assert(m_value.array != nullptr);
            to_vector.reserve(m_value.array->size());
            std::transform(m_value.array->begin(), m_value.array->end(),
                           std::inserter(to_vector, to_vector.end()), [](basic_json i)
            {
                return i.get<T>();
            });
            return to_vector;
        }
        else
        {
            throw std::domain_error("type must be array, but is " + type_name());
        }
    }

    template <class T, typename
              std::enable_if<
                  std::is_same<basic_json, typename T::value_type>::value and
                  not has_mapped_type<T>::value
                  , int>::type = 0>
    T get_impl(T*) const
    {
        if (is_array())
        {
            assert(m_value.array != nullptr);
            return T(m_value.array->begin(), m_value.array->end());
        }
        else
        {
            throw std::domain_error("type must be array, but is " + type_name());
        }
    }

    array_t get_impl(array_t*) const
    {
        if (is_array())
        {
            assert(m_value.array != nullptr);
            return *(m_value.array);
        }
        else
        {
            throw std::domain_error("type must be array, but is " + type_name());
        }
    }

    template <typename T, typename
              std::enable_if<
                  std::is_convertible<string_t, T>::value
                  , int>::type = 0>
    T get_impl(T*) const
    {
        if (is_string())
        {
            assert(m_value.string != nullptr);
            return *m_value.string;
        }
        else
        {
            throw std::domain_error("type must be string, but is " + type_name());
        }
    }

    template<typename T, typename
             std::enable_if<
                 std::is_arithmetic<T>::value
                 , int>::type = 0>
    T get_impl(T*) const
    {
        switch (m_type)
        {
            case value_t::number_integer:
            {
                return static_cast<T>(m_value.number_integer);
            }

            case value_t::number_unsigned:
            {
                return static_cast<T>(m_value.number_unsigned);
            }

            case value_t::number_float:
            {
                return static_cast<T>(m_value.number_float);
            }

            default:
            {
                throw std::domain_error("type must be number, but is " + type_name());
            }
        }
    }

    constexpr boolean_t get_impl(boolean_t*) const
    {
        return is_boolean()
               ? m_value.boolean
               : throw std::domain_error("type must be boolean, but is " + type_name());
    }

    object_t* get_impl_ptr(object_t*) noexcept
    {
        return is_object() ? m_value.object : nullptr;
    }

    constexpr const object_t* get_impl_ptr(const object_t*) const noexcept
    {
        return is_object() ? m_value.object : nullptr;
    }

    array_t* get_impl_ptr(array_t*) noexcept
    {
        return is_array() ? m_value.array : nullptr;
    }

    constexpr const array_t* get_impl_ptr(const array_t*) const noexcept
    {
        return is_array() ? m_value.array : nullptr;
    }

    string_t* get_impl_ptr(string_t*) noexcept
    {
        return is_string() ? m_value.string : nullptr;
    }

    constexpr const string_t* get_impl_ptr(const string_t*) const noexcept
    {
        return is_string() ? m_value.string : nullptr;
    }

    boolean_t* get_impl_ptr(boolean_t*) noexcept
    {
        return is_boolean() ? &m_value.boolean : nullptr;
    }

    constexpr const boolean_t* get_impl_ptr(const boolean_t*) const noexcept
    {
        return is_boolean() ? &m_value.boolean : nullptr;
    }

    number_integer_t* get_impl_ptr(number_integer_t*) noexcept
    {
        return is_number_integer() ? &m_value.number_integer : nullptr;
    }

    constexpr const number_integer_t* get_impl_ptr(const number_integer_t*) const noexcept
    {
        return is_number_integer() ? &m_value.number_integer : nullptr;
    }

    number_unsigned_t* get_impl_ptr(number_unsigned_t*) noexcept
    {
        return is_number_unsigned() ? &m_value.number_unsigned : nullptr;
    }

    constexpr const number_unsigned_t* get_impl_ptr(const number_unsigned_t*) const noexcept
    {
        return is_number_unsigned() ? &m_value.number_unsigned : nullptr;
    }

    number_float_t* get_impl_ptr(number_float_t*) noexcept
    {
        return is_number_float() ? &m_value.number_float : nullptr;
    }

    constexpr const number_float_t* get_impl_ptr(const number_float_t*) const noexcept
    {
        return is_number_float() ? &m_value.number_float : nullptr;
    }

    template<typename ReferenceType, typename ThisType>
    static ReferenceType get_ref_impl(ThisType& obj)
    {
        // delegate the call to get_ptr<>()
        using PointerType = typename std::add_pointer<ReferenceType>::type;
        auto ptr = obj.template get_ptr<PointerType>();

        if (ptr != nullptr)
        {
            return *ptr;
        }
        else
        {
            throw std::domain_error("incompatible ReferenceType for get_ref, actual type is " +
                                    obj.type_name());
        }
    }

  public:


    template<typename ValueType, typename
             std::enable_if<
                 not std::is_pointer<ValueType>::value
                 , int>::type = 0>
    ValueType get() const
    {
        return get_impl(static_cast<ValueType*>(nullptr));
    }

    template<typename PointerType, typename
             std::enable_if<
                 std::is_pointer<PointerType>::value
                 , int>::type = 0>
    PointerType get() noexcept
    {
        // delegate the call to get_ptr
        return get_ptr<PointerType>();
    }

    template<typename PointerType, typename
             std::enable_if<
                 std::is_pointer<PointerType>::value
                 , int>::type = 0>
    constexpr const PointerType get() const noexcept
    {
        // delegate the call to get_ptr
        return get_ptr<PointerType>();
    }

    template<typename PointerType, typename
             std::enable_if<
                 std::is_pointer<PointerType>::value
                 , int>::type = 0>
    PointerType get_ptr() noexcept
    {
        // delegate the call to get_impl_ptr<>()
        return get_impl_ptr(static_cast<PointerType>(nullptr));
    }

    template<typename PointerType, typename
             std::enable_if<
                 std::is_pointer<PointerType>::value
                 and std::is_const<typename std::remove_pointer<PointerType>::type>::value
                 , int>::type = 0>
    constexpr const PointerType get_ptr() const noexcept
    {
        // delegate the call to get_impl_ptr<>() const
        return get_impl_ptr(static_cast<const PointerType>(nullptr));
    }

    template<typename ReferenceType, typename
             std::enable_if<
                 std::is_reference<ReferenceType>::value
                 , int>::type = 0>
    ReferenceType get_ref()
    {
        // delegate call to get_ref_impl
        return get_ref_impl<ReferenceType>(*this);
    }

    template<typename ReferenceType, typename
             std::enable_if<
                 std::is_reference<ReferenceType>::value
                 and std::is_const<typename std::remove_reference<ReferenceType>::type>::value
                 , int>::type = 0>
    ReferenceType get_ref() const
    {
        // delegate call to get_ref_impl
        return get_ref_impl<ReferenceType>(*this);
    }

    template < typename ValueType, typename
               std::enable_if <
                   not std::is_pointer<ValueType>::value
                   and not std::is_same<ValueType, typename string_t::value_type>::value
#ifndef _MSC_VER  // Fix for issue #167 operator<< abiguity under VS2015
                   and not std::is_same<ValueType, std::initializer_list<typename string_t::value_type>>::value
#endif
                   , int >::type = 0 >
    operator ValueType() const
    {
        // delegate the call to get<>() const
        return get<ValueType>();
    }



    // element access //


    reference at(size_type idx)
    {
        // at only works for arrays
        if (is_array())
        {
            try
            {
                assert(m_value.array != nullptr);
                return m_value.array->at(idx);
            }
            catch (std::out_of_range&)
            {
                // create better exception explanation
                throw std::out_of_range("array index " + std::to_string(idx) + " is out of range");
            }
        }
        else
        {
            throw std::domain_error("cannot use at() with " + type_name());
        }
    }

    const_reference at(size_type idx) const
    {
        // at only works for arrays
        if (is_array())
        {
            try
            {
                assert(m_value.array != nullptr);
                return m_value.array->at(idx);
            }
            catch (std::out_of_range&)
            {
                // create better exception explanation
                throw std::out_of_range("array index " + std::to_string(idx) + " is out of range");
            }
        }
        else
        {
            throw std::domain_error("cannot use at() with " + type_name());
        }
    }

    reference at(const typename object_t::key_type& key)
    {
        // at only works for objects
        if (is_object())
        {
            try
            {
                assert(m_value.object != nullptr);
                return m_value.object->at(key);
            }
            catch (std::out_of_range&)
            {
                // create better exception explanation
                throw std::out_of_range("key '" + key + "' not found");
            }
        }
        else
        {
            throw std::domain_error("cannot use at() with " + type_name());
        }
    }

    const_reference at(const typename object_t::key_type& key) const
    {
        // at only works for objects
        if (is_object())
        {
            try
            {
                assert(m_value.object != nullptr);
                return m_value.object->at(key);
            }
            catch (std::out_of_range&)
            {
                // create better exception explanation
                throw std::out_of_range("key '" + key + "' not found");
            }
        }
        else
        {
            throw std::domain_error("cannot use at() with " + type_name());
        }
    }

    reference operator[](size_type idx)
    {
        // implicitly convert null value to an empty array
        if (is_null())
        {
            m_type = value_t::array;
            m_value.array = create<array_t>();
        }

        // operator[] only works for arrays
        if (is_array())
        {
            // fill up array with null values until given idx is reached
            assert(m_value.array != nullptr);
            for (size_t i = m_value.array->size(); i <= idx; ++i)
            {
                m_value.array->push_back(basic_json());
            }

            return m_value.array->operator[](idx);
        }
        else
        {
            throw std::domain_error("cannot use operator[] with " + type_name());
        }
    }

    const_reference operator[](size_type idx) const
    {
        // const operator[] only works for arrays
        if (is_array())
        {
            assert(m_value.array != nullptr);
            return m_value.array->operator[](idx);
        }
        else
        {
            throw std::domain_error("cannot use operator[] with " + type_name());
        }
    }

    reference operator[](const typename object_t::key_type& key)
    {
        // implicitly convert null value to an empty object
        if (is_null())
        {
            m_type = value_t::object;
            m_value.object = create<object_t>();
        }

        // operator[] only works for objects
        if (is_object())
        {
            assert(m_value.object != nullptr);
            return m_value.object->operator[](key);
        }
        else
        {
            throw std::domain_error("cannot use operator[] with " + type_name());
        }
    }

    const_reference operator[](const typename object_t::key_type& key) const
    {
        // const operator[] only works for objects
        if (is_object())
        {
            assert(m_value.object != nullptr);
            assert(m_value.object->find(key) != m_value.object->end());
            return m_value.object->find(key)->second;
        }
        else
        {
            throw std::domain_error("cannot use operator[] with " + type_name());
        }
    }

    template<typename T, std::size_t n>
    reference operator[](T * (&key)[n])
    {
        return operator[](static_cast<const T>(key));
    }

    template<typename T, std::size_t n>
    const_reference operator[](T * (&key)[n]) const
    {
        return operator[](static_cast<const T>(key));
    }

    template<typename T>
    reference operator[](T* key)
    {
        // implicitly convert null to object
        if (is_null())
        {
            m_type = value_t::object;
            m_value = value_t::object;
        }

        // at only works for objects
        if (is_object())
        {
            assert(m_value.object != nullptr);
            return m_value.object->operator[](key);
        }
        else
        {
            throw std::domain_error("cannot use operator[] with " + type_name());
        }
    }

    template<typename T>
    const_reference operator[](T* key) const
    {
        // at only works for objects
        if (is_object())
        {
            assert(m_value.object != nullptr);
            assert(m_value.object->find(key) != m_value.object->end());
            return m_value.object->find(key)->second;
        }
        else
        {
            throw std::domain_error("cannot use operator[] with " + type_name());
        }
    }

    template <class ValueType, typename
              std::enable_if<
                  std::is_convertible<basic_json_t, ValueType>::value
                  , int>::type = 0>
    ValueType value(const typename object_t::key_type& key, ValueType default_value) const
    {
        // at only works for objects
        if (is_object())
        {
            // if key is found, return value and given default value otherwise
            const auto it = find(key);
            if (it != end())
            {
                return *it;
            }
            else
            {
                return default_value;
            }
        }
        else
        {
            throw std::domain_error("cannot use value() with " + type_name());
        }
    }

    string_t value(const typename object_t::key_type& key, const char* default_value) const
    {
        return value(key, string_t(default_value));
    }

    reference front()
    {
        return *begin();
    }

    const_reference front() const
    {
        return *cbegin();
    }

    reference back()
    {
        auto tmp = end();
        --tmp;
        return *tmp;
    }

    const_reference back() const
    {
        auto tmp = cend();
        --tmp;
        return *tmp;
    }

    template <class InteratorType, typename
              std::enable_if<
                  std::is_same<InteratorType, typename basic_json_t::iterator>::value or
                  std::is_same<InteratorType, typename basic_json_t::const_iterator>::value
                  , int>::type
              = 0>
    InteratorType erase(InteratorType pos)
    {
        // make sure iterator fits the current value
        if (this != pos.m_object)
        {
            throw std::domain_error("iterator does not fit current value");
        }

        InteratorType result = end();

        switch (m_type)
        {
            case value_t::boolean:
            case value_t::number_float:
            case value_t::number_integer:
            case value_t::number_unsigned:
            case value_t::string:
            {
                if (not pos.m_it.primitive_iterator.is_begin())
                {
                    throw std::out_of_range("iterator out of range");
                }

                if (is_string())
                {
                    delete m_value.string;
                    m_value.string = nullptr;
                }

                m_type = value_t::null;
                break;
            }

            case value_t::object:
            {
                assert(m_value.object != nullptr);
                result.m_it.object_iterator = m_value.object->erase(pos.m_it.object_iterator);
                break;
            }

            case value_t::array:
            {
                assert(m_value.array != nullptr);
                result.m_it.array_iterator = m_value.array->erase(pos.m_it.array_iterator);
                break;
            }

            default:
            {
                throw std::domain_error("cannot use erase() with " + type_name());
            }
        }

        return result;
    }

    template <class InteratorType, typename
              std::enable_if<
                  std::is_same<InteratorType, typename basic_json_t::iterator>::value or
                  std::is_same<InteratorType, typename basic_json_t::const_iterator>::value
                  , int>::type
              = 0>
    InteratorType erase(InteratorType first, InteratorType last)
    {
        // make sure iterator fits the current value
        if (this != first.m_object or this != last.m_object)
        {
            throw std::domain_error("iterators do not fit current value");
        }

        InteratorType result = end();

        switch (m_type)
        {
            case value_t::boolean:
            case value_t::number_float:
            case value_t::number_integer:
            case value_t::number_unsigned:
            case value_t::string:
            {
                if (not first.m_it.primitive_iterator.is_begin() or not last.m_it.primitive_iterator.is_end())
                {
                    throw std::out_of_range("iterators out of range");
                }

                if (is_string())
                {
                    delete m_value.string;
                    m_value.string = nullptr;
                }

                m_type = value_t::null;
                break;
            }

            case value_t::object:
            {
                assert(m_value.object != nullptr);
                result.m_it.object_iterator = m_value.object->erase(first.m_it.object_iterator,
                                              last.m_it.object_iterator);
                break;
            }

            case value_t::array:
            {
                assert(m_value.array != nullptr);
                result.m_it.array_iterator = m_value.array->erase(first.m_it.array_iterator,
                                             last.m_it.array_iterator);
                break;
            }

            default:
            {
                throw std::domain_error("cannot use erase() with " + type_name());
            }
        }

        return result;
    }

    size_type erase(const typename object_t::key_type& key)
    {
        // this erase only works for objects
        if (is_object())
        {
            assert(m_value.object != nullptr);
            return m_value.object->erase(key);
        }
        else
        {
            throw std::domain_error("cannot use erase() with " + type_name());
        }
    }

    void erase(const size_type idx)
    {
        // this erase only works for arrays
        if (is_array())
        {
            if (idx >= size())
            {
                throw std::out_of_range("index out of range");
            }

            assert(m_value.array != nullptr);
            m_value.array->erase(m_value.array->begin() + static_cast<difference_type>(idx));
        }
        else
        {
            throw std::domain_error("cannot use erase() with " + type_name());
        }
    }



    // lookup //


    iterator find(typename object_t::key_type key)
    {
        auto result = end();

        if (is_object())
        {
            assert(m_value.object != nullptr);
            result.m_it.object_iterator = m_value.object->find(key);
        }

        return result;
    }

    const_iterator find(typename object_t::key_type key) const
    {
        auto result = cend();

        if (is_object())
        {
            assert(m_value.object != nullptr);
            result.m_it.object_iterator = m_value.object->find(key);
        }

        return result;
    }

    size_type count(typename object_t::key_type key) const
    {
        // return 0 for all nonobject types
        assert(not is_object() or m_value.object != nullptr);
        return is_object() ? m_value.object->count(key) : 0;
    }



    // iterators //


    iterator begin() noexcept
    {
        iterator result(this);
        result.set_begin();
        return result;
    }

    const_iterator begin() const noexcept
    {
        return cbegin();
    }

    const_iterator cbegin() const noexcept
    {
        const_iterator result(this);
        result.set_begin();
        return result;
    }

    iterator end() noexcept
    {
        iterator result(this);
        result.set_end();
        return result;
    }

    const_iterator end() const noexcept
    {
        return cend();
    }

    const_iterator cend() const noexcept
    {
        const_iterator result(this);
        result.set_end();
        return result;
    }

    reverse_iterator rbegin() noexcept
    {
        return reverse_iterator(end());
    }

    const_reverse_iterator rbegin() const noexcept
    {
        return crbegin();
    }

    reverse_iterator rend() noexcept
    {
        return reverse_iterator(begin());
    }

    const_reverse_iterator rend() const noexcept
    {
        return crend();
    }

    const_reverse_iterator crbegin() const noexcept
    {
        return const_reverse_iterator(cend());
    }

    const_reverse_iterator crend() const noexcept
    {
        return const_reverse_iterator(cbegin());
    }

  private:
    // forward declaration
    template<typename IteratorType> class iteration_proxy;

  public:
    static iteration_proxy<iterator> iterator_wrapper(reference cont)
    {
        return iteration_proxy<iterator>(cont);
    }

    static iteration_proxy<const_iterator> iterator_wrapper(const_reference cont)
    {
        return iteration_proxy<const_iterator>(cont);
    }



    // capacity //


    bool empty() const noexcept
    {
        switch (m_type)
        {
            case value_t::null:
            {
                // null values are empty
                return true;
            }

            case value_t::array:
            {
                assert(m_value.array != nullptr);
                return m_value.array->empty();
            }

            case value_t::object:
            {
                assert(m_value.object != nullptr);
                return m_value.object->empty();
            }

            default:
            {
                // all other types are nonempty
                return false;
            }
        }
    }

    size_type size() const noexcept
    {
        switch (m_type)
        {
            case value_t::null:
            {
                // null values are empty
                return 0;
            }

            case value_t::array:
            {
                assert(m_value.array != nullptr);
                return m_value.array->size();
            }

            case value_t::object:
            {
                assert(m_value.object != nullptr);
                return m_value.object->size();
            }

            default:
            {
                // all other types have size 1
                return 1;
            }
        }
    }

    size_type max_size() const noexcept
    {
        switch (m_type)
        {
            case value_t::array:
            {
                assert(m_value.array != nullptr);
                return m_value.array->max_size();
            }

            case value_t::object:
            {
                assert(m_value.object != nullptr);
                return m_value.object->max_size();
            }

            default:
            {
                // all other types have max_size() == size()
                return size();
            }
        }
    }



    // modifiers //


    void clear() noexcept
    {
        switch (m_type)
        {
            case value_t::number_integer:
            {
                m_value.number_integer = 0;
                break;
            }

            case value_t::number_unsigned:
            {
                m_value.number_unsigned = 0;
                break;
            }

            case value_t::number_float:
            {
                m_value.number_float = 0.0;
                break;
            }

            case value_t::boolean:
            {
                m_value.boolean = false;
                break;
            }

            case value_t::string:
            {
                assert(m_value.string != nullptr);
                m_value.string->clear();
                break;
            }

            case value_t::array:
            {
                assert(m_value.array != nullptr);
                m_value.array->clear();
                break;
            }

            case value_t::object:
            {
                assert(m_value.object != nullptr);
                m_value.object->clear();
                break;
            }

            default:
            {
                break;
            }
        }
    }

    void push_back(basic_json&& val)
    {
        // push_back only works for null objects or arrays
        if (not(is_null() or is_array()))
        {
            throw std::domain_error("cannot use push_back() with " + type_name());
        }

        // transform null object into an array
        if (is_null())
        {
            m_type = value_t::array;
            m_value = value_t::array;
        }

        // add element to array (move semantics)
        assert(m_value.array != nullptr);
        m_value.array->push_back(std::move(val));
        // invalidate object
        val.m_type = value_t::null;
    }

    reference operator+=(basic_json&& val)
    {
        push_back(std::move(val));
        return *this;
    }

    void push_back(const basic_json& val)
    {
        // push_back only works for null objects or arrays
        if (not(is_null() or is_array()))
        {
            throw std::domain_error("cannot use push_back() with " + type_name());
        }

        // transform null object into an array
        if (is_null())
        {
            m_type = value_t::array;
            m_value = value_t::array;
        }

        // add element to array
        assert(m_value.array != nullptr);
        m_value.array->push_back(val);
    }

    reference operator+=(const basic_json& val)
    {
        push_back(val);
        return *this;
    }

    void push_back(const typename object_t::value_type& val)
    {
        // push_back only works for null objects or objects
        if (not(is_null() or is_object()))
        {
            throw std::domain_error("cannot use push_back() with " + type_name());
        }

        // transform null object into an object
        if (is_null())
        {
            m_type = value_t::object;
            m_value = value_t::object;
        }

        // add element to array
        assert(m_value.object != nullptr);
        m_value.object->insert(val);
    }

    reference operator+=(const typename object_t::value_type& val)
    {
        push_back(val);
        return operator[](val.first);
    }

    iterator insert(const_iterator pos, const basic_json& val)
    {
        // insert only works for arrays
        if (is_array())
        {
            // check if iterator pos fits to this JSON value
            if (pos.m_object != this)
            {
                throw std::domain_error("iterator does not fit current value");
            }

            // insert to array and return iterator
            iterator result(this);
            assert(m_value.array != nullptr);
            result.m_it.array_iterator = m_value.array->insert(pos.m_it.array_iterator, val);
            return result;
        }
        else
        {
            throw std::domain_error("cannot use insert() with " + type_name());
        }
    }

    iterator insert(const_iterator pos, basic_json&& val)
    {
        return insert(pos, val);
    }

    iterator insert(const_iterator pos, size_type cnt, const basic_json& val)
    {
        // insert only works for arrays
        if (is_array())
        {
            // check if iterator pos fits to this JSON value
            if (pos.m_object != this)
            {
                throw std::domain_error("iterator does not fit current value");
            }

            // insert to array and return iterator
            iterator result(this);
            assert(m_value.array != nullptr);
            result.m_it.array_iterator = m_value.array->insert(pos.m_it.array_iterator, cnt, val);
            return result;
        }
        else
        {
            throw std::domain_error("cannot use insert() with " + type_name());
        }
    }

    iterator insert(const_iterator pos, const_iterator first, const_iterator last)
    {
        // insert only works for arrays
        if (not is_array())
        {
            throw std::domain_error("cannot use insert() with " + type_name());
        }

        // check if iterator pos fits to this JSON value
        if (pos.m_object != this)
        {
            throw std::domain_error("iterator does not fit current value");
        }

        if (first.m_object != last.m_object)
        {
            throw std::domain_error("iterators do not fit");
        }

        if (first.m_object == this or last.m_object == this)
        {
            throw std::domain_error("passed iterators may not belong to container");
        }

        // insert to array and return iterator
        iterator result(this);
        assert(m_value.array != nullptr);
        result.m_it.array_iterator = m_value.array->insert(
                                         pos.m_it.array_iterator,
                                         first.m_it.array_iterator,
                                         last.m_it.array_iterator);
        return result;
    }

    iterator insert(const_iterator pos, std::initializer_list<basic_json> ilist)
    {
        // insert only works for arrays
        if (not is_array())
        {
            throw std::domain_error("cannot use insert() with " + type_name());
        }

        // check if iterator pos fits to this JSON value
        if (pos.m_object != this)
        {
            throw std::domain_error("iterator does not fit current value");
        }

        // insert to array and return iterator
        iterator result(this);
        assert(m_value.array != nullptr);
        result.m_it.array_iterator = m_value.array->insert(pos.m_it.array_iterator, ilist);
        return result;
    }

    void swap(reference other) noexcept (
        std::is_nothrow_move_constructible<value_t>::value and
        std::is_nothrow_move_assignable<value_t>::value and
        std::is_nothrow_move_constructible<json_value>::value and
        std::is_nothrow_move_assignable<json_value>::value
    )
    {
        std::swap(m_type, other.m_type);
        std::swap(m_value, other.m_value);
    }

    void swap(array_t& other)
    {
        // swap only works for arrays
        if (is_array())
        {
            assert(m_value.array != nullptr);
            std::swap(*(m_value.array), other);
        }
        else
        {
            throw std::domain_error("cannot use swap() with " + type_name());
        }
    }

    void swap(object_t& other)
    {
        // swap only works for objects
        if (is_object())
        {
            assert(m_value.object != nullptr);
            std::swap(*(m_value.object), other);
        }
        else
        {
            throw std::domain_error("cannot use swap() with " + type_name());
        }
    }

    void swap(string_t& other)
    {
        // swap only works for strings
        if (is_string())
        {
            assert(m_value.string != nullptr);
            std::swap(*(m_value.string), other);
        }
        else
        {
            throw std::domain_error("cannot use swap() with " + type_name());
        }
    }



    // lexicographical comparison operators //


  private:
    friend bool operator<(const value_t lhs, const value_t rhs) noexcept
    {
        static constexpr std::array<uint8_t, 8> order = {{
                0, // null
                3, // object
                4, // array
                5, // string
                1, // boolean
                2, // integer
                2, // unsigned
                2, // float
            }
        };

        // discarded values are not comparable
        if (lhs == value_t::discarded or rhs == value_t::discarded)
        {
            return false;
        }

        return order[static_cast<std::size_t>(lhs)] < order[static_cast<std::size_t>(rhs)];
    }

  public:
    friend bool operator==(const_reference lhs, const_reference rhs) noexcept
    {
        const auto lhs_type = lhs.type();
        const auto rhs_type = rhs.type();

        if (lhs_type == rhs_type)
        {
            switch (lhs_type)
            {
                case value_t::array:
                {
                    assert(lhs.m_value.array != nullptr);
                    assert(rhs.m_value.array != nullptr);
                    return *lhs.m_value.array == *rhs.m_value.array;
                }
                case value_t::object:
                {
                    assert(lhs.m_value.object != nullptr);
                    assert(rhs.m_value.object != nullptr);
                    return *lhs.m_value.object == *rhs.m_value.object;
                }
                case value_t::null:
                {
                    return true;
                }
                case value_t::string:
                {
                    assert(lhs.m_value.string != nullptr);
                    assert(rhs.m_value.string != nullptr);
                    return *lhs.m_value.string == *rhs.m_value.string;
                }
                case value_t::boolean:
                {
                    return lhs.m_value.boolean == rhs.m_value.boolean;
                }
                case value_t::number_integer:
                {
                    return lhs.m_value.number_integer == rhs.m_value.number_integer;
                }
                case value_t::number_unsigned:
                {
                    return lhs.m_value.number_unsigned == rhs.m_value.number_unsigned;
                }
                case value_t::number_float:
                {
                    return lhs.m_value.number_float == rhs.m_value.number_float;
                }
                default:
                {
                    return false;
                }
            }
        }
        else if (lhs_type == value_t::number_integer and rhs_type == value_t::number_float)
        {
            return static_cast<number_float_t>(lhs.m_value.number_integer) == rhs.m_value.number_float;
        }
        else if (lhs_type == value_t::number_float and rhs_type == value_t::number_integer)
        {
            return lhs.m_value.number_float == static_cast<number_float_t>(rhs.m_value.number_integer);
        }
        else if (lhs_type == value_t::number_unsigned and rhs_type == value_t::number_float)
        {
            return static_cast<number_float_t>(lhs.m_value.number_unsigned) == rhs.m_value.number_float;
        }
        else if (lhs_type == value_t::number_float and rhs_type == value_t::number_unsigned)
        {
            return lhs.m_value.number_float == static_cast<number_float_t>(rhs.m_value.number_unsigned);
        }
        else if (lhs_type == value_t::number_unsigned and rhs_type == value_t::number_integer)
        {
            return static_cast<number_integer_t>(lhs.m_value.number_unsigned) == rhs.m_value.number_integer;
        }
        else if (lhs_type == value_t::number_integer and rhs_type == value_t::number_unsigned)
        {
            return lhs.m_value.number_integer == static_cast<number_integer_t>(rhs.m_value.number_unsigned);
        }

        return false;
    }

    friend bool operator==(const_reference v, std::nullptr_t) noexcept
    {
        return v.is_null();
    }

    friend bool operator==(std::nullptr_t, const_reference v) noexcept
    {
        return v.is_null();
    }

    friend bool operator!=(const_reference lhs, const_reference rhs) noexcept
    {
        return not (lhs == rhs);
    }

    friend bool operator!=(const_reference v, std::nullptr_t) noexcept
    {
        return not v.is_null();
    }

    friend bool operator!=(std::nullptr_t, const_reference v) noexcept
    {
        return not v.is_null();
    }

    friend bool operator<(const_reference lhs, const_reference rhs) noexcept
    {
        const auto lhs_type = lhs.type();
        const auto rhs_type = rhs.type();

        if (lhs_type == rhs_type)
        {
            switch (lhs_type)
            {
                case value_t::array:
                {
                    assert(lhs.m_value.array != nullptr);
                    assert(rhs.m_value.array != nullptr);
                    return *lhs.m_value.array < *rhs.m_value.array;
                }
                case value_t::object:
                {
                    assert(lhs.m_value.object != nullptr);
                    assert(rhs.m_value.object != nullptr);
                    return *lhs.m_value.object < *rhs.m_value.object;
                }
                case value_t::null:
                {
                    return false;
                }
                case value_t::string:
                {
                    assert(lhs.m_value.string != nullptr);
                    assert(rhs.m_value.string != nullptr);
                    return *lhs.m_value.string < *rhs.m_value.string;
                }
                case value_t::boolean:
                {
                    return lhs.m_value.boolean < rhs.m_value.boolean;
                }
                case value_t::number_integer:
                {
                    return lhs.m_value.number_integer < rhs.m_value.number_integer;
                }
                case value_t::number_unsigned:
                {
                    return lhs.m_value.number_unsigned < rhs.m_value.number_unsigned;
                }
                case value_t::number_float:
                {
                    return lhs.m_value.number_float < rhs.m_value.number_float;
                }
                default:
                {
                    return false;
                }
            }
        }
        else if (lhs_type == value_t::number_integer and rhs_type == value_t::number_float)
        {
            return static_cast<number_float_t>(lhs.m_value.number_integer) < rhs.m_value.number_float;
        }
        else if (lhs_type == value_t::number_float and rhs_type == value_t::number_integer)
        {
            return lhs.m_value.number_float < static_cast<number_float_t>(rhs.m_value.number_integer);
        }
        else if (lhs_type == value_t::number_unsigned and rhs_type == value_t::number_float)
        {
            return static_cast<number_float_t>(lhs.m_value.number_unsigned) < rhs.m_value.number_float;
        }
        else if (lhs_type == value_t::number_float and rhs_type == value_t::number_unsigned)
        {
            return lhs.m_value.number_float < static_cast<number_float_t>(rhs.m_value.number_unsigned);
        }
        else if (lhs_type == value_t::number_integer and rhs_type == value_t::number_unsigned)
        {
            return lhs.m_value.number_integer < static_cast<number_integer_t>(rhs.m_value.number_unsigned);
        }
        else if (lhs_type == value_t::number_unsigned and rhs_type == value_t::number_integer)
        {
            return static_cast<number_integer_t>(lhs.m_value.number_unsigned) < rhs.m_value.number_integer;
        }

        // We only reach this line if we cannot compare values. In that case,
        // we compare types. Note we have to call the operator explicitly,
        // because MSVC has problems otherwise.
        return operator<(lhs_type, rhs_type);
    }

    friend bool operator<=(const_reference lhs, const_reference rhs) noexcept
    {
        return not (rhs < lhs);
    }

    friend bool operator>(const_reference lhs, const_reference rhs) noexcept
    {
        return not (lhs <= rhs);
    }

    friend bool operator>=(const_reference lhs, const_reference rhs) noexcept
    {
        return not (lhs < rhs);
    }



    // serialization //


    friend std::ostream& operator<<(std::ostream& o, const basic_json& j)
    {
        // read width member and use it as indentation parameter if nonzero
        const bool pretty_print = (o.width() > 0);
        const auto indentation = (pretty_print ? o.width() : 0);

        // reset width to 0 for subsequent calls to this stream
        o.width(0);

        // do the actual serialization
        j.dump(o, pretty_print, static_cast<unsigned int>(indentation));
        return o;
    }

    friend std::ostream& operator>>(const basic_json& j, std::ostream& o)
    {
        return o << j;
    }



    // deserialization //


    static basic_json parse(const string_t& s, parser_callback_t cb = nullptr)
    {
        return parser(s, cb).parse();
    }

    static basic_json parse(std::istream& i, parser_callback_t cb = nullptr)
    {
        return parser(i, cb).parse();
    }

    static basic_json parse(std::istream&& i, parser_callback_t cb = nullptr)
    {
        return parser(i, cb).parse();
    }

    friend std::istream& operator<<(basic_json& j, std::istream& i)
    {
        j = parser(i).parse();
        return i;
    }

    friend std::istream& operator>>(std::istream& i, basic_json& j)
    {
        j = parser(i).parse();
        return i;
    }



  private:
    // convenience functions //

    string_t type_name() const noexcept
    {
        switch (m_type)
        {
            case value_t::null:
                return "null";
            case value_t::object:
                return "object";
            case value_t::array:
                return "array";
            case value_t::string:
                return "string";
            case value_t::boolean:
                return "boolean";
            case value_t::discarded:
                return "discarded";
            default:
                return "number";
        }
    }

    static std::size_t extra_space(const string_t& s) noexcept
    {
        std::size_t result = 0;

        for (const auto& c : s)
        {
            switch (c)
            {
                case '"':
                case '\\':
                case '\b':
                case '\f':
                case '\n':
                case '\r':
                case '\t':
                {
                    // from c (1 byte) to \x (2 bytes)
                    result += 1;
                    break;
                }

                default:
                {
                    if (c >= 0x00 and c <= 0x1f)
                    {
                        // from c (1 byte) to \uxxxx (6 bytes)
                        result += 5;
                    }
                    break;
                }
            }
        }

        return result;
    }

    static string_t escape_string(const string_t& s)
    {
        const auto space = extra_space(s);
        if (space == 0)
        {
            return s;
        }

        // create a result string of necessary size
        string_t result(s.size() + space, '\\');
        std::size_t pos = 0;

        for (const auto& c : s)
        {
            switch (c)
            {
                // quotation mark (0x22)
                case '"':
                {
                    result[pos + 1] = '"';
                    pos += 2;
                    break;
                }

                // reverse solidus (0x5c)
                case '\\':
                {
                    // nothing to change
                    pos += 2;
                    break;
                }

                // backspace (0x08)
                case '\b':
                {
                    result[pos + 1] = 'b';
                    pos += 2;
                    break;
                }

                // formfeed (0x0c)
                case '\f':
                {
                    result[pos + 1] = 'f';
                    pos += 2;
                    break;
                }

                // newline (0x0a)
                case '\n':
                {
                    result[pos + 1] = 'n';
                    pos += 2;
                    break;
                }

                // carriage return (0x0d)
                case '\r':
                {
                    result[pos + 1] = 'r';
                    pos += 2;
                    break;
                }

                // horizontal tab (0x09)
                case '\t':
                {
                    result[pos + 1] = 't';
                    pos += 2;
                    break;
                }

                default:
                {
                    if (c >= 0x00 and c <= 0x1f)
                    {
                        // convert a number 0..15 to its hex representation
                        // (0..f)
                        auto hexify = [](const char v) -> char
                        {
                            return (v < 10) ? ('0' + v) : ('a' + v - 10);
                        };

                        // print character c as \uxxxx
                        for (const char m :
                    { 'u', '0', '0', hexify(c >> 4), hexify(c & 0x0f)
                        })
                        {
                            result[++pos] = m;
                        }

                        ++pos;
                    }
                    else
                    {
                        // all other characters are added as-is
                        result[pos++] = c;
                    }
                    break;
                }
            }
        }

        return result;
    }

    void dump(std::ostream& o,
              const bool pretty_print,
              const unsigned int indent_step,
              const unsigned int current_indent = 0) const
    {
        // variable to hold indentation for recursive calls
        unsigned int new_indent = current_indent;

        switch (m_type)
        {
            case value_t::object:
            {
                assert(m_value.object != nullptr);

                if (m_value.object->empty())
                {
                    o << "{}";
                    return;
                }

                o << "{";

                // increase indentation
                if (pretty_print)
                {
                    new_indent += indent_step;
                    o << "\n";
                }

                for (auto i = m_value.object->cbegin(); i != m_value.object->cend(); ++i)
                {
                    if (i != m_value.object->cbegin())
                    {
                        o << (pretty_print ? ",\n" : ",");
                    }
                    o << string_t(new_indent, ' ') << "\""
                      << escape_string(i->first) << "\":"
                      << (pretty_print ? " " : "");
                    i->second.dump(o, pretty_print, indent_step, new_indent);
                }

                // decrease indentation
                if (pretty_print)
                {
                    new_indent -= indent_step;
                    o << "\n";
                }

                o << string_t(new_indent, ' ') + "}";
                return;
            }

            case value_t::array:
            {
                assert(m_value.array != nullptr);

                if (m_value.array->empty())
                {
                    o << "[]";
                    return;
                }

                o << "[";

                // increase indentation
                if (pretty_print)
                {
                    new_indent += indent_step;
                    o << "\n";
                }

                for (auto i = m_value.array->cbegin(); i != m_value.array->cend(); ++i)
                {
                    if (i != m_value.array->cbegin())
                    {
                        o << (pretty_print ? ",\n" : ",");
                    }
                    o << string_t(new_indent, ' ');
                    i->dump(o, pretty_print, indent_step, new_indent);
                }

                // decrease indentation
                if (pretty_print)
                {
                    new_indent -= indent_step;
                    o << "\n";
                }

                o << string_t(new_indent, ' ') << "]";
                return;
            }

            case value_t::string:
            {
                assert(m_value.string != nullptr);
                o << string_t("\"") << escape_string(*m_value.string) << "\"";
                return;
            }

            case value_t::boolean:
            {
                o << (m_value.boolean ? "true" : "false");
                return;
            }

            case value_t::number_integer:
            {
                o << m_value.number_integer;
                return;
            }

            case value_t::number_unsigned:
            {
                o << m_value.number_unsigned;
                return;
            }

            case value_t::number_float:
            {
                // If the number is an integer then output as a fixed with with
                // precision 1 to output "0.0", "1.0" etc as expected for some
                // round trip tests otherwise  15 digits of precision allows
                // round-trip IEEE 754 string->double->string; to be safe, we
                // read this value from
                // std::numeric_limits<number_float_t>::digits10
                if (std::fmod(m_value.number_float, 1) == 0)
                {
                    o << std::fixed << std::setprecision(1);
                }
                else
                {
                    // std::defaultfloat not supported in gcc version < 5
                    o.unsetf(std::ios_base::floatfield);
                    o << std::setprecision(std::numeric_limits<double>::digits10);
                }
                o << m_value.number_float;
                return;
            }

            case value_t::discarded:
            {
                o << "<discarded>";
                return;
            }

            case value_t::null:
            {
                o << "null";
                return;
            }
        }
    }

  private:
    // member variables //

    value_t m_type = value_t::null;

    json_value m_value = {};


  private:
    // iterators //

    class primitive_iterator_t
    {
      public:
        void set_begin() noexcept
        {
            m_it = begin_value;
        }

        void set_end() noexcept
        {
            m_it = end_value;
        }

        constexpr bool is_begin() const noexcept
        {
            return (m_it == begin_value);
        }

        constexpr bool is_end() const noexcept
        {
            return (m_it == end_value);
        }

        operator difference_type& () noexcept
        {
            return m_it;
        }

        constexpr operator difference_type () const noexcept
        {
            return m_it;
        }

      private:
        static constexpr difference_type begin_value = 0;
        static constexpr difference_type end_value = begin_value + 1;

        difference_type m_it = std::numeric_limits<std::ptrdiff_t>::denorm_min();
    };

    struct internal_iterator
    {
        typename object_t::iterator object_iterator;
        typename array_t::iterator array_iterator;
        primitive_iterator_t primitive_iterator;

        internal_iterator() noexcept
            : object_iterator(), array_iterator(), primitive_iterator()
        {}
    };

    template<typename IteratorType>
    class iteration_proxy
    {
      private:
        class iteration_proxy_internal
        {
          private:
            IteratorType anchor;
            size_t array_index = 0;

          public:
            explicit iteration_proxy_internal(IteratorType it) noexcept
                : anchor(it)
            {}

            iteration_proxy_internal& operator*()
            {
                return *this;
            }

            iteration_proxy_internal& operator++()
            {
                ++anchor;
                ++array_index;

                return *this;
            }

            bool operator!= (const iteration_proxy_internal& o) const
            {
                return anchor != o.anchor;
            }

            typename basic_json::string_t key() const
            {
                assert(anchor.m_object != nullptr);

                switch (anchor.m_object->type())
                {
                    // use integer array index as key
                    case value_t::array:
                    {
                        return std::to_string(array_index);
                    }

                    // use key from the object
                    case value_t::object:
                    {
                        return anchor.key();
                    }

                    // use an empty key for all primitive types
                    default:
                    {
                        return "";
                    }
                }
            }

            typename IteratorType::reference value() const
            {
                return anchor.value();
            }
        };

        typename IteratorType::reference container;

      public:
        explicit iteration_proxy(typename IteratorType::reference cont)
            : container(cont)
        {}

        iteration_proxy_internal begin() noexcept
        {
            return iteration_proxy_internal(container.begin());
        }

        iteration_proxy_internal end() noexcept
        {
            return iteration_proxy_internal(container.end());
        }
    };

  public:
    class const_iterator : public std::iterator<std::random_access_iterator_tag, const basic_json>
    {
        friend class basic_json;

      public:
        using value_type = typename basic_json::value_type;
        using difference_type = typename basic_json::difference_type;
        using pointer = typename basic_json::const_pointer;
        using reference = typename basic_json::const_reference;
        using iterator_category = std::bidirectional_iterator_tag;

        const_iterator() = default;

        explicit const_iterator(pointer object) noexcept
            : m_object(object)
        {
            assert(m_object != nullptr);

            switch (m_object->m_type)
            {
                case basic_json::value_t::object:
                {
                    m_it.object_iterator = typename object_t::iterator();
                    break;
                }

                case basic_json::value_t::array:
                {
                    m_it.array_iterator = typename array_t::iterator();
                    break;
                }

                default:
                {
                    m_it.primitive_iterator = primitive_iterator_t();
                    break;
                }
            }
        }

        explicit const_iterator(const iterator& other) noexcept
            : m_object(other.m_object)
        {
            assert(m_object != nullptr);

            switch (m_object->m_type)
            {
                case basic_json::value_t::object:
                {
                    m_it.object_iterator = other.m_it.object_iterator;
                    break;
                }

                case basic_json::value_t::array:
                {
                    m_it.array_iterator = other.m_it.array_iterator;
                    break;
                }

                default:
                {
                    m_it.primitive_iterator = other.m_it.primitive_iterator;
                    break;
                }
            }
        }

        const_iterator(const const_iterator& other) noexcept
            : m_object(other.m_object), m_it(other.m_it)
        {}

        const_iterator& operator=(const_iterator other) noexcept(
            std::is_nothrow_move_constructible<pointer>::value and
            std::is_nothrow_move_assignable<pointer>::value and
            std::is_nothrow_move_constructible<internal_iterator>::value and
            std::is_nothrow_move_assignable<internal_iterator>::value
        )
        {
            std::swap(m_object, other.m_object);
            std::swap(m_it, other.m_it);
            return *this;
        }

      private:
        void set_begin() noexcept
        {
            assert(m_object != nullptr);

            switch (m_object->m_type)
            {
                case basic_json::value_t::object:
                {
                    assert(m_object->m_value.object != nullptr);
                    m_it.object_iterator = m_object->m_value.object->begin();
                    break;
                }

                case basic_json::value_t::array:
                {
                    assert(m_object->m_value.array != nullptr);
                    m_it.array_iterator = m_object->m_value.array->begin();
                    break;
                }

                case basic_json::value_t::null:
                {
                    // set to end so begin()==end() is true: null is empty
                    m_it.primitive_iterator.set_end();
                    break;
                }

                default:
                {
                    m_it.primitive_iterator.set_begin();
                    break;
                }
            }
        }

        void set_end() noexcept
        {
            assert(m_object != nullptr);

            switch (m_object->m_type)
            {
                case basic_json::value_t::object:
                {
                    assert(m_object->m_value.object != nullptr);
                    m_it.object_iterator = m_object->m_value.object->end();
                    break;
                }

                case basic_json::value_t::array:
                {
                    assert(m_object->m_value.array != nullptr);
                    m_it.array_iterator = m_object->m_value.array->end();
                    break;
                }

                default:
                {
                    m_it.primitive_iterator.set_end();
                    break;
                }
            }
        }

      public:
        reference operator*() const
        {
            assert(m_object != nullptr);

            switch (m_object->m_type)
            {
                case basic_json::value_t::object:
                {
                    assert(m_object->m_value.object);
                    assert(m_it.object_iterator != m_object->m_value.object->end());
                    return m_it.object_iterator->second;
                }

                case basic_json::value_t::array:
                {
                    assert(m_object->m_value.array);
                    assert(m_it.array_iterator != m_object->m_value.array->end());
                    return *m_it.array_iterator;
                }

                case basic_json::value_t::null:
                {
                    throw std::out_of_range("cannot get value");
                }

                default:
                {
                    if (m_it.primitive_iterator.is_begin())
                    {
                        return *m_object;
                    }
                    else
                    {
                        throw std::out_of_range("cannot get value");
                    }
                }
            }
        }

        pointer operator->() const
        {
            assert(m_object != nullptr);

            switch (m_object->m_type)
            {
                case basic_json::value_t::object:
                {
                    assert(m_object->m_value.object);
                    assert(m_it.object_iterator != m_object->m_value.object->end());
                    return &(m_it.object_iterator->second);
                }

                case basic_json::value_t::array:
                {
                    assert(m_object->m_value.array);
                    assert(m_it.array_iterator != m_object->m_value.array->end());
                    return &*m_it.array_iterator;
                }

                default:
                {
                    if (m_it.primitive_iterator.is_begin())
                    {
                        return m_object;
                    }
                    else
                    {
                        throw std::out_of_range("cannot get value");
                    }
                }
            }
        }

        const_iterator operator++(int)
        {
            auto result = *this;
            ++(*this);
            return result;
        }

        const_iterator& operator++()
        {
            assert(m_object != nullptr);

            switch (m_object->m_type)
            {
                case basic_json::value_t::object:
                {
                    ++m_it.object_iterator;
                    break;
                }

                case basic_json::value_t::array:
                {
                    ++m_it.array_iterator;
                    break;
                }

                default:
                {
                    ++m_it.primitive_iterator;
                    break;
                }
            }

            return *this;
        }

        const_iterator operator--(int)
        {
            auto result = *this;
            --(*this);
            return result;
        }

        const_iterator& operator--()
        {
            assert(m_object != nullptr);

            switch (m_object->m_type)
            {
                case basic_json::value_t::object:
                {
                    --m_it.object_iterator;
                    break;
                }

                case basic_json::value_t::array:
                {
                    --m_it.array_iterator;
                    break;
                }

                default:
                {
                    --m_it.primitive_iterator;
                    break;
                }
            }

            return *this;
        }

        bool operator==(const const_iterator& other) const
        {
            // if objects are not the same, the comparison is undefined
            if (m_object != other.m_object)
            {
                throw std::domain_error("cannot compare iterators of different containers");
            }

            assert(m_object != nullptr);

            switch (m_object->m_type)
            {
                case basic_json::value_t::object:
                {
                    return (m_it.object_iterator == other.m_it.object_iterator);
                }

                case basic_json::value_t::array:
                {
                    return (m_it.array_iterator == other.m_it.array_iterator);
                }

                default:
                {
                    return (m_it.primitive_iterator == other.m_it.primitive_iterator);
                }
            }
        }

        bool operator!=(const const_iterator& other) const
        {
            return not operator==(other);
        }

        bool operator<(const const_iterator& other) const
        {
            // if objects are not the same, the comparison is undefined
            if (m_object != other.m_object)
            {
                throw std::domain_error("cannot compare iterators of different containers");
            }

            assert(m_object != nullptr);

            switch (m_object->m_type)
            {
                case basic_json::value_t::object:
                {
                    throw std::domain_error("cannot compare order of object iterators");
                }

                case basic_json::value_t::array:
                {
                    return (m_it.array_iterator < other.m_it.array_iterator);
                }

                default:
                {
                    return (m_it.primitive_iterator < other.m_it.primitive_iterator);
                }
            }
        }

        bool operator<=(const const_iterator& other) const
        {
            return not other.operator < (*this);
        }

        bool operator>(const const_iterator& other) const
        {
            return not operator<=(other);
        }

        bool operator>=(const const_iterator& other) const
        {
            return not operator<(other);
        }

        const_iterator& operator+=(difference_type i)
        {
            assert(m_object != nullptr);

            switch (m_object->m_type)
            {
                case basic_json::value_t::object:
                {
                    throw std::domain_error("cannot use offsets with object iterators");
                }

                case basic_json::value_t::array:
                {
                    m_it.array_iterator += i;
                    break;
                }

                default:
                {
                    m_it.primitive_iterator += i;
                    break;
                }
            }

            return *this;
        }

        const_iterator& operator-=(difference_type i)
        {
            return operator+=(-i);
        }

        const_iterator operator+(difference_type i)
        {
            auto result = *this;
            result += i;
            return result;
        }

        const_iterator operator-(difference_type i)
        {
            auto result = *this;
            result -= i;
            return result;
        }

        difference_type operator-(const const_iterator& other) const
        {
            assert(m_object != nullptr);

            switch (m_object->m_type)
            {
                case basic_json::value_t::object:
                {
                    throw std::domain_error("cannot use offsets with object iterators");
                }

                case basic_json::value_t::array:
                {
                    return m_it.array_iterator - other.m_it.array_iterator;
                }

                default:
                {
                    return m_it.primitive_iterator - other.m_it.primitive_iterator;
                }
            }
        }

        reference operator[](difference_type n) const
        {
            assert(m_object != nullptr);

            switch (m_object->m_type)
            {
                case basic_json::value_t::object:
                {
                    throw std::domain_error("cannot use operator[] for object iterators");
                }

                case basic_json::value_t::array:
                {
                    return *(m_it.array_iterator + n);
                }

                case basic_json::value_t::null:
                {
                    throw std::out_of_range("cannot get value");
                }

                default:
                {
                    if (m_it.primitive_iterator == -n)
                    {
                        return *m_object;
                    }
                    else
                    {
                        throw std::out_of_range("cannot get value");
                    }
                }
            }
        }

        typename object_t::key_type key() const
        {
            assert(m_object != nullptr);

            if (m_object->is_object())
            {
                return m_it.object_iterator->first;
            }
            else
            {
                throw std::domain_error("cannot use key() for non-object iterators");
            }
        }

        reference value() const
        {
            return operator*();
        }

      private:
        pointer m_object = nullptr;
        internal_iterator m_it = internal_iterator();
    };

    class iterator : public const_iterator
    {
      public:
        using base_iterator = const_iterator;
        using pointer = typename basic_json::pointer;
        using reference = typename basic_json::reference;

        iterator() = default;

        explicit iterator(pointer object) noexcept
            : base_iterator(object)
        {}

        iterator(const iterator& other) noexcept
            : base_iterator(other)
        {}

        iterator& operator=(iterator other) noexcept(
            std::is_nothrow_move_constructible<pointer>::value and
            std::is_nothrow_move_assignable<pointer>::value and
            std::is_nothrow_move_constructible<internal_iterator>::value and
            std::is_nothrow_move_assignable<internal_iterator>::value
        )
        {
            base_iterator::operator=(other);
            return *this;
        }

        reference operator*()
        {
            return const_cast<reference>(base_iterator::operator*());
        }

        pointer operator->()
        {
            return const_cast<pointer>(base_iterator::operator->());
        }

        iterator operator++(int)
        {
            iterator result = *this;
            base_iterator::operator++();
            return result;
        }

        iterator& operator++()
        {
            base_iterator::operator++();
            return *this;
        }

        iterator operator--(int)
        {
            iterator result = *this;
            base_iterator::operator--();
            return result;
        }

        iterator& operator--()
        {
            base_iterator::operator--();
            return *this;
        }

        iterator& operator+=(difference_type i)
        {
            base_iterator::operator+=(i);
            return *this;
        }

        iterator& operator-=(difference_type i)
        {
            base_iterator::operator-=(i);
            return *this;
        }

        iterator operator+(difference_type i)
        {
            auto result = *this;
            result += i;
            return result;
        }

        iterator operator-(difference_type i)
        {
            auto result = *this;
            result -= i;
            return result;
        }

        difference_type operator-(const iterator& other) const
        {
            return base_iterator::operator-(other);
        }

        reference operator[](difference_type n) const
        {
            return const_cast<reference>(base_iterator::operator[](n));
        }

        reference value() const
        {
            return const_cast<reference>(base_iterator::value());
        }
    };

    template<typename Base>
    class json_reverse_iterator : public std::reverse_iterator<Base>
    {
      public:
        using base_iterator = std::reverse_iterator<Base>;
        using reference = typename Base::reference;

        json_reverse_iterator(const typename base_iterator::iterator_type& it) noexcept
            : base_iterator(it)
        {}

        json_reverse_iterator(const base_iterator& it) noexcept
            : base_iterator(it)
        {}

        json_reverse_iterator operator++(int)
        {
            return base_iterator::operator++(1);
        }

        json_reverse_iterator& operator++()
        {
            base_iterator::operator++();
            return *this;
        }

        json_reverse_iterator operator--(int)
        {
            return base_iterator::operator--(1);
        }

        json_reverse_iterator& operator--()
        {
            base_iterator::operator--();
            return *this;
        }

        json_reverse_iterator& operator+=(difference_type i)
        {
            base_iterator::operator+=(i);
            return *this;
        }

        json_reverse_iterator operator+(difference_type i) const
        {
            auto result = *this;
            result += i;
            return result;
        }

        json_reverse_iterator operator-(difference_type i) const
        {
            auto result = *this;
            result -= i;
            return result;
        }

        difference_type operator-(const json_reverse_iterator& other) const
        {
            return this->base() - other.base();
        }

        reference operator[](difference_type n) const
        {
            return *(this->operator+(n));
        }

        typename object_t::key_type key() const
        {
            auto it = --this->base();
            return it.key();
        }

        reference value() const
        {
            auto it = --this->base();
            return it.operator * ();
        }
    };


  private:
    // lexer and parser //

    class lexer
    {
      public:
        enum class token_type
        {
            uninitialized,   
            literal_true,    
            literal_false,   
            literal_null,    
            value_string,    
            value_number,    
            begin_array,     
            begin_object,    
            end_array,       
            end_object,      
            name_separator,  
            value_separator, 
            parse_error,     
            end_of_input     
        };

        using lexer_char_t = unsigned char;

        explicit lexer(const string_t& s) noexcept
            : m_stream(nullptr), m_buffer(s)
        {
            m_content = reinterpret_cast<const lexer_char_t*>(s.c_str());
            assert(m_content != nullptr);
            m_start = m_cursor = m_content;
            m_limit = m_content + s.size();
        }

        explicit lexer(std::istream* s) noexcept
            : m_stream(s), m_buffer()
        {
            assert(m_stream != nullptr);
            getline(*m_stream, m_buffer);
            m_content = reinterpret_cast<const lexer_char_t*>(m_buffer.c_str());
            assert(m_content != nullptr);
            m_start = m_cursor = m_content;
            m_limit = m_content + m_buffer.size();
        }

        lexer() = default;

        // switch off unwanted functions
        lexer(const lexer&) = delete;
        lexer operator=(const lexer&) = delete;

        static string_t to_unicode(const std::size_t codepoint1,
                                   const std::size_t codepoint2 = 0)
        {
            // calculate the codepoint from the given code points
            std::size_t codepoint = codepoint1;

            // check if codepoint1 is a high surrogate
            if (codepoint1 >= 0xD800 and codepoint1 <= 0xDBFF)
            {
                // check if codepoint2 is a low surrogate
                if (codepoint2 >= 0xDC00 and codepoint2 <= 0xDFFF)
                {
                    codepoint =
                        // high surrogate occupies the most significant 22 bits
                        (codepoint1 << 10)
                        // low surrogate occupies the least significant 15 bits
                        + codepoint2
                        // there is still the 0xD800, 0xDC00 and 0x10000 noise
                        // in the result so we have to subtract with:
                        // (0xD800 << 10) + DC00 - 0x10000 = 0x35FDC00
                        - 0x35FDC00;
                }
                else
                {
                    throw std::invalid_argument("missing or wrong low surrogate");
                }
            }

            string_t result;

            if (codepoint < 0x80)
            {
                // 1-byte characters: 0xxxxxxx (ASCII)
                result.append(1, static_cast<typename string_t::value_type>(codepoint));
            }
            else if (codepoint <= 0x7ff)
            {
                // 2-byte characters: 110xxxxx 10xxxxxx
                result.append(1, static_cast<typename string_t::value_type>(0xC0 | ((codepoint >> 6) & 0x1F)));
                result.append(1, static_cast<typename string_t::value_type>(0x80 | (codepoint & 0x3F)));
            }
            else if (codepoint <= 0xffff)
            {
                // 3-byte characters: 1110xxxx 10xxxxxx 10xxxxxx
                result.append(1, static_cast<typename string_t::value_type>(0xE0 | ((codepoint >> 12) & 0x0F)));
                result.append(1, static_cast<typename string_t::value_type>(0x80 | ((codepoint >> 6) & 0x3F)));
                result.append(1, static_cast<typename string_t::value_type>(0x80 | (codepoint & 0x3F)));
            }
            else if (codepoint <= 0x10ffff)
            {
                // 4-byte characters: 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
                result.append(1, static_cast<typename string_t::value_type>(0xF0 | ((codepoint >> 18) & 0x07)));
                result.append(1, static_cast<typename string_t::value_type>(0x80 | ((codepoint >> 12) & 0x3F)));
                result.append(1, static_cast<typename string_t::value_type>(0x80 | ((codepoint >> 6) & 0x3F)));
                result.append(1, static_cast<typename string_t::value_type>(0x80 | (codepoint & 0x3F)));
            }
            else
            {
                throw std::out_of_range("code points above 0x10FFFF are invalid");
            }

            return result;
        }

        static std::string token_type_name(token_type t)
        {
            switch (t)
            {
                case token_type::uninitialized:
                    return "<uninitialized>";
                case token_type::literal_true:
                    return "true literal";
                case token_type::literal_false:
                    return "false literal";
                case token_type::literal_null:
                    return "null literal";
                case token_type::value_string:
                    return "string literal";
                case token_type::value_number:
                    return "number literal";
                case token_type::begin_array:
                    return "'['";
                case token_type::begin_object:
                    return "'{'";
                case token_type::end_array:
                    return "']'";
                case token_type::end_object:
                    return "'}'";
                case token_type::name_separator:
                    return "':'";
                case token_type::value_separator:
                    return "','";
                case token_type::parse_error:
                    return "<parse error>";
                case token_type::end_of_input:
                    return "end of input";
                default:
                {
                    // catch non-enum values
                    return "unknown token"; // LCOV_EXCL_LINE
                }
            }
        }

        token_type scan() noexcept
        {
            // pointer for backtracking information
            m_marker = nullptr;

            // remember the begin of the token
            m_start = m_cursor;
            assert(m_start != nullptr);


            {
                lexer_char_t yych;
                unsigned int yyaccept = 0;
                static const unsigned char yybm[] =
                {
                    0,   0,   0,   0,   0,   0,   0,   0,
                    0,  32,  32,   0,   0,  32,   0,   0,
                    128, 128, 128, 128, 128, 128, 128, 128,
                    128, 128, 128, 128, 128, 128, 128, 128,
                    160, 128,   0, 128, 128, 128, 128, 128,
                    128, 128, 128, 128, 128, 128, 128, 128,
                    192, 192, 192, 192, 192, 192, 192, 192,
                    192, 192, 128, 128, 128, 128, 128, 128,
                    128, 128, 128, 128, 128, 128, 128, 128,
                    128, 128, 128, 128, 128, 128, 128, 128,
                    128, 128, 128, 128, 128, 128, 128, 128,
                    128, 128, 128, 128,   0, 128, 128, 128,
                    128, 128, 128, 128, 128, 128, 128, 128,
                    128, 128, 128, 128, 128, 128, 128, 128,
                    128, 128, 128, 128, 128, 128, 128, 128,
                    128, 128, 128, 128, 128, 128, 128, 128,
                    128, 128, 128, 128, 128, 128, 128, 128,
                    128, 128, 128, 128, 128, 128, 128, 128,
                    128, 128, 128, 128, 128, 128, 128, 128,
                    128, 128, 128, 128, 128, 128, 128, 128,
                    128, 128, 128, 128, 128, 128, 128, 128,
                    128, 128, 128, 128, 128, 128, 128, 128,
                    128, 128, 128, 128, 128, 128, 128, 128,
                    128, 128, 128, 128, 128, 128, 128, 128,
                    128, 128, 128, 128, 128, 128, 128, 128,
                    128, 128, 128, 128, 128, 128, 128, 128,
                    128, 128, 128, 128, 128, 128, 128, 128,
                    128, 128, 128, 128, 128, 128, 128, 128,
                    128, 128, 128, 128, 128, 128, 128, 128,
                    128, 128, 128, 128, 128, 128, 128, 128,
                    128, 128, 128, 128, 128, 128, 128, 128,
                    128, 128, 128, 128, 128, 128, 128, 128,
                };
                if ((m_limit - m_cursor) < 5)
                {
                    yyfill();    // LCOV_EXCL_LINE;
                }
                yych = *m_cursor;
                if (yybm[0 + yych] & 32)
                {
                    goto basic_json_parser_6;
                }
                if (yych <= '\\')
                {
                    if (yych <= '-')
                    {
                        if (yych <= '"')
                        {
                            if (yych <= 0x00)
                            {
                                goto basic_json_parser_2;
                            }
                            if (yych <= '!')
                            {
                                goto basic_json_parser_4;
                            }
                            goto basic_json_parser_9;
                        }
                        else
                        {
                            if (yych <= '+')
                            {
                                goto basic_json_parser_4;
                            }
                            if (yych <= ',')
                            {
                                goto basic_json_parser_10;
                            }
                            goto basic_json_parser_12;
                        }
                    }
                    else
                    {
                        if (yych <= '9')
                        {
                            if (yych <= '/')
                            {
                                goto basic_json_parser_4;
                            }
                            if (yych <= '0')
                            {
                                goto basic_json_parser_13;
                            }
                            goto basic_json_parser_15;
                        }
                        else
                        {
                            if (yych <= ':')
                            {
                                goto basic_json_parser_17;
                            }
                            if (yych == '[')
                            {
                                goto basic_json_parser_19;
                            }
                            goto basic_json_parser_4;
                        }
                    }
                }
                else
                {
                    if (yych <= 't')
                    {
                        if (yych <= 'f')
                        {
                            if (yych <= ']')
                            {
                                goto basic_json_parser_21;
                            }
                            if (yych <= 'e')
                            {
                                goto basic_json_parser_4;
                            }
                            goto basic_json_parser_23;
                        }
                        else
                        {
                            if (yych == 'n')
                            {
                                goto basic_json_parser_24;
                            }
                            if (yych <= 's')
                            {
                                goto basic_json_parser_4;
                            }
                            goto basic_json_parser_25;
                        }
                    }
                    else
                    {
                        if (yych <= '|')
                        {
                            if (yych == '{')
                            {
                                goto basic_json_parser_26;
                            }
                            goto basic_json_parser_4;
                        }
                        else
                        {
                            if (yych <= '}')
                            {
                                goto basic_json_parser_28;
                            }
                            if (yych == 0xEF)
                            {
                                goto basic_json_parser_30;
                            }
                            goto basic_json_parser_4;
                        }
                    }
                }
basic_json_parser_2:
                ++m_cursor;
                {
                    return token_type::end_of_input;
                }
basic_json_parser_4:
                ++m_cursor;
basic_json_parser_5:
                {
                    return token_type::parse_error;
                }
basic_json_parser_6:
                ++m_cursor;
                if (m_limit <= m_cursor)
                {
                    yyfill();    // LCOV_EXCL_LINE;
                }
                yych = *m_cursor;
                if (yybm[0 + yych] & 32)
                {
                    goto basic_json_parser_6;
                }
                {
                    return scan();
                }
basic_json_parser_9:
                yyaccept = 0;
                yych = *(m_marker = ++m_cursor);
                if (yych <= 0x0F)
                {
                    goto basic_json_parser_5;
                }
                goto basic_json_parser_32;
basic_json_parser_10:
                ++m_cursor;
                {
                    return token_type::value_separator;
                }
basic_json_parser_12:
                yych = *++m_cursor;
                if (yych <= '/')
                {
                    goto basic_json_parser_5;
                }
                if (yych <= '0')
                {
                    goto basic_json_parser_13;
                }
                if (yych <= '9')
                {
                    goto basic_json_parser_15;
                }
                goto basic_json_parser_5;
basic_json_parser_13:
                yyaccept = 1;
                yych = *(m_marker = ++m_cursor);
                if (yych <= 'D')
                {
                    if (yych == '.')
                    {
                        goto basic_json_parser_37;
                    }
                }
                else
                {
                    if (yych <= 'E')
                    {
                        goto basic_json_parser_38;
                    }
                    if (yych == 'e')
                    {
                        goto basic_json_parser_38;
                    }
                }
basic_json_parser_14:
                {
                    return token_type::value_number;
                }
basic_json_parser_15:
                yyaccept = 1;
                m_marker = ++m_cursor;
                if ((m_limit - m_cursor) < 3)
                {
                    yyfill();    // LCOV_EXCL_LINE;
                }
                yych = *m_cursor;
                if (yybm[0 + yych] & 64)
                {
                    goto basic_json_parser_15;
                }
                if (yych <= 'D')
                {
                    if (yych == '.')
                    {
                        goto basic_json_parser_37;
                    }
                    goto basic_json_parser_14;
                }
                else
                {
                    if (yych <= 'E')
                    {
                        goto basic_json_parser_38;
                    }
                    if (yych == 'e')
                    {
                        goto basic_json_parser_38;
                    }
                    goto basic_json_parser_14;
                }
basic_json_parser_17:
                ++m_cursor;
                {
                    return token_type::name_separator;
                }
basic_json_parser_19:
                ++m_cursor;
                {
                    return token_type::begin_array;
                }
basic_json_parser_21:
                ++m_cursor;
                {
                    return token_type::end_array;
                }
basic_json_parser_23:
                yyaccept = 0;
                yych = *(m_marker = ++m_cursor);
                if (yych == 'a')
                {
                    goto basic_json_parser_39;
                }
                goto basic_json_parser_5;
basic_json_parser_24:
                yyaccept = 0;
                yych = *(m_marker = ++m_cursor);
                if (yych == 'u')
                {
                    goto basic_json_parser_40;
                }
                goto basic_json_parser_5;
basic_json_parser_25:
                yyaccept = 0;
                yych = *(m_marker = ++m_cursor);
                if (yych == 'r')
                {
                    goto basic_json_parser_41;
                }
                goto basic_json_parser_5;
basic_json_parser_26:
                ++m_cursor;
                {
                    return token_type::begin_object;
                }
basic_json_parser_28:
                ++m_cursor;
                {
                    return token_type::end_object;
                }
basic_json_parser_30:
                yyaccept = 0;
                yych = *(m_marker = ++m_cursor);
                if (yych == 0xBB)
                {
                    goto basic_json_parser_42;
                }
                goto basic_json_parser_5;
basic_json_parser_31:
                ++m_cursor;
                if (m_limit <= m_cursor)
                {
                    yyfill();    // LCOV_EXCL_LINE;
                }
                yych = *m_cursor;
basic_json_parser_32:
                if (yybm[0 + yych] & 128)
                {
                    goto basic_json_parser_31;
                }
                if (yych <= 0x0F)
                {
                    goto basic_json_parser_33;
                }
                if (yych <= '"')
                {
                    goto basic_json_parser_34;
                }
                goto basic_json_parser_36;
basic_json_parser_33:
                m_cursor = m_marker;
                if (yyaccept == 0)
                {
                    goto basic_json_parser_5;
                }
                else
                {
                    goto basic_json_parser_14;
                }
basic_json_parser_34:
                ++m_cursor;
                {
                    return token_type::value_string;
                }
basic_json_parser_36:
                ++m_cursor;
                if (m_limit <= m_cursor)
                {
                    yyfill();    // LCOV_EXCL_LINE;
                }
                yych = *m_cursor;
                if (yych <= 'e')
                {
                    if (yych <= '/')
                    {
                        if (yych == '"')
                        {
                            goto basic_json_parser_31;
                        }
                        if (yych <= '.')
                        {
                            goto basic_json_parser_33;
                        }
                        goto basic_json_parser_31;
                    }
                    else
                    {
                        if (yych <= '\\')
                        {
                            if (yych <= '[')
                            {
                                goto basic_json_parser_33;
                            }
                            goto basic_json_parser_31;
                        }
                        else
                        {
                            if (yych == 'b')
                            {
                                goto basic_json_parser_31;
                            }
                            goto basic_json_parser_33;
                        }
                    }
                }
                else
                {
                    if (yych <= 'q')
                    {
                        if (yych <= 'f')
                        {
                            goto basic_json_parser_31;
                        }
                        if (yych == 'n')
                        {
                            goto basic_json_parser_31;
                        }
                        goto basic_json_parser_33;
                    }
                    else
                    {
                        if (yych <= 's')
                        {
                            if (yych <= 'r')
                            {
                                goto basic_json_parser_31;
                            }
                            goto basic_json_parser_33;
                        }
                        else
                        {
                            if (yych <= 't')
                            {
                                goto basic_json_parser_31;
                            }
                            if (yych <= 'u')
                            {
                                goto basic_json_parser_43;
                            }
                            goto basic_json_parser_33;
                        }
                    }
                }
basic_json_parser_37:
                yych = *++m_cursor;
                if (yych <= '/')
                {
                    goto basic_json_parser_33;
                }
                if (yych <= '9')
                {
                    goto basic_json_parser_44;
                }
                goto basic_json_parser_33;
basic_json_parser_38:
                yych = *++m_cursor;
                if (yych <= ',')
                {
                    if (yych == '+')
                    {
                        goto basic_json_parser_46;
                    }
                    goto basic_json_parser_33;
                }
                else
                {
                    if (yych <= '-')
                    {
                        goto basic_json_parser_46;
                    }
                    if (yych <= '/')
                    {
                        goto basic_json_parser_33;
                    }
                    if (yych <= '9')
                    {
                        goto basic_json_parser_47;
                    }
                    goto basic_json_parser_33;
                }
basic_json_parser_39:
                yych = *++m_cursor;
                if (yych == 'l')
                {
                    goto basic_json_parser_49;
                }
                goto basic_json_parser_33;
basic_json_parser_40:
                yych = *++m_cursor;
                if (yych == 'l')
                {
                    goto basic_json_parser_50;
                }
                goto basic_json_parser_33;
basic_json_parser_41:
                yych = *++m_cursor;
                if (yych == 'u')
                {
                    goto basic_json_parser_51;
                }
                goto basic_json_parser_33;
basic_json_parser_42:
                yych = *++m_cursor;
                if (yych == 0xBF)
                {
                    goto basic_json_parser_52;
                }
                goto basic_json_parser_33;
basic_json_parser_43:
                ++m_cursor;
                if (m_limit <= m_cursor)
                {
                    yyfill();    // LCOV_EXCL_LINE;
                }
                yych = *m_cursor;
                if (yych <= '@')
                {
                    if (yych <= '/')
                    {
                        goto basic_json_parser_33;
                    }
                    if (yych <= '9')
                    {
                        goto basic_json_parser_54;
                    }
                    goto basic_json_parser_33;
                }
                else
                {
                    if (yych <= 'F')
                    {
                        goto basic_json_parser_54;
                    }
                    if (yych <= '`')
                    {
                        goto basic_json_parser_33;
                    }
                    if (yych <= 'f')
                    {
                        goto basic_json_parser_54;
                    }
                    goto basic_json_parser_33;
                }
basic_json_parser_44:
                yyaccept = 1;
                m_marker = ++m_cursor;
                if ((m_limit - m_cursor) < 3)
                {
                    yyfill();    // LCOV_EXCL_LINE;
                }
                yych = *m_cursor;
                if (yych <= 'D')
                {
                    if (yych <= '/')
                    {
                        goto basic_json_parser_14;
                    }
                    if (yych <= '9')
                    {
                        goto basic_json_parser_44;
                    }
                    goto basic_json_parser_14;
                }
                else
                {
                    if (yych <= 'E')
                    {
                        goto basic_json_parser_38;
                    }
                    if (yych == 'e')
                    {
                        goto basic_json_parser_38;
                    }
                    goto basic_json_parser_14;
                }
basic_json_parser_46:
                yych = *++m_cursor;
                if (yych <= '/')
                {
                    goto basic_json_parser_33;
                }
                if (yych >= ':')
                {
                    goto basic_json_parser_33;
                }
basic_json_parser_47:
                ++m_cursor;
                if (m_limit <= m_cursor)
                {
                    yyfill();    // LCOV_EXCL_LINE;
                }
                yych = *m_cursor;
                if (yych <= '/')
                {
                    goto basic_json_parser_14;
                }
                if (yych <= '9')
                {
                    goto basic_json_parser_47;
                }
                goto basic_json_parser_14;
basic_json_parser_49:
                yych = *++m_cursor;
                if (yych == 's')
                {
                    goto basic_json_parser_55;
                }
                goto basic_json_parser_33;
basic_json_parser_50:
                yych = *++m_cursor;
                if (yych == 'l')
                {
                    goto basic_json_parser_56;
                }
                goto basic_json_parser_33;
basic_json_parser_51:
                yych = *++m_cursor;
                if (yych == 'e')
                {
                    goto basic_json_parser_58;
                }
                goto basic_json_parser_33;
basic_json_parser_52:
                ++m_cursor;
                {
                    return scan();
                }
basic_json_parser_54:
                ++m_cursor;
                if (m_limit <= m_cursor)
                {
                    yyfill();    // LCOV_EXCL_LINE;
                }
                yych = *m_cursor;
                if (yych <= '@')
                {
                    if (yych <= '/')
                    {
                        goto basic_json_parser_33;
                    }
                    if (yych <= '9')
                    {
                        goto basic_json_parser_60;
                    }
                    goto basic_json_parser_33;
                }
                else
                {
                    if (yych <= 'F')
                    {
                        goto basic_json_parser_60;
                    }
                    if (yych <= '`')
                    {
                        goto basic_json_parser_33;
                    }
                    if (yych <= 'f')
                    {
                        goto basic_json_parser_60;
                    }
                    goto basic_json_parser_33;
                }
basic_json_parser_55:
                yych = *++m_cursor;
                if (yych == 'e')
                {
                    goto basic_json_parser_61;
                }
                goto basic_json_parser_33;
basic_json_parser_56:
                ++m_cursor;
                {
                    return token_type::literal_null;
                }
basic_json_parser_58:
                ++m_cursor;
                {
                    return token_type::literal_true;
                }
basic_json_parser_60:
                ++m_cursor;
                if (m_limit <= m_cursor)
                {
                    yyfill();    // LCOV_EXCL_LINE;
                }
                yych = *m_cursor;
                if (yych <= '@')
                {
                    if (yych <= '/')
                    {
                        goto basic_json_parser_33;
                    }
                    if (yych <= '9')
                    {
                        goto basic_json_parser_63;
                    }
                    goto basic_json_parser_33;
                }
                else
                {
                    if (yych <= 'F')
                    {
                        goto basic_json_parser_63;
                    }
                    if (yych <= '`')
                    {
                        goto basic_json_parser_33;
                    }
                    if (yych <= 'f')
                    {
                        goto basic_json_parser_63;
                    }
                    goto basic_json_parser_33;
                }
basic_json_parser_61:
                ++m_cursor;
                {
                    return token_type::literal_false;
                }
basic_json_parser_63:
                ++m_cursor;
                if (m_limit <= m_cursor)
                {
                    yyfill();    // LCOV_EXCL_LINE;
                }
                yych = *m_cursor;
                if (yych <= '@')
                {
                    if (yych <= '/')
                    {
                        goto basic_json_parser_33;
                    }
                    if (yych <= '9')
                    {
                        goto basic_json_parser_31;
                    }
                    goto basic_json_parser_33;
                }
                else
                {
                    if (yych <= 'F')
                    {
                        goto basic_json_parser_31;
                    }
                    if (yych <= '`')
                    {
                        goto basic_json_parser_33;
                    }
                    if (yych <= 'f')
                    {
                        goto basic_json_parser_31;
                    }
                    goto basic_json_parser_33;
                }
            }

        }

        void yyfill() noexcept
        {
            if (m_stream == nullptr or not * m_stream)
            {
                return;
            }

            const auto offset_start = m_start - m_content;
            const auto offset_marker = m_marker - m_start;
            const auto offset_cursor = m_cursor - m_start;

            m_buffer.erase(0, static_cast<size_t>(offset_start));
            std::string line;
            assert(m_stream != nullptr);
            std::getline(*m_stream, line);
            m_buffer += "\n" + line; // add line with newline symbol

            m_content = reinterpret_cast<const lexer_char_t*>(m_buffer.c_str());
            assert(m_content != nullptr);
            m_start  = m_content;
            m_marker = m_start + offset_marker;
            m_cursor = m_start + offset_cursor;
            m_limit  = m_start + m_buffer.size() - 1;
        }

        string_t get_token() const
        {
            assert(m_start != nullptr);
            return string_t(reinterpret_cast<typename string_t::const_pointer>(m_start),
                            static_cast<size_t>(m_cursor - m_start));
        }

        string_t get_string() const
        {
            string_t result;
            result.reserve(static_cast<size_t>(m_cursor - m_start - 2));

            // iterate the result between the quotes
            for (const lexer_char_t* i = m_start + 1; i < m_cursor - 1; ++i)
            {
                // process escaped characters
                if (*i == '\\')
                {
                    // read next character
                    ++i;

                    switch (*i)
                    {
                        // the default escapes
                        case 't':
                        {
                            result += "\t";
                            break;
                        }
                        case 'b':
                        {
                            result += "\b";
                            break;
                        }
                        case 'f':
                        {
                            result += "\f";
                            break;
                        }
                        case 'n':
                        {
                            result += "\n";
                            break;
                        }
                        case 'r':
                        {
                            result += "\r";
                            break;
                        }
                        case '\\':
                        {
                            result += "\\";
                            break;
                        }
                        case '/':
                        {
                            result += "/";
                            break;
                        }
                        case '"':
                        {
                            result += "\"";
                            break;
                        }

                        // unicode
                        case 'u':
                        {
                            // get code xxxx from uxxxx
                            auto codepoint = std::strtoul(std::string(reinterpret_cast<typename string_t::const_pointer>(i + 1),
                                                          4).c_str(), nullptr, 16);

                            // check if codepoint is a high surrogate
                            if (codepoint >= 0xD800 and codepoint <= 0xDBFF)
                            {
                                // make sure there is a subsequent unicode
                                if ((i + 6 >= m_limit) or * (i + 5) != '\\' or * (i + 6) != 'u')
                                {
                                    throw std::invalid_argument("missing low surrogate");
                                }

                                // get code yyyy from uxxxx\uyyyy
                                auto codepoint2 = std::strtoul(std::string(reinterpret_cast<typename string_t::const_pointer>
                                                               (i + 7), 4).c_str(), nullptr, 16);
                                result += to_unicode(codepoint, codepoint2);
                                // skip the next 10 characters (xxxx\uyyyy)
                                i += 10;
                            }
                            else
                            {
                                // add unicode character(s)
                                result += to_unicode(codepoint);
                                // skip the next four characters (xxxx)
                                i += 4;
                            }
                            break;
                        }
                    }
                }
                else
                {
                    // all other characters are just copied to the end of the
                    // string
                    result.append(1, static_cast<typename string_t::value_type>(*i));
                }
            }

            return result;
        }

        long double str_to_float_t(long double* /* type */, char** endptr) const
        {
            return std::strtold(reinterpret_cast<typename string_t::const_pointer>(m_start), endptr);
        }

        double str_to_float_t(double* /* type */, char** endptr) const
        {
            return std::strtod(reinterpret_cast<typename string_t::const_pointer>(m_start), endptr);
        }

        float str_to_float_t(float* /* type */, char** endptr) const
        {
            return std::strtof(reinterpret_cast<typename string_t::const_pointer>(m_start), endptr);
        }

        template <typename T_A, typename T_B>
        static bool attempt_cast(T_A source, T_B& dest)
        {
            dest = static_cast<T_B>(source);
            return (source == static_cast<T_A>(dest));
        }

        void get_number(basic_json& result) const
        {
            typename string_t::value_type* endptr;
            assert(m_start != nullptr);
            errno = 0;

            // attempt to parse it as an integer - first checking for a
            // negative number
            if (*reinterpret_cast<typename string_t::const_pointer>(m_start) != '-')
            {
                // positive, parse with strtoull and attempt cast to
                // number_unsigned_t
                if (attempt_cast(std::strtoull(reinterpret_cast<typename string_t::const_pointer>(m_start), &endptr,
                                               10), result.m_value.number_unsigned))
                {
                    result.m_type = value_t::number_unsigned;
                }
                else
                {
                    // cast failed due to overflow - store as float
                    result.m_type = value_t::number_float;
                }
            }
            else
            {
                // Negative, parse with strtoll and attempt cast to
                // number_integer_t
                if (attempt_cast(std::strtoll(reinterpret_cast<typename string_t::const_pointer>(m_start), &endptr,
                                              10), result.m_value.number_integer))
                {
                    result.m_type = value_t::number_integer;
                }
                else
                {
                    // cast failed due to overflow - store as float
                    result.m_type = value_t::number_float;
                }
            }

            // check the end of the number was reached and no range error
            // occurred
            if (reinterpret_cast<lexer_char_t*>(endptr) != m_cursor || errno == ERANGE)
            {
                result.m_type = value_t::number_float;
            }

            if (result.m_type  == value_t::number_float)
            {
                // either the number won't fit in an integer (range error from
                // strtoull/strtoll or overflow on cast) or there was something
                // else after the number, which could be an exponent

                // parse with strtod
                result.m_value.number_float = str_to_float_t(static_cast<number_float_t*>(nullptr), &endptr);

                // anything after the number is an error
                if (reinterpret_cast<lexer_char_t*>(endptr) != m_cursor)
                {
                    throw std::invalid_argument(std::string("parse error - ") + get_token() + " is not a number");
                }
            }
        }

      private:
        std::istream* m_stream = nullptr;
        string_t m_buffer;
        const lexer_char_t* m_content = nullptr;
        const lexer_char_t* m_start = nullptr;
        const lexer_char_t* m_marker = nullptr;
        const lexer_char_t* m_cursor = nullptr;
        const lexer_char_t* m_limit = nullptr;
    };

    class parser
    {
      public:
        parser(const string_t& s, parser_callback_t cb = nullptr) noexcept
            : callback(cb), m_lexer(s)
        {
            // read first token
            get_token();
        }

        parser(std::istream& _is, parser_callback_t cb = nullptr) noexcept
            : callback(cb), m_lexer(&_is)
        {
            // read first token
            get_token();
        }

        basic_json parse()
        {
            basic_json result = parse_internal(true);

            expect(lexer::token_type::end_of_input);

            // return parser result and replace it with null in case the
            // top-level value was discarded by the callback function
            return result.is_discarded() ? basic_json() : result;
        }

      private:
        basic_json parse_internal(bool keep)
        {
            auto result = basic_json(value_t::discarded);

            switch (last_token)
            {
                case lexer::token_type::begin_object:
                {
                    if (keep and (not callback or (keep = callback(depth++, parse_event_t::object_start, result))))
                    {
                        // explicitly set result to object to cope with {}
                        result.m_type = value_t::object;
                        result.m_value = json_value(value_t::object);
                    }

                    // read next token
                    get_token();

                    // closing } -> we are done
                    if (last_token == lexer::token_type::end_object)
                    {
                        get_token();
                        if (keep and callback and not callback(--depth, parse_event_t::object_end, result))
                        {
                            result = basic_json(value_t::discarded);
                        }
                        return result;
                    }

                    // no comma is expected here
                    unexpect(lexer::token_type::value_separator);

                    // otherwise: parse key-value pairs
                    do
                    {
                        // ugly, but could be fixed with loop reorganization
                        if (last_token == lexer::token_type::value_separator)
                        {
                            get_token();
                        }

                        // store key
                        expect(lexer::token_type::value_string);
                        const auto key = m_lexer.get_string();

                        bool keep_tag = false;
                        if (keep)
                        {
                            if (callback)
                            {
                                basic_json k(key);
                                keep_tag = callback(depth, parse_event_t::key, k);
                            }
                            else
                            {
                                keep_tag = true;
                            }
                        }

                        // parse separator (:)
                        get_token();
                        expect(lexer::token_type::name_separator);

                        // parse and add value
                        get_token();
                        auto value = parse_internal(keep);
                        if (keep and keep_tag and not value.is_discarded())
                        {
                            result[key] = std::move(value);
                        }
                    }
                    while (last_token == lexer::token_type::value_separator);

                    // closing }
                    expect(lexer::token_type::end_object);
                    get_token();
                    if (keep and callback and not callback(--depth, parse_event_t::object_end, result))
                    {
                        result = basic_json(value_t::discarded);
                    }

                    return result;
                }

                case lexer::token_type::begin_array:
                {
                    if (keep and (not callback or (keep = callback(depth++, parse_event_t::array_start, result))))
                    {
                        // explicitly set result to object to cope with []
                        result.m_type = value_t::array;
                        result.m_value = json_value(value_t::array);
                    }

                    // read next token
                    get_token();

                    // closing ] -> we are done
                    if (last_token == lexer::token_type::end_array)
                    {
                        get_token();
                        if (callback and not callback(--depth, parse_event_t::array_end, result))
                        {
                            result = basic_json(value_t::discarded);
                        }
                        return result;
                    }

                    // no comma is expected here
                    unexpect(lexer::token_type::value_separator);

                    // otherwise: parse values
                    do
                    {
                        // ugly, but could be fixed with loop reorganization
                        if (last_token == lexer::token_type::value_separator)
                        {
                            get_token();
                        }

                        // parse value
                        auto value = parse_internal(keep);
                        if (keep and not value.is_discarded())
                        {
                            result.push_back(std::move(value));
                        }
                    }
                    while (last_token == lexer::token_type::value_separator);

                    // closing ]
                    expect(lexer::token_type::end_array);
                    get_token();
                    if (keep and callback and not callback(--depth, parse_event_t::array_end, result))
                    {
                        result = basic_json(value_t::discarded);
                    }

                    return result;
                }

                case lexer::token_type::literal_null:
                {
                    get_token();
                    result.m_type = value_t::null;
                    break;
                }

                case lexer::token_type::value_string:
                {
                    const auto s = m_lexer.get_string();
                    get_token();
                    result = basic_json(s);
                    break;
                }

                case lexer::token_type::literal_true:
                {
                    get_token();
                    result.m_type = value_t::boolean;
                    result.m_value = true;
                    break;
                }

                case lexer::token_type::literal_false:
                {
                    get_token();
                    result.m_type = value_t::boolean;
                    result.m_value = false;
                    break;
                }

                case lexer::token_type::value_number:
                {
                    m_lexer.get_number(result);
                    get_token();
                    break;
                }

                default:
                {
                    // the last token was unexpected
                    unexpect(last_token);
                }
            }

            if (keep and callback and not callback(depth, parse_event_t::value, result))
            {
                result = basic_json(value_t::discarded);
            }
            return result;
        }

        typename lexer::token_type get_token() noexcept
        {
            last_token = m_lexer.scan();
            return last_token;
        }

        void expect(typename lexer::token_type t) const
        {
            if (t != last_token)
            {
                std::string error_msg = "parse error - unexpected ";
                error_msg += (last_token == lexer::token_type::parse_error ? ("'" +  m_lexer.get_token() + "'") :
                              lexer::token_type_name(last_token));
                error_msg += "; expected " + lexer::token_type_name(t);
                throw std::invalid_argument(error_msg);
            }
        }

        void unexpect(typename lexer::token_type t) const
        {
            if (t == last_token)
            {
                std::string error_msg = "parse error - unexpected ";
                error_msg += (last_token == lexer::token_type::parse_error ? ("'" +  m_lexer.get_token() + "'") :
                              lexer::token_type_name(last_token));
                throw std::invalid_argument(error_msg);
            }
        }

      private:
        int depth = 0;
        parser_callback_t callback;
        typename lexer::token_type last_token = lexer::token_type::uninitialized;
        lexer m_lexer;
    };
};


// presets //

using json = basic_json<>;
}


// nonmember functions //

// specialization of std::swap, and std::hash
namespace std
{
template <>
inline void swap(nlohmann::json& j1,
                 nlohmann::json& j2) noexcept(
                     is_nothrow_move_constructible<nlohmann::json>::value and
                     is_nothrow_move_assignable<nlohmann::json>::value
                 )
{
    j1.swap(j2);
}

template <>
struct hash<nlohmann::json>
{
    std::size_t operator()(const nlohmann::json& j) const
    {
        // a naive hashing via the string representation
        const auto& h = hash<nlohmann::json::string_t>();
        return h(j.dump());
    }
};
}

inline nlohmann::json operator "" _json(const char* s, std::size_t)
{
    return nlohmann::json::parse(reinterpret_cast<const nlohmann::json::string_t::value_type*>(s));
}

// restore GCC/clang diagnostic settings
#if defined(__clang__) || defined(__GNUC__) || defined(__GNUG__)
    #pragma GCC diagnostic pop
#endif

#endif