json/src/json.hpp.re2c

/*!
@file
@copyright The code is licensed under the MIT License
           <http://opensource.org/licenses/MIT>,
           Copyright (c) 2013-2015 Niels Lohmann.
@author Niels Lohmann <http://nlohmann.me>
@see https://github.com/nlohmann/json
*/

#ifndef _NLOHMANN_JSON
#define _NLOHMANN_JSON

#include <algorithm>
#include <cmath>
#include <functional>
#include <initializer_list>
#include <iostream>
#include <iterator>
#include <limits>
#include <map>
#include <memory>
#include <string>
#include <type_traits>
#include <utility>
#include <vector>

/*
- ObjectType trick from http://stackoverflow.com/a/9860911
*/

/*!
@see https://github.com/nlohmann
*/
namespace nlohmann
{

/*!
@brief JSON

@tparam ObjectType         type for JSON objects
                           (@c std::map by default)
@tparam ArrayType          type for JSON arrays
                           (@c std::vector by default)
@tparam StringType         type for JSON strings and object keys
                           (@c std::string by default)
@tparam BooleanType        type for JSON booleans
                           (@c bool by default)
@tparam NumberIntegerType  type for JSON integer numbers
                           (@c int64_t by default)
@tparam NumberFloatType    type for JSON floating-point numbers
                           (@c double by default)

@see RFC 7159 <http://rfc7159.net/rfc7159>
@see ECMA 404 <http://www.ecma-international.org/publications/standards/Ecma-404.htm>
*/
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 = int64_t,
    class NumberFloatType = double,
    template<typename U> class Allocator = std::allocator
    >
class basic_json
{
  public:
    /////////////////////
    // container types //
    /////////////////////

    // forward declarations
    class iterator;
    class const_iterator;

    /// the type of elements in a basic_json container
    using value_type = basic_json;
    /// the type of an element reference
    using reference = basic_json&;
    /// the type of an element const reference
    using const_reference = const basic_json&;
    /// the type of an element pointer
    using pointer = basic_json*;
    /// the type of an element const pointer
    using const_pointer = const basic_json*;
    /// a type to represent differences between iterators
    using difference_type = std::ptrdiff_t;
    /// a type to represent container sizes
    using size_type = std::size_t;
    /// an iterator for a basic_json container
    using iterator = basic_json::iterator;
    /// a const iterator for a basic_json container
    using const_iterator = basic_json::const_iterator;
    /// a reverse iterator for a basic_json container
    using reverse_iterator = std::reverse_iterator<iterator>;
    /// a const reverse iterator for a basic_json container
    using const_reverse_iterator = std::reverse_iterator<const_iterator>;


    ///////////////////////////
    // JSON value data types //
    ///////////////////////////

    /// a type for an object
    using object_t = ObjectType<StringType, basic_json>;
    /// a type for an array
    using array_t = ArrayType<basic_json>;
    /// a type for a string
    using string_t = StringType;
    /// a type for a boolean
    using boolean_t = BooleanType;
    /// a type for a number (integer)
    using number_integer_t = NumberIntegerType;
    /// a type for a number (floating-point)
    using number_float_t = NumberFloatType;
    /// a type for list initialization
    using list_init_t = std::initializer_list<basic_json>;


    ////////////////////////
    // JSON value storage //
    ////////////////////////

    /// a JSON value
    union json_value
    {
        /// object (stored with pointer to save storage)
        object_t* object;
        /// array (stored with pointer to save storage)
        array_t* array;
        /// string (stored with pointer to save storage)
        string_t* string;
        /// bolean
        boolean_t boolean;
        /// number (integer)
        number_integer_t number_integer;
        /// number (floating-point)
        number_float_t number_float;

        /// default constructor (for null values)
        json_value() = default;
        /// constructor for objects
        json_value(object_t* v) : object(v) {}
        /// constructor for arrays
        json_value(array_t* v) : array(v) {}
        /// constructor for strings
        json_value(string_t* v) : string(v) {}
        /// constructor for booleans
        json_value(boolean_t v) : boolean(v) {}
        /// constructor for numbers (integer)
        json_value(number_integer_t v) : number_integer(v) {}
        /// constructor for numbers (floating-point)
        json_value(number_float_t v) : number_float(v) {}
    };


    /////////////////////////////////
    // JSON value type enumeration //
    /////////////////////////////////

    /// JSON value type enumeration
    enum class value_t : uint8_t
    {
        null,           ///< null value
        object,         ///< object (unordered set of name/value pairs)
        array,          ///< array (ordered collection of values)
        string,         ///< string value
        boolean,        ///< boolean value
        number_integer, ///< number value (integer)
        number_float    ///< number value (floating-point)
    };


    //////////////////
    // constructors //
    //////////////////

    /// create an empty value with a given type
    inline basic_json(const value_t value)
        : m_type(value)
    {
        switch (m_type)
        {
            case (value_t::null):
            {
                break;
            }

            case (value_t::object):
            {
                m_value.object = new object_t();
                break;
            }

            case (value_t::array):
            {
                m_value.array = new array_t();
                break;
            }

            case (value_t::string):
            {
                Allocator<string_t> alloc;
                m_value.string = alloc.allocate(1);
                alloc.construct(m_value.string, "");

                //m_value.string = new string_t("");
                break;
            }

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

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

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

    /// create a null object (implicitly)
    inline basic_json() noexcept
        : m_type(value_t::null)
    {}

    /// create a null object (explicitly)
    inline basic_json(std::nullptr_t) noexcept
        : m_type(value_t::null)
    {}

    /// create an object (explicit)
    inline basic_json(const object_t& value)
        : m_type(value_t::object), m_value(new object_t(value))
    {}

    /// create an object (implicit)
    template <class V, typename
              std::enable_if<
                  std::is_constructible<string_t, typename V::key_type>::value and
                  std::is_constructible<basic_json, typename V::mapped_type>::value, int>::type
              = 0>
    inline basic_json(const V& value)
        : m_type(value_t::object), m_value(new object_t(value.begin(), value.end()))
    {}

    /// create an array (explicit)
    inline basic_json(const array_t& value)
        : m_type(value_t::array), m_value(new array_t(value))
    {}

    /// create an array (implicit)
    template <class V, typename
              std::enable_if<
                  not std::is_same<V, basic_json::iterator>::value and
                  not std::is_same<V, basic_json::const_iterator>::value and
                  not std::is_same<V, basic_json::reverse_iterator>::value and
                  not std::is_same<V, basic_json::const_reverse_iterator>::value and
                  not std::is_same<V, typename array_t::iterator>::value and
                  not std::is_same<V, typename array_t::const_iterator>::value and
                  std::is_constructible<basic_json, typename V::value_type>::value, int>::type
              = 0>
    inline basic_json(const V& value)
        : m_type(value_t::array), m_value(new array_t(value.begin(), value.end()))
    {}

    /// create a string (explicit)
    inline basic_json(const string_t& value)
        : m_type(value_t::string)//, m_value(new string_t(value))
    {
        Allocator<string_t> alloc;
        m_value.string = alloc.allocate(1);
        alloc.construct(m_value.string, value);
    }

    /// create a string (explicit)
    inline basic_json(const typename string_t::value_type* value)
        : m_type(value_t::string)//, m_value(new string_t(value))
    {
        Allocator<string_t> alloc;
        m_value.string = alloc.allocate(1);
        alloc.construct(m_value.string, value);
    }

    /// create a string (implicit)
    template <class V, typename
              std::enable_if<
                  std::is_constructible<string_t, V>::value, int>::type
              = 0>
    inline basic_json(const V& value)
        : basic_json(string_t(value))
    {}

    /// create a boolean (explicit)
    inline basic_json(boolean_t value)
        : m_type(value_t::boolean), m_value(value)
    {}

    /// create an integer number (explicit)
    inline basic_json(const number_integer_t& value)
        : m_type(value_t::number_integer), m_value(value)
    {}

    /// create an integer number (implicit)
    template<typename T, typename
             std::enable_if<
                 std::is_constructible<number_integer_t, T>::value and
                 std::numeric_limits<T>::is_integer, T>::type
             = 0>
    inline basic_json(const T value) noexcept
        : m_type(value_t::number_integer), m_value(number_integer_t(value))
    {}

    /// create a floating-point number (explicit)
    inline basic_json(const number_float_t& value)
        : m_type(value_t::number_float), m_value(value)
    {}

    /// create a floating-point number (implicit)
    template<typename T, typename = typename
             std::enable_if<
                 std::is_constructible<number_float_t, T>::value and
                 std::is_floating_point<T>::value>::type
             >
    inline basic_json(const T value) noexcept
        : m_type(value_t::number_float), m_value(number_float_t(value))
    {}

    /// create a container (array or object) from an initializer list
    inline basic_json(list_init_t l, bool type_deduction = true, value_t manual_type = value_t::array)
    {
        // the initializer list could describe an object
        bool is_object = true;

        // check if each element is an array with two elements whose first element
        // is a string
        for (const auto& element : l)
        {
            if ((element.m_final and element.m_type == value_t::array)
                    or (element.m_type != value_t::array or element.size() != 2
                        or element[0].m_type != value_t::string))
            {
                // we found an element that makes it impossible to use the
                // initializer list as object
                is_object = false;
                break;
            }
        }

        // adjust type if type deduction is not wanted
        if (not type_deduction)
        {
            // mark this object's type as final
            m_final = true;

            // if array is wanted, do not create an object though possible
            if (manual_type == value_t::array)
            {
                is_object = false;
            }

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

        if (is_object)
        {
            // the initializer list is a list of pairs -> create object
            m_type = value_t::object;
            m_value = new object_t();
            for (auto& element : l)
            {
                m_value.object->emplace(std::move(*(element[0].m_value.string)), std::move(element[1]));
            }
        }
        else
        {
            // the initializer list describes an array -> create array
            m_type = value_t::array;
            m_value = new array_t(std::move(l));
        }
    }

    /// explicitly create an array from an initializer list
    inline static basic_json array(list_init_t l = list_init_t())
    {
        return basic_json(l, false, value_t::array);
    }

    /// explicitly create an object from an initializer list
    inline static basic_json object(list_init_t l = list_init_t())
    {
        return basic_json(l, false, value_t::object);
    }

    ///////////////////////////////////////
    // other constructors and destructor //
    ///////////////////////////////////////

    /// copy constructor
    inline basic_json(const basic_json& other)
        : m_type(other.m_type)
    {
        switch (m_type)
        {
            case (value_t::null):
            {
                break;
            }
            case (value_t::object):
            {
                m_value.object = new object_t(*other.m_value.object);
                break;
            }
            case (value_t::array):
            {
                m_value.array = new array_t(*other.m_value.array);
                break;
            }
            case (value_t::string):
            {
                // m_value.string = new string_t(*other.m_value.string);
                Allocator<string_t> alloc;
                m_value.string = alloc.allocate(1);
                alloc.construct(m_value.string, *other.m_value.string);
                break;
            }
            case (value_t::boolean):
            {
                m_value.boolean = other.m_value.boolean;
                break;
            }
            case (value_t::number_integer):
            {
                m_value.number_integer = other.m_value.number_integer;
                break;
            }
            case (value_t::number_float):
            {
                m_value.number_float = other.m_value.number_float;
                break;
            }
        }
    }

    /// move constructor
    inline 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 = {};
    }

    /// copy assignment
    inline 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
    )
    {
        std::swap(m_type, other.m_type);
        std::swap(m_value, other.m_value);
        return *this;
    }

    /// destructor
    inline ~basic_json() noexcept
    {
        switch (m_type)
        {
            case (value_t::object):
            {
                delete m_value.object;
                m_value.object = nullptr;
                break;
            }

            case (value_t::array):
            {
                delete m_value.array;
                m_value.array = nullptr;
                break;
            }

            case (value_t::string):
            {
                Allocator<string_t> alloc;
                alloc.deallocate(m_value.string, 1);
                m_value.string = nullptr;

                // delete m_value.string;
                // m_value.string = nullptr;
                break;
            }

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


  public:
    ///////////////////////
    // object inspection //
    ///////////////////////

    /*!
    @brief serialization

    Serialization function for JSON objects. The function tries to mimick Python's
    @p json.dumps() function, and currently supports its @p indent parameter.

    @param indent  if indent is nonnegative, then array elements and object members
                   will be pretty-printed with that indent level. An indent level
                   of 0 will only insert newlines. -1 (the default) selects the
                   most compact representation

    @see https://docs.python.org/2/library/json.html#json.dump
    */
    inline string_t dump(const int indent = -1) const noexcept
    {
        if (indent >= 0)
        {
            return dump(true, static_cast<unsigned int>(indent));
        }
        else
        {
            return dump(false, 0);
        }
    }

    /// return the type of the object (explicit)
    inline value_t type() const noexcept
    {
        return m_type;
    }

    /// return the type of the object (implicit)
    operator value_t() const noexcept
    {
        return m_type;
    }


    //////////////////////
    // value conversion //
    //////////////////////

    /// get an object (explicit)
    template <class T, typename
              std::enable_if<
                  std::is_constructible<string_t, typename T::key_type>::value and
                  std::is_constructible<basic_json, typename T::mapped_type>::value, int>::type
              = 0>
    inline T get() const
    {
        switch (m_type)
        {
            case (value_t::object):
                return T(m_value.object->begin(), m_value.object->end());
            default:
                throw std::logic_error("cannot cast " + type_name() + " to " + typeid(T).name());
        }
    }

    /// get an array (explicit)
    template <class T, typename
              std::enable_if<
                  not std::is_same<T, string_t>::value and
                  std::is_constructible<basic_json, typename T::value_type>::value, int>::type
              = 0>
    inline T get() const
    {
        switch (m_type)
        {
            case (value_t::array):
                return T(m_value.array->begin(), m_value.array->end());
            default:
                throw std::logic_error("cannot cast " + type_name() + " to " + typeid(T).name());
        }
    }

    /// get a string (explicit)
    template <typename T, typename
              std::enable_if<
                  std::is_constructible<T, string_t>::value, int>::type
              = 0>
    inline T get() const
    {
        switch (m_type)
        {
            case (value_t::string):
                return *m_value.string;
            default:
                throw std::logic_error("cannot cast " + type_name() + " to " + typeid(T).name());
        }
    }

    /// get a boolean (explicit)
    template <typename T, typename
              std::enable_if<
                  std::is_same<boolean_t, T>::value, int>::type
              = 0>
    inline T get() const
    {
        switch (m_type)
        {
            case (value_t::boolean):
                return m_value.boolean;
            default:
                throw std::logic_error("cannot cast " + type_name() + " to " + typeid(T).name());
        }
    }

    /// get a number (explicit)
    template<typename T, typename
             std::enable_if<
                 not std::is_same<boolean_t, T>::value and
                 std::is_arithmetic<T>::value, int>::type
             = 0>
    inline T get() const
    {
        switch (m_type)
        {
            case (value_t::number_integer):
                return static_cast<T>(m_value.number_integer);
            case (value_t::number_float):
                return static_cast<T>(m_value.number_float);
            default:
                throw std::logic_error("cannot cast " + type_name() + " to " + typeid(T).name());
        }
    }

    /// get a value (implicit)
    template<typename T>
    inline operator T() const
    {
        return get<T>();
    }


    ////////////////////
    // element access //
    ////////////////////

    /// access specified element with bounds checking
    inline reference at(size_type pos)
    {
        // at only works for arrays
        if (m_type != value_t::array)
        {
            throw std::runtime_error("cannot use at with " + type_name());
        }

        return m_value.array->at(pos);
    }

    /// access specified element with bounds checking
    inline const_reference at(size_type pos) const
    {
        // at only works for arrays
        if (m_type != value_t::array)
        {
            throw std::runtime_error("cannot use at with " + type_name());
        }

        return m_value.array->at(pos);
    }

    /// access specified element
    inline reference operator[](size_type pos)
    {
        // at only works for arrays
        if (m_type != value_t::array)
        {
            throw std::runtime_error("cannot use [] with " + type_name());
        }

        return m_value.array->operator[](pos);
    }

    /// access specified element
    inline const_reference operator[](size_type pos) const
    {
        // at only works for arrays
        if (m_type != value_t::array)
        {
            throw std::runtime_error("cannot use [] with " + type_name());
        }

        return m_value.array->operator[](pos);
    }

    /// access specified element with bounds checking
    inline reference at(const typename object_t::key_type& key)
    {
        // at only works for objects
        if (m_type != value_t::object)
        {
            throw std::runtime_error("cannot use at with " + type_name());
        }

        return m_value.object->at(key);
    }

    /// access specified element with bounds checking
    inline const_reference at(const typename object_t::key_type& key) const
    {
        // at only works for objects
        if (m_type != value_t::object)
        {
            throw std::runtime_error("cannot use at with " + type_name());
        }

        return m_value.object->at(key);
    }

    /// access specified element
    inline reference operator[](const typename object_t::key_type& key)
    {
        // at only works for objects
        if (m_type != value_t::object)
        {
            throw std::runtime_error("cannot use [] with " + type_name());
        }

        return m_value.object->operator[](key);
    }

    /// access specified element
    inline const_reference operator[](const typename object_t::key_type& key) const
    {
        // at only works for objects
        if (m_type != value_t::object)
        {
            throw std::runtime_error("cannot use [] with " + type_name());
        }

        return m_value.object->operator[](key);
    }

    /// access specified element (needed for clang)
    template<typename T, size_t n>
    inline reference operator[](const T (&key)[n])
    {
        // at only works for objects
        if (m_type != value_t::object)
        {
            throw std::runtime_error("cannot use [] with " + type_name());
        }

        return m_value.object->operator[](key);
    }

    /// access specified element (needed for clang)
    template<typename T, size_t n>
    inline const_reference operator[](const T (&key)[n]) const
    {
        // at only works for objects
        if (m_type != value_t::object)
        {
            throw std::runtime_error("cannot use [] with " + type_name());
        }

        return m_value.object->operator[](key);
    }


    /// find an element in an object
    inline iterator find(typename object_t::key_type key)
    {
        auto result = end();

        if (m_type == value_t::object)
        {
            result.m_it.object_iterator = m_value.object->find(key);
        }

        return result;
    }

    /// find an element in an object
    inline const_iterator find(typename object_t::key_type key) const
    {
        auto result = cend();

        if (m_type == value_t::object)
        {
            result.m_it.object_iterator = m_value.object->find(key);
        }

        return result;
    }


    ///////////////
    // iterators //
    ///////////////

    /// returns an iterator to the beginning of the container
    inline iterator begin() noexcept
    {
        iterator result(this);
        result.set_begin();
        return result;
    }

    /// returns a const iterator to the beginning of the container
    inline const_iterator begin() const noexcept
    {
        const_iterator result(this);
        result.set_begin();
        return result;
    }

    /// returns a const iterator to the beginning of the container
    inline const_iterator cbegin() const noexcept
    {
        const_iterator result(this);
        result.set_begin();
        return result;
    }

    /// returns an iterator to the end of the container
    inline iterator end() noexcept
    {
        iterator result(this);
        result.set_end();
        return result;
    }

    /// returns a const iterator to the end of the container
    inline const_iterator end() const noexcept
    {
        const_iterator result(this);
        result.set_end();
        return result;
    }

    /// returns a const iterator to the end of the container
    inline const_iterator cend() const noexcept
    {
        const_iterator result(this);
        result.set_end();
        return result;
    }

    /// returns a reverse iterator to the beginning
    inline reverse_iterator rbegin() noexcept
    {
        return reverse_iterator(end());
    }

    /// returns a reverse iterator to the beginning
    inline const_reverse_iterator rbegin() const noexcept
    {
        return const_reverse_iterator(end());
    }

    /// returns a reverse iterator to the end
    inline reverse_iterator rend() noexcept
    {
        return reverse_iterator(begin());
    }

    /// returns a reverse iterator to the end
    inline const_reverse_iterator rend() const noexcept
    {
        return const_reverse_iterator(begin());
    }

    /// returns a reverse iterator to the beginning
    inline const_reverse_iterator crbegin() const noexcept
    {
        return const_reverse_iterator(cend());
    }

    /// returns a reverse iterator to the end
    inline const_reverse_iterator crend() const noexcept
    {
        return const_reverse_iterator(cbegin());
    }


    //////////////
    // capacity //
    //////////////

    /// checks whether the container is empty
    inline bool empty() const noexcept
    {
        switch (m_type)
        {
            case (value_t::null):
            {
                return true;
            }

            case (value_t::array):
            {
                return m_value.array->empty();
            }

            case (value_t::object):
            {
                return m_value.object->empty();
            }

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

    /// returns the number of elements
    inline size_type size() const noexcept
    {
        switch (m_type)
        {
            case (value_t::null):
            {
                return 0;
            }

            case (value_t::array):
            {
                return m_value.array->size();
            }

            case (value_t::object):
            {
                return m_value.object->size();
            }

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

    /// returns the maximum possible number of elements
    inline size_type max_size() const noexcept
    {
        switch (m_type)
        {
            case (value_t::null):
            {
                return 0;
            }

            case (value_t::array):
            {
                return m_value.array->max_size();
            }

            case (value_t::object):
            {
                return m_value.object->max_size();
            }

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


    ///////////////
    // modifiers //
    ///////////////

    /// clears the contents
    inline void clear() noexcept
    {
        switch (m_type)
        {
            case (value_t::null):
            {
                break;
            }

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

            case (value_t::array):
            {
                m_value.array->clear();
                break;
            }

            case (value_t::object):
            {
                m_value.object->clear();
                break;
            }
        }
    }

    /// add an object to an array
    inline void push_back(basic_json&& value)
    {
        // push_back only works for null objects or arrays
        if (not(m_type == value_t::null or m_type == value_t::array))
        {
            throw std::runtime_error("cannot add element to " + type_name());
        }

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

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

    /// add an object to an array
    inline reference operator+=(basic_json&& value)
    {
        push_back(std::move(value));
        return *this;
    }

    /// add an object to an array
    inline void push_back(const basic_json& value)
    {
        // push_back only works for null objects or arrays
        if (not(m_type == value_t::null or m_type == value_t::array))
        {
            throw std::runtime_error("cannot add element to " + type_name());
        }

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

        // add element to array
        m_value.array->push_back(value);
    }

    /// add an object to an array
    inline reference operator+=(const basic_json& value)
    {
        push_back(value);
        return *this;
    }

    /// add an object to an object
    inline void push_back(const typename object_t::value_type& value)
    {
        // push_back only works for null objects or objects
        if (not(m_type == value_t::null or m_type == value_t::object))
        {
            throw std::runtime_error("cannot add element to " + type_name());
        }

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

        // add element to array
        m_value.object->insert(value);
    }

    /// add an object to an object
    inline reference operator+=(const typename object_t::value_type& value)
    {
        push_back(value);
        return operator[](value.first);
    }

    /// swaps the contents
    inline 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);
    }

    /// swaps the contents
    inline void swap(array_t& other)
    {
        // swap only works for arrays
        if (m_type != value_t::array)
        {
            throw std::runtime_error("cannot use swap with " + type_name());
        }

        // swap arrays
        std::swap(*(m_value.array), other);
    }

    /// swaps the contents
    inline void swap(object_t& other)
    {
        // swap only works for objects
        if (m_type != value_t::object)
        {
            throw std::runtime_error("cannot use swap with " + type_name());
        }

        // swap arrays
        std::swap(*(m_value.object), other);
    }

    /// swaps the contents
    inline void swap(string_t& other)
    {
        // swap only works for strings
        if (m_type != value_t::string)
        {
            throw std::runtime_error("cannot use swap with " + type_name());
        }

        // swap arrays
        std::swap(*(m_value.string), other);
    }


    //////////////////////////////////////////
    // lexicographical comparison operators //
    //////////////////////////////////////////

    /// comparison: equal
    friend bool operator==(const_reference lhs, const_reference rhs)
    {
        switch (lhs.type())
        {
            case (value_t::array):
            {
                if (rhs.type() == value_t::array)
                {
                    return *lhs.m_value.array == *rhs.m_value.array;
                }
                break;
            }
            case (value_t::object):
            {
                if (rhs.type() == value_t::object)
                {
                    return *lhs.m_value.object == *rhs.m_value.object;
                }
                break;
            }
            case (value_t::null):
            {
                if (rhs.type() == value_t::null)
                {
                    return true;
                }
                break;
            }
            case (value_t::string):
            {
                if (rhs.type() == value_t::string)
                {
                    return *lhs.m_value.string == *rhs.m_value.string;
                }
                break;
            }
            case (value_t::boolean):
            {
                if (rhs.type() == value_t::boolean)
                {
                    return lhs.m_value.boolean == rhs.m_value.boolean;
                }
                break;
            }
            case (value_t::number_integer):
            {
                if (rhs.type() == value_t::number_integer)
                {
                    return lhs.m_value.number_integer == rhs.m_value.number_integer;
                }
                if (rhs.type() == value_t::number_float)
                {
                    return lhs.m_value.number_integer == static_cast<number_integer_t>(rhs.m_value.number_float);
                }
                break;
            }
            case (value_t::number_float):
            {
                if (rhs.type() == value_t::number_integer)
                {
                    return lhs.m_value.number_float == static_cast<number_float_t>(rhs.m_value.number_integer);
                }
                if (rhs.type() == value_t::number_float)
                {
                    return lhs.m_value.number_float == rhs.m_value.number_float;
                }
                break;
            }
        }

        return false;
    }

    /// comparison: not equal
    friend bool operator!=(const_reference lhs, const_reference rhs)
    {
        return not (lhs == rhs);
    }

    /// comparison: less than
    friend bool operator<(const_reference lhs, const_reference rhs)
    {
        switch (lhs.type())
        {
            case (value_t::array):
            {
                if (rhs.type() == value_t::array)
                {
                    return *lhs.m_value.array < *rhs.m_value.array;
                }
                break;
            }
            case (value_t::object):
            {
                if (rhs.type() == value_t::object)
                {
                    return *lhs.m_value.object < *rhs.m_value.object;
                }
                break;
            }
            case (value_t::null):
            {
                if (rhs.type() == value_t::null)
                {
                    return false;
                }
                break;
            }
            case (value_t::string):
            {
                if (rhs.type() == value_t::string)
                {
                    return *lhs.m_value.string < *rhs.m_value.string;
                }
                break;
            }
            case (value_t::boolean):
            {
                if (rhs.type() == value_t::boolean)
                {
                    return lhs.m_value.boolean < rhs.m_value.boolean;
                }
                break;
            }
            case (value_t::number_integer):
            {
                if (rhs.type() == value_t::number_integer)
                {
                    return lhs.m_value.number_integer < rhs.m_value.number_integer;
                }
                if (rhs.type() == value_t::number_float)
                {
                    return lhs.m_value.number_integer < static_cast<number_integer_t>(rhs.m_value.number_float);
                }
                break;
            }
            case (value_t::number_float):
            {
                if (rhs.type() == value_t::number_integer)
                {
                    return lhs.m_value.number_float < static_cast<number_float_t>(rhs.m_value.number_integer);
                }
                if (rhs.type() == value_t::number_float)
                {
                    return lhs.m_value.number_float < rhs.m_value.number_float;
                }
                break;
            }
        }

        return false;
    }

    /// comparison: less than or equal
    friend bool operator<=(const_reference lhs, const_reference rhs)
    {
        return not (rhs < lhs);
    }

    /// comparison: greater than
    friend bool operator>(const_reference lhs, const_reference rhs)
    {
        return not (lhs <= rhs);
    }

    /// comparison: greater than or equal
    friend bool operator>=(const_reference lhs, const_reference rhs)
    {
        return not (lhs < rhs);
    }


    ///////////////////
    // serialization //
    ///////////////////

    /// serialize to stream
    friend std::ostream& operator<<(std::ostream& o, const basic_json& j)
    {
        // read width member and use it as indentation parameter if nonzero
        const int indentation = (o.width() == 0) ? -1 : o.width();

        o << j.dump(indentation);
        return o;
    }

    /// serialize to stream
    friend std::ostream& operator>>(const basic_json& j, std::ostream& o)
    {
        // read width member and use it as indentation parameter if nonzero
        const int indentation = (o.width() == 0) ? -1 : o.width();

        o << j.dump(indentation);
        return o;
    }


    /////////////////////
    // deserialization //
    /////////////////////

    /// deserialize from string
    static basic_json parse(const string_t& s)
    {
        return parser(s).parse();
    }

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

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


  private:
    ///////////////////////////
    // convenience functions //
    ///////////////////////////

    /// return the type as string
    inline 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";
            }

            default:
            {
                return "number";
            }
        }
    }

    /*!
    @brief escape a string

    Escape a string by replacing certain special characters by a sequence of an
    escape character (backslash) and another character and other control
    characters by a sequence of "\u" followed by a four-digit hex
    representation.

    @param s  the string to escape
    @return escaped string
    */
    static string_t escape_string(const string_t& s) noexcept
    {
        // create a result string of at least the size than s
        string_t result;
        result.reserve(s.size());

        for (const auto c : s)
        {
            switch (c)
            {
                // quotation mark (0x22)
                case '"':
                {
                    result += "\\\"";
                    break;
                }
                // reverse solidus (0x5c)
                case '\\':
                {
                    result += "\\\\";
                    break;
                }
                // backspace (0x08)
                case '\b':
                {
                    result += "\\b";
                    break;
                }
                // formfeed (0x0c)
                case '\f':
                {
                    result += "\\f";
                    break;
                }
                // newline (0x0a)
                case '\n':
                {
                    result += "\\n";
                    break;
                }
                // carriage return (0x0d)
                case '\r':
                {
                    result += "\\r";
                    break;
                }
                // horizontal tab (0x09)
                case '\t':
                {
                    result += "\\t";
                    break;
                }

                default:
                {
                    if (c >= 0 and c <= 0x1f)
                    {
                        // control characters (everything between 0x00 and 0x1f)
                        // -> create four-digit hex representation
                        std::stringstream ss;
                        ss << "\\u" << std::hex << std::setw(4) << std::setfill('0') << int(c);
                        result += ss.str();
                    }
                    else
                    {
                        // all other characters are added as-is
                        result.append(1, c);
                    }
                    break;
                }
            }
        }

        return result;
    }


    /*!
    @brief internal implementation of the serialization function

    This function is called by the public member function dump and organizes
    the serializaion internally. The indentation level is propagated as
    additional parameter. In case of arrays and objects, the function is called
    recursively. Note that

    - strings and object keys are escaped using escape_string()
    - numbers are converted to a string before output using std::to_string()

    @param prettyPrint    whether the output shall be pretty-printed
    @param indentStep     the indent level
    @param currentIndent  the current indent level (only used internally)
    */
    inline string_t dump(const bool prettyPrint, const unsigned int indentStep,
                         const unsigned int currentIndent = 0) const noexcept
    {
        // variable to hold indentation for recursive calls
        auto new_indent = currentIndent;

        // helper function to return whitespace as indentation
        const auto indent = [prettyPrint, &new_indent]()
        {
            return prettyPrint ? string_t(new_indent, ' ') : string_t();
        };

        switch (m_type)
        {
            case (value_t::object):
            {
                if (m_value.object->empty())
                {
                    return "{}";
                }

                string_t result = "{";

                // increase indentation
                if (prettyPrint)
                {
                    new_indent += indentStep;
                    result += "\n";
                }

                for (auto i = m_value.object->cbegin(); i != m_value.object->cend(); ++i)
                {
                    if (i != m_value.object->cbegin())
                    {
                        result += prettyPrint ? ",\n" : ",";
                    }
                    result += indent() + "\"" + escape_string(i->first) + "\":" + (prettyPrint ? " " : "")
                              + i->second.dump(prettyPrint, indentStep, new_indent);
                }

                // decrease indentation
                if (prettyPrint)
                {
                    new_indent -= indentStep;
                    result += "\n";
                }

                return result + indent() + "}";
            }

            case (value_t::array):
            {
                if (m_value.array->empty())
                {
                    return "[]";
                }

                string_t result = "[";

                // increase indentation
                if (prettyPrint)
                {
                    new_indent += indentStep;
                    result += "\n";
                }

                for (auto i = m_value.array->cbegin(); i != m_value.array->cend(); ++i)
                {
                    if (i != m_value.array->cbegin())
                    {
                        result += prettyPrint ? ",\n" : ",";
                    }
                    result += indent() + i->dump(prettyPrint, indentStep, new_indent);
                }

                // decrease indentation
                if (prettyPrint)
                {
                    new_indent -= indentStep;
                    result += "\n";
                }

                return result + indent() + "]";
            }

            case (value_t::string):
            {
                return string_t("\"") + escape_string(*m_value.string) + "\"";
            }

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

            case (value_t::number_integer):
            {
                return std::to_string(m_value.number_integer);
            }

            case (value_t::number_float):
            {
                return std::to_string(m_value.number_float);
            }

            default:
            {
                return "null";
            }
        }
    }


  private:
    //////////////////////
    // member variables //
    //////////////////////

    /// the type of the current element
    value_t m_type = value_t::null;

    /// whether the type of JSON object may change later
    bool m_final = false;

    /// the value of the current element
    json_value m_value = {};


  private:
    ///////////////
    // iterators //
    ///////////////

    /// values of a generic iterator type of non-container JSON values
    enum class generic_iterator_value
    {
        /// the iterator was not initialized
        uninitialized,
        /// the iterator points to the only value
        begin,
        /// the iterator points past the only value
        end,
        /// the iterator points to an invalid value
        invalid
    };

    /// an iterator value
    template<typename array_iterator_t, typename object_iterator_t>
    union internal_iterator
    {
        /// iterator for JSON objects
        object_iterator_t object_iterator;
        /// iterator for JSON arrays
        array_iterator_t array_iterator;
        /// generic iteraotr for all other value types
        generic_iterator_value generic_iterator;

        /// default constructor
        internal_iterator() : generic_iterator(generic_iterator_value::uninitialized) {}
        /// constructor for object iterators
        internal_iterator(object_iterator_t v) : object_iterator(v) {}
        /// constructor for array iterators
        internal_iterator(array_iterator_t v) : array_iterator(v) {}
        /// constructor for generic iterators
        internal_iterator(generic_iterator_value v) : generic_iterator(v) {}
    };

  public:
    /// a bidirectional iterator for the basic_json class
    class iterator : public std::iterator<std::bidirectional_iterator_tag, basic_json>
    {
      public:
        /// the type of the values when the iterator is dereferenced
        using value_type = basic_json::value_type;
        /// a type to represent differences between iterators
        using difference_type = basic_json::difference_type;
        /// defines a pointer to the type iterated over (value_type)
        using pointer = basic_json::pointer;
        /// defines a reference to the type iterated over (value_type)
        using reference = basic_json::reference;
        /// the category of the iterator
        using iterator_category = std::bidirectional_iterator_tag;

        /// default constructor
        inline iterator() = default;

        /// constructor for a given JSON instance
        inline iterator(pointer object) : m_object(object)
        {
            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.generic_iterator = generic_iterator_value::uninitialized;
                    break;
                }
            }
        }

        /// copy assignment
        inline iterator& operator=(const iterator& other) noexcept
        {
            m_object = other.m_object;
            m_it = other.m_it;
            return *this;
        }

        /// set the iterator to the first value
        inline void set_begin() noexcept
        {
            switch (m_object->m_type)
            {
                case (basic_json::value_t::object):
                {
                    m_it.object_iterator = m_object->m_value.object->begin();
                    break;
                }

                case (basic_json::value_t::array):
                {
                    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.generic_iterator = generic_iterator_value::end;
                    break;
                }

                default:
                {
                    m_it.generic_iterator = generic_iterator_value::begin;
                    break;
                }
            }
        }

        /// set the iterator past the last value
        inline void set_end() noexcept
        {
            switch (m_object->m_type)
            {
                case (basic_json::value_t::object):
                {
                    m_it.object_iterator = m_object->m_value.object->end();
                    break;
                }

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

                default:
                {
                    m_it.generic_iterator = generic_iterator_value::end;
                    break;
                }
            }
        }

        /// return a reference to the value pointed to by the iterator
        inline reference operator*() const
        {
            switch (m_object->m_type)
            {
                case (basic_json::value_t::object):
                {
                    return m_it.object_iterator->second;
                }

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

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

                default:
                {
                    if (m_it.generic_iterator == generic_iterator_value::begin)
                    {
                        return *m_object;
                    }
                    else
                    {
                        throw std::out_of_range("cannot get value");
                    }
                }
            }
        }

        /// dereference the iterator
        inline pointer operator->() const
        {
            switch (m_object->m_type)
            {
                case (basic_json::value_t::object):
                {
                    return &(m_it.object_iterator->second);
                }

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

                default:
                {
                    if (m_it.generic_iterator == generic_iterator_value::begin)
                    {
                        return m_object;
                    }
                    else
                    {
                        throw std::out_of_range("cannot get value");
                    }
                }
            }
        }

        /// post-increment (it++)
        inline iterator operator++(int)
        {
            iterator result = *this;

            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:
                {
                    if (m_it.generic_iterator == generic_iterator_value::begin)
                    {
                        m_it.generic_iterator = generic_iterator_value::end;
                    }
                    else
                    {
                        m_it.generic_iterator = generic_iterator_value::invalid;
                    }
                    break;
                }
            }

            return result;
        }

        /// pre-increment (++it)
        inline iterator& operator++()
        {
            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:
                {
                    if (m_it.generic_iterator == generic_iterator_value::begin)
                    {
                        m_it.generic_iterator = generic_iterator_value::end;
                    }
                    else
                    {
                        m_it.generic_iterator = generic_iterator_value::invalid;
                    }
                    break;
                }
            }

            return *this;
        }

        /// post-decrement (it--)
        inline iterator operator--(int)
        {
            iterator result = *this;

            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;
                }

                case (basic_json::value_t::null):
                {
                    m_it.generic_iterator = generic_iterator_value::invalid;
                    break;
                }

                default:
                {
                    if (m_it.generic_iterator == generic_iterator_value::end)
                    {
                        m_it.generic_iterator = generic_iterator_value::begin;
                    }
                    else
                    {
                        m_it.generic_iterator = generic_iterator_value::invalid;
                    }
                    break;
                }
            }

            return result;
        }

        /// pre-decrement (--it)
        inline iterator& operator--()
        {
            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;
                }

                case (basic_json::value_t::null):
                {
                    m_it.generic_iterator = generic_iterator_value::invalid;
                    break;
                }

                default:
                {
                    if (m_it.generic_iterator == generic_iterator_value::end)
                    {
                        m_it.generic_iterator = generic_iterator_value::begin;
                    }
                    else
                    {
                        m_it.generic_iterator = generic_iterator_value::invalid;
                    }
                    break;
                }
            }

            return *this;
        }

        /// comparison: equal
        inline bool operator==(const iterator& other) const
        {
            if (m_object != other.m_object or m_object->m_type != other.m_object->m_type)
            {
                return false;
            }

            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.generic_iterator == other.m_it.generic_iterator);
                }
            }
        }

        /// comparison: not equal
        inline bool operator!=(const iterator& other) const
        {
            return not operator==(other);
        }

      private:
        /// associated JSON instance
        pointer m_object = nullptr;
        /// the actual iterator of the associated instance
        internal_iterator<typename array_t::iterator, typename object_t::iterator> m_it;
    };

    /// a const bidirectional iterator for the basic_json class
    class const_iterator : public std::iterator<std::bidirectional_iterator_tag, const basic_json>
    {
      public:
        /// the type of the values when the iterator is dereferenced
        using value_type = basic_json::value_type;
        /// a type to represent differences between iterators
        using difference_type = basic_json::difference_type;
        /// defines a pointer to the type iterated over (value_type)
        using pointer = basic_json::const_pointer;
        /// defines a reference to the type iterated over (value_type)
        using reference = basic_json::const_reference;
        /// the category of the iterator
        using iterator_category = std::bidirectional_iterator_tag;

        /// default constructor
        inline const_iterator() = default;

        /// constructor for a given JSON instance
        inline const_iterator(pointer object) : m_object(object)
        {
            switch (m_object->m_type)
            {
                case (basic_json::value_t::object):
                {
                    m_it.object_iterator = typename object_t::const_iterator();
                    break;
                }
                case (basic_json::value_t::array):
                {
                    m_it.array_iterator = typename array_t::const_iterator();
                    break;
                }
                default:
                {
                    m_it.generic_iterator = generic_iterator_value::uninitialized;
                    break;
                }
            }
        }

        /// copy constructor given a nonconst iterator
        inline const_iterator(const iterator& other) : m_object(other.m_object)
        {
            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.generic_iterator = other.m_it.generic_iterator;
                    break;
                }
            }
        }

        /// copy assignment
        inline const_iterator& operator=(const const_iterator& other) noexcept
        {
            m_object = other.m_object;
            m_it = other.m_it;
            return *this;
        }

        /// set the iterator to the first value
        inline void set_begin() noexcept
        {
            switch (m_object->m_type)
            {
                case (basic_json::value_t::object):
                {
                    m_it.object_iterator = m_object->m_value.object->cbegin();
                    break;
                }

                case (basic_json::value_t::array):
                {
                    m_it.array_iterator = m_object->m_value.array->cbegin();
                    break;
                }

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

                default:
                {
                    m_it.generic_iterator = generic_iterator_value::begin;
                    break;
                }
            }
        }

        /// set the iterator past the last value
        inline void set_end() noexcept
        {
            switch (m_object->m_type)
            {
                case (basic_json::value_t::object):
                {
                    m_it.object_iterator = m_object->m_value.object->cend();
                    break;
                }

                case (basic_json::value_t::array):
                {
                    m_it.array_iterator = m_object->m_value.array->cend();
                    break;
                }

                default:
                {
                    m_it.generic_iterator = generic_iterator_value::end;
                    break;
                }
            }
        }

        /// return a reference to the value pointed to by the iterator
        inline reference operator*() const
        {
            switch (m_object->m_type)
            {
                case (basic_json::value_t::object):
                {
                    return m_it.object_iterator->second;
                }

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

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

                default:
                {
                    if (m_it.generic_iterator == generic_iterator_value::begin)
                    {
                        return *m_object;
                    }
                    else
                    {
                        throw std::out_of_range("cannot get value");
                    }
                }
            }
        }

        /// dereference the iterator
        inline pointer operator->() const
        {
            switch (m_object->m_type)
            {
                case (basic_json::value_t::object):
                {
                    return &(m_it.object_iterator->second);
                }

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

                default:
                {
                    if (m_it.generic_iterator == generic_iterator_value::begin)
                    {
                        return m_object;
                    }
                    else
                    {
                        throw std::out_of_range("cannot get value");
                    }
                }
            }
        }

        /// post-increment (it++)
        inline const_iterator operator++(int)
        {
            const_iterator result = *this;

            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:
                {
                    if (m_it.generic_iterator == generic_iterator_value::begin)
                    {
                        m_it.generic_iterator = generic_iterator_value::end;
                    }
                    else
                    {
                        m_it.generic_iterator = generic_iterator_value::invalid;
                    }
                    break;
                }
            }

            return result;
        }

        /// pre-increment (++it)
        inline const_iterator& operator++()
        {
            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:
                {
                    if (m_it.generic_iterator == generic_iterator_value::begin)
                    {
                        m_it.generic_iterator = generic_iterator_value::end;
                    }
                    else
                    {
                        m_it.generic_iterator = generic_iterator_value::invalid;
                    }
                    break;
                }
            }

            return *this;
        }

        /// post-decrement (it--)
        inline const_iterator operator--(int)
        {
            const_iterator result = *this;

            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;
                }

                case (basic_json::value_t::null):
                {
                    m_it.generic_iterator = generic_iterator_value::invalid;
                    break;
                }

                default:
                {
                    if (m_it.generic_iterator == generic_iterator_value::end)
                    {
                        m_it.generic_iterator = generic_iterator_value::begin;
                    }
                    else
                    {
                        m_it.generic_iterator = generic_iterator_value::invalid;
                    }
                    break;
                }
            }

            return result;
        }

        /// pre-decrement (--it)
        inline const_iterator& operator--()
        {
            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;
                }

                case (basic_json::value_t::null):
                {
                    m_it.generic_iterator = generic_iterator_value::invalid;
                    break;
                }

                default:
                {
                    if (m_it.generic_iterator == generic_iterator_value::end)
                    {
                        m_it.generic_iterator = generic_iterator_value::begin;
                    }
                    else
                    {
                        m_it.generic_iterator = generic_iterator_value::invalid;
                    }
                    break;
                }
            }

            return *this;
        }

        /// comparison: equal
        inline bool operator==(const const_iterator& other) const
        {
            if (m_object != other.m_object or m_object->m_type != other.m_object->m_type)
            {
                return false;
            }

            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.generic_iterator == other.m_it.generic_iterator);
                }
            }
        }

        /// comparison: not equal
        inline bool operator!=(const const_iterator& other) const
        {
            return not operator==(other);
        }

      private:
        /// associated JSON instance
        pointer m_object = nullptr;
        /// the actual iterator of the associated instance
        internal_iterator<typename array_t::const_iterator, typename object_t::const_iterator> m_it;
    };


  private:
    //////////////////////
    // lexer and parser //
    //////////////////////

    /*!
    @brief lexical analysis

    This class organizes the lexical analysis during JSON deserialization. The
    core of it is a scanner generated by re2c <http://re2c.org> that processes
    a buffer and recognizes tokens according to RFC 7159 and ECMA-404.
    */
    class lexer
    {
      public:
        /// token types for the parser
        enum class token_type
        {
            uninitialized,    ///< indicating the scanner is uninitialized
            literal_true,     ///< the "true" literal
            literal_false,    ///< the "false" literal
            literal_null,     ///< the "null" literal
            value_string,     ///< a string - use get_string() for actual value
            value_number,     ///< a number - use get_number() for actual value
            begin_array,      ///< the character for array begin "["
            begin_object,     ///< the character for object begin "{"
            end_array,        ///< the character for array end "]"
            end_object,       ///< the character for object end "}"
            name_separator,   ///< the name separator ":"
            value_separator,  ///< the value separator ","
            parse_error,      ///< indicating a parse error
            end_of_input      ///< indicating the end of the input buffer
        };

        /// the char type to use in the lexer
        using lexer_char_t = typename string_t::value_type;

        /// constructor with a given buffer
        inline lexer(const string_t& s) noexcept
            : m_content(s.c_str())
        {
            m_start = m_cursor = m_content;
            m_limit = m_content + s.size();
        }

        /// default constructor
        inline lexer() = default;

        /*!
        @brief create a string from a Unicode code point

        @param codepoint  the code point (must be in [0x0, 0x10ffff]
        @return string representation of the code point
        @exception std::out_of_range if code point is >0x10ffff
        @exception std::invalid_argument if the low surrogate is invalid

        @see <http://en.wikipedia.org/wiki/UTF-8#Sample_code>
        */
        inline static string_t to_unicode(const size_t codepoint1, size_t codepoint2 = 0)
        {
            string_t result;

            // calculate the codepoint from the given code points
            size_t codepoint = codepoint1;
            if (codepoint1 >= 0xD800 and codepoint1 <= 0xDBFF)
            {
                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 substract with:
                        // (0xD800 << 10) + DC00 - 0x10000 = 0x35FDC00
                        - 0x35FDC00;
                }
                else
                {
                    throw std::invalid_argument("missing or wrong low surrogate");
                }
            }

            if (codepoint <= 0x7f)
            {
                // 1-byte characters: 0xxxxxxx (ASCI)
                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;
        }

        /// return name of values of type token_type
        inline static std::string token_type_name(token_type t) noexcept
        {
            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::end_of_input):
                    return "<end of input>";
                default:
                    return "<parse error>";
            }
        }

        /*!
        This function implements a scanner for JSON. It is specified using
        regular expressions that try to follow RFC 7159 and ECMA-404 as close
        as possible. These regular expressions are then translated into a
        deterministic finite automaton (DFA) by the tool re2c
        <http://re2c.org>. As a result, the translated code for this function
        consists of a large block of code with goto jumps.

        @return the class of the next token read from the buffer
        */
        inline token_type scan() noexcept
        {
            // pointer for backtracking information
            const lexer_char_t* m_marker = nullptr;

            // remember the begin of the token
            m_start = m_cursor;

            /*!re2c
                re2c:define:YYCTYPE  = lexer_char_t;
                re2c:define:YYCURSOR = m_cursor;
                re2c:define:YYLIMIT  = m_limit;
                re2c:define:YYMARKER = m_marker;
                re2c:indent:string   = "    ";
                re2c:indent:top      = 1;
                re2c:labelprefix     = "basic_json_parser_";
                re2c:yyfill:enable   = 0;

                // whitespace
                ws = [ \t\n\r]+;
                ws   { return scan(); }

                // structural characters
                "[" { return token_type::begin_array; }
                "]" { return token_type::end_array; }
                "{" { return token_type::begin_object; }
                "}" { return token_type::end_object; }
                "," { return token_type::value_separator; }
                ":" { return token_type::name_separator; }

                // literal names
                "null"  { return token_type::literal_null; }
                "true"  { return token_type::literal_true; }
                "false" { return token_type::literal_false; }

                // number
                decimal_point = [.];
                digit         = [0-9];
                digit_1_9     = [1-9];
                e             = [eE];
                minus         = [-];
                plus          = [+];
                zero          = [0];
                exp           = e (minus|plus)? digit+;
                frac          = decimal_point digit+;
                int           = (zero|digit_1_9 digit*);
                number        = minus? int frac? exp?;
                number        { return token_type::value_number; }

                // string
                quotation_mark  = [\"];
                escape          = [\\];
                unescaped       = [^\"\\\000];
                single_escaped  = [\"\\/bfnrt];
                unicode_escaped = [u][0-9a-fA-F]{4};
                escaped         = escape (single_escaped | unicode_escaped);
                char            = unescaped | escaped;
                string          = quotation_mark char* quotation_mark;
                string          { return token_type::value_string; }

                // end of file
                '\000'         { return token_type::end_of_input; }

                // anything else is an error
                .              { return token_type::parse_error; }
             */
        }

        /// return string representation of last read token
        inline string_t get_token() const noexcept
        {
            return string_t(m_start, static_cast<size_t>(m_cursor - m_start));
        }

        /*!
        @brief return string value for string tokens

        The function iterates the characters between the opening and closing
        quotes of the string value. The complete string is the range
        [m_start,m_cursor). Consequently, we iterate from m_start+1 to
        m_cursor-1.

        We differentiate two cases:

        1. Escaped characters. In this case, a new character is constructed
           according to the nature of the escape. Some escapes create new
           characters (e.g., @c "\\n" is replaced by @c "\n"), some are copied
           as is (e.g., @c "\\\\"). Furthermore, Unicode escapes of the shape
           @c "\\uxxxx" need special care. In this case, to_unicode takes care
           of the construction of the values.
        2. Unescaped characters are copied as is.

        @return string value of current token without opening and closing quotes
        @exception std::out_of_range if to_unicode fails
        */
        inline 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 typename string_t::value_type* 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;
                        }

                        // characters that are not "un"escsaped
                        case '\\':
                        {
                            result += "\\\\";
                            break;
                        }
                        case '/':
                        {
                            result += "\\/";
                            break;
                        }
                        case '"':
                        {
                            result += "\\\"";
                            break;
                        }

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

                            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(i + 7, 4).c_str(), nullptr, 16);
                                result += to_unicode(codepoint, codepoint2);
                                // skip the next 11 characters (xxxx\uyyyy)
                                i += 11;
                            }
                            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, *i);
                }
            }

            return result;
        }

        /*!
        @brief return number value for number tokens

        This function translates the last token into a floating point number.
        The pointer m_begin points to the beginning of the parsed number. We
        pass this pointer to std::strtod which sets endptr to the first
        character past the converted number. If this pointer is not the same as
        m_cursor, then either more or less characters have been used during the
        comparison. This can happen for inputs like "01" which will be treated
        like number 0 followed by number 1.

        @return the result of the number conversion or NAN if the conversion
        read past the current token. The latter case needs to be treated by the
        caller function.

        @exception std::range_error if passed value is out of range
        */
        inline number_float_t get_number() const
        {
            // conversion
            lexer_char_t* endptr;
            const auto float_val = std::strtod(reinterpret_cast<const lexer_char_t*>(m_start),
                                               &endptr);

            // return float_val if the whole number was translated and NAN
            // otherwise
            return (endptr == m_cursor) ? float_val : NAN;
        }

      private:
        /// the buffer
        const lexer_char_t* m_content = nullptr;
        /// pointer to he beginning of the current symbol
        const lexer_char_t* m_start = nullptr;
        /// pointer to the current symbol
        const lexer_char_t* m_cursor = nullptr;
        /// pointer to the end of the buffer
        const lexer_char_t* m_limit = nullptr;
    };

    class parser
    {
      public:
        /// constructor for strings
        inline parser(const string_t& s) : m_buffer(s), m_lexer(m_buffer)
        {
            // read first token
            get_token();
        }

        /// a parser reading from an input stream
        inline parser(std::istream& _is)
        {
            while (_is)
            {
                string_t input_line;
                std::getline(_is, input_line);
                m_buffer += input_line;
            }

            // initializer lexer
            m_lexer = lexer(m_buffer);

            // read first token
            get_token();
        }

        /// public parser interface
        inline basic_json parse()
        {
            basic_json result = parse_internal();

            expect(lexer::token_type::end_of_input);

            return result;
        }

      private:
        /// the actual parser
        inline basic_json parse_internal()
        {
            switch (last_token)
            {
                case (lexer::token_type::begin_object):
                {
                    // explicitly set result to object to cope with {}
                    basic_json result(value_t::object);

                    // read next token
                    get_token();

                    // closing } -> we are done
                    if (last_token == lexer::token_type::end_object)
                    {
                        get_token();
                        return result;
                    }

                    // 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();

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

                        // parse value
                        get_token();
                        result[key] = parse_internal();
                    }
                    while (last_token == lexer::token_type::value_separator);

                    // closing }
                    expect(lexer::token_type::end_object);
                    get_token();

                    return result;
                }

                case (lexer::token_type::begin_array):
                {
                    // explicitly set result to object to cope with []
                    basic_json result(value_t::array);

                    // read next token
                    get_token();

                    // closing ] -> we are done
                    if (last_token == lexer::token_type::end_array)
                    {
                        get_token();
                        return result;
                    }

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

                        // parse value
                        result.push_back(parse_internal());
                    }
                    while (last_token == lexer::token_type::value_separator);

                    // closing ]
                    expect(lexer::token_type::end_array);
                    get_token();

                    return result;
                }

                case (lexer::token_type::literal_null):
                {
                    get_token();
                    return basic_json(nullptr);
                }

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

                case (lexer::token_type::literal_true):
                {
                    get_token();
                    return basic_json(true);
                }

                case (lexer::token_type::literal_false):
                {
                    get_token();
                    return basic_json(false);
                }

                case (lexer::token_type::value_number):
                {
                    auto float_val = m_lexer.get_number();

                    // NAN is returned if token could not be translated
                    // completely
                    if (std::isnan(float_val))
                    {
                        throw std::invalid_argument(std::string("parse error - ") +
                                                    m_lexer.get_token() + " is not a number");
                    }

                    get_token();

                    // check if conversion loses precision
                    const auto int_val = static_cast<number_integer_t>(float_val);
                    if (float_val == int_val)
                    {
                        // we basic_json not lose precision -> return int
                        return basic_json(int_val);
                    }
                    else
                    {
                        // we would lose precision -> returnfloat
                        return basic_json(float_val);
                    }
                }

                default:
                {
                    std::string error_msg = "parse error - unexpected \'";
                    error_msg += m_lexer.get_token();
                    error_msg += "\' (";
                    error_msg += lexer::token_type_name(last_token) + ")";
                    throw std::invalid_argument(error_msg);
                }
            }
        }

        /// get next token from lexer
        inline typename lexer::token_type get_token()
        {
            last_token = m_lexer.scan();
            return last_token;
        }

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

      private:
        /// the buffer
        string_t m_buffer;
        /// the type of the last read token
        typename lexer::token_type last_token = lexer::token_type::uninitialized;
        /// the lexer
        lexer m_lexer;
    };
};


/////////////
// presets //
/////////////

/// default JSON class
using json = basic_json<>;

}


/////////////////////////
// nonmember functions //
/////////////////////////

// specialization of std::swap, and std::hash
namespace std
{
/// swaps the values of two JSON objects
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);
}

/// hash value for JSON objects
template <>
struct hash<nlohmann::json>
{
    /// return a hash value for a JSON object
    inline size_t operator()(const nlohmann::json& j) const
    {
        // a naive hashing via the string representation
        return hash<std::string>()(j.dump());
    }
};
}

/*!
This operator implements a user-defined string literal for JSON objects. It can
be used by adding \p "_json" to a string literal and returns a JSON object if
no parse error occurred.

@param s  a string representation of a JSON object
@return a JSON object
*/
inline nlohmann::json operator "" _json(const char* s, std::size_t)
{
    return nlohmann::json::parse(s);
}

#endif