json.hpp

    bool end_array() override
    {
        bool keep = true;

        if (ref_stack.back())
        {
            keep = callback(static_cast<int>(ref_stack.size()) - 1, parse_event_t::array_end, *ref_stack.back());
            if (not keep)
            {
                // discard array
                *ref_stack.back() = discarded;
            }
        }

        assert(not ref_stack.empty());
        assert(not keep_stack.empty());
        ref_stack.pop_back();
        keep_stack.pop_back();

        // remove discarded value
        if (not keep and not ref_stack.empty())
        {
            if (ref_stack.back()->is_array())
            {
                ref_stack.back()->m_value.array->pop_back();
            }
        }

        return true;
    }

    bool parse_error(std::size_t, const std::string&,
                     const detail::exception& ex) override
    {
        errored = true;
        if (allow_exceptions)
        {
            // determine the proper exception type from the id
            switch ((ex.id / 100) % 100)
            {
                case 1:
                    JSON_THROW(*reinterpret_cast<const detail::parse_error*>(&ex));
                case 2:
                    JSON_THROW(*reinterpret_cast<const detail::invalid_iterator*>(&ex));  // LCOV_EXCL_LINE
                case 3:
                    JSON_THROW(*reinterpret_cast<const detail::type_error*>(&ex));  // LCOV_EXCL_LINE
                case 4:
                    JSON_THROW(*reinterpret_cast<const detail::out_of_range*>(&ex));
                case 5:
                    JSON_THROW(*reinterpret_cast<const detail::other_error*>(&ex));  // LCOV_EXCL_LINE
                default:
                    assert(false);  // LCOV_EXCL_LINE
            }
        }
        return false;
    }

    constexpr bool is_errored() const
    {
        return errored;
    }

  private:
    /*!
    @param[in] v  value to add to the JSON value we build during parsing
    @param[in] skip_callback  whether we should skip calling the callback
               function; this is required after start_array() and
               start_object() SAX events, because otherwise we would call the
               callback function with an empty array or object, respectively.

    @invariant If the ref stack is empty, then the passed value will be the new
               root.
    @invariant If the ref stack contains a value, then it is an array or an
               object to which we can add elements

    @return pair of boolean (whether value should be kept) and pointer (to the
            passed value in the ref_stack hierarchy; nullptr if not kept)
    */
    template<typename Value>
    std::pair<bool, BasicJsonType*> handle_value(Value&& v, const bool skip_callback = false)
    {
        assert(not keep_stack.empty());

        // do not handle this value if we know it would be added to a discarded
        // container
        if (not keep_stack.back())
        {
            return {false, nullptr};
        }

        // create value
        auto value = BasicJsonType(std::forward<Value>(v));

        // check callback
        const bool keep = skip_callback or callback(static_cast<int>(ref_stack.size()), parse_event_t::value, value);

        // do not handle this value if we just learnt it shall be discarded
        if (not keep)
        {
            return {false, nullptr};
        }

        if (ref_stack.empty())
        {
            root = std::move(value);
            return {true, &root};
        }
        else
        {
            assert(ref_stack.back()->is_array() or ref_stack.back()->is_object());
            if (ref_stack.back()->is_array())
            {
                ref_stack.back()->m_value.array->push_back(std::move(value));
                return {true, &(ref_stack.back()->m_value.array->back())};
            }
            else
            {
                // check if we should store an element for the current key
                assert(not key_keep_stack.empty());
                const bool store_element = key_keep_stack.back();
                key_keep_stack.pop_back();

                if (not store_element)
                {
                    return {false, nullptr};
                }

                assert(object_element);
                *object_element = std::move(value);
                return {true, object_element};
            }
        }
    }

    /// the parsed JSON value
    BasicJsonType& root;
    /// stack to model hierarchy of values
    std::vector<BasicJsonType*> ref_stack;
    /// stack to manage which values to keep
    std::vector<bool> keep_stack;
    /// stack to manage which object keys to keep
    std::vector<bool> key_keep_stack;
    /// helper to hold the reference for the next object element
    BasicJsonType* object_element = nullptr;
    /// whether a syntax error occurred
    bool errored = false;
    /// callback function
    const parser_callback_t callback = nullptr;
    /// whether to throw exceptions in case of errors
    const bool allow_exceptions = true;
    /// a discarded value for the callback
    BasicJsonType discarded = BasicJsonType::value_t::discarded;
};

template<typename BasicJsonType>
class json_sax_acceptor : public json_sax<BasicJsonType>
{
  public:
    using number_integer_t = typename BasicJsonType::number_integer_t;
    using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
    using number_float_t = typename BasicJsonType::number_float_t;
    using string_t = typename BasicJsonType::string_t;

    bool null() override
    {
        return true;
    }

    bool boolean(bool) override
    {
        return true;
    }

    bool number_integer(number_integer_t) override
    {
        return true;
    }

    bool number_unsigned(number_unsigned_t) override
    {
        return true;
    }

    bool number_float(number_float_t, const string_t&) override
    {
        return true;
    }

    bool string(string_t&) override
    {
        return true;
    }

    bool start_object(std::size_t) override
    {
        return true;
    }

    bool key(string_t&) override
    {
        return true;
    }

    bool end_object() override
    {
        return true;
    }

    bool start_array(std::size_t) override
    {
        return true;
    }

    bool end_array() override
    {
        return true;
    }

    bool parse_error(std::size_t, const std::string&, const detail::exception&) override
    {
        return false;
    }
};
}

}

// #include <nlohmann/detail/input/lexer.hpp>

// #include <nlohmann/detail/value_t.hpp>


namespace nlohmann
{
namespace detail
{
////////////
// parser //
////////////

/*!
@brief syntax analysis

This class implements a recursive decent parser.
*/
template<typename BasicJsonType>
class parser
{
    using number_integer_t = typename BasicJsonType::number_integer_t;
    using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
    using number_float_t = typename BasicJsonType::number_float_t;
    using string_t = typename BasicJsonType::string_t;
    using lexer_t = lexer<BasicJsonType>;
    using token_type = typename lexer_t::token_type;

  public:
    enum class parse_event_t : uint8_t
    {
        /// the parser read `{` and started to process a JSON object
        object_start,
        /// the parser read `}` and finished processing a JSON object
        object_end,
        /// the parser read `[` and started to process a JSON array
        array_start,
        /// the parser read `]` and finished processing a JSON array
        array_end,
        /// the parser read a key of a value in an object
        key,
        /// the parser finished reading a JSON value
        value
    };

    using json_sax_t = json_sax<BasicJsonType>;

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

    /// a parser reading from an input adapter
    explicit parser(detail::input_adapter_t&& adapter,
                    const parser_callback_t cb = nullptr,
                    const bool allow_exceptions_ = true)
        : callback(cb), m_lexer(std::move(adapter)), allow_exceptions(allow_exceptions_)
    {
        // read first token
        get_token();
    }

    /*!
    @brief public parser interface

    @param[in] strict      whether to expect the last token to be EOF
    @param[in,out] result  parsed JSON value

    @throw parse_error.101 in case of an unexpected token
    @throw parse_error.102 if to_unicode fails or surrogate error
    @throw parse_error.103 if to_unicode fails
    */
    void parse(const bool strict, BasicJsonType& result)
    {
        if (callback)
        {
            json_sax_dom_callback_parser<BasicJsonType> sdp(result, callback, allow_exceptions);
            sax_parse_internal(&sdp);
            result.assert_invariant();

            // in strict mode, input must be completely read
            if (strict and (get_token() != token_type::end_of_input))
            {
                sdp.parse_error(m_lexer.get_position(),
                                m_lexer.get_token_string(),
                                parse_error::create(101, m_lexer.get_position(), exception_message(token_type::end_of_input)));
            }

            // in case of an error, return discarded value
            if (sdp.is_errored())
            {
                result = value_t::discarded;
                return;
            }

            // set top-level value to null if it was discarded by the callback
            // function
            if (result.is_discarded())
            {
                result = nullptr;
            }
        }
        else
        {
            json_sax_dom_parser<BasicJsonType> sdp(result, allow_exceptions);
            sax_parse_internal(&sdp);
            result.assert_invariant();

            // in strict mode, input must be completely read
            if (strict and (get_token() != token_type::end_of_input))
            {
                sdp.parse_error(m_lexer.get_position(),
                                m_lexer.get_token_string(),
                                parse_error::create(101, m_lexer.get_position(), exception_message(token_type::end_of_input)));
            }

            // in case of an error, return discarded value
            if (sdp.is_errored())
            {
                result = value_t::discarded;
                return;
            }
        }
    }

    /*!
    @brief public accept interface

    @param[in] strict  whether to expect the last token to be EOF
    @return whether the input is a proper JSON text
    */
    bool accept(const bool strict = true)
    {
        json_sax_acceptor<BasicJsonType> sax_acceptor;
        return sax_parse(&sax_acceptor, strict);
    }

    bool sax_parse(json_sax_t* sax, const bool strict = true)
    {
        const bool result = sax_parse_internal(sax);

        // strict mode: next byte must be EOF
        if (result and strict and (get_token() != token_type::end_of_input))
        {
            return sax->parse_error(m_lexer.get_position(),
                                    m_lexer.get_token_string(),
                                    parse_error::create(101, m_lexer.get_position(), exception_message(token_type::end_of_input)));
        }

        return result;
    }

  private:
    bool sax_parse_internal(json_sax_t* sax)
    {
        // stack to remember the hieararchy of structured values we are parsing
        // true = array; false = object
        std::vector<bool> states;
        // value to avoid a goto (see comment where set to true)
        bool skip_to_state_evaluation = false;

        while (true)
        {
            if (not skip_to_state_evaluation)
            {
                // invariant: get_token() was called before each iteration
                switch (last_token)
                {
                    case token_type::begin_object:
                    {
                        if (JSON_UNLIKELY(not sax->start_object()))
                        {
                            return false;
                        }

                        // closing } -> we are done
                        if (get_token() == token_type::end_object)
                        {
                            if (JSON_UNLIKELY(not sax->end_object()))
                            {
                                return false;
                            }
                            break;
                        }

                        // parse key
                        if (JSON_UNLIKELY(last_token != token_type::value_string))
                        {
                            return sax->parse_error(m_lexer.get_position(),
                                                    m_lexer.get_token_string(),
                                                    parse_error::create(101, m_lexer.get_position(), exception_message(token_type::value_string)));
                        }
                        else
                        {
                            if (JSON_UNLIKELY(not sax->key(m_lexer.get_string())))
                            {
                                return false;
                            }
                        }

                        // parse separator (:)
                        if (JSON_UNLIKELY(get_token() != token_type::name_separator))
                        {
                            return sax->parse_error(m_lexer.get_position(),
                                                    m_lexer.get_token_string(),
                                                    parse_error::create(101, m_lexer.get_position(), exception_message(token_type::name_separator)));
                        }

                        // remember we are now inside an object
                        states.push_back(false);

                        // parse values
                        get_token();
                        continue;
                    }

                    case token_type::begin_array:
                    {
                        if (JSON_UNLIKELY(not sax->start_array()))
                        {
                            return false;
                        }

                        // closing ] -> we are done
                        if (get_token() == token_type::end_array)
                        {
                            if (JSON_UNLIKELY(not sax->end_array()))
                            {
                                return false;
                            }
                            break;
                        }

                        // remember we are now inside an array
                        states.push_back(true);

                        // parse values (no need to call get_token)
                        continue;
                    }

                    case token_type::value_float:
                    {
                        const auto res = m_lexer.get_number_float();

                        if (JSON_UNLIKELY(not std::isfinite(res)))
                        {
                            return sax->parse_error(m_lexer.get_position(),
                                                    m_lexer.get_token_string(),
                                                    out_of_range::create(406, "number overflow parsing '" + m_lexer.get_token_string() + "'"));
                        }
                        else
                        {
                            if (JSON_UNLIKELY(not sax->number_float(res, m_lexer.get_string())))
                            {
                                return false;
                            }
                            break;
                        }
                    }

                    case token_type::literal_false:
                    {
                        if (JSON_UNLIKELY(not sax->boolean(false)))
                        {
                            return false;
                        }
                        break;
                    }

                    case token_type::literal_null:
                    {
                        if (JSON_UNLIKELY(not sax->null()))
                        {
                            return false;
                        }
                        break;
                    }

                    case token_type::literal_true:
                    {
                        if (JSON_UNLIKELY(not sax->boolean(true)))
                        {
                            return false;
                        }
                        break;
                    }

                    case token_type::value_integer:
                    {
                        if (JSON_UNLIKELY(not sax->number_integer(m_lexer.get_number_integer())))
                        {
                            return false;
                        }
                        break;
                    }

                    case token_type::value_string:
                    {
                        if (JSON_UNLIKELY(not sax->string(m_lexer.get_string())))
                        {
                            return false;
                        }
                        break;
                    }

                    case token_type::value_unsigned:
                    {
                        if (JSON_UNLIKELY(not sax->number_unsigned(m_lexer.get_number_unsigned())))
                        {
                            return false;
                        }
                        break;
                    }

                    case token_type::parse_error:
                    {
                        // using "uninitialized" to avoid "expected" message
                        return sax->parse_error(m_lexer.get_position(),
                                                m_lexer.get_token_string(),
                                                parse_error::create(101, m_lexer.get_position(), exception_message(token_type::uninitialized)));
                    }

                    default: // the last token was unexpected
                    {
                        return sax->parse_error(m_lexer.get_position(),
                                                m_lexer.get_token_string(),
                                                parse_error::create(101, m_lexer.get_position(), exception_message(token_type::literal_or_value)));
                    }
                }
            }
            else
            {
                skip_to_state_evaluation = false;
            }

            // we reached this line after we successfully parsed a value
            if (states.empty())
            {
                // empty stack: we reached the end of the hieararchy: done
                return true;
            }
            else
            {
                if (states.back())  // array
                {
                    // comma -> next value
                    if (get_token() == token_type::value_separator)
                    {
                        // parse a new value
                        get_token();
                        continue;
                    }

                    // closing ]
                    if (JSON_LIKELY(last_token == token_type::end_array))
                    {
                        if (JSON_UNLIKELY(not sax->end_array()))
                        {
                            return false;
                        }

                        // We are done with this array. Before we can parse a
                        // new value, we need to evaluate the new state first.
                        // By setting skip_to_state_evaluation to false, we
                        // are effectively jumping to the beginning of this if.
                        assert(not states.empty());
                        states.pop_back();
                        skip_to_state_evaluation = true;
                        continue;
                    }
                    else
                    {
                        return sax->parse_error(m_lexer.get_position(),
                                                m_lexer.get_token_string(),
                                                parse_error::create(101, m_lexer.get_position(), exception_message(token_type::end_array)));
                    }
                }
                else  // object
                {
                    // comma -> next value
                    if (get_token() == token_type::value_separator)
                    {
                        // parse key
                        if (JSON_UNLIKELY(get_token() != token_type::value_string))
                        {
                            return sax->parse_error(m_lexer.get_position(),
                                                    m_lexer.get_token_string(),
                                                    parse_error::create(101, m_lexer.get_position(), exception_message(token_type::value_string)));
                        }
                        else
                        {
                            if (JSON_UNLIKELY(not sax->key(m_lexer.get_string())))
                            {
                                return false;
                            }
                        }

                        // parse separator (:)
                        if (JSON_UNLIKELY(get_token() != token_type::name_separator))
                        {
                            return sax->parse_error(m_lexer.get_position(),
                                                    m_lexer.get_token_string(),
                                                    parse_error::create(101, m_lexer.get_position(), exception_message(token_type::name_separator)));
                        }

                        // parse values
                        get_token();
                        continue;
                    }

                    // closing }
                    if (JSON_LIKELY(last_token == token_type::end_object))
                    {
                        if (JSON_UNLIKELY(not sax->end_object()))
                        {
                            return false;
                        }

                        // We are done with this object. Before we can parse a
                        // new value, we need to evaluate the new state first.
                        // By setting skip_to_state_evaluation to false, we
                        // are effectively jumping to the beginning of this if.
                        assert(not states.empty());
                        states.pop_back();
                        skip_to_state_evaluation = true;
                        continue;
                    }
                    else
                    {
                        return sax->parse_error(m_lexer.get_position(),
                                                m_lexer.get_token_string(),
                                                parse_error::create(101, m_lexer.get_position(), exception_message(token_type::end_object)));
                    }
                }
            }
        }
    }

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

    std::string exception_message(const token_type expected)
    {
        std::string error_msg = "syntax error - ";
        if (last_token == token_type::parse_error)
        {
            error_msg += std::string(m_lexer.get_error_message()) + "; last read: '" +
                         m_lexer.get_token_string() + "'";
        }
        else
        {
            error_msg += "unexpected " + std::string(lexer_t::token_type_name(last_token));
        }

        if (expected != token_type::uninitialized)
        {
            error_msg += "; expected " + std::string(lexer_t::token_type_name(expected));
        }

        return error_msg;
    }

  private:
    /// callback function
    const parser_callback_t callback = nullptr;
    /// the type of the last read token
    token_type last_token = token_type::uninitialized;
    /// the lexer
    lexer_t m_lexer;
    /// whether to throw exceptions in case of errors
    const bool allow_exceptions = true;
};
}
}

// #include <nlohmann/detail/iterators/primitive_iterator.hpp>


#include <cstddef> // ptrdiff_t
#include <limits>  // numeric_limits

namespace nlohmann
{
namespace detail
{
/*
@brief an iterator for primitive JSON types

This class models an iterator for primitive JSON types (boolean, number,
string). It's only purpose is to allow the iterator/const_iterator classes
to "iterate" over primitive values. Internally, the iterator is modeled by
a `difference_type` variable. Value begin_value (`0`) models the begin,
end_value (`1`) models past the end.
*/
class primitive_iterator_t
{
  private:
    using difference_type = std::ptrdiff_t;
    static constexpr difference_type begin_value = 0;
    static constexpr difference_type end_value = begin_value + 1;

    /// iterator as signed integer type
    difference_type m_it = (std::numeric_limits<std::ptrdiff_t>::min)();

  public:
    constexpr difference_type get_value() const noexcept
    {
        return m_it;
    }

    /// set iterator to a defined beginning
    void set_begin() noexcept
    {
        m_it = begin_value;
    }

    /// set iterator to a defined past the end
    void set_end() noexcept
    {
        m_it = end_value;
    }

    /// return whether the iterator can be dereferenced
    constexpr bool is_begin() const noexcept
    {
        return m_it == begin_value;
    }

    /// return whether the iterator is at end
    constexpr bool is_end() const noexcept
    {
        return m_it == end_value;
    }

    friend constexpr bool operator==(primitive_iterator_t lhs, primitive_iterator_t rhs) noexcept
    {
        return lhs.m_it == rhs.m_it;
    }

    friend constexpr bool operator<(primitive_iterator_t lhs, primitive_iterator_t rhs) noexcept
    {
        return lhs.m_it < rhs.m_it;
    }

    primitive_iterator_t operator+(difference_type n) noexcept
    {
        auto result = *this;
        result += n;
        return result;
    }

    friend constexpr difference_type operator-(primitive_iterator_t lhs, primitive_iterator_t rhs) noexcept
    {
        return lhs.m_it - rhs.m_it;
    }

    primitive_iterator_t& operator++() noexcept
    {
        ++m_it;
        return *this;
    }

    primitive_iterator_t const operator++(int) noexcept
    {
        auto result = *this;
        ++m_it;
        return result;
    }

    primitive_iterator_t& operator--() noexcept
    {
        --m_it;
        return *this;
    }

    primitive_iterator_t const operator--(int) noexcept
    {
        auto result = *this;
        --m_it;
        return result;
    }

    primitive_iterator_t& operator+=(difference_type n) noexcept
    {
        m_it += n;
        return *this;
    }

    primitive_iterator_t& operator-=(difference_type n) noexcept
    {
        m_it -= n;
        return *this;
    }
};
}
}

// #include <nlohmann/detail/iterators/internal_iterator.hpp>


// #include <nlohmann/detail/iterators/primitive_iterator.hpp>


namespace nlohmann
{
namespace detail
{
/*!
@brief an iterator value

@note This structure could easily be a union, but MSVC currently does not allow
unions members with complex constructors, see https://github.com/nlohmann/json/pull/105.
*/
template<typename BasicJsonType> struct internal_iterator
{
    /// iterator for JSON objects
    typename BasicJsonType::object_t::iterator object_iterator {};
    /// iterator for JSON arrays
    typename BasicJsonType::array_t::iterator array_iterator {};
    /// generic iterator for all other types
    primitive_iterator_t primitive_iterator {};
};
}
}

// #include <nlohmann/detail/iterators/iter_impl.hpp>


#include <ciso646> // not
#include <iterator> // iterator, random_access_iterator_tag, bidirectional_iterator_tag, advance, next
#include <type_traits> // conditional, is_const, remove_const

// #include <nlohmann/detail/exceptions.hpp>

// #include <nlohmann/detail/iterators/internal_iterator.hpp>

// #include <nlohmann/detail/iterators/primitive_iterator.hpp>

// #include <nlohmann/detail/macro_scope.hpp>

// #include <nlohmann/detail/meta.hpp>

// #include <nlohmann/detail/value_t.hpp>


namespace nlohmann
{
namespace detail
{
// forward declare, to be able to friend it later on
template<typename IteratorType> class iteration_proxy;

/*!
@brief a template for a bidirectional iterator for the @ref basic_json class

This class implements a both iterators (iterator and const_iterator) for the
@ref basic_json class.

@note An iterator is called *initialized* when a pointer to a JSON value has
      been set (e.g., by a constructor or a copy assignment). If the iterator is
      default-constructed, it is *uninitialized* and most methods are undefined.
      **The library uses assertions to detect calls on uninitialized iterators.**

@requirement The class satisfies the following concept requirements:
-
[BidirectionalIterator](https://en.cppreference.com/w/cpp/named_req/BidirectionalIterator):
  The iterator that can be moved can be moved in both directions (i.e.
  incremented and decremented).

@since version 1.0.0, simplified in version 2.0.9, change to bidirectional
       iterators in version 3.0.0 (see https://github.com/nlohmann/json/issues/593)
*/
template<typename BasicJsonType>
class iter_impl
{
    /// allow basic_json to access private members
    friend iter_impl<typename std::conditional<std::is_const<BasicJsonType>::value, typename std::remove_const<BasicJsonType>::type, const BasicJsonType>::type>;
    friend BasicJsonType;
    friend iteration_proxy<iter_impl>;

    using object_t = typename BasicJsonType::object_t;
    using array_t = typename BasicJsonType::array_t;
    // make sure BasicJsonType is basic_json or const basic_json
    static_assert(is_basic_json<typename std::remove_const<BasicJsonType>::type>::value,
                  "iter_impl only accepts (const) basic_json");

  public:

    /// The std::iterator class template (used as a base class to provide typedefs) is deprecated in C++17.
    /// The C++ Standard has never required user-defined iterators to derive from std::iterator.
    /// A user-defined iterator should provide publicly accessible typedefs named
    /// iterator_category, value_type, difference_type, pointer, and reference.
    /// Note that value_type is required to be non-const, even for constant iterators.
    using iterator_category = std::bidirectional_iterator_tag;

    /// the type of the values when the iterator is dereferenced
    using value_type = typename BasicJsonType::value_type;
    /// a type to represent differences between iterators
    using difference_type = typename BasicJsonType::difference_type;
    /// defines a pointer to the type iterated over (value_type)
    using pointer = typename std::conditional<std::is_const<BasicJsonType>::value,
          typename BasicJsonType::const_pointer,
          typename BasicJsonType::pointer>::type;
    /// defines a reference to the type iterated over (value_type)
    using reference =
        typename std::conditional<std::is_const<BasicJsonType>::value,
        typename BasicJsonType::const_reference,
        typename BasicJsonType::reference>::type;

    /// default constructor
    iter_impl() = default;

    /*!
    @brief constructor for a given JSON instance
    @param[in] object  pointer to a JSON object for this iterator
    @pre object != nullptr
    @post The iterator is initialized; i.e. `m_object != nullptr`.
    */
    explicit iter_impl(pointer object) noexcept : m_object(object)
    {
        assert(m_object != nullptr);

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

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

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

    /*!
    @note The conventional copy constructor and copy assignment are implicitly
          defined. Combined with the following converting constructor and
          assignment, they support: (1) copy from iterator to iterator, (2)
          copy from const iterator to const iterator, and (3) conversion from
          iterator to const iterator. However conversion from const iterator
          to iterator is not defined.
    */

    /*!
    @brief converting constructor
    @param[in] other  non-const iterator to copy from
    @note It is not checked whether @a other is initialized.
    */
    iter_impl(const iter_impl<typename std::remove_const<BasicJsonType>::type>& other) noexcept
        : m_object(other.m_object), m_it(other.m_it) {}

    /*!
    @brief converting assignment
    @param[in,out] other  non-const iterator to copy from
    @return const/non-const iterator
    @note It is not checked whether @a other is initialized.
    */
    iter_impl& operator=(const iter_impl<typename std::remove_const<BasicJsonType>::type>& other) noexcept
    {
        m_object = other.m_object;
        m_it = other.m_it;
        return *this;