json.hpp

/*
    __ _____ _____ _____
 __|  |   __|     |   | |  JSON for Modern C++
|  |  |__   |  |  | | | |  version 2.1.1
|_____|_____|_____|_|___|  https://github.com/nlohmann/json

Licensed under the MIT License <http://opensource.org/licenses/MIT>.
Copyright (c) 2013-2017 Niels Lohmann <http://nlohmann.me>.

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

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

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

#ifndef NLOHMANN_JSON_HPP
#define NLOHMANN_JSON_HPP

#include <algorithm> // all_of, copy, fill, find, for_each, none_of, remove, reverse, transform
#include <array>   // array
#include <cassert> // assert
#include <ciso646> // and, not, or
#include <clocale> // lconv, localeconv
#include <cmath>   // isfinite, labs, ldexp, signbit
#include <cstddef> // nullptr_t, ptrdiff_t, size_t
#include <cstdint> // int64_t, uint64_t
#include <cstdlib> // abort, strtod, strtof, strtold, strtoul, strtoll, strtoull
#include <cstring> // strlen
#include <forward_list>     // forward_list
#include <functional>       // function, hash, less
#include <initializer_list> // initializer_list
#include <iostream>         // istream, ostream
#include <iterator>         // advance, begin, back_inserter, bidirectional_iterator_tag, distance, end, inserter, iterator, iterator_traits, next, random_access_iterator_tag, reverse_iterator
#include <limits>           // numeric_limits
#include <locale>           // locale
#include <map>              // map
#include <memory>      // addressof, allocator, allocator_traits, unique_ptr
#include <numeric>     // accumulate
#include <sstream>     // stringstream
#include <string>      // getline, stoi, string, to_string
#include <type_traits> // add_pointer, conditional, decay, enable_if, false_type, integral_constant, is_arithmetic, is_base_of, is_const, is_constructible, is_convertible, is_default_constructible, is_enum, is_floating_point, is_integral, is_nothrow_move_assignable, is_nothrow_move_constructible, is_pointer, is_reference, is_same, is_scalar, is_signed, remove_const, remove_cv, remove_pointer, remove_reference, true_type, underlying_type
#include <utility>     // declval, forward, make_pair, move, pair, swap
#include <vector>      // vector

// exclude unsupported compilers
#if defined(__clang__)
#if (__clang_major__ * 10000 + __clang_minor__ * 100 + __clang_patchlevel__) < \
    30400
#error                                                                         \
    "unsupported Clang version - see https://github.com/nlohmann/json#supported-compilers"
#endif
#elif defined(__GNUC__)
#if (__GNUC__ * 10000 + __GNUC_MINOR__ * 100 + __GNUC_PATCHLEVEL__) < 40805
#error                                                                         \
    "unsupported GCC version - see https://github.com/nlohmann/json#supported-compilers"
#endif
#endif

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

// disable documentation warnings on clang
#if defined(__clang__)
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdocumentation"
#endif

// allow for portable deprecation warnings
#if defined(__clang__) || defined(__GNUC__) || defined(__GNUG__)
#define JSON_DEPRECATED __attribute__((deprecated))
#elif defined(_MSC_VER)
#define JSON_DEPRECATED __declspec(deprecated)
#else
#define JSON_DEPRECATED
#endif

// allow to disable exceptions
#if (defined(__cpp_exceptions) || defined(__EXCEPTIONS) ||                     \
     defined(_CPPUNWIND)) &&                                                   \
    not defined(JSON_NOEXCEPTION)
#define JSON_THROW(exception) throw exception
#define JSON_TRY try
#define JSON_CATCH(exception) catch (exception)
#else
#define JSON_THROW(exception) std::abort()
#define JSON_TRY if (true)
#define JSON_CATCH(exception) if (false)
#endif

/*!
@brief namespace for Niels Lohmann
@see https://github.com/nlohmann
@since version 1.0.0
*/
namespace nlohmann
{

/*!
@brief unnamed namespace with internal helper functions

This namespace collects some functions that could not be defined inside the
@ref basic_json class.

@since version 2.1.0
*/
namespace detail
{
////////////////
// exceptions //
////////////////

/*!
@brief general exception of the @ref basic_json class

Extension of std::exception objects with a member @a id for exception ids.

@note To have nothrow-copy-constructible exceptions, we internally use
      std::runtime_error which can cope with arbitrary-length error messages.
      Intermediate strings are built with static functions and then passed to
      the actual constructor.

@since version 3.0.0
*/
class exception : public std::exception
{
public:
    /// returns the explanatory string
    virtual const char *what() const noexcept override { return m.what(); }

    /// the id of the exception
    const int id;

protected:
    exception(int id_, const char *what_arg) : id(id_), m(what_arg) {}

    static std::string name(const std::string &ename, int id)
    {
        return "[json.exception." + ename + "." + std::to_string(id) + "] ";
    }

private:
    /// an exception object as storage for error messages
    std::runtime_error m;
};

/*!
@brief exception indicating a parse error

This excpetion is thrown by the library when a parse error occurs. Parse
errors can occur during the deserialization of JSON text as well as when
using JSON Patch.

Member @a byte holds the byte index of the last read character in the input
file.

@note For an input with n bytes, 1 is the index of the first character
      and n+1 is the index of the terminating null byte or the end of
      file. This also holds true when reading a byte vector (CBOR or
      MessagePack).

Exceptions have ids 1xx.

name / id                      | example massage | description
------------------------------ | --------------- | -------------------------
json.exception.parse_error.101 | parse error at 2: unexpected end of input;
expected string literal | This error indicates a syntax error while
deserializing a JSON text. The error message describes that an unexpected token
(character) was encountered, and the member @a byte indicates the error
position.
json.exception.parse_error.102 | parse error at 14: missing or wrong low
surrogate | JSON uses the `\uxxxx` format to describe Unicode characters. Code
points above above 0xFFFF are split into two `\uxxxx` entries ("surrogate
pairs"). This error indicates that the surrogate pair is incomplete or contains
an invalid code point.
json.exception.parse_error.103 | parse error: code points above 0x10FFFF are
invalid | Unicode supports code points up to 0x10FFFF. Code points above
0x10FFFF are invalid.
json.exception.parse_error.104 | parse error: JSON patch must be an array of
objects | [RFC 6902](https://tools.ietf.org/html/rfc6902) requires a JSON Patch
document to be a JSON document that represents an array of objects.
json.exception.parse_error.105 | parse error: operation must have string member
'op' | An operation of a JSON Patch document must contain exactly one "op"
member, whose value indicates the operation to perform. Its value must be one of
"add", "remove", "replace", "move", "copy", or "test"; other values are errors.
json.exception.parse_error.106 | parse error: array index '01' must not begin
with '0' | An array index in a JSON Pointer ([RFC
6901](https://tools.ietf.org/html/rfc6901)) may be `0` or any number wihtout a
leading `0`.
json.exception.parse_error.107 | parse error: JSON pointer must be empty or
begin with '/' - was: 'foo' | A JSON Pointer must be a Unicode string containing
a sequence of zero or more reference tokens, each prefixed by a `/` character.
json.exception.parse_error.108 | parse error: escape character '~' must be
followed with '0' or '1' | In a JSON Pointer, only `~0` and `~1` are valid
escape sequences.
json.exception.parse_error.109 | parse error: array index 'one' is not a number
| A JSON Pointer array index must be a number.
json.exception.parse_error.110 | parse error at 1: cannot read 2 bytes from
vector | When parsing CBOR or MessagePack, the byte vector ends before the
complete value has been read.
json.exception.parse_error.111 | parse error: bad input stream | Parsing CBOR or
MessagePack from an input stream where the [`badbit` or
`failbit`](http://en.cppreference.com/w/cpp/io/ios_base/iostate) is set.
json.exception.parse_error.112 | parse error at 1: error reading CBOR; last
byte: 0xf8 | Not all types of CBOR or MessagePack are supported. This exception
occurs if an unsupported byte was read.
json.exception.parse_error.113 | parse error at 2: expected a CBOR string; last
byte: 0x98 | While parsing a map key, a value that is not a string has been
read.

@since version 3.0.0
*/
class parse_error : public exception
{
public:
    /*!
    @brief create a parse error exception
    @param[in] id         the id of the exception
    @param[in] byte_      the byte index where the error occured (or 0 if
                          the position cannot be determined)
    @param[in] what_arg   the explanatory string
    @return parse_error object
    */
    static parse_error create(int id, size_t byte_, const std::string &what_arg)
    {
        std::string w = exception::name("parse_error", id) + "parse error" +
                        (byte_ != 0 ? (" at " + std::to_string(byte_)) : "") +
                        ": " + what_arg;
        return parse_error(id, byte_, w.c_str());
    }

    /*!
    @brief byte index of the parse error

    The byte index of the last read character in the input file.

    @note For an input with n bytes, 1 is the index of the first character
          and n+1 is the index of the terminating null byte or the end of
          file. This also holds true when reading a byte vector (CBOR or
          MessagePack).
    */
    const size_t byte;

private:
    parse_error(int id_, size_t byte_, const char *what_arg)
    : exception(id_, what_arg), byte(byte_)
    {
    }
};

/*!
@brief exception indicating errors with iterators

Exceptions have ids 2xx.

name / id                           | example massage | description
----------------------------------- | --------------- |
-------------------------
json.exception.invalid_iterator.201 | iterators are not compatible | The
iterators passed to constructor @ref basic_json(InputIT first, InputIT last) are
not compatible, meaning they do not belong to the same container. Therefore, the
range (@a first, @a last) is invalid.
json.exception.invalid_iterator.202 | iterator does not fit current value | In
an erase or insert function, the passed iterator @a pos does not belong to the
JSON value for which the function was called. It hence does not define a valid
position for the deletion/insertion.
json.exception.invalid_iterator.203 | iterators do not fit current value |
Either iterator passed to function @ref erase(IteratorType first, IteratorType
last) does not belong to the JSON value from which values shall be erased. It
hence does not define a valid range to delete values from.
json.exception.invalid_iterator.204 | iterators out of range | When an iterator
range for a primitive type (number, boolean, or string) is passed to a
constructor or an erase function, this range has to be exactly (@ref begin(),
@ref end()), because this is the only way the single stored value is expressed.
All other ranges are invalid.
json.exception.invalid_iterator.205 | iterator out of range | When an iterator
for a primitive type (number, boolean, or string) is passed to an erase
function, the iterator has to be the @ref begin() iterator, because it is the
only way to address the stored value. All other iterators are invalid.
json.exception.invalid_iterator.206 | cannot construct with iterators from null
| The iterators passed to constructor @ref basic_json(InputIT first, InputIT
last) belong to a JSON null value and hence to not define a valid range.
json.exception.invalid_iterator.207 | cannot use key() for non-object iterators
| The key() member function can only be used on iterators belonging to a JSON
object, because other types do not have a concept of a key.
json.exception.invalid_iterator.208 | cannot use operator[] for object iterators
| The operator[] to specify a concrete offset cannot be used on iterators
belonging to a JSON object, because JSON objects are unordered.
json.exception.invalid_iterator.209 | cannot use offsets with object iterators |
The offset operators (+, -, +=, -=) cannot be used on iterators belonging to a
JSON object, because JSON objects are unordered.
json.exception.invalid_iterator.210 | iterators do not fit | The iterator range
passed to the insert function are not compatible, meaning they do not belong to
the same container. Therefore, the range (@a first, @a last) is invalid.
json.exception.invalid_iterator.211 | passed iterators may not belong to
container | The iterator range passed to the insert function must not be a
subrange of the container to insert to.
json.exception.invalid_iterator.212 | cannot compare iterators of different
containers | When two iterators are compared, they must belong to the same
container.
json.exception.invalid_iterator.213 | cannot compare order of object iterators |
The order of object iterators cannot be compated, because JSON objects are
unordered.
json.exception.invalid_iterator.214 | cannot get value | Cannot get value for
iterator: Either the iterator belongs to a null value or it is an iterator to a
primitive type (number, boolean, or string), but the iterator is different to
@ref begin().

@since version 3.0.0
*/
class invalid_iterator : public exception
{
public:
    static invalid_iterator create(int id, const std::string &what_arg)
    {
        std::string w = exception::name("invalid_iterator", id) + what_arg;
        return invalid_iterator(id, w.c_str());
    }

private:
    invalid_iterator(int id_, const char *what_arg) : exception(id_, what_arg)
    {
    }
};

/*!
@brief exception indicating executing a member function with a wrong type

Exceptions have ids 3xx.

name / id                     | example massage | description
----------------------------- | --------------- | -------------------------
json.exception.type_error.301 | cannot create object from initializer list | To
create an object from an initializer list, the initializer list must consist
only of a list of pairs whose first element is a string. When this constraint is
violated, an array is created instead.
json.exception.type_error.302 | type must be object, but is array | During
implicit or explicit value conversion, the JSON type must be compatible to the
target type. For instance, a JSON string can only be converted into string
types, but not into numbers or boolean types.
json.exception.type_error.303 | incompatible ReferenceType for get_ref, actual
type is object | To retrieve a reference to a value stored in a @ref basic_json
object with @ref get_ref, the type of the reference must match the value type.
For instance, for a JSON array, the @a ReferenceType must be @ref array_t&.
json.exception.type_error.304 | cannot use at() with string | The @ref at()
member functions can only be executed for certain JSON types.
json.exception.type_error.305 | cannot use operator[] with string | The @ref
operator[] member functions can only be executed for certain JSON types.
json.exception.type_error.306 | cannot use value() with string | The @ref
value() member functions can only be executed for certain JSON types.
json.exception.type_error.307 | cannot use erase() with string | The @ref
erase() member functions can only be executed for certain JSON types.
json.exception.type_error.308 | cannot use push_back() with string | The @ref
push_back() and @ref operator+= member functions can only be executed for
certain JSON types.
json.exception.type_error.309 | cannot use insert() with | The @ref insert()
member functions can only be executed for certain JSON types.
json.exception.type_error.310 | cannot use swap() with number | The @ref swap()
member functions can only be executed for certain JSON types.
json.exception.type_error.311 | cannot use emplace_back() with string | The @ref
emplace_back() member function can only be executed for certain JSON types.
json.exception.type_error.313 | invalid value to unflatten | The @ref unflatten
function converts an object whose keys are JSON Pointers back into an arbitrary
nested JSON value. The JSON Pointers must not overlap, because then the
resulting value would not be well defined.
json.exception.type_error.314 | only objects can be unflattened | The @ref
unflatten function only works for an object whose keys are JSON Pointers.
json.exception.type_error.315 | values in object must be primitive | The @ref
unflatten function only works for an object whose keys are JSON Pointers and
whose values are primitive.

@since version 3.0.0
*/
class type_error : public exception
{
public:
    static type_error create(int id, const std::string &what_arg)
    {
        std::string w = exception::name("type_error", id) + what_arg;
        return type_error(id, w.c_str());
    }

private:
    type_error(int id_, const char *what_arg) : exception(id_, what_arg) {}
};

/*!
@brief exception indicating access out of the defined range

Exceptions have ids 4xx.

name / id                       | example massage | description
------------------------------- | --------------- | -------------------------
json.exception.out_of_range.401 | array index 3 is out of range | The provided
array index @a i is larger than @a size-1.
json.exception.out_of_range.402 | array index '-' (3) is out of range | The
special array index `-` in a JSON Pointer never describes a valid element of the
array, but the index past the end. That is, it can only be used to add elements
at this position, but not to read it.
json.exception.out_of_range.403 | key 'foo' not found | The provided key was not
found in the JSON object.
json.exception.out_of_range.404 | unresolved reference token 'foo' | A reference
token in a JSON Pointer could not be resolved.
json.exception.out_of_range.405 | JSON pointer has no parent | The JSON Patch
operations 'remove' and 'add' can not be applied to the root element of the JSON
value.
json.exception.out_of_range.406 | number overflow parsing '10E1000' | A parsed
number could not be stored as without changing it to NaN or INF.

@since version 3.0.0
*/
class out_of_range : public exception
{
public:
    static out_of_range create(int id, const std::string &what_arg)
    {
        std::string w = exception::name("out_of_range", id) + what_arg;
        return out_of_range(id, w.c_str());
    }

private:
    out_of_range(int id_, const char *what_arg) : exception(id_, what_arg) {}
};

/*!
@brief exception indicating other errors

Exceptions have ids 5xx.

name / id                      | example massage | description
------------------------------ | --------------- | -------------------------
json.exception.other_error.501 | unsuccessful: {"op":"test","path":"/baz",
"value":"bar"} | A JSON Patch operation 'test' failed. The unsuccessful
operation is also printed.

@since version 3.0.0
*/
class other_error : public exception
{
public:
    static other_error create(int id, const std::string &what_arg)
    {
        std::string w = exception::name("other_error", id) + what_arg;
        return other_error(id, w.c_str());
    }

private:
    other_error(int id_, const char *what_arg) : exception(id_, what_arg) {}
};

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

/*!
@brief the JSON type enumeration

This enumeration collects the different JSON types. It is internally used to
distinguish the stored values, and the functions @ref basic_json::is_null(),
@ref basic_json::is_object(), @ref basic_json::is_array(),
@ref basic_json::is_string(), @ref basic_json::is_boolean(),
@ref basic_json::is_number() (with @ref basic_json::is_number_integer(),
@ref basic_json::is_number_unsigned(), and @ref basic_json::is_number_float()),
@ref basic_json::is_discarded(), @ref basic_json::is_primitive(), and
@ref basic_json::is_structured() rely on it.

@note There are three enumeration entries (number_integer, number_unsigned, and
number_float), because the library distinguishes these three types for numbers:
@ref basic_json::number_unsigned_t is used for unsigned integers,
@ref basic_json::number_integer_t is used for signed integers, and
@ref basic_json::number_float_t is used for floating-point numbers or to
approximate integers which do not fit in the limits of their respective type.

@sa @ref basic_json::basic_json(const value_t value_type) -- create a JSON
value with the default value for a given type

@since version 1.0.0
*/
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 (signed integer)
    number_unsigned, ///< number value (unsigned integer)
    number_float,    ///< number value (floating-point)
    discarded        ///< discarded by the the parser callback function
};

/*!
@brief comparison operator for JSON types

Returns an ordering that is similar to Python:
- order: null < boolean < number < object < array < string
- furthermore, each type is not smaller than itself

@since version 1.0.0
*/
inline bool operator<(const value_t lhs, const value_t rhs) noexcept
{
    static constexpr std::array<uint8_t, 8> order = {{
        0, // null
        3, // object
        4, // array
        5, // string
        1, // boolean
        2, // integer
        2, // unsigned
        2, // float
    }};

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

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

/////////////
// helpers //
/////////////

// alias templates to reduce boilerplate
template <bool B, typename T = void>
using enable_if_t = typename std::enable_if<B, T>::type;

template <typename T>
using uncvref_t =
    typename std::remove_cv<typename std::remove_reference<T>::type>::type;

/*
Implementation of two C++17 constructs: conjunction, negation. This is needed
to avoid evaluating all the traits in a condition

For example: not std::is_same<void, T>::value and has_value_type<T>::value
will not compile when T = void (on MSVC at least). Whereas
conjunction<negation<std::is_same<void, T>>, has_value_type<T>>::value will
stop evaluating if negation<...>::value == false

Please note that those constructs must be used with caution, since symbols can
become very long quickly (which can slow down compilation and cause MSVC
internal compiler errors). Only use it when you have to (see example ahead).
*/
template <class...>
struct conjunction : std::true_type
{
};
template <class B1>
struct conjunction<B1> : B1
{
};
template <class B1, class... Bn>
struct conjunction<B1, Bn...>
    : std::conditional<bool(B1::value), conjunction<Bn...>, B1>::type
{
};

template <class B>
struct negation : std::integral_constant<bool, !B::value>
{
};

// dispatch utility (taken from ranges-v3)
template <unsigned N>
struct priority_tag : priority_tag<N - 1>
{
};
template <>
struct priority_tag<0>
{
};

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

template <value_t>
struct external_constructor;

template <>
struct external_constructor<value_t::boolean>
{
    template <typename BasicJsonType>
    static void construct(BasicJsonType &j,
                          typename BasicJsonType::boolean_t b) noexcept
    {
        j.m_type = value_t::boolean;
        j.m_value = b;
        j.assert_invariant();
    }
};

template <>
struct external_constructor<value_t::string>
{
    template <typename BasicJsonType>
    static void construct(BasicJsonType &j,
                          const typename BasicJsonType::string_t &s)
    {
        j.m_type = value_t::string;
        j.m_value = s;
        j.assert_invariant();
    }
};

template <>
struct external_constructor<value_t::number_float>
{
    template <typename BasicJsonType>
    static void construct(BasicJsonType &j,
                          typename BasicJsonType::number_float_t val) noexcept
    {
        j.m_type = value_t::number_float;
        j.m_value = val;
        j.assert_invariant();
    }
};

template <>
struct external_constructor<value_t::number_unsigned>
{
    template <typename BasicJsonType>
    static void
    construct(BasicJsonType &j,
              typename BasicJsonType::number_unsigned_t val) noexcept
    {
        j.m_type = value_t::number_unsigned;
        j.m_value = val;
        j.assert_invariant();
    }
};

template <>
struct external_constructor<value_t::number_integer>
{
    template <typename BasicJsonType>
    static void construct(BasicJsonType &j,
                          typename BasicJsonType::number_integer_t val) noexcept
    {
        j.m_type = value_t::number_integer;
        j.m_value = val;
        j.assert_invariant();
    }
};

template <>
struct external_constructor<value_t::array>
{
    template <typename BasicJsonType>
    static void construct(BasicJsonType &j,
                          const typename BasicJsonType::array_t &arr)
    {
        j.m_type = value_t::array;
        j.m_value = arr;
        j.assert_invariant();
    }

    template <
        typename BasicJsonType, typename CompatibleArrayType,
        enable_if_t<not std::is_same<CompatibleArrayType,
                                     typename BasicJsonType::array_t>::value,
                    int> = 0>
    static void construct(BasicJsonType &j, const CompatibleArrayType &arr)
    {
        using std::begin;
        using std::end;
        j.m_type = value_t::array;
        j.m_value.array = j.template create<typename BasicJsonType::array_t>(
            begin(arr), end(arr));
        j.assert_invariant();
    }

    template <typename BasicJsonType>
    static void construct(BasicJsonType &j, const std::vector<bool> &arr)
    {
        j.m_type = value_t::array;
        j.m_value = value_t::array;
        j.m_value.array->reserve(arr.size());
        for (bool x : arr)
        {
            j.m_value.array->push_back(x);
        }
        j.assert_invariant();
    }
};

template <>
struct external_constructor<value_t::object>
{
    template <typename BasicJsonType>
    static void construct(BasicJsonType &j,
                          const typename BasicJsonType::object_t &obj)
    {
        j.m_type = value_t::object;
        j.m_value = obj;
        j.assert_invariant();
    }

    template <
        typename BasicJsonType, typename CompatibleObjectType,
        enable_if_t<not std::is_same<CompatibleObjectType,
                                     typename BasicJsonType::object_t>::value,
                    int> = 0>
    static void construct(BasicJsonType &j, const CompatibleObjectType &obj)
    {
        using std::begin;
        using std::end;

        j.m_type = value_t::object;
        j.m_value.object = j.template create<typename BasicJsonType::object_t>(
            begin(obj), end(obj));
        j.assert_invariant();
    }
};

////////////////////////
// has_/is_ functions //
////////////////////////

/*!
@brief Helper to determine whether there's a key_type for T.

This helper is used to tell associative containers apart from other containers
such as sequence containers. For instance, `std::map` passes the test as it
contains a `mapped_type`, whereas `std::vector` fails the test.

@sa http://stackoverflow.com/a/7728728/266378
@since version 1.0.0, overworked in version 2.0.6
*/
#define NLOHMANN_JSON_HAS_HELPER(type)                                         \
    template <typename T>                                                      \
    struct has_##type                                                          \
    {                                                                          \
    private:                                                                   \
        template <typename U, typename = typename U::type>                     \
        static int detect(U &&);                                               \
        static void detect(...);                                               \
                                                                               \
    public:                                                                    \
        static constexpr bool value =                                          \
            std::is_integral<decltype(detect(std::declval<T>()))>::value;      \
    }

NLOHMANN_JSON_HAS_HELPER(mapped_type);
NLOHMANN_JSON_HAS_HELPER(key_type);
NLOHMANN_JSON_HAS_HELPER(value_type);
NLOHMANN_JSON_HAS_HELPER(iterator);

#undef NLOHMANN_JSON_HAS_HELPER

template <bool B, class RealType, class CompatibleObjectType>
struct is_compatible_object_type_impl : std::false_type
{
};

template <class RealType, class CompatibleObjectType>
struct is_compatible_object_type_impl<true, RealType, CompatibleObjectType>
{
    static constexpr auto value =
        std::is_constructible<
            typename RealType::key_type,
            typename CompatibleObjectType::key_type>::value and
        std::is_constructible<
            typename RealType::mapped_type,
            typename CompatibleObjectType::mapped_type>::value;
};

template <class BasicJsonType, class CompatibleObjectType>
struct is_compatible_object_type
{
    static auto constexpr value = is_compatible_object_type_impl<
        conjunction<negation<std::is_same<void, CompatibleObjectType>>,
                    has_mapped_type<CompatibleObjectType>,
                    has_key_type<CompatibleObjectType>>::value,
        typename BasicJsonType::object_t, CompatibleObjectType>::value;
};

template <typename BasicJsonType, typename T>
struct is_basic_json_nested_type
{
    static auto constexpr value =
        std::is_same<T, typename BasicJsonType::iterator>::value or
        std::is_same<T, typename BasicJsonType::const_iterator>::value or
        std::is_same<T, typename BasicJsonType::reverse_iterator>::value or
        std::is_same<T,
                     typename BasicJsonType::const_reverse_iterator>::value or
        std::is_same<T, typename BasicJsonType::json_pointer>::value;
};

template <class BasicJsonType, class CompatibleArrayType>
struct is_compatible_array_type
{
    static auto constexpr value = conjunction<
        negation<std::is_same<void, CompatibleArrayType>>,
        negation<is_compatible_object_type<BasicJsonType, CompatibleArrayType>>,
        negation<std::is_constructible<typename BasicJsonType::string_t,
                                       CompatibleArrayType>>,
        negation<is_basic_json_nested_type<BasicJsonType, CompatibleArrayType>>,
        has_value_type<CompatibleArrayType>,
        has_iterator<CompatibleArrayType>>::value;
};

template <bool, typename, typename>
struct is_compatible_integer_type_impl : std::false_type
{
};

template <typename RealIntegerType, typename CompatibleNumberIntegerType>
struct is_compatible_integer_type_impl<true, RealIntegerType,
                                       CompatibleNumberIntegerType>
{
    // is there an assert somewhere on overflows?
    using RealLimits = std::numeric_limits<RealIntegerType>;
    using CompatibleLimits = std::numeric_limits<CompatibleNumberIntegerType>;

    static constexpr auto value =
        std::is_constructible<RealIntegerType,
                              CompatibleNumberIntegerType>::value and
        CompatibleLimits::is_integer and
        RealLimits::is_signed == CompatibleLimits::is_signed;
};

template <typename RealIntegerType, typename CompatibleNumberIntegerType>
struct is_compatible_integer_type
{
    static constexpr auto
        value = is_compatible_integer_type_impl <
                    std::is_integral<CompatibleNumberIntegerType>::value and
                not std::is_same<bool, CompatibleNumberIntegerType>::value,
        RealIntegerType, CompatibleNumberIntegerType > ::value;
};

// trait checking if JSONSerializer<T>::from_json(json const&, udt&) exists
template <typename BasicJsonType, typename T>
struct has_from_json
{
private:
    // also check the return type of from_json
    template <typename U, typename = enable_if_t<std::is_same<
                              void, decltype(uncvref_t<U>::from_json(
                                        std::declval<BasicJsonType>(),
                                        std::declval<T &>()))>::value>>
    static int detect(U &&);
    static void detect(...);

public:
    static constexpr bool value = std::is_integral<decltype(
        detect(std::declval<typename BasicJsonType::template json_serializer<
                   T, void>>()))>::value;
};

// This trait checks if JSONSerializer<T>::from_json(json const&) exists
// this overload is used for non-default-constructible user-defined-types
template <typename BasicJsonType, typename T>
struct has_non_default_from_json
{
private:
    template <typename U, typename = enable_if_t<std::is_same<
                              T, decltype(uncvref_t<U>::from_json(
                                     std::declval<BasicJsonType>()))>::value>>
    static int detect(U &&);
    static void detect(...);

public:
    static constexpr bool value = std::is_integral<decltype(
        detect(std::declval<typename BasicJsonType::template json_serializer<
                   T, void>>()))>::value;
};

// This trait checks if BasicJsonType::json_serializer<T>::to_json exists
template <typename BasicJsonType, typename T>
struct has_to_json
{
private:
    template <typename U,
              typename = decltype(uncvref_t<U>::to_json(
                  std::declval<BasicJsonType &>(), std::declval<T>()))>
    static int detect(U &&);
    static void detect(...);

public:
    static constexpr bool value = std::is_integral<decltype(
        detect(std::declval<typename BasicJsonType::template json_serializer<
                   T, void>>()))>::value;
};

/////////////
// to_json //
/////////////

template <typename BasicJsonType, typename T,
          enable_if_t<std::is_same<T, typename BasicJsonType::boolean_t>::value,
                      int> = 0>
void to_json(BasicJsonType &j, T b) noexcept
{
    external_constructor<value_t::boolean>::construct(j, b);
}

template <typename BasicJsonType, typename CompatibleString,
          enable_if_t<std::is_constructible<typename BasicJsonType::string_t,
                                            CompatibleString>::value,
                      int> = 0>
void to_json(BasicJsonType &j, const CompatibleString &s)
{
    external_constructor<value_t::string>::construct(j, s);
}

template <typename BasicJsonType, typename FloatType,
          enable_if_t<std::is_floating_point<FloatType>::value, int> = 0>
void to_json(BasicJsonType &j, FloatType val) noexcept
{
    external_constructor<value_t::number_float>::construct(
        j, static_cast<typename BasicJsonType::number_float_t>(val));
}

template <typename BasicJsonType, typename CompatibleNumberUnsignedType,
          enable_if_t<is_compatible_integer_type<
                          typename BasicJsonType::number_unsigned_t,
                          CompatibleNumberUnsignedType>::value,
                      int> = 0>
void to_json(BasicJsonType &j, CompatibleNumberUnsignedType val) noexcept
{
    external_constructor<value_t::number_unsigned>::construct(
        j, static_cast<typename BasicJsonType::number_unsigned_t>(val));
}

template <typename BasicJsonType, typename CompatibleNumberIntegerType,
          enable_if_t<is_compatible_integer_type<
                          typename BasicJsonType::number_integer_t,
                          CompatibleNumberIntegerType>::value,
                      int> = 0>
void to_json(BasicJsonType &j, CompatibleNumberIntegerType val) noexcept
{
    external_constructor<value_t::number_integer>::construct(
        j, static_cast<typename BasicJsonType::number_integer_t>(val));
}

template <typename BasicJsonType, typename EnumType,
          enable_if_t<std::is_enum<EnumType>::value, int> = 0>
void to_json(BasicJsonType &j, EnumType e) noexcept
{
    using underlying_type = typename std::underlying_type<EnumType>::type;
    external_constructor<value_t::number_integer>::construct(
        j, static_cast<underlying_type>(e));
}

template <typename BasicJsonType>
void to_json(BasicJsonType &j, const std::vector<bool> &e)
{
    external_constructor<value_t::array>::construct(j, e);
}

template <typename BasicJsonType, typename CompatibleArrayType,
          enable_if_t<is_compatible_array_type<BasicJsonType,
                                               CompatibleArrayType>::value or
                          std::is_same<typename BasicJsonType::array_t,
                                       CompatibleArrayType>::value,
                      int> = 0>
void to_json(BasicJsonType &j, const CompatibleArrayType &arr)
{
    external_constructor<value_t::array>::construct(j, arr);
}

template <typename BasicJsonType, typename CompatibleObjectType,
          enable_if_t<is_compatible_object_type<BasicJsonType,
                                                CompatibleObjectType>::value,
                      int> = 0>
void to_json(BasicJsonType &j, const CompatibleObjectType &arr)
{
    external_constructor<value_t::object>::construct(j, arr);
}

template <typename BasicJsonType, typename T, std::size_t N,
          enable_if_t<not std::is_constructible<
                          typename BasicJsonType::string_t, T (&)[N]>::value,
                      int> = 0>
void to_json(BasicJsonType &j, T (&arr)[N])
{
    external_constructor<value_t::array>::construct(j, arr);
}