nlohmann::basic_json::with_t¶

Member alias templates with_object_t, with_array_t, with_string_t, with_boolean_t, with_integers_t, with_float_t, with_allocator_t, with_json_serializer_t, with_binary_t, and with_base_class_t.

template<template<typename, typename, typename...> class ObjectType2>
using with_object_t = basic_json<ObjectType2, ArrayType, StringType, BooleanType,
      NumberIntegerType, NumberUnsignedType, NumberFloatType,
      AllocatorType, JSONSerializer, BinaryType, CustomBaseClass>;

template<template<typename, typename...> class ArrayType2>
using with_array_t = basic_json<ObjectType, ArrayType2, StringType, BooleanType,
      NumberIntegerType, NumberUnsignedType, NumberFloatType,
      AllocatorType, JSONSerializer, BinaryType, CustomBaseClass>;

template<class StringType2>
using with_string_t = basic_json<ObjectType, ArrayType, StringType2, BooleanType,
      NumberIntegerType, NumberUnsignedType, NumberFloatType,
      AllocatorType, JSONSerializer, BinaryType, CustomBaseClass>;

template<class BooleanType2>
using with_boolean_t = basic_json<ObjectType, ArrayType, StringType, BooleanType2,
      NumberIntegerType, NumberUnsignedType, NumberFloatType,
      AllocatorType, JSONSerializer, BinaryType, CustomBaseClass>;

template<class NumberIntegerType2, class NumberUnsignedType2>
using with_integers_t = basic_json<ObjectType, ArrayType, StringType, BooleanType,
      NumberIntegerType2, NumberUnsignedType2, NumberFloatType,
      AllocatorType, JSONSerializer, BinaryType, CustomBaseClass>;

template<class NumberFloatType2>
using with_float_t = basic_json<ObjectType, ArrayType, StringType, BooleanType,
      NumberIntegerType, NumberUnsignedType, NumberFloatType2,
      AllocatorType, JSONSerializer, BinaryType, CustomBaseClass>;

template<template<typename> class AllocatorType2>
using with_allocator_t = basic_json<ObjectType, ArrayType, StringType, BooleanType,
      NumberIntegerType, NumberUnsignedType, NumberFloatType,
      AllocatorType2, JSONSerializer, BinaryType, CustomBaseClass>;

template<template<typename, typename = void> class JSONSerializer2>
using with_json_serializer_t = basic_json<ObjectType, ArrayType, StringType, BooleanType,
      NumberIntegerType, NumberUnsignedType, NumberFloatType,
      AllocatorType, JSONSerializer2, BinaryType, CustomBaseClass>;

template<class BinaryType2>
using with_binary_t = basic_json<ObjectType, ArrayType, StringType, BooleanType,
      NumberIntegerType, NumberUnsignedType, NumberFloatType,
      AllocatorType, JSONSerializer, BinaryType2, CustomBaseClass>;

template<class CustomBaseClass2>
using with_base_class_t = basic_json<ObjectType, ArrayType, StringType, BooleanType,
      NumberIntegerType, NumberUnsignedType, NumberFloatType,
      AllocatorType, JSONSerializer, BinaryType, CustomBaseClass2>;

These member alias templates make it easier to create a basic_json type that is identical to the current type except for one (or, in the case of with_integers_t, two) of its template parameters. Spelling out all 11 template parameters of basic_json just to change a single one is verbose and error-prone; these aliases only require the replacement type(s).

with_object_t<ObjectType2>: replaces ObjectType
with_array_t<ArrayType2>: replaces ArrayType
with_string_t<StringType2>: replaces StringType
with_boolean_t<BooleanType2>: replaces BooleanType
with_integers_t<NumberIntegerType2, NumberUnsignedType2>: replaces both NumberIntegerType and NumberUnsignedType; the two are combined into a single alias because they are usually changed together (for instance, when switching to fixed-width integer types)
with_float_t<NumberFloatType2>: replaces NumberFloatType
with_allocator_t<AllocatorType2>: replaces AllocatorType
with_json_serializer_t<JSONSerializer2>: replaces JSONSerializer
with_binary_t<BinaryType2>: replaces BinaryType
with_base_class_t<CustomBaseClass2>: replaces CustomBaseClass; see also json_base_class_t

Notes¶

All other template parameters are kept unchanged, so the resulting type still uses, for instance, the same ObjectType unless with_object_t itself is used.

The aliases are members of every basic_json specialization, including ordered_json, and the type they produce is again a basic_json specialization. They can therefore be chained to replace several template parameters at once:

using my_json = nlohmann::json::with_integers_t<int, unsigned int>::with_float_t<float>;
using my_ordered_json = nlohmann::ordered_json::with_string_t<std::wstring>;

The result is the same type as spelling out all template parameters, so the order of the chained aliases does not matter. For instance, nlohmann::json::with_object_t<nlohmann::ordered_map> is nlohmann::ordered_json.

Examples¶

Example

The following code shows how with_object_t can be used to create a JSON type that stores object elements in a std::map and therefore keeps them sorted by key, unlike the default type which preserves insertion order only when nlohmann::ordered_json is used.

#include <iostream>
#include <map>
#include <nlohmann/json.hpp>

// a JSON type that stores objects in a std::map (which keeps keys sorted)
// instead of the default ordered associative container
using sorted_json = nlohmann::json::with_object_t<std::map>;

int main()
{
    sorted_json j;
    j["c"] = 1;
    j["a"] = 2;
    j["b"] = 3;

    // keys are sorted, because std::map is used to store the object
    std::cout << j.dump() << std::endl;
}

Output:

{"a":2,"b":3,"c":1}

Version history¶

Added in version 3.13.0 unreleased.

nlohmann::basic_json::with_t¶

Notes¶

Examples¶

See also¶

Version history¶