json/docs/mkdocs/docs/api/basic_json/with_t.md

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.

```cpp
--8<-- "examples/with_t.cpp"
```

Output:

```json
--8<-- "examples/with_t.output"
```

See also

• basic_json - the template parameters that can be replaced
• json_base_class_t - the type used for CustomBaseClass

Version history

• Added in version 3.13.0.