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137 lines
5.5 KiB
Markdown
137 lines
5.5 KiB
Markdown
# <small>nlohmann::basic_json::</small>with_t
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Member alias templates `with_object_t`, `with_array_t`, `with_string_t`, `with_boolean_t`, `with_integers_t`,
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`with_float_t`, `with_allocator_t`, `with_json_serializer_t`, `with_binary_t`, and `with_base_class_t`.
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```cpp
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template<template<typename, typename, typename...> class ObjectType2>
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using with_object_t = basic_json<ObjectType2, ArrayType, StringType, BooleanType,
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NumberIntegerType, NumberUnsignedType, NumberFloatType,
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AllocatorType, JSONSerializer, BinaryType, CustomBaseClass>;
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template<template<typename, typename...> class ArrayType2>
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using with_array_t = basic_json<ObjectType, ArrayType2, StringType, BooleanType,
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NumberIntegerType, NumberUnsignedType, NumberFloatType,
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AllocatorType, JSONSerializer, BinaryType, CustomBaseClass>;
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template<class StringType2>
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using with_string_t = basic_json<ObjectType, ArrayType, StringType2, BooleanType,
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NumberIntegerType, NumberUnsignedType, NumberFloatType,
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AllocatorType, JSONSerializer, BinaryType, CustomBaseClass>;
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template<class BooleanType2>
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using with_boolean_t = basic_json<ObjectType, ArrayType, StringType, BooleanType2,
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NumberIntegerType, NumberUnsignedType, NumberFloatType,
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AllocatorType, JSONSerializer, BinaryType, CustomBaseClass>;
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template<class NumberIntegerType2, class NumberUnsignedType2>
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using with_integers_t = basic_json<ObjectType, ArrayType, StringType, BooleanType,
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NumberIntegerType2, NumberUnsignedType2, NumberFloatType,
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AllocatorType, JSONSerializer, BinaryType, CustomBaseClass>;
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template<class NumberFloatType2>
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using with_float_t = basic_json<ObjectType, ArrayType, StringType, BooleanType,
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NumberIntegerType, NumberUnsignedType, NumberFloatType2,
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AllocatorType, JSONSerializer, BinaryType, CustomBaseClass>;
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template<template<typename> class AllocatorType2>
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using with_allocator_t = basic_json<ObjectType, ArrayType, StringType, BooleanType,
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NumberIntegerType, NumberUnsignedType, NumberFloatType,
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AllocatorType2, JSONSerializer, BinaryType, CustomBaseClass>;
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template<template<typename, typename = void> class JSONSerializer2>
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using with_json_serializer_t = basic_json<ObjectType, ArrayType, StringType, BooleanType,
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NumberIntegerType, NumberUnsignedType, NumberFloatType,
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AllocatorType, JSONSerializer2, BinaryType, CustomBaseClass>;
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template<class BinaryType2>
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using with_binary_t = basic_json<ObjectType, ArrayType, StringType, BooleanType,
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NumberIntegerType, NumberUnsignedType, NumberFloatType,
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AllocatorType, JSONSerializer, BinaryType2, CustomBaseClass>;
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template<class CustomBaseClass2>
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using with_base_class_t = basic_json<ObjectType, ArrayType, StringType, BooleanType,
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NumberIntegerType, NumberUnsignedType, NumberFloatType,
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AllocatorType, JSONSerializer, BinaryType, CustomBaseClass2>;
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```
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These member alias templates make it easier to create a `basic_json` type that is identical to the current type except
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for one (or, in the case of `with_integers_t`, two) of its [template parameters](index.md#template-parameters).
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Spelling out all 11 template parameters of `basic_json` just to change a single one is verbose and error-prone; these
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aliases only require the replacement type(s).
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with_object_t<ObjectType2>
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: replaces `ObjectType`
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with_array_t<ArrayType2>
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: replaces `ArrayType`
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with_string_t<StringType2>
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: replaces `StringType`
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with_boolean_t<BooleanType2>
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: replaces `BooleanType`
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with_integers_t<NumberIntegerType2, NumberUnsignedType2>
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: replaces both `NumberIntegerType` and `NumberUnsignedType`; the two are combined into a single alias because they
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are usually changed together (for instance, when switching to fixed-width integer types)
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with_float_t<NumberFloatType2>
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: replaces `NumberFloatType`
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with_allocator_t<AllocatorType2>
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: replaces `AllocatorType`
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with_json_serializer_t<JSONSerializer2>
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: replaces `JSONSerializer`
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with_binary_t<BinaryType2>
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: replaces `BinaryType`
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with_base_class_t<CustomBaseClass2>
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: replaces `CustomBaseClass`; see also [`json_base_class_t`](json_base_class_t.md)
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## Notes
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All other template parameters are kept unchanged, so the resulting type still uses, for instance, the same
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`ObjectType` unless `with_object_t` itself is used.
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The aliases are members of every `basic_json` specialization, including [`ordered_json`](../ordered_json.md), and the
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type they produce is again a `basic_json` specialization. They can therefore be chained to replace several template
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parameters at once:
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```cpp
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using my_json = nlohmann::json::with_integers_t<int, unsigned int>::with_float_t<float>;
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using my_ordered_json = nlohmann::ordered_json::with_string_t<std::wstring>;
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```
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The result is the same type as spelling out all template parameters, so the order of the chained aliases does not
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matter. For instance, `nlohmann::json::with_object_t<nlohmann::ordered_map>` is `nlohmann::ordered_json`.
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## Examples
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??? example
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The following code shows how `with_object_t` can be used to create a JSON type that stores object elements in a
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`std::map` and therefore keeps them sorted by key, unlike the default type which preserves insertion order
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only when `nlohmann::ordered_json` is used.
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```cpp
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--8<-- "examples/with_t.cpp"
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```
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Output:
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```json
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--8<-- "examples/with_t.output"
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```
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## See also
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- [basic_json](index.md#template-parameters) - the template parameters that can be replaced
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- [json_base_class_t](json_base_class_t.md) - the type used for `CustomBaseClass`
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## Version history
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- Added in version 3.13.0.
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