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nlohmann
61 lines
1.7 KiB
Markdown
61 lines
1.7 KiB
Markdown
# JSON_USE_IMPLICIT_CONVERSIONS
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```cpp
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#define JSON_USE_IMPLICIT_CONVERSIONS /* value */
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```
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When defined to `0`, implicit conversions are switched off. By default, implicit conversions are switched on. The
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value directly affects [`operator ValueType`](../basic_json/operator_ValueType.md).
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## Default definition
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By default, implicit conversions are enabled.
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```cpp
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#define JSON_USE_IMPLICIT_CONVERSIONS 1
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```
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## Notes
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!!! info "Future behavior change"
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Implicit conversions will be switched off by default in the next major release of the library.
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You can prepare existing code by already defining `JSON_USE_IMPLICIT_CONVERSIONS` to `0` and replace any implicit
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conversions with calls to [`get`](../basic_json/get.md).
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!!! hint "CMake option"
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Implicit conversions can also be controlled with the CMake option
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[`JSON_ImplicitConversions`](../../integration/cmake.md#json_implicitconversions)
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(`ON` by default) which defines `JSON_USE_IMPLICIT_CONVERSIONS` accordingly.
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## Examples
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??? example
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This is an example for an implicit conversion:
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```cpp
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json j = "Hello, world!";
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std::string s = j;
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```
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When `JSON_USE_IMPLICIT_CONVERSIONS` is defined to `0`, the code above does no longer compile. Instead, it must be
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written like this:
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```cpp
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json j = "Hello, world!";
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auto s = j.get<std::string>();
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```
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## See also
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- [**operator ValueType**](../basic_json/operator_ValueType.md) - get a value (implicit)
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- [**get**](../basic_json/get.md) - get a value (explicit)
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- [:simple-cmake: JSON_ImplicitConversions](../../integration/cmake.md#json_implicitconversions) - CMake option to control the macro
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## Version history
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- Added in version 3.9.0.
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