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nlohmann
101 lines
3.0 KiB
Markdown
101 lines
3.0 KiB
Markdown
# <small>nlohmann::basic_json::</small>operator<=>
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```cpp
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// since C++20
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class basic_json {
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std::partial_ordering operator<=>(const_reference rhs) const noexcept; // (1)
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template<typename ScalarType>
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std::partial_ordering operator<=>(const ScalarType rhs) const noexcept; // (2)
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};
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```
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1. 3-way compares two JSON values producing a result of type `std::partial_ordering` according to the following rules:
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- Two JSON values compare with a result of `std::partial_ordering::unordered` if either value is discarded.
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- If both JSON values are of the same type, the result is produced by 3-way comparing their stored values using
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their respective `operator<=>`.
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- Integer and floating-point numbers are converted to their common type and then 3-way compared using their
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respective `operator<=>`.
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For instance, comparing an integer and a floating-point value will 3-way compare the first value converted to
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floating-point with the second value.
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- Otherwise, yields a result by comparing the type (see [`value_t`](value_t.md)).
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2. 3-way compares a JSON value and a scalar or a scalar and a JSON value by converting the scalar to a JSON value and
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3-way comparing both JSON values (see 1).
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## Template parameters
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`ScalarType`
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: a scalar type according to `std::is_scalar<ScalarType>::value`
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## Parameters
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`rhs` (in)
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: second value to consider
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## Return value
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the `std::partial_ordering` of the 3-way comparison of `*this` and `rhs`
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## Exception safety
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No-throw guarantee: this function never throws exceptions.
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## Complexity
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Linear.
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## Notes
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!!! note "Comparing `NaN`"
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- `NaN` values are unordered within the domain of numbers.
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The following comparisons all yield `std::partial_ordering::unordered`:
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1. Comparing a `NaN` with itself.
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2. Comparing a `NaN` with another `NaN`.
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3. Comparing a `NaN` and any other number.
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## Examples
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??? example "Example: (1) comparing JSON values"
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The example demonstrates comparing several JSON values.
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```cpp
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--8<-- "examples/operator_spaceship__const_reference.c++20.cpp"
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```
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Output:
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```json
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--8<-- "examples/operator_spaceship__const_reference.c++20.output"
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```
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??? example "Example: (2) comparing JSON values and scalars"
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The example demonstrates comparing several JSON values and scalars.
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```cpp
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--8<-- "examples/operator_spaceship__scalartype.c++20.cpp"
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```
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Output:
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```json
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--8<-- "examples/operator_spaceship__scalartype.c++20.output"
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```
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## See also
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- [**operator==**](operator_eq.md) - comparison: equal
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- [**operator!=**](operator_ne.md) - comparison: not equal
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- [**operator<**](operator_lt.md) - comparison: less than
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- [**operator<=**](operator_le.md) - comparison: less than or equal
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- [**operator>**](operator_gt.md) - comparison: greater than
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- [**operator>=**](operator_ge.md) - comparison: greater than or equal
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## Version history
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1. Added in version 3.11.0.
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2. Added in version 3.11.0.
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