// since C++20 class basic_json { std::partial_ordering operator<=>(const_reference rhs) const noexcept; // (1) template<typename ScalarType> std::partial_ordering operator<=>(const ScalarType rhs) const noexcept; // (2) };
3-way compares two JSON values producing a result of type std::partial_ordering
according to the following rules:
std::partial_ordering::unordered
if either value is discarded.operator<=>
.operator<=>
. For instance, comparing an integer and a floating-point value will 3-way compare the first value convertered to floating-point with the second value.value_t
).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 3-way comparing both JSON values (see 1).
ScalarType
: a scalar type according to std::is_scalar<ScalarType>::value
rhs
(in) : second value to consider
the std::partial_ordering
of the 3-way comparison of *this
and rhs
No-throw guarantee: this function never throws exceptions.
Linear.
!!! note “Comparing NaN
”
- `NaN` values are unordered within the domain of numbers. The following comparisons all yield `std::partial_ordering::unordered`: 1. Comparing a `NaN` with itself. 2. Comparing a `NaN` with another `NaN`. 3. Comparing a `NaN` and any other number.
??? example “Example: (1) comparing JSON values”
The example demonstrates comparing several JSON values. ```cpp --8<-- "examples/operator_spaceship__const_reference.c++20.cpp" ``` Output: ```json --8<-- "examples/operator_spaceship__const_reference.c++20.output" ```
??? example “Example: (2) comparing JSON values and scalars”
The example demonstrates comparing several JSON values and scalars. ```cpp --8<-- "examples/operator_spaceship__scalartype.c++20.cpp" ``` Output: ```json --8<-- "examples/operator_spaceship__scalartype.c++20.output" ```