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2026-07-09 12:05:10 +00:00 · 2026-07-08 18:19:46 +00:00
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+# <small>nlohmann::basic_json::</small>operator<=>
+
+```cpp
+// 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)
+};
+```
+
+1. 3-way compares two JSON values producing a result of type `std::partial_ordering` according to the following rules:
+    - Two JSON values compare with a result of `std::partial_ordering::unordered` if either value is discarded.
+    - If both JSON values are of the same type, the result is produced by 3-way comparing their stored values using
+      their respective `operator<=>`.
+    - Integer and floating-point numbers are converted to their common type and then 3-way compared using their
+      respective `operator<=>`.
+      For instance, comparing an integer and a floating-point value will 3-way compare the first value converted to
+      floating-point with the second value.
+    - Otherwise, yields a result by comparing the type (see [`value_t`](value_t.md)).
+  
+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
+   3-way comparing both JSON values (see 1).
+
+## Template parameters
+
+`ScalarType`
+:   a scalar type according to `std::is_scalar<ScalarType>::value`
+
+## Parameters
+
+`rhs` (in)
+:   second value to consider 
+
+## Return value
+
+the `std::partial_ordering` of the 3-way comparison of `*this` and `rhs`
+
+## Exception safety
+
+No-throw guarantee: this function never throws exceptions.
+
+## Complexity
+
+Linear.
+
+## Notes
+
+!!! 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.
+
+## Examples
+
+??? 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"
+    ```
+
+## See also
+
+- [**operator==**](operator_eq.md) - comparison: equal
+- [**operator!=**](operator_ne.md) - comparison: not equal
+- [**operator<**](operator_lt.md) - comparison: less than
+- [**operator<=**](operator_le.md) - comparison: less than or equal
+- [**operator>**](operator_gt.md) - comparison: greater than
+- [**operator>=**](operator_ge.md) - comparison: greater than or equal
+
+## Version history
+
+1. Added in version 3.11.0.
+2. Added in version 3.11.0.