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api/basic_json/operator_lt.md

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+# <small>nlohmann::basic_json::</small>operator<
+
+```cpp
+// until C++20
+bool operator<(const_reference lhs, const_reference rhs) noexcept;   // (1)
+
+template<typename ScalarType>
+bool operator<(const_reference lhs, const ScalarType rhs) noexcept;  // (2)
+
+template<typename ScalarType>
+bool operator<(ScalarType lhs, const const_reference rhs) noexcept;  // (2)
+```
+
+1. Compares whether one JSON value `lhs` is less than another JSON value `rhs` according to the
+  following rules:
+    - If either operand is discarded, the comparison yields `#!cpp false`.
+    - If both operands have the same type, the values are compared using their respective `operator<`.
+    - Integer and floating-point numbers are automatically converted before comparison.
+    - In case `lhs` and `rhs` have different types, the values are ignored and the order of the types
+      is considered, which is:
+        1. null
+        2. boolean
+        3. number (all types)
+        4. object
+        5. array
+        6. string
+        7. binary
+      For instance, any boolean value is considered less than any string.
+
+2. Compares whether a JSON value is less than a scalar or a scalar is less than a JSON value by converting
+   the scalar to a JSON value and comparing both JSON values according to 1.
+
+## Template parameters
+
+`ScalarType`
+:   a scalar type according to `std::is_scalar<ScalarType>::value`
+
+## Parameters
+
+`lhs` (in)
+:   first value to consider 
+
+`rhs` (in)
+:   second value to consider 
+
+## Return value
+
+whether `lhs` is less than `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 `#!cpp false`:
+      1. Comparing a `NaN` with itself.
+      2. Comparing a `NaN` with another `NaN`.
+      3. Comparing a `NaN` and any other number.
+
+!!! note "Operator overload resolution"
+
+    Since C++20 overload resolution will consider the _rewritten candidate_ generated from
+    [`operator<=>`](operator_spaceship.md).
+
+## Examples
+
+??? example
+
+    The example demonstrates comparing several JSON types.
+        
+    ```cpp
+    --8<-- "examples/operator__less.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/operator__less.output"
+    ```
+
+## See also
+
+- [**operator<=>**](operator_spaceship.md) comparison: 3-way
+
+## Version history
+
+1. Added in version 1.0.0. Conditionally removed since C++20 in version 3.11.0.
+2. Added in version 1.0.0. Conditionally removed since C++20 in version 3.11.0.