Function contract specifiers (since C++26)

 

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Function contract specifiers (preconditions spelled with pre and postconditions spelled with post) are specifiers that may be applied to the declarator of a function or of a lambda expression to introduce a function contract assertion of the respective kind to the corresponding function.

They ensure the specified condition holds during execution, triggering a violation (e.g. termination) in debug builds if the condition evaluates to false or the evaluation exits via an exception, and can be ignored in release builds for performance.