std::predicate (since C++20)

 

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Core language concepts same_as (C++20) derived_from (C++20) convertible_to (C++20) common_reference_with (C++20) common_with (C++20) integral (C++20) signed_integral (C++20) unsigned_integral (C++20) floating_point (C++20) swappableswappable_with (C++20)(C++20) destructible (C++20) constructible_from (C++20) default_initializable (C++20)   move_constructible (C++20) copy_constructible (C++20) assignable_from (C++20)

Comparison concepts equality_comparableequality_comparable_with (C++20)(C++20) totally_orderedtotally_ordered_with (C++20)(C++20) Object concepts movable (C++20) copyable (C++20) semiregular (C++20) regular (C++20) Callable concepts invocableregular_invocable (C++20)(C++20) predicate (C++20) relation (C++20) equivalence_relation (C++20) strict_weak_order (C++20)

Exposition-only concepts boolean-testable  (C++20)

 

Defined in header <concepts>
template< class F, class... Args > concept predicate =     std::regular_invocable<F, Args...> &&     boolean-testable<std::invoke_result_t<F, Args...>>;		(since C++20)

The concept std::predicate<F, Args...> specifies that F is a predicate that accepts arguments whose types and value categories are encoded by Args..., i.e., it can be invoked with these arguments to produce a boolean-testable result.

Note that regular_invocable requires the invocation to not modify either the callable object or the arguments and be equality-preserving.

Equality preservation

Expressions declared in requires expressions of the standard library concepts are required to be equality-preserving (except where stated otherwise).

References

• C++23 standard (ISO/IEC 14882:2024):

• 18.7.4 Concept predicate [concept.predicate]

• C++20 standard (ISO/IEC 14882:2020):

• 18.7.4 Concept predicate [concept.predicate]