std::indirect_unary_predicate

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Iterator library
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Algorithm concepts and utilities
Indirect callable concepts
indirect_unary_predicate
(C++20)
(C++20)
Common algorithm requirements
(C++20)
(C++20)
(C++20)
Utilities
(C++20)
Iterator adaptors
Range access
(C++11)(C++14)
(C++14)(C++14)
(C++11)(C++14)
(C++14)(C++14)
(C++17)(C++20)
(C++17)
(C++17)
Defined in header <iterator>
template < class F, class I >

concept indirect_unary_predicate =
std::indirectly_readable <I> &&
std::copy_constructible <F> &&
std::predicate <F&, /*indirect-value-t*/ <I>> &&

std::predicate <F&, std::iter_reference_t <I>> ;
(since C++20)

The concept indirect_unary_predicate specifies requirements for algorithms that call unary predicates as their arguments. The key difference between this concept and std::predicate is that it is applied to the type that I references, rather than I

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
P2609R3 C++20 one of the requirements was defined in terms of std::iter_value_t<I>&
which mishandled projections resulting in incompatibility with predicate F& 		defined in terms of /*indirect-value-t*/<I>
to correctly handle such projections
P2997R1 C++20 indirect_unary_predicate required F& to satisfy predicate with
std::iter_common_reference_t<I> 		does not require
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