std:: indirect_unary_predicate

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C++
Iterator library
Iterator concepts
Iterator primitives
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 itself.

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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