std::indirect_binary_predicate

std::indirect_binary_predicate - cppreference.com

From cppreference.com


`template< class F, class I1, class I2 > concept indirect_binary_predicate = std::indirectly_readable<I1> && std::indirectly_readable<I2> && std::copy_constructible<F> && std::predicate<F&, /indirect-value-t/<I1>, /indirect-value-t/<I2>> && std::predicate<F&, /indirect-value-t/<I1>, std::iter_reference_t<I2>> && std::predicate<F&, std::iter_reference_t<I1>, /indirect-value-t/<I2>> && std::predicate<F&, std::iter_reference_t<I1>, std::iter_reference_t<I2>>;`		(since C++20)

The concept indirect_binary_predicate specifies requirements for algorithms that call binary predicates as their arguments. The key difference between this concept and std::predicate is that it is applied to the types that I1 and I2 references, rather than I1 and I2 themselves.

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	some requirements were 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_binary_predicate` required `F&` to satisfy `predicate` with `std::iter_common_reference_t<I>`	does not require