std::indirect_binary_predicate - cppreference.com (original) (raw)

| | | | | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | ------------- | | 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.

[edit] 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 withstd::iter_common_reference_t<I> does not require