std::indirect_binary_predicate
<iterator>
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>> &&
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.
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 |