std::indirect_equivalence_relation

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Iterator library

Iterator concepts

indirectly_readable (C++20)
indirectly_writable (C++20)
weakly_incrementable (C++20)
incrementable (C++20)
is-integer-like is-signed-integer-like (C++20)(C++20)

sentinel_for (C++20)
sized_sentinel_for (C++20)
input_iterator (C++20)
output_iterator (C++20)
input_or_output_iterator (C++20)

forward_iterator (C++20)
bidirectional_iterator (C++20)
random_access_iterator (C++20)
contiguous_iterator (C++20)

Iterator primitives

input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tagcontiguous_iterator_tag

(C++20)

iter_value_titer_difference_titer_reference_titer_const_reference_titer_rvalue_reference_titer_common_reference_t

(C++20)(C++20)(C++20)(C++23)(C++20)(C++20)

iterator (deprecated in C++17)
iterator_traits
incrementable_traits (C++20)
indirectly_readable_traits (C++20)

Algorithm concepts and utilities

Indirect callable concepts

indirectly_unary_invocableindirectly_regular_unary_invocable

(C++20)(C++20)

indirect_unary_predicate (C++20)
indirect_binary_predicate (C++20)

indirect_equivalence_relation (C++20)
indirect_strict_weak_order (C++20)

Common algorithm requirements

indirectly_movable (C++20)
indirectly_movable_storable (C++20)
indirectly_copyable (C++20)

indirectly_copyable_storable (C++20)
indirectly_swappable (C++20)
indirectly_comparable (C++20)

permutable (C++20)
mergeable (C++20)
sortable (C++20)

(C++20)

(C++20)

(C++26)

reverse_iterator
make_reverse_iterator (C++14)
move_iterator (C++11)
make_move_iterator (C++11)
default_sentinel_tdefault_sentinel (C++20)(C++20)
unreachable_sentinel_tunreachable_sentinel (C++20)(C++20)

front_insert_iterator
back_insert_iterator
inserter
insert_iterator
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move_sentinel (C++20)

common_iterator (C++20)
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make_const_iterator (C++23)
make_const_sentinel (C++23)

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Range access

begincbegin (C++11)(C++14)
rbegincrbegin (C++14)(C++14)

endcend (C++11)(C++14)
rendcrend (C++14)(C++14)

sizessize (C++17)(C++20)
empty (C++17)
data (C++17)

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Defined in header`<iterator>`
template<class F,class I1,class I2= I1> concept indirect_equivalence_relation= std::indirectly_readable<I1>&& std::indirectly_readable<I2>&& std::copy_constructible<F>&& std::equivalence_relation <F&,/indirect-value-t/<I1>,/indirect-value-t/<I2>>&& std::equivalence_relation <F&,/indirect-value-t/<I1>,std::iter_reference_t<I2>>&& std::equivalence_relation <F&,std::iter_reference_t<I1>,/indirect-value-t/<I2>>&& std::equivalence_relation <F&,std::iter_reference_t<I1>,std::iter_reference_t<I2>>;		(since C++20)

The conceptindirect_equivalence_relation specifies requirements for algorithms that call equivalence relations as their arguments. The key difference between this concept andstd::equivalence_relation is that it is applied to the types thatI1 andI2 references, rather thanI1 andI2 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 ofstd::iter_value_t<I>& which mishandled projections resulting in incompatibility with equivalence relationF&	defined in terms of/indirect-value-t/<I> to correctly handle such projections
P2997R1	C++20	`indirect_equivalence_relation` requiredF& to satisfy`equivalence_relation` with std::iter_common_reference_t<I>	does not require

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std::indirect_equivalence_relation

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