std:: indirect_equivalence_relation

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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_tag output_iterator_tag forward_iterator_tag bidirectional_iterator_tag random_access_iterator_tag contiguous_iterator_tag

(C++20)

iter_value_t iter_difference_t iter_reference_t iter_const_reference_t iter_rvalue_reference_t iter_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_invocable indirectly_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)

Utilities

indirect_result_t

(C++20)

projected

(C++20)

projected_value_t

(C++26)

Iterator adaptors

reverse_iterator
make_reverse_iterator (C++14)
move_iterator (C++11)
make_move_iterator (C++11)
default_sentinel_t default_sentinel (C++20) (C++20)
unreachable_sentinel_t unreachable_sentinel (C++20) (C++20)

front_insert_iterator
back_insert_iterator
inserter
insert_iterator
front_inserter
back_inserter
move_sentinel (C++20)

common_iterator (C++20)
counted_iterator (C++20)
basic_const_iterator (C++23)
const_iterator (C++23)
const_sentinel (C++23)
make_const_iterator (C++23)
make_const_sentinel (C++23)

Stream iterators

istream_iterator
ostream_iterator

istreambuf_iterator
ostreambuf_iterator

Iterator customization points
ranges::iter_move (C++20)
ranges::iter_swap (C++20)

Iterator operations

advance
distance
prev (C++11)
next (C++11)

ranges::advance (C++20)
ranges::distance (C++20)
ranges::prev (C++20)
ranges::next (C++20)

Range access

begin cbegin (C++11) (C++14)
rbegin crbegin (C++14) (C++14)

end cend (C++11) (C++14)
rend crend (C++14) (C++14)

size ssize (C++17) (C++20)
empty (C++17)
data (C++17)

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 concept indirect_equivalence_relation specifies requirements for algorithms that call equivalence relations as their arguments. The key difference between this concept and std::equivalence_relation 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 equivalence relation F &	defined in terms of /indirect-value-t/ < I > to correctly handle such projections
P2997R1	C++20	`indirect_equivalence_relation` required F & to satisfy `equivalence_relation` with std:: iter_common_reference_t < I >	does not require

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std:: indirect_equivalence_relation

Defect reports

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