std::equivalence_relation

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Diagnostics library

Memory management library

Metaprogramming library (C++11)

General utilities library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Strings library

Text processing library

Numerics library

Date and time library

Input/output library

Filesystem library (C++17)

Concurrency support library (C++11)

Execution control library (C++26)

Technical specifications

Symbols index

External libraries

 

Concepts library

Core language concepts same_as (C++20) derived_from (C++20) convertible_to (C++20) common_reference_with (C++20) common_with (C++20) integral (C++20) signed_integral (C++20) unsigned_integral (C++20) floating_point (C++20) swappableswappable_with (C++20)(C++20) destructible (C++20) constructible_from (C++20) default_initializable (C++20)   move_constructible (C++20) copy_constructible (C++20) assignable_from (C++20)

Comparison concepts equality_comparableequality_comparable_with (C++20)(C++20) totally_orderedtotally_ordered_with (C++20)(C++20) Object concepts movable (C++20) copyable (C++20) semiregular (C++20) regular (C++20) Callable concepts invocableregular_invocable (C++20)(C++20) predicate (C++20) relation (C++20) equivalence_relation (C++20) strict_weak_order (C++20)

Exposition-only concepts boolean-testable  (C++20)

 

Defined in header <concepts>
template< class R, class T, class U > concept equivalence_relation = std::relation<R, T, U>;		(since C++20)

The concept equivalence_relation<R, T, U> specifies that the relation R imposes an equivalence relation on its arguments.

Semantic requirements

A relation r is an equivalence relation if

• it is reflexive: for all x, r(x, x) is true;
• it is symmetric: for all a and b, r(a, b) is true if and only if r(b, a) is true;
• it is transitive: r(a, b) && r(b, c) implies r(a, c).

Notes

The distinction between relation and equivalence_relation is purely semantic.

References

• C++23 standard (ISO/IEC 14882:2024):

• 18.7.6 Concept equivalence_relation [concept.equiv]

• C++20 standard (ISO/IEC 14882:2020):

• 18.7.6 Concept equivalence_relation [concept.equiv]

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