std::equivalence_relation

template< class R, class T, class U >
concept equivalence_relation = std::relation<R, T, U>;

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]