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

The concept strict_weak_order<R, T, U> specifies that the relation R imposes a strict weak ordering on its arguments.

[edit] Semantic requirements

A relation r is a strict weak ordering if

  • it is irreflexive: for all x, r(x, x) is false;
  • it is transitive: for all a, b and c, if r(a, b) and r(b, c) are both true then r(a, c) is true;
  • let e(a, b) be !r(a, b) && !r(b, a), then e is transitive: e(a, b) && e(b, c) implies e(a, c).

Under these conditions, it can be shown that e is an equivalence relation, and r induces a strict total ordering on the equivalence classes determined by e.

[edit] Notes

The distinction between relation and strict_weak_order is purely semantic.