std::strict_weak_order

 

C++

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Feature test macros (C++20)

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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 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.

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.

Notes

The distinction between relation and strict_weak_order is purely semantic.