std::experimental::ranges::Relation

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template < class R, class T, class U >

concept bool Relation =
    Predicate<R, T, T> &&
    Predicate<R, U, U> &&
    CommonReference<
const std::remove_reference_t <T> &,
const std::remove_reference_t <U> & > &&
    Predicate<R,
ranges::common_reference_t <
const std::remove_reference_t <T> &,
const std::remove_reference_t <U> & >,
ranges::common_reference_t <
const std::remove_reference_t <T> &,
const std::remove_reference_t <U> & >> &&
    Predicate<R, T, U> &&

    Predicate<R, U, T> ;
(1) (ranges TS)

The concept Relation<R, T, U> specifies that R defines a binary relation over the set of expressions whose type and value category are those encoded by either T or U.

Given

  • r, an expression such that decltype((r)) is R
  • t, an expression such that decltype((t)) is T
  • u, an expression such that decltype((u)) is U

and let C be ranges::common_reference_t < const std::remove_reference_t <T> &, const std::remove_reference_t <U> & >

then Relation<R, T, U> is satisfied only if

  • bool (r(t, u) ) == bool (r(C(t), C(u) ) )
  • bool (r(u, t) ) == bool (r(C(u), C(t) ) )