std::Relation

Defined in header `<concepts>`
template <class R, class T, class U> concept Relation = std::Predicate<R, T, T> && std::Predicate<R, U, U> && std::CommonReference< const std::remove_reference_t<T>&, const std::remove_reference_t<U>&> && std::Predicate<R, std::common_reference_t< const std::remove_reference_t<T>&, const std::remove_reference_t<U>&>, std::common_reference_t< const std::remove_reference_t<T>&, const std::remove_reference_t<U>&>> && std::Predicate<R, T, U> && std::Predicate<R, U, T>;	(1)	(since C++20)

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 std::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))) and
bool(r(u, t)) == bool(r(C(u), C(t))).

Language
Headers
Freestanding and hosted implementations
Named requirements
Language support library
Concepts library (C++20)
Diagnostics library
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)
Filesystem library (C++17)
Technical Specifications