std::experimental::ranges::WeaklyEqualityComparableWith(3)

NAME
std::experimental::ranges::WeaklyEqualityComparableWith - std::experimental::ranges::WeaklyEqualityComparableWith

Synopsis
   Defined in header <experimental/ranges/concepts>
   template <class T, class U>
   concept bool WeaklyEqualityComparableWith =
   requires(const std::remove_reference_t<T>& t,
   const std::remove_reference_t<U>& u) {
   { t == u } -> Boolean&&; (ranges TS)
   { t != u } -> Boolean&&;
   { u == t } -> Boolean&&;
   { u != t } -> Boolean&&;
   };
   The concept WeaklyEqualityComparableWith<T, U> specifies that an object of type T
   and an object of type U can be compared for equality with each other (in either
   order) using both == and !=, and the results of the comparisons are consistent. More
   formally, WeaklyEqualityComparableWith<T, U> is satisfied only if given
     * t, an lvalue of type const std::remove_reference_t<T> and
     * u, an lvalue of type const std::remove_reference_t<U>,
   the following are true:
     * t == u, u == t, t != u,u != t have the same domain;
     * bool(u == t) == bool(t == u);
     * bool(t != u) == !bool(t == u); and
     * bool(u != t) == bool(t != u).
  Equality preservation
   An expression is equality preserving if it results in equal outputs given equal
   inputs.
     * The inputs to an expression consist of its operands.
     * The outputs of an expression consist of its result and all operands modified by
       the expression (if any).
   Every expression required to be equality preserving is further required to be
   stable: two evaluations of such an expression with the same input objects must have
   equal outputs absent any explicit intervening modification of those input objects.
   Unless noted otherwise, every expression used in a requires-expression is required
   to be equality preserving and stable, and the evaluation of the expression may only
   modify its non-constant operands. Operands that are constant must not be modified.
  Implicit expression variations
   A requires-expression that uses an expression that is non-modifying for some
   constant lvalue operand also implicitly requires additional variations of that
   expression that accept a non-constant lvalue or (possibly constant) rvalue for the
   given operand unless such an expression variation is explicitly required with
   differing semantics. These implicit expression variations must meet the same
   semantic requirements of the declared expression. The extent to which an
   implementation validates the syntax of the variations is unspecified.

See also
   EqualityComparable specifies that operator == is an equivalence relation
   EqualityComparableWith (concept)