Differentiate a refined concept from its more general case by adding new use patterns.

Reason

Otherwise they cannot be distinguished automatically by the compiler.

Example

template<typename I>
// Note: input_iterator is defined in <iterator>
concept Input_iter = requires(I iter) { ++iter; };

template<typename I>
// Note: forward_iterator is defined in <iterator>
concept Fwd_iter = Input_iter<I> && requires(I iter) { iter++; };

The compiler can determine refinement based on the sets of required operations (here, suffix ++). This decreases the burden on implementers of these types since they do not need any special declarations to "hook into the concept". If two concepts have exactly the same requirements, they are logically equivalent (there is no refinement).

Enforcement

To disambiguate them, see T.24.

• Flag a concept that has exactly the same requirements as another already-seen concept (neither is more refined).