std::experimental::ranges:: Regular

From cppreference.com
template < class T >
concept bool Regular = Semiregular < T > && EqualityComparable < T > ;
(ranges TS)

The Regular concept specifies that a type is regular , that is, it is copyable, default constructible, and equality comparable. It is satisfied by types that behave similarly to built-in types like int , and that are comparable with == .