<experimental/ranges/concepts>
template< class T > concept bool Regular = Semiregular<T> && EqualityComparable<T>;
Regular 概念指定类型为常规,即它为可复制、可默认构造、且可比较相等。表现类似如 int 的内建类型,且能以 == 比较的类型满足该概念。
Regular
int
==