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std::experimental::ranges:: iterator_t, std::experimental::ranges:: sentinel_t

From cppreference.net
template < class T >
using iterator_t = decltype ( ranges:: begin ( std:: declval < T & > ( ) ) ) ;
(1) (ranges TS)
template < class T >
using sentinel_t = decltype ( ranges:: end ( std:: declval < T & > ( ) ) ) ;
(2) (ranges TS)

获取范围 T 的迭代器和哨兵类型。