21 Strings library [strings]

21.4 String view classes [string.view]

21.4.4 Deduction guides [string.view.deduct]

template<class It, class End> basic_string_view(It, End) -> basic_string_view<iter_value_t<It>>;
Constraints:
template<class R> basic_string_view(R&&) -> basic_string_view<ranges::range_value_t<R>>;
Constraints: R satisfies ranges​::​contiguous_­range.