constexpr explicit basic_istream_view(basic_istream<CharT, Traits>& stream);
constexpr default_sentinel_t end() const noexcept;
constexpr explicit iterator(basic_istream_view& parent) noexcept;
iterator& operator++();
void operator++(int);
Val& operator*() const;
friend bool operator==(const iterator& x, default_sentinel_t);