constexpr const_reference operator[](size_type pos) const;
Requires: pos < size().
Returns: data_[pos].
Throws: Nothing.
[ Note: Unlike basic_string::operator[], basic_string_view::operator[](size()) has undefined behavior instead of returning charT(). — end note ]
constexpr const_reference at(size_type pos) const;
Throws: out_of_range if pos >= size().
Returns: data_[pos].
constexpr const_reference front() const;
Requires: !empty().
Returns: data_[0].
Throws: Nothing.
constexpr const_reference back() const;
Requires: !empty().
Returns: data_[size() - 1].
Throws: Nothing.
constexpr const_pointer data() const noexcept;
Returns: data_.
[ Note: Unlike basic_string::data() and string literals, data() may return a pointer to a buffer that is not null-terminated. Therefore it is typically a mistake to pass data() to a routine that takes just a const charT* and expects a null-terminated string. — end note ]