Function get_data

extlibs/fmt/include/fmt/format.h:331–333

// A workaround for std::string not having mutable data() until C++17.
template <typename Char> inline Char* get_data(std::basic_string<Char>& s) {
  return &s[0];
}
template <typename Container>
inline typename Container::value_type* get_data(Container& c) {
  return c.data();