Method arg

extlibs/fmt/include/fmt/format.h:3127–3134

template <typename Range, typename Char>
typename basic_format_context<Range, Char>::format_arg
basic_format_context<Range, Char>::arg(basic_string_view<char_type> name) {
  map_.init(args_);
  format_arg arg = map_.find(name);
  if (arg.type() == internal::type::none_type)
    this->on_error("argument not found");
  return arg;
}

template <typename Char, typename ErrorHandler>
FMT_CONSTEXPR void advance_to(