Function arg

include/fmt/format.h:3878–3880

  void operator=(const generic_context&) = delete;

  constexpr auto arg(int id) const -> basic_format_arg<generic_context> {
    return args_.get(id);
  }
  auto arg(basic_string_view<Char> name) const
      -> basic_format_arg<generic_context> {
    return args_.get(name);