Method check_dynamic_spec

include/fmt/base.h:1255–1258

  using base::check_arg_id;

  FMT_CONSTEXPR void check_dynamic_spec(int arg_id) {
    if (arg_id < num_args_ && types_ && !is_integral_type(types_[arg_id]))
      report_error("width/precision is not integer");
  }
};

// An argument reference.