Function push_back

extlibs/fmt/include/fmt/core.h:1455–1460

    a formating function.
  */
  template <typename T> void push_back(std::reference_wrapper<T> arg) {
    static_assert(
        need_copy<T>::value,
        "objects of built-in types and string views are always copied");
    emplace_arg(arg.get());
  }
};

/**