23 General utilities library [utilities]

namespace std {
  template <class T> class reference_wrapper {
  public :
    // types
    using type = T;

    // construct/copy/destroy
    reference_wrapper(T&) noexcept;
    reference_wrapper(T&&) = delete;     // do not bind to temporary objects
    reference_wrapper(const reference_wrapper& x) noexcept;

    // assignment
    reference_wrapper& operator=(const reference_wrapper& x) noexcept;

    // access
    operator T& () const noexcept;
    T& get() const noexcept;

    // invocation
    template <class... ArgTypes>
      invoke_result_t<T&, ArgTypes...>
      operator() (ArgTypes&&...) const;
  };

  template<class T>
    reference_wrapper(reference_wrapper<T>) -> reference_wrapper<T>;
}