19 General utilities library [utilities]

19.14 Function objects [function.objects]

19.14.10 Class identity [func.identity]

struct identity {
  template<class T>
    constexpr T&& operator()(T&& t) const noexcept;

  using is_transparent = unspecified;
};

template<class T>
  constexpr T&& operator()(T&& t) const noexcept;

Effects: Equivalent to: return std::forward<T>(t);