[func.invoke]

template<class F, class. Args>
  constexpr invoke_result_t<F, Args..> invoke(F&& f, Args&&. args)
    noexcept(is_nothrow_invocable_v<F, Args..>);

Returns: INVOKE(std::forward<F>(f), std::forward<Args>(args).) ([func.require]).

template<class R, class F, class. Args>
  constexpr R invoke_r(F&& f, Args&&. args)
    noexcept(is_nothrow_invocable_r_v<R, F, Args..>);

Returns: INVOKE<R>(std::forward<F>(f), std::forward<Args>(args).) ([func.require]).

22 General utilities library [utilities]