namespace std::chrono { class weekday_last { chrono::weekday wd_; // exposition only public: constexpr explicit weekday_last(const chrono::weekday& wd) noexcept; constexpr chrono::weekday weekday() const noexcept; constexpr bool ok() const noexcept; }; }
constexpr auto wdl = Sunday[last]; // wdl is the last Sunday of an as yet unspecified month static_assert(wdl.weekday() == Sunday);— end example