* Waits for the promise to be either fufilled or invalidated, and then * returns an optional, holding the value used to fufill it or nullopt * if

* Indicates whether the promise has been invalidated. * * @return true if this promise has been invalidated; false otherwise. */

* Indicates whether this promise is guaranteed to not be invalidated. * * @return True if this promise is guaranteed to not be invalidated; false