Future<T>.delayed constructor Null safety

Future<T>.delayed(
  1. Duration duration,
  2. [FutureOr<T> computation(
      )?]
    )

    Creates a future that runs its computation after a delay.

    The computation will be executed after the given duration has passed, and the future is completed with the result of the computation.

    If computation returns a future, the future returned by this constructor will complete with the value or error of that future.

    If the duration is 0 or less, it completes no sooner than in the next event-loop iteration, after all microtasks have run.

    If computation is omitted, it will be treated as if computation was () => null, and the future will eventually complete with the null value. In that case, T must be nullable.

    If calling computation throws, the created future will complete with the error.

    See also Completer for a way to create and complete a future at a later time that isn't necessarily after a known fixed duration.

    Implementation

    factory Future.delayed(Duration duration, [FutureOr<T> computation()?]) {
  if (computation == null && !typeAcceptsNull<T>()) {
    throw ArgumentError.value(
        null, "computation", "The type parameter is not nullable");
  }
  _Future<T> result = new _Future<T>();
  new Timer(duration, () {
    if (computation == null) {
      result._complete(null as T);
    } else {
      try {
        result._complete(computation());
      } catch (e, s) {
        _completeWithErrorCallback(result, e, s);
      }
    }
  });
  return result;
}