Future<T>.sync constructor Null safety

  1. FutureOr<T> computation(

    Returns a future containing the result of immediately calling computation.

    If calling computation throws, the returned future is completed with the error.

    If calling computation returns a Future<T>, that future is returned.

    If calling computation returns a non-future value, a future is returned which has been completed with that value.


    factory Future.sync(FutureOr<T> computation()) {
      try {
        var result = computation();
        if (result is Future<T>) {
          return result;
        } else {
          // TODO(40014): Remove cast when type promotion works.
          return new _Future<T>.value(result as dynamic);
      } catch (error, stackTrace) {
        var future = new _Future<T>();
        AsyncError? replacement = Zone.current.errorCallback(error, stackTrace);
        if (replacement != null) {
          future._asyncCompleteError(replacement.error, replacement.stackTrace);
        } else {
          future._asyncCompleteError(error, stackTrace);
        return future;