1. override
Stream<T> asStream()

Creates a Stream containing the result of this future.

The stream will produce single data or error event containing the completion result of this future, and then it will close with a done event.

If the future never completes, the stream will not produce any events.

Source 

@override
Stream<T> asStream() {
  final StreamController<T> controller = new StreamController<T>();
  controller.add(_value);
  controller.close();
  return controller.stream;
}