What is the difference between using a compose() and a simple flatMap()?

Question

I just watched the conference by Jake Wharton The State of Managing State with RxJava .

He proposes to transform the events from view to action in this way:

Observable<Event> events = RxView.clicks(view).map(__ -> new Event());
ObservableTransformer<Event, Action> action = events -> events.flatMap(/* ... */);
events.compose(action).subscribe();

I would like to know the difference with this implementation:

Observable<Event> events = RxView.clicks(view).map(__ -> new Event());    
Observable<Action> action = events.flatMap(/* ... */);
action.subscribe();

What is the difference between using a compose() with an ObservableTransformer and a simple flatMap() with two Observable?

Answer 1

There is a good explanation, from Daniel Lew, about the differences. In short:

The difference is that compose() is a higher level abstraction: it operates on the entire stream, not individually emitted items.

For more details look at the complete explanation in this article (in the section named What About flatMap()? )