How Indefinite Observables work

An Observable is a bridge, connecting an event source to a listener. You’ve used lots of different event sources:

element.addEventListener('click', listener);
fetch(someURL).then(listener);
self.onmessage = listener;

gesture.addTarget(listener, action: #selector(gestureDidUpdate))
viewController.delegate = listener

gesture.addStateChangeListener(listener);
view.setOnClickListener(listener);

Each one puts the listener in a different place. An Observable is just a wrapper that gives them all the same interface:

clickStream.subscribe({
  next: listener
});

fetchResponseStream.subscribe({
  next: listener
});

messageStream.subscribe({
  next: listener
});

observableGesture.subscribe { value in
  listener.gestureDidUpdate(with: value)
}
observableViewController.subscribe { value in
  listener.didUpdate(with: value)
}

As you can see, each observable has a subscribe method. When you call subscribe, the Observable connects your listener to the event source, and returns an object with an unsubscribe method. Calling unsubscribe will disconnect the listener from the source.