Completable.subscribe(onError, onComplete) design issue

[artem-zinnatullin]

This particular overload of Completable.subscribe() looks out of design in compare to other RxJava classes like Observable and Single.

Spent ~5 minutes trying to understand why such code didn't compile:

Completable
  .fromAction(() -> doSomething())
  .subscribe(
    () -> ui.success(), 
    error -> ui.error(error)
  );

And the reason is because this overload accepts error handler first and complete handler second.

I do understand that it comes from Observable.subscribe(onNext, onError, onComplete).

But in compare to many other overloads like:

• Observable.subscribe(onNext, onError)
• Single.subscribe(onSuccess, onError) // this one has very similar semantic to target overload.
• Observable.subscribe(onNext)
• Single.subscribe(onSuccess)

Error handler is never first parameter in Observable.subscribe() and Single.subscribe().

Another point is that compiler error displayed in IDE makes it even worse:

---

Completable is still in @Experimental, so, we can change this signature as we want. We can @Deprecate this overload and add "better" alternative and then delete deprecated overload after one-two releases.

[akarnokd]

The design pattern was:

subscribe(Action0 onComplete)
subscribe(Action0 onComplete, Action1<Throwable> onError)

[artem-zinnatullin]

@akarnokd what do you mean by

was

?

[akarnokd]

I mean that is your suggestion but the current is swapped for case 2 because it is in the same order as the 3 arg Observable.subscribe minus onNext. Not sure which order feels more consistent with the other classes.

[artem-zinnatullin]

Right, I pointed that in the issue description, but we do have Single.subscribe(onSuccess, onError) even though it's also Observable.subscribe(onNext, onError, onComplete) minus onNext.

As said before: no other overloads of subscribe() in any classes accept onError first -> makes Completable inconsistent.

[akarnokd]

Okay. Since Completable is experimental, lets swap the arguments as you suggested.

[artem-zinnatullin]

Oh great, will do PR soon!