*Breaking changes* Change toArray() to return Single

[lucas34]

Hi,

Current implementation of toArray() method in Observable will return another Observable. Since RxSwift now have all Traits. For me it will make more sense to return Single Instead.

let array: Single<[Int]> = Observable<Int>.just(1, 2, 3).toArray()
Observable<Int>.empty().toArray() // equivalent to Single<Int>.just([])

Unless there is any case that toArray will emit multiple items. But like the documentation says
Converts an Observable into another Observable that emits the whole sequence as a Single array and then terminates.

I'm migrating to Traits to make my streams more representative and more strict. If you agree to have more methods to return another type like some methods in Observable returns something else than Observable (Single, Maybe, Completable) I can suggest more operators.
But if operator in Observable should only return another Observable it's also understandable.

[kzaher]

Hi @lucas34 ,

I think your complaint makes sense. It would be great if we could make this a non breaking change somehow.

ToArraySingle looks a bit ugly to me, but maybe there is some obvious and elegant way we can encorporate these changes

[freak4pc]

For non-breaking I don't think there's much you can do besides either:

1. You can have asArray that would do single and "phase out" toArray
2. You can have toSingleArray, but agree this is a tad ugly

[lucas34]

Actually changing the return type has already been done for ignoreElements.
#1436

I think it would be acceptable to change the return type for the next major release. Like 4.2.0. or 5.X. I'm scare that if we start to have toArray then toSingleArray we will have later toMaybeArray and so on for other operators as well.

[freak4pc]

The only problem I see here is that the most common use case is working with Observable, and not with Traits. (e.g. it's the "common grounds" of all RxSwift users)

Using this sort of "Catchall" that would always return a Single might not be beneficial to people who do not see (or are interested) in the benefits of traits.

Do we prefer people using .asSingle() sometimes or people using .asObservable() sometimes? I guess that's the question.

Anyways If there is a consensus switching to Single is correct I agree with you @lucas34 that a breaking change makes most sense here, unfortunately.

[lucas34]

Do you have any branch yet for the RxSwift 5.0 to target the PR ?

[freak4pc]

Hey @lucas34 - We'd like to include this change in RxSwift 5, could you rebase on develop and finalize this in the next few days? Thanks !

[lucas34]

@freak4pc I created this MR to return Single instead of observable #1923

However I did with type conversions from observable to Single. Let me know what do you think. Not sure if it's the ideal solution.

[freak4pc]

Fixed in #1923.