switch-map-completable-does-not-complete.md

Observable#switchMapCompletable does not complete

This already got me twice

When flatMapCompletable won't complete?

Observable.create<String> { emitter ->
    emitter.onNext("foobar")
}.flatMapCompletable {
    Completable.complete()
}.test()
    .assertComplete()

This won't pass as emitter doesn't call onComplete. My intuition was that flatMapCompletable will take first element, map it to Completable and then complete the stream. This intuition is not correct.

Looking at documentation:

flatMapCompletable will complete only when Observable completes.

When flatMapCompletable will complete?

Observable.create<String> { emitter ->
    emitter.onNext("foobar")
}.firstOrError()
    .flatMapCompletable {
        Completable.complete()
    }.test()
    .assertComplete()

This will pass, as we map Observable to Single with Observable#firstOrError. Single#flatMapCompletable "completes based on applying a specified function to the item emitted by the source Single"