Nested Completable stops observer chain

Question

I want to execute a Completable in flatMap and "map" it to a specific value I need. The subscribe block is never executed. Why?

I'm aware of the existence of flatMapCompletable and andThen, but these don't solve my problem. This code is also a little simplified, in my real code I need to apply more operators to the nested Observable (derived from Completable), so I really need the conversion to Observable.

disposables += myPublishSubject.withLatestFrom(myObservable).flatMap { (_, result) ->
    myCompletable()
        .toObservable<Unit>()
        .map { result } // Return result of "parent" observable after Completable completes
}.subscribe { result ->
    Timber.i("result: $result") // Not executed!
}

Answer 1

Completables have no items thus when converted back to Observable, that Observable is also empty and thus never calls map. Use andThen(Observable.just(result)),

disposables += myPublishSubject.withLatestFrom(myObservable).flatMap { (_, result) ->
    myCompletable()
        .andThen(Observable.just(result))
}.subscribe { result ->
    Timber.i("result: $result") // Not executed!
}

or convert the Completable back to single with a default:

disposables += myPublishSubject.withLatestFrom(myObservable)
.flatMapSingle { (_, result) ->
    myCompletable()
        .toSingleDefault(result)
}.subscribe { result ->
    Timber.i("result: $result") // Not executed!
}