Proper way to dispose a one-off observable in RxSwift

Question

I have an observable that I only want to kick off once. The docs say:

Using dispose bags or takeUntil operator is a robust way of making sure resources are cleaned up. We recommend using them in production even if the sequences will terminate in finite time.

My observable terminates after just one event

let observable = Observable.create() { observer in
  webservice.makeHTTPRequestWithCompletionBlock {
    if something {
      observer.on(.Next(...))
      observer.onCompleted()
    } else {
      observer.on(.Error(...))
    }
  }
}

Say I wasn't interested in cancelling subscribers to this observable, I just want it run once and complete. I want the lifecycle of this observable to end when the work itself is completed. Meaning there are no good candidates for disposeBag that I can see. takeUntil also expects an 'event', and there are no good ones that I can see.

Right now I just solve the warning by throwing away the disposable:

_ = observeable.subscribeNext { ... }

Is there a way to do this, or a different paradigm that I should use?

Answer 1

Both DiposeBag and takeUntil are used to cancel a subscription prior to receiving the .Completed/.Error event.

When an Observable completes, all the resources used to manage subscription are disposed of automatically.

As of RxSwift 2.2, You can witness an example of implementation for this behavior in AnonymousObservable.swift

func on(event: Event<E>) {
    switch event {
    case .Next:
        if _isStopped == 1 {
            return
        }
        forwardOn(event)
    case .Error, .Completed:
        if AtomicCompareAndSwap(0, 1, &_isStopped) {
            forwardOn(event)
            dispose()
        }
    }
}

See how AnonymousObservableSink calls dispose on itself when receiving either an .Error or a .Completed event, after forwarding the event.

In conclusion, for this use case, _ = is the way to go.