Hi, I have a

fun getResources(): Single<Resources>

and with that I need to do 2 things, 1️⃣ a flatMap with another call

fun doSomething(r: Resources): Single<OtherThing>

and 2️⃣ send a metric if some condition occurs

fun sendMetric(r: Resources): Completable

. I’m looking for something better than this:

getResources()
    .doOnSuccess { 
      if (someCondition(it)) sendMetric(it).subscribe()
    }.flatMap { doSomething(it) }

Note that if

sendMetrics

fails it’s not critical and I don’t want to interrupt the

doSomething

flow. Is there a more elegant way to do this?

You could do something like

getResources()
    .flatMap { resources ->
        if (someCondition(resources) {
            sendMetric(resources)
                .onErrorComplete()
                .andThen(doSomething(it))
        } else {
            doSomething(it)
        }
    }

I usually create an extension function for things like that, eg.

inline fun <T> Single<T>.forEachCompletable(block: (T) -> Completable) = flatMap { /* like in the previous snippet */ }

So you could do

getResources()
    .forEachCompletable { if (someCondition(it)) sendMetric(it) else Completable.complete() }
    .flatMap { doSomething(it) }

I don't suppose that looks very elegant, but if you abstract it behind a reusable function, it's alright. 🙂 This won't help if you need

sendMetric

to happen in parallel with

doSomething

, though.

Thank you! Your right with this code I can handle this scenario but, as you said, I’d prefer if it could be concurrent... I think that a more general question would be “How do I manage ‘fire and forget’ flows with observables”? Maybe observables it’s not the best way to do this because I don’t want to observe anything about that?

If it's an Android situation, I would probably add a method to the Application class, something like

fun fireAndForget(observable: Observable<*>)

, and subscribe there. Don't really have to worry about memory leaks or anything, it's not an Activity. Of course, generally, I'd prefer to have, say, an

Analytics

class that is a singleton, to which you can feed metrics and it will send them, to load off that responsibility from whatever class is doing it.

it’s a server app, maybe I can launch a coroutine in this case, thanks for the help!