I know Flow lt T gt combineLatest is deprecated as it is jus kotlinlang #coroutines

I know Flow<T>.combineLatest is deprecated as it is just called combine but is there a true combineLatest (in the same vain as transformLatest, collectLatest, mapLatest, flatMapLatest) or does combine already behave this way (I don't believe so because the docs don't mention it)

Alex Vasilkov

02/14/2021, 3:07 PM

It is not deprecated in a sense that it was ever a thing in Kotlin, it was added just to ease the migration from libs like RxJava. From

Flow.comabine

docs:

Returns a [Flow] whose values are generated with [transform] function by combining the most recently emitted values by each flow.

I think this is what you would expect from this kind of operator. “Latest” in operators like

flatMapLatest

has a bit different meaning, it actually subscribes to latest produced

Flow

and unsubscribes from any previous flows (like RxJava’s

switchMap

wasyl

02/14/2021, 3:10 PM

(and I deleted my answer because I realised it was wrong)

Anyway if I understand correctly you’re right, if you suspend in

transform

block and new values are emitted from the combined flows, then the transformation is not cancelled. If you want cancellation then I suppose the simplest way would be moving the work you want cancelled to a separate,

*Latest

operator, for example instead of

flow1
  .combine(flow2) { a, b -> heavyTransform(a, b) }

you can do

flow1
  .combine(flow2) { a, b -> a to b }
  .mapLatest { (a, b) -> heavyTransform(a, b) }

Nick Williams

02/14/2021, 3:21 PM

@wasyl yes this is exactly what I was thinking, in fact I think I will create a extension function that chains these two calls together and call it combineLatest... which is back to my original point: feels like this operator should exist in the library already, I suspect the only reason it doesn't is to avoid the confusion for people coming from Rx

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