I know Flow<T>.combineLatest is deprecated a...

# coroutines

[Nick Williams]

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]

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]

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

[wasyl]

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]

@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