I've got two deferred values. I want to wait for both, execute something after one of them completes and cancel the other one, not yet completed. What'd be the mechanism to achieve it?

If you can represent them with

Flow

, then I believe

Flow.zip

is the operator you’re looking for here

that's what I was looking for, thanks! I was thinking about saving the job in the field but that looked really ugly

Instead of

onEach()

, you could try

first()

You could use

select

https://kotlinlang.org/docs/reference/coroutines/select-expression.html

zip

will wait for an emission from both flows. It alone doesn't allow you to race 2 flows and cancel the loser once you have a winner.

I had this use case a while ago, and I implemented a function called

raceOf

where the winner coroutine cancels the others, and where its value is used. https://github.com/LouisCAD/Splitties/blob/017c21aaa03fc14859ea6b8e2500b3093f8dbc62/modules/coroutines/src/commonMain/kotlin/splitties/coroutines/Racing.kt#L29-52 The other code in the file supports the

race

function which allows to launch racers dynamically, if some coroutines need to join the race only based on some conditions.

@julian From the zip docs

 The resulting flow completes as soon as one of the flows completes and cancel is called on the remaining flow

I took this to mean that it does not wait for both flows to emit. Am I misinterpreting the docs?

A flow completing is different from a flow emitting. Completion of a flow cannot happen while an element is being collected (but can before and after).

Oh, of course. I mistook completion for emission. Thanks

@Tim Malseed

zip

waits for an emission from both flows being zipped before executing the lambda supplied to it. This lambda is the first opportunity one has to do anything with the flows. The next opportunity is downstream from the

zip

operator. Problem is, you can't cancel either flow from inside the `zip`'s lambda. And by the time you cancel downstream of

zip

, both flows have already emitted.

Thanks - I was indeed misinterpreting the docs