Is there an way to `select<T> { ... }` using two `Flow` ? I would like to choose between which...

# coroutines

[Jonathan]

Is there an way to select<T> { ... } using two Flow ? I would like to choose between which ever returns a response first. One flow is a stream of data and the other is a StateFlow indicating the current connection state. If the connection state flow is != CONNECTED I’d like my return an error, but if I get the data before the connection state is no longer CONNECTED, I’d like to return the data.

[Sam]

Since you want to collect the two flows concurrently, you'll need to produce them and then select between the resulting channels

[Jonathan]

I’m unfamiliar with the produce. Thank you for the suggestion.

[Sam]

I think for a flow it's produceIn, let me find the docs

[Sam]

This is the one: https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.flow/produce-in.html

[Zach Klippenstein (he/him) [MOD]]

I think you could also just merge the flows and operate on the result?

[Sam]

Was about to say, now I think about it, maybe there's a flow operator for this instead

[Jonathan]

The two flows return two different data types so I don’t think merge would work.

[Zach Klippenstein (he/him) [MOD]]

RxJava has an operator for this: amb. I'm not sure it exists for Flow Looks like nope.

[Jonathan]

So the recommended approach is produceIn ?

[Zach Klippenstein (he/him) [MOD]]

I can't think of an easier way to do it

[Jonathan]

You’re suggestion of the merge could work if I add a map operator to my source flows and returned a sealed type. I will investigate both options. Thank you and @Sam for the suggestions. I have an idea of the path forward.

[Zach Klippenstein (he/him) [MOD]]

There's lots of articles about how to implement amb in flow (often renamed to something like "race", which makes much more sense). If you want to factor out your business logic a bit from the flow wiring you could do that.