Is there a way to do a cartesian product of two fl...

# coroutines

[Brais Gabin]

Is there a way to do a cartesian product of two flows? Something similar to join in RxJava? I have a flow of files and a flow of processors and I need to run all the processors through all the files. I'm looking for something like: filesFlow.join(processorsFlow) { file, processor -> processor.invoke(file) } (proccessor.invoke returns the result of the processor so I get new flow of type result)

[Brais Gabin]

I was thinking in something like this

fun <A, B, AB> Flow<A>.join(
    flowB: Flow<B>,
    selector: (A, B) -> AB
): Flow<AB> {
    return this.flatMapMerge { a -> flowB.map { b -> selector(a, b) } }
}

But with this solution I'm subscribing multiple times to flowB.

[Dominaezzz]

There isn't a built in operator for this, I'm guessing the expectation is to write one yourself (or maybe they haven't gotten to it yet).

[Dominaezzz]

This is an interesting use case. I guess you could use a SharedFlow with infinite replay buffer to only subscribe once.

[Brais Gabin]

I was thinking about it... but then I need to handle the no-end problem of SharedFlow too. 😭 we need a sharable & finishable Flow.

[Dominaezzz]

Yeah, passing a finish token through is a bit of a faff.

[ephemient]

Untitled

[Erik]

@ephemient nice solution. If the types (in this case files and processors) are different and known, then you might not need the intermediate step of mapping to an Either-Left or -Right type, but you can immediately check for the known types. Or am I missing something?

[ephemient]

@Erik correct, if you can distinguish them in other ways then you don't need the wrapping type. any other method of tagging would work fine