Service functions returning flows must not be susp...

# kotlinx-rpc

[S.]

Service functions returning flows must not be suspending anymore? https://kotlin.github.io/kotlinx-rpc/features.html#send-and-receive-flows
Why is this a requirement, it's rather disturbing when my flow comes from a suspend call like a db. and what's the best way to handle such cases?

[CLOVIS]

suspend () -> Flow<T> is always a code smell, it's code that suspends in two different ways

[CLOVIS]

If you need to initialize something before processing elements, do so within the flow:

fun foo(): Flow<T> = flow {
    // initialize your stuff
    emitAll(/* your request */)
}

[S.]

isn't emitAll suspending as well?

[CLOVIS]

Yes. Within flow {} you can suspend, so it's not a problem.

[S.]

ohh.. well that changes things, almost all my functions here are suspending so I never even noticed

[CLOVIS]

It's a common mistake, yeah…

Flow<T> means "a suspending function that returns multiple values", so suspend () -> Flow<T> is "a suspending function which returns a suspending function which returns multiple values", which is repetitive and confusing, because you don't know what happens at each of the suspensions

[CLOVIS]

kinda of similar to why a suspend function shouldn't have a CoroutineScope receiver

[S.]

yeah that makes sense. I suppose I have a lot of code to change. thanks!

[CLOVIS]

No worries! Good luck!

[CLOVIS]

As a temporary solution, you can use:

fun <T> realFlow(block: suspend () -> Flow<T>) = flow {
    emitAll(block())
}

to adapt between your old functions and the well-written ones

[Alexander Sysoev]

Exactly, thank you Ivan for answering this!