Hey there! - Using Flows from KMM in Swift is poss...

# multiplatform

[Marc Reichelt]

Hey there!
• Using Flows from KMM in Swift is possible thanks to https://github.com/rickclephas/KMP-NativeCoroutines ✅
• But: how can we pass Swift publishers (AnyPublisher<Boolean>) to KMM as Flows?

[Marc Reichelt]

Say we have this code in Kotlin:

fun doSomething(flow: Flow<Boolean>)

Now we have a publisher like this in Swift:

func swiftFunction(publisher: AnyPublisher<Boolean, Never>) {
   doSomething(publisher.asFlow())
}

Is there anything like asFlow() (which currently is not available) - or what would you do instead?

[Rick Clephas]

Not really helpful, but I am planning on adding support for such Swift to Kotlin cases.

[Marc Reichelt]

Thank you for answering - and thank you for providing this library, which is really useful to us! 👏 🎉

I saw the issue you referenced, but thought it would be a different problem 🙂

[Rick Clephas]

The whole issue is somewhat more complicated, but it mainly consists of 3 parts:
• adding support for Flow arguments
• adding support for suspend arguments
• adding support for Swift implementations of coroutine declarations (e.g. subclassing a Kotlin class in Swift and overriding a suspend or Flow declaration)
The first two aren’t that complex, the later causes more headache 😅.

[Marc Reichelt]

Yeah, it sounded a bit more complicated - that’s why I was asking 🙂

[Marc Reichelt]

We’ll try to implement something ourselves, maybe we can just use MutableSharedFlow for example

[Marc Reichelt]

I just wondered how others do it - because this seems to be a problem which more people should run into.
Maybe most people just add a parameter like onValueChanged: (Boolean) -> Unit and call it a day 😄

[Rick Clephas]

Yeah depending on the use case that might actually work. I guess it really depends on the architecture if you need something like this. E.g. if you expose ViewModels you are less likely to have to expose a Flow back to Kotlin.

[Marc Reichelt]

TL;DR: So we tried it out a bit, and it’s possible to make this work. The tricky bit is where to store the subscription of Combine somewhere, along with the type conversions for KotlinInt, KotlinBoolean etc.

We stopped investigating this for now. Hopefully we’ll have something to share sometime in the future.