Anyone know current state of using lambas with a return value of Unit in native? Currently in swift...

# multiplatform

[Patrick Jackson]

Anyone know current state of using lambas with a return value of Unit in native? Currently in swift I have to always return a KotlinUnit() from a lambda. I've seen an open issue. Has this changed, or will this change in future versions of KN? i.e. to pass a lamda to a Kotlin function we must do:

myKtFun { dostuff()
    return KotlinUnit() }

[Thomas]

If you enable the generics then the return type changes to Void. So you don’t need to add a return statement anymore.

[Patrick Jackson]

I'm using 1.3.41 with generics and still have to use return statements. I suppose that is in a newer release

[Thomas]

I am using 1.3.41 as well and don’t have to add the return to lamdas. Are you sure the generics are enabled correctly using -Xobjc-generics?

[Marc Dietrichstein]

I also didn’t not have to return KotlinUnit() anymore with 1.3.41. `-Xobjc-generics`wasn’t enabled in my case.

[Thomas]

Kotlin 1.3.40 has the following in the release notes:

In addition to this, the Kotlin type Unit will turn into Void in the produced frameworks.

It was just below the generics supports so I thought you needed the generics for this. But it looks like it works without the generics as well.

[Thomas]

The docs still say you need to add the return. I guess this still needs to be updated? https://github.com/JetBrains/kotlin-native/blob/master/OBJC_INTEROP.md#function-types

[Patrick Jackson]

It is working on 1.3.41 for me now that I go back and clean & rebuild. Thanks Thomas

[kpgalligan]

I was pretty surprised by the generics part and was going to comment, but got distracted …

[Thomas]

@kpgalligan yes, sorry about that. I don't think it is really clear in the 1.3.40 change log if this was in addition to generics or to the whole update. It says "in addition to this..". I thought it referred to the generics part.

[kpgalligan]

Yeah, I can see that getting confused. I was surprised when we updated to 1.3.4x that Unit went away. It’s pretty nice not having to do that.

[basher]

They improved it in many cases in 1.3.41. If you found a case they missed, you should file a GH issue

[svyatoslav.scherbina]

Generics are irrelevant here.

The docs still say you need to add the return. I guess this still needs to be updated?

Yes, thanks.

myKtFun { dostuff()

return KotlinUnit() }

myKtFun is likely not a function but a function-typed object here. Unit is not represented as Void when in is that deep. I.e. () -> Unit type becomes () -> Void, but (() -> Unit) -> Unit becomes (() -> Unit) -> Void.

[Patrick Jackson]

@svyatoslav.scherbina Ok, yes I still have to

return KotlinUnit()

in some situations. My usecase is a

typealias Subscriber = () -> Unit
fun subscribe(subscriber: Subscriber) { ... }

Think this will ever go away? or is there some limitation that is blocking

[svyatoslav.scherbina]

Then you either use older version of Kotlin or the usecase is more complex.
This subscribe case works properly for me.
Could you recheck?

[Patrick Jackson]

I see now, yes it is more complex.

typealias Subscription = () -> Unit
val subscribe: (Subscriber) -> Subscription

using

subscribe  { }

from swift forces me to

return KotlinUnit()

[svyatoslav.scherbina]

Then how is it different from what i’ve described above?
https://kotlinlang.slack.com/archives/C3PQML5NU/p1565681457378500?thread_ts=1565633800.374800&cid=C3PQML5NU

[Patrick Jackson]

yes, see that sorry...just asking if you think this will likely change in a future version of kotlin. If you think the more complex function-typed objects (such as (

() -> Unit) -> Unit)

ever be able to return Void from Swift. Bit of a pain point when using from swift.

[svyatoslav.scherbina]

We have no ETA for this.