Hello! Is there any way to share Kotlin code between iOS frameworks? In architecture like on screens...

# multiplatform

[Rafał Kuźmiński]

Hello! Is there any way to share Kotlin code between iOS frameworks? In architecture like on screenshot, we have conflict with classes or interfaces located in "Shared Kotlin library". If in shared library there would be a class "Foo" then in iOS we would have 2 classess FrameworkAFoo and FrameworkBFoo and we have to map between them
Is there any way to link kotlin libraries instead of "merging" them into framework?

[Ciaran Sloan]

no unfortunately, I don't believe this is currently possible with KMP

[Ciaran Sloan]

each framework will generate its own set of classes that will not be able to be shared across other frameworks. Even the dependencies of the shared module itself (for example kotlin Flow will become FrameworkAFlow and FrameworkBFlow)

[Ciaran Sloan]

this blog by touchlab does a good deep dive into the topic. You can theoretically have multiple frameworks, but you cannot share models across those frameworks

[Rafał Kuźmiński]

I see, thank you

[juliocbcotta]

So, we can have multiple libraries, they just can't share code among themselves?

[Rafał Kuźmiński]

Yes, even if we have same class "Foo" then iOS will read this like FrameworkAFoo and FrameworkBFoo and you have to provide mappers in Swift to communicate between libraries

[juliocbcotta]

Ok, but is there a way for splitting the shared code in different gradle modules and compiling them for iOS as if it was just one artefact? I think multiple namespaces are not possible at the moment, right? This is kinda of a big restriction for some teams..

[Ciaran Sloan]

> So, we can have multiple libraries, they just can't share code among themselves?
You can share code, but you cannot share models as Foo from frameworkA will not have type equality of Foo from frameworkB.

> but is there a way for splitting the shared code in different gradle modules and compiling them for iOS as if it was just one artefact?
Yes, this is what we currently do. We split our kmp codebase into feature modules and add each of these feature modules as dependencies of a shared module that is then used to generate the Framework on iOS. So iOS imports this one framework as one package.

[Rafał Kuźmiński]

So the best approach for now would be to gather all Kotlin libraries into one project and build single framework? And somehow refactor our iOS libraries to use intermediate models instead of Kotlin, something like this:

[Ciaran Sloan]

> And somehow refactor our iOS libraries to use intermediate models instead of Kotlin
I'm not sure I understand what you mean here, but essentially this is close to what we do.

We have :kmp:feature-a :kmp:feature-b :kmp:feature-c :kmp:shared. Where :kmp:shared depends on each of the feature modules.

On Android we then have :android:feature-a that depends on :kmp:feature-a and then :android:feature-b that depends on :kmp:feature-b and so on....

But for iOS the :kmp:shared generates a Framework which the iOS codebase depends on

[Ciaran Sloan]

And somehow refactor our iOS libraries to use intermediate models instead of Kotlin

Yeah I'd say thats your best bet

[Rafał Kuźmiński]

Yes I understand that, we use it exactly the same but issue is that our "iOS App" depends on kmpshared and also on other frameworks, created by iOS programmers which are also using same Shared Kotlin library. In our company all of our products are using a few common algorithms and data structures that are essential and shared between a lot of libraries. It is not an issue in Android world, but it is in iOS

[Ciaran Sloan]

yes gotcha understand now. You'll have difficulty if trying to share classes across these frameworks. You'll need to either use c-interop to provide these to the kotlin shared library, or write some kind of intermediary layer like youve mentioned

[Rafał Kuźmiński]

Sure, that sounds like a good idea, thanks!

[Ciaran Sloan]

you bet! Thanks for sharing your use case 👌🏼