Does the module where I declare an interface with ...

# multiplatform

[curioustechizen]

Does the module where I declare an interface with a companion object have any impact on what is exported to Swift/ObjC?

I have the following module structure:
• :kmp:shared - This contains ClassId as shown in the thread
• :kmp:feature1 - This contains AuthToken as shown in the thread
I can access ClassIdCompanion from my Swift code, but I don't see AuthTokenCompanion

[curioustechizen]

ClassId defined in :kmp:shared module - this is the one that is exported to Swift:

interface ClassId {
    val value: Int
    fun isValid(): Boolean = value >= 0
    companion object {
        val Invalid = withValue(-1)
        fun withValue(value: Int): ClassId = ClassIdImpl(value)
    }
}

@JvmInline
private value class ClassIdImpl(override val value: Int) : ClassId

[curioustechizen]

AuthToken defined in :kmp:feature1 module - this is not exported to Swift; just the implementation(projects.kmp.feature1) dependency is declared

interface AuthToken {
    val token: String
    companion object {
        fun of(token: String): AuthToken = AuthTokenImpl(token)
    }
}

@JvmInline
private value class AuthTokenImpl(override val token: String) : AuthToken

[curioustechizen]

I can see AuthToken with a package prefix in my swift code but I cannot see the companion object.

I can see MypackageAuthToken but I cannot see MypackageAuthTokenCompanion that allows me to create an instance.

[Jan Holešovský]

It's likely to be some MypackageAuthToken.Companion.shared.<your method> or something like that, don't recall off the top of my head exactly; but the Xcode will offer it when you start typing

[curioustechizen]

I thought I had tried that and I did not see the Companion being generated. I even went through the generated Swift header file and I did not find it there either.
Right now I've changed my approach in order to avoid having to call this companion from Swift but I'm still interested in knowing how to achieve it.

[curioustechizen]

For example I wonder if the ObjCName annotations would help?

[curioustechizen]

I also see that only the :kmp:shared module has this snippet that configures the binaries. I don't have this snippet in any other multiplatform module that :kmp:shared depends on. Wonder if that has any impact:

target.binaries.framework {
    baseName = "KMPShared"
}

[Jan Holešovský]

Ah OK; then I guess it is probably stripped out as it is not called anywhere. To test if that's the case, call the function in the companion from some piece of code that you know is executed, and see if then it is included in the Swift header file.
If yes - then try to find out how to make it not stripped out; no idea if there's annotation for that or something; for my project it was enough to declare an interface { val x: ClassIWantedExported }, but it is a bit hacky, and not sure if it helps in your case.

[Jan Holešovský]

[Oh and to be clear - executed from the kmpshared]

[Daniel Seither]

If you want to export more than one module to iOS, you can use `export(project(":moduleName"))`: https://kotlinlang.org/docs/multiplatform-build-native-binaries.html#export-dependencies-to-binaries

[curioustechizen]

@Daniel Seither But is that necessary if I'm already depending on the other module in the commonMain { dependencies {}} block?
Another way of asking the same question is, if I don't use export(project(":moduleName")), will symbols present in ":moduleName" not be visible to Swift?

[Daniel Seither]

Yes. Dependencies of the main module are not automatically exported to Objective-C/Swift, only the types from the dependencies that are used in any interfaces exported by the main module. export(…) changes this.

[curioustechizen]

only the types from the dependencies that are used in any interfaces exported by the main module

This was the missing part of the puzzle. Thanks.