hey all, I keep running into this error on iOS whe...

# multiplatform

[Ryan Simon]

hey all, I keep running into this error on iOS when trying to cast a type of Any to a more concrete type

Could not cast value of type 'kobjcc0'

[Ryan Simon]

I think this may be due to some issues with generics.

I’m using an Either/Result class to wrap my return type in my Kotlin Native code.

In iOS, it apparently doesn’t see the type at all, and instead refers to it as kobjcc0

[Ryan Simon]

The frustrating part is that when I print the description of my object out in Xcode, the object that I want is there in the type I expect it to be represented (as a pair)

[Ryan Simon]

I’ve tried using the generics compiler flag

binaries.framework {
     freeCompilerArgs += "-Xobjc-generics"
}

But it didn’t really help with this case

[Ryan Simon]

Here’s what my Either class looks like

sealed class Either<out L, out R> {
    data class Error<out L>(val value: L) : Either<L, Nothing>()
    data class Success<out R>(val value: R) : Either<Nothing, R>()

    val isSuccess get() = this is Success<R>
    val isError get() = this is Error<L>

    fun <L> error(value: L) = Error(value)
    fun <R> success(value: R) = Success(value)

    fun either(fnL: (L) -> Any, fnR: (R) -> Any): Any =
            when (this) {
                is Error -> fnL(value)
                is Success -> fnR(value)
            }

    suspend fun eitherSuspend(fnL: suspend (L) -> Any, fnR: suspend (R) -> Any): Any =
            when (this) {
                is Error -> fnL(value)
                is Success -> fnR(value)
            }
}

[Artyom Degtyarev [JB]]

Hello! Am I getting it correct, that everything breaks when you do something like ReturnedSuccessWithAnyValue.value as! String ? I just tried with a simple piece of code but cannot reproduce the error for now.

[russhwolf]

Make sure your generic parameters have nonnull upper bounds (eg L : Any) or else objc will see them as Any?. Might not be the only issue you're having though.

[Ryan Simon]

Yeah, I made sure of that, thanks @russhwolf

[Ryan Simon]

@Artyom Degtyarev [JB] I'm not sure what you mean, since I usually have to access the Either values by using the either folding function

[Ryan Simon]

Here's the project repo if it helps https://github.com/RyanSimon/kmp-experiment

[Ryan Simon]

The problem specifically manifests at the ViewController call site in the iOS project

[basher]

Def recommend filing a K/N GitHub issue

[Ryan Simon]

okay, thanks @basher. i looked at the work @kpgalligan did on generics, and it seems like my repo respects the limitations. but 🤷‍♂️

[Ryan Simon]

this worked for me

tasks.withType<org.jetbrains.kotlin.gradle.tasks.KotlinNativeLink>().configureEach {
    this.binary.freeCompilerArgs += "-Xobjc-generics"
}

[Ryan Simon]

i was just messing up the compiler args

[basher]

ah 👍

[Ryan Simon]

since i was using cocoapods plugin, i needed to override the binary args for ios