Hi! We use our common module for communicating wit...

# kotlin-native

[dambakk]

Hi! We use our common module for communicating with an API and, as everyone else, use a sealed class for the response:

sealed class Response<out T : Any> {
    data class Success<out T : Any>(val data: T) : Response<T>()
    data class Error(val reason: ErrorReason) : Response<Nothing>()
}

Receiving success in ios is ok. However, we are not able to cast the result to an Response.Error . When printing the object to console ((lldb) e dump(response)) we can see that it is an Optional(Error) object with all the params we are looking for, but we cannot cast it to en Error in any way. Anyone knows what we have to do?

[dambakk]

@louiscad, you are active here and seem to know a lot 🙂 Do you have any idea what to do?

[louiscad]

Option(Error) looks like the NSError? type, which cannot be cast to your custom type

[louiscad]

@dambakk Can you show the definition of ErrorReason?

[dambakk]

Yeah, its another sealed class defining our specific error cases or fall backs to an Exception:

sealed class ErrorReason(override val message: String) : Throwable(message) {
    object TokenExpired : ErrorReason("Token expired")
    object MissingToken : ErrorReason("Missing token")
...
}

[louiscad]

However, we are not able to cast the result to an Response.Error .

It's unclear what you're trying to cast… Do you know?

[dambakk]

Yeah, let me give some more context

[dambakk]

Consider this way of making a request from swift calling a suspend function in the common module:

api.someSuspendMethod(params...) { result, error in

}

where result could be a Result.Success or Result.Error. Makes sense? I’m not an ios dev, but as I have understood result could have a value or error can have a value, hence the Option wrapper. (Tho the errors will be in the result variables in this case).
It seems like the result we receive is of type Result.Success even though its a Result.Error which we can see when printing the result to the console. So we want to cast the result variable to Success if it is a success or an Error if it is an error.
someSuspendMethod is defined as something like this:

suspend fun someSuspendMethod(params): Result<ResponseType> { ... }

Is anything else unclear?

[dambakk]

And we’re using 1.4.10 if that’s relevant

[louiscad]

Result.Error or Response.Error? Juding from that, it seems that your issue takes its root in not knowing what type is exposed/used exactly in the API.

[dambakk]

Yeah, the classes isnt named exactly what I wrote in this post, so I might mixed up the terms a bit while writing this question, sorry ’bout that 😅
But yeah, we figured it out! We could not cast the response object to an Error due to an issue saying something like kotlinNothing was not ResponseType. So changing the Response class from the question to this:

sealed class Response<out T : Any> {
    data class Success<out T : Any>(val data: T) : Response<T>()
    data class Error<out T : Any>(val reason: ErrorReason) : Response<T>()
}

did the trick.
Thansks for your time 🙌