This is my function that returns the RequestState wrapped in the flow:

fun fetchProducts(limit: Int):  Flow<RequestState<List<Product>>> {
    return flow {
        emit(RequestState.Loading)
        // Delay to show a loading state.
        delay(2000)
        try {
            emit(
                RequestState.Success(
                    data = httpClient.get(urlString = "${baseUrl}products?limit=$limit").body()
                )
            )
        } catch (e: Exception) {
            emit(RequestState.Error(e.message.toString()))
        }
    }
}

Unfortunately this is not possible in this specific case due to a limitation of Obj-C. The problem is that the

List<Product>

type is usually converted to

[Product]

- which would retain the type. However, here the type is used as a type argument (in generics) which cannot be converted to

[Product]

( Swift Array) because it’s not a reference type which is required for Obj-C type arguments. Therefore it’s automatically converted by the Swift compiler to

NSArray

instead - which does not have generics in Swift and therefore the

Product

type is lost. (but if you had just

RequestState<Product>

then it would work)

@Filip Dolník I thought of that, I've made another data class Products, that has only one property:

val items: List<Product>

If I understand correctly, the subclasses of a sealed class will be converted as regular classes in Swift. As a someone who's coming from Android world, I would want to declare a variable something like:

val fetchedProducts: MutableState<RequestState<Products>> = remember {
    mutableStateOf(RequestState.Idle)
}
LaunchedEffect(key1 = Unit) {
    ProductApi().fetchProducts(limit = 10).collectLatest {
        fetchedProducts.value = it
    }
}

But in swift a RequestStateIdle class is not recognized as a subclass of RequestState? 🤔

Yeah, that’s because Swift generics do not support covariance. It would work if you defined the RequestState.Idle as

class Idle<T> : RequestState<T>

and then in Swift wrote

= RequestStateIdle<Products>()

@Filip Dolník Thanks Filip, I'll continue exploring it furthermore, will try your suggestions. Good tips.

as for the crash: hm, the problem in this case seems to be that Nothing does not behave the same way in Kotlin and Obj-C. In Kotlin it’s a subtype of all types, however, such concept doesn’t exist in Obj-C / Swift so it’s a regular class.