Question about generics, I've function like this: ...

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[MR3Y]

Question about generics, I've function like this:

expect fun <T : HttpClientEngineConfig> getEngineFactory(): HttpClientEngineFactory<T>

where HttpClientEngineFactory is defined as:

public interface HttpClientEngineFactory<out T : HttpClientEngineConfig>

and on Jvm actual implementation is:

actual fun <T : HttpClientEngineConfig> getEngineFactory(): HttpClientEngineFactory<T> {
    return OkHttp
}

where OkHttp is defined as:

public object OkHttp : HttpClientEngineFactory<OkHttpConfig>

and for OkHttpConfig :

public class OkHttpConfig : HttpClientEngineConfig

the problem is that the actual implementation doesn't compile because of type mismatch, required: HttpClientEngineFactory<T> found: OkHttp

[MR3Y]

I can do:

return OkHttp as HttpClientEngineFactory<T>

but I want to understand what is the problem here and if there is a better solution than the Unchecked cast

[ephemient]

OkHttp isn't a HttpClientEngineFactory<T>, it's a HttpClientEngineFactory<OkHttpConfig>, and it's possible the caller may use !(T : OkHttpConfig)

[MR3Y]

I've control over where it can be called (actually it is called only in one place in a function's implementation), does that make it safe to cast it to HttpClientEngineFactory<T>?

[ephemient]

IMO it's more accurate to write

fun getEngineFactory(): HttpClientEngineFactory<*>

since the caller doesn't get to choose the type

[MR3Y]

Yeah, this works. this what I wanted actually since I don't care about the type in my dependent function's implementation. Thanks.