Function getting class of retrofit interface to be created causes wrong return type

Question

I am working on an app that has 3 weather APIs and I want my user to be able to choose which one should be used. Each of those APIs has each own data format, so I wanted to create a function that creates proper interface and than wrapps it, so the result is something common, so that I could handle it the same way for each interface. So my code looks like that:

fun create(api: Apis): ApiDataSource = retrofitBuilder
        .baseUrl(getBaseUrlFor(api))
        .build()
        .create(getInterfaceClassFor(api))
        .convertWith(interfaceConverter)
}

fun Api1.convertWith(interfaceConverter: InterfaceConverter): CommonWeatherDataEntity = ...

private fun getInterfaceClass(api: Apis): Class<*> = when (api) {
    Apis.Api1 -> Api1Interface::class.java
    Apis.Api2 -> Api2Interface::class.java
}

However line after .create(...) is highlighted red and error says "Unresolved reference". That's because create is returning Any!

What I don't understand (are generics obviously) is why the following code works fine:

fun Apis.createInterface(retrofitBuilder: Retrofit.Builder) =
    retrofitBuilder.baseUrl(getBaseUrlFor(this))
        .build()
        .create(
            when (this) {
                Apis.Api1 -> Api1Interface::class.java
                Apis.Api2 -> Api2Interface::class.java
            }
        ).convertWith(interfaceConverter)

Answer 1

Because the type inferred for when(...) is not Class<*> , but Class<out X> , where X is the common supertype of Api1Interface and Api2Interface . So create returns X .

You should be able to see that by removing the return type for getInterfaceClass and checking what the IDE shows.