Generic class with sub class that is not generic

Support
1

Null is compatible across different Types:

fun foo(i: Int?) {
    if (i == null) {
        val s: String? = i
    }
}

I want to recreate this behavior but am unsure how. The following is invalid and I’m not sure why as it seems sound as far as I can tell. As Nothing can never exist this would always be valid.
I could change it to Nullable<out T> but I can’t see why that’s necessary, and the ability to have in parameters of T is lost.

sealed class Nullable<T>
class Actual<T>(val it: T) : Nullable<T>()
object Null : Nullable<Nothing>()

fun bar(): Nullable<Int> {
    return Null  // Type mismatch
}
2

You forgot to make the Nullable class covariant :wink:

sealed class Nullable<out T>
class Actual<out T>(val it: T) : Nullable<T>()
object Null : Nullable<Nothing>()

fun bar(): Nullable<Int> {
	return Null  // compiles fine
}