Could you please explain why this does not compile?

abstract class BaseClass<BaseType> {

    fun f1(p: BaseType) {}
}

sealed interface IBase<T1, T2> {

    class I1<T1>: IBase<T1, Unit>
}

class InheritedClass<T1, T2>: BaseClass<IBase<T1, T2>>() {

    fun f2() {
        // Compile error:
        // Type mismatch.
        // Required: IBase<T1, T2>
        // Found: IBase.I1<T1>
        f1(IBase.I1<T1>())
    }
}

Thanks.

because

IBase.I1<T>

's supertype is

IBase<T1, Unit>

not

IBase<T1, T2>

Since compiler can't prove that

Unit

==

T2

it's a type mismatch Imagine you did this:

val test = InheritedClass<String, Int>()
test.f2()

now,

T2

is

Int

which is definitely not

Unit

as you want to assign to it

It is an excerpt from a fairly complex code, so I cannot easily explain - probably I over-complicated the generics part of it 🙂 Thanks for your reply.