Does someone know how I can bring nullable in the following parameter in terms of a type parameter

class A<T>(val a: B<T>.()->Unit)

I tried:

class A<T1, T2: (B<T>.()->Unit)? >(val a: T2)

But that failes stating that an extension function type cannot be used as upper bound. I want to be able to have the parameter nullable in some places and not nullable in others without creating two classes for it

Just using

T2 : ((B<T>) -> Unit)?

should work fine.

what version of kotlin are you using?

1.2.10, why?

ah... I did not spot the difference at first.