This decompiles as

List listOfDouble = CollectionsKt.listOf(1.0D);
      if (listOfDouble == null) {
         throw new TypeCastException("null cannot be cast to non-null type kotlin.collections.List<kotlin.Int>");
      } else {
         int first = ((Number)listOfDouble.get(0)).intValue();
         System.out.println("first=" + first + " (" + Integer.TYPE.getName() + ')');
      }

So the reason the cast is not failing is due to the unboxing?

No idea. From my understanding, a conversion from Double to Int is made which is different from a cast

I think it's attempting to do a conversion from

Integer

to

int

but through a cast to the

Number

superclass to invoke the

intValue()

method. Because of this it's actually casting the boxed

Double

value to

Number

(which succeeds) instead of the expected cast of the

Double

to

Integer

which would fail

The conversion from boxed Int to Int is identical to the conversion from boxed Double to Int because it uses Number superclass.

I see. That feels weird though

Weird things can happen when you cast generic type parameters. It's not advisable.