Did you understand why it would be ambiguous to

addAll(vararg)

? I didn't quite see a possible confusion there

Would you be adding the elements from the list? Or the list itself?

Exactly the example I posted, what is the last line supposed to do? What if it's a

List<List<Any>>

?

The object is to have the following syntax possible:

val list = mutableListOf(1, 2, 3)
list.addAll(4, 5, 6)
Assert.assertEquals(listOf(1,2,3,4,5,6), list)