covariant type T occurs in contravariant position

Question

I know this question has been asked before, but either the answers don\'t apply to this case, or I don\'t understand them.

Basically, why doesn\'t the following (simp

Answer 1

Making test covariant in T means that Test[A] is a subtype of Test[Any] for any A. So lets create a Test:

val test_string = new Test[String]

Now we have a Test[String] and the contained list is type List[String].

Since Test[String] is a subtype of Test[Any], the following should be allowed:

val test_any : Test[Any] = test_string

And now, we have a Test[Any], and therefore test_any.list is type List[Any], which means the following should be valid:

test_any.list = List[Any]()

Which means we just assigned a List[Any] to test_strings list member, which shouldn't be allowed, since that is supposed to be a List[String], not a List[Any]. It also means you could prepend anything at all to the list, since it is type List[Any].