Why does Scala warn about type erasure in the first case but not the second?

Question

I have two functions (not these have been edited since the original -- some of the answers below are responding to the original ones which returned a sequence of ()):

Answer 1

1) The second one does not produce a warning probably because you are constructing the list (or the pattern) by prepending elements to the Nil object, which extends List parameterising it with Nothing. And since everything is Nothing, there is nothing to be worried about ;) But I'm not sure, really guessing here.

2) Why don't you just use:

def foo[A](ls: Iterable[A]) =
    for (list <- ls sliding 2) yield ()