in reply to Why does this even compile?

To complement what PodMaster said: check out Indirect Object Syntax. Particularly:

But what if there are no arguments? In that case, Perl must guess what you want. Even worse, it must make that guess at compile time. Usually Perl gets it right, but when it doesn't you get a function call compiled as a method, or vice versa. This can introduce subtle bugs that are hard to detect.

Liz

Update:
Some related nodes:

In Section Seekers of Perl Wisdom