Largely unrelated question: In the code about a third of the way into the article, there is,

    impl<'a> Drop for Foo<'a> {
        fn drop(&mut self) {
            *self.0 += 1;
        }
    }

What does the line "self.0 += 1;" do? Specifically, the ".0"? Foo is a basically a reference to an i32, so I would have thought that would be "self += 1;".