test.rs

mod config {
    pub enum Node<T> {
        Directory(~str, ~[Node<T>]),
        Entry(~str, T)
    }

    impl<T> Node<T> {
        pub fn add(&mut self, entry: Node<T>) -> bool {
            match *self {
                Directory(_, ref mut list) => { list.push(entry); true }
                _ => false
            }
        }
    }
}

fn main() {
    let mut dir = config::Directory(~"dir", ~[]);
    dir.add(config::Entry(~"test", 0.0));
}