#[derive(Clone, Debug)]
enum UVec<T> {
    Zero,
    One(T),
    Many(Vec<T>),
}

impl<T> UVec<T> {
    fn new() -> UVec<T> {
        UVec::Zero
    }

    fn push(&mut self, value: T) {
        match *self {
            UVec::Zero => { *self = UVec::One(value); }
            UVec::One(v) => { *self = UVec::Many(vec![v, value]); }
            UVec::Many(ref mut v) => { v.push(value); }
        };
    }

    fn pop(&mut self) -> Option<T> {
        match *self {
            UVec::Zero => None,
            UVec::One(v) => { *self = UVec::Zero; Some(v) }
            UVec::Many(ref mut v) => v.pop()
        }
    }

    fn truncate(&mut self, len: usize) {
        match *self {
            UVec::Zero => {},
            UVec::One(_) => { if len < 1 { *self = UVec::Zero } }
            UVec::Many(ref mut v) => v.truncate(len)
        }
    }
}

fn main() {
}