#[derive(Debug)]
struct Thing {
    list: Vec<i32>,
}

impl Thing {
    fn do_more(&mut self, x: &mut i32) {
        *x *= 2;
    }
    fn do_mut(&mut self, v: i32) {
        self.list.push(v);
        let x = self.list.last_mut().unwrap();
        self.do_more(x);
    }
}

fn main() {
    let mut t = Thing { list: Vec::new() };

    t.do_mut(1);

    println!("Done!");
}