iter.rs

fn main() {
    let mut data = Data::new(10);
    println!("{:?}", data);
    for n in data.iter() {
        // you can't use data here
        // this line fail:
        // println!("{:?}", data);
        println!("{}", n);
    }
    println!("{:?}", data);
}

#[derive(Debug)]
struct Data {
    num: u8,
    finished: bool,
}

struct Iter<'a>(&'a mut Data);

impl Data {
    fn new(n: u8) -> Self {
        Data { num: n, finished: false }
    }
    fn iter(&mut self) -> Iter {
        Iter(self)
    }
}

impl<'a> Iterator for Iter<'a> {
    type Item = u8;
    fn next(&mut self) -> Option<u8> {
        if self.0.num < 1 {
            self.0.finished = true;
            None
        } else {
            let num = self.0.num;
            self.0.num -= 1;
            Some(num)
        }
    }
}