rust/src/iterators.rs

struct Fibonacci {
    limit: u32,
    a: u32,
    b: u32,
}

impl Fibonacci {
    fn new(limit: u32) -> Self {
        Fibonacci { limit, a: 0, b: 1 }
    }
}

impl Iterator for Fibonacci {
    type Item = u32;

    fn next(&mut self) -> Option<Self::Item> {
        if self.a > self.limit {
            return None;
        }
        let val = self.a;
        self.a = self.b;
        self.b = val + self.b;
        Some(val)
    }
}

fn main() {
    for i in Fibonacci::new(100) {
        println!("{}", i);
    }
}