Fibonacci iterator

main.rs

struct Fibonacci(usize, usize);
impl Iterator for Fibonacci {
    type Item = usize;
    fn next(&mut self) -> Option<Self::Item> {
        let second = self.1;
        self.1 = self.0 + self.1;
        self.0 = second;
        Some(self.1)
    }
}
impl Default for Fibonacci {
    fn default() -> Self { Self(0, 1) }
}

fn main() {
    Fibonacci::default().take(30).for_each(|x| println!("{}", x))
}