# Iterators You can implement the `Iterator` trait on your own types: ```rust,editable struct Fibonacci { curr: u32, next: u32, } impl Iterator for Fibonacci { type Item = u32; fn next(&mut self) -> Option { let new_next = self.curr + self.next; self.curr = self.next; self.next = new_next; Some(self.curr) } } fn main() { let fib = Fibonacci { curr: 0, next: 1 }; for (i, n) in fib.enumerate().take(5) { println!("fib({i}): {n}"); } } ```