How to implement Iterator trait

Implement the Iterator trait by defining the Item associated type and the next method to return Option<Self::Item>.

struct Counter {
    count: u32,
}

impl Iterator for Counter {
    type Item = u32;

    fn next(&mut self) -> Option<Self::Item> {
        if self.count < 5 {
            self.count += 1;
            Some(self.count)
        } else {
            None
        }
    }
}

The Iterator trait lets your custom data types be looped over just like built-in lists. You define what type of item comes next and write a function that returns the next value or signals the end. Think of it like a vending machine that gives you one snack at a time until it runs out.