How to Implement Iterator for Custom Types

Implement the Iterator trait for your custom type by defining the Item associated type and the next method.

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
        }
    }
}

Implementing an Iterator for Custom Types makes your custom data structure work with standard loops and collection tools. It tells Rust how to get the next item one by one until the list is finished. Think of it like teaching a vending machine exactly how to dispense the next snack when you press the button.