Rust Platform

🎯 In Python, you make any object iterable by implementing __iter__ and __next__:

class Countdown:
    def __init__(self, start):
        self.current = start

    def __iter__(self):
        return self

    def __next__(self):
        if self.current <= 0:
            raise StopIteration
        val = self.current
        self.current -= 1
        return val

Or more commonly, you use a generator:

def countdown(start):
    while start > 0:
        yield start
        start -= 1

Rust uses the same idea — a trait with a next() method — but the payoff is bigger. Implement one method, and you get 70+ iterator methods (.map(), .filter(), .take(), .sum(), .collect(), etc.) for free.

The Iterator trait

To make your type iterable, implement the Iterator trait:

struct Countdown {
    current: u32,
}

impl Iterator for Countdown {
    type Item = u32;

    fn next(&mut self) -> Option<Self::Item> {
        if self.current > 0 {
            let val = self.current;
            self.current -= 1;
            Some(val)
        } else {
            None
        }
    }
}

Two …