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devexamples

Custom Iterator for Fibonacci Numbers

Implement the Iterator trait to produce a lazy Fibonacci sequence, showing how infinity can be represented without allocating a collection.

RustData Integrity

Code

snippet
struct Fibonacci {
    current: u64,
    next: u64,
    remaining: usize,
}

impl Fibonacci {
    fn new(remaining: usize) -> Self {
        Fibonacci { current: 0, next: 1, remaining }
    }
}

impl Iterator for Fibonacci {
    type Item = u64;

    fn next(&mut self) -> Option<u64> {
        if self.remaining == 0 {
            return None;
        }
        let value = self.current;
        let following = self.current + self.next;
        self.current = self.next;
        self.next = following;
        self.remaining -= 1;
        Some(value)
    }
}

fn main() {
    let sum: u64 = Fibonacci::new(10).filter(|n| n % 2 == 0).sum();
    println!("even fibonacci sum = {sum}");
}

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