rust_euler2.rs

// Fibonacci from http://rustbyexample.com/trait/iter.html
struct Fibonacci {
    curr: u32,
    next: u32,
}

impl Iterator for Fibonacci {
    type Item = u32;

    fn next(&mut self) -> Option<u32> {
        let new_next = self.curr + self.next;
        self.curr = self.next;
        self.next = new_next;
        Some(self.curr)
    }
}

fn fibonacci() -> Fibonacci {
    Fibonacci { curr: 1, next: 1 }
}

pub fn euler2() -> u32 {
    fibonacci()
        .take_while(|n: &u32| *n < 4000000)
        .filter(|n: &u32| *n % 2 == 0)
        .fold(0, |acc: u32, n: u32| acc + n)
}