How to zip two iterators of unequal length with a default?

Question

I'm trying to zip two iterators of unequal length, it only returns when when there is value in both and ignores the rest in the longest iterator.

fn main() {
    let num1 = vec![1, 2];
    let num2 = vec![3];

    for i in num1.iter().rev().zip(num2.iter().rev()) {
        println!("{:?}", i);
    }
}

This returns (2, 3). How do i make it return:

(2, 3)
(1, 0) // default is the 0 here.

Is there any other way to do it?

Answer 1

You could use the zip_longest provided by the itertools crate.

use itertools::{
    Itertools,
    EitherOrBoth::*,
};

fn main() {
    let num1 = vec![1, 2];
    let num2 = vec![3];

    for pair in num1.iter().rev().zip_longest(num2.iter().rev()) {
        match pair {
            Both(l, r) => println!("({:?}, {:?})", l, r),
            Left(l) => println!("({:?}, 0)", l),
            Right(r) => println!("(0, {:?})", r),
        }
    }
}

Which would produce the following output:

(2, 3)
(1, 0)