fn main() {
    let mut items = vec![1, 2, 3, 4, 5];

    for i0 in 0..items.len() {
        for i1 in i0 + 1..items.len() {
            if matches(items[i0], items[i1]) {
                items[i1] = 40; // for example
            }
        }
    }

    println!("{:?}", items);
}

fn matches(i0: i32, i1: i32) -> bool {
    i0 + i1 == 5 // for example
}