Efficiently mutate a vector while also iterating over the same vector

Question

I have a vector of structs, and I\'m comparing every element in the vector against every other element, and in certain cases mutating the current element.

My issue

Answer 1

The simplest way is to just use indices, which don't involve any long-lived borrows:

for i in 0..v.len() {
    for j in 0..v.len() {
        if i == j { continue; }
        if v[j].a > v[i].a {
            v[i].a += 1;
        }
    }
}

If you really, really want to use iterators, you can do it by dividing up the Vec into disjoint slices:

fn process(elem: &mut MyStruct, other: &MyStruct) {
    if other.a > elem.a {
        elem.a += 1;
    }
}

for i in 0..v.len() {
    let (left, mid_right) = v.split_at_mut(i);
    let (mid, right) = mid_right.split_at_mut(1);
    let elem = &mut mid[0];

    for other in left {
        process(elem, other);
    }
    for other in right {
        process(elem, other);
    }
}