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

If you can modify type type of v, and the elements of v are Copy, you can wrap MyStruct in Cell.

#[derive(Copy, Clone)] 
struct MyStruct {
    a: i32,
}

fn main() {
    use std::cell::Cell;
    let v = vec![
        Cell::new(MyStruct { a: 1 }),
        Cell::new(MyStruct { a: 2 }),
        Cell::new(MyStruct { a: 3 }),
    ];

    for elem in v.iter() {
        for other_elem in v.iter() {
            let mut e = elem.get();
            if other_elem.get().a > e.a {
                e.a += 1;
                elem.set(e);
            }
        }
    }
}

If instead you're passed a &mut to a slice (or &mut that can be converted into a slice), use Cell::from_mut and Cell::as_slice_of_cells and use the same trick as above (assuming the elements of the slice are Copy).