How can I modify a collection while also iterating over it?

Question

I have a Board (a.k.a. &mut Vec>) which I would like to update while iterating over it. The new value I want to update wi

Answer 1

Is there a way that I could make this code update the board "in place"?

There exists a type specially made for situations such as these. It's coincidentally called std::cell::Cell. You're allowed to mutate the contents of a Cell even when it has been immutably borrowed multiple times. Cell is limited to types that implement Copy (for others you have to use RefCell, and if multiple threads are involved then you must use an Arc in combination with somethinng like a Mutex).

use std::cell::Cell;

fn main() {
    let board = vec![Cell::new(0), Cell::new(1), Cell::new(2)];

    for a in board.iter() {
        for b in board.iter() {
            a.set(a.get() + b.get());
        }
    }
    println!("{:?}", board);
}