What's the difference between ref and & when assigning a variable from a reference?

Question

What is wrong with this code?

fn example() {
    let vec = vec![1, 2, 3];
    let &_y = &vec;
}

Answer 1

First of all, you do not need the & in your working example. If you use it, you end up with a &&Vec<_>, which you don't really need.

let vec = vec![1, 2, 3];
let ref y = vec;

The problem with your first code is that you are doing two things at once. Lets split it up into two:

The first part creates a reference to vec

let y1 = &vec;

The second part (the & before the variable binding), destructures.

let &y2 = y1;

This means you are trying to move out of the reference, which only works if the type is Copy, because then any attempt to move will copy the object instead.