How to swap two vectors in a mutable struct

There is the following struct:

struct Data {
    xs: Vec<i32>,
    ys: Vec<i32>
}

At attempt to assign one vector of the struct to the other as follows leads to an error:

impl Data {
    fn proc(&mut self) {
        self.xs = self.ys;
    }
}

The error is move occurs because self.ys has type Vec<i32>, which does not implement the Copy trait.

The struct is borrowed as mutable, why it is not possible to move from self.ys there?

>Solution :

Use std::mem::swap to swap the values in-place:

impl Data {
    fn proc(&mut self) {
        std::mem::swap(&mut self.xs, &mut self.ys);
    }
}

(playground)

self.xs = self.ys doesn’t work because Vec doesn’t implement Copy: you’d have to .clone() ys.