Utilizing closures as snapshots for single or multiple values.

snapshots.rs

fn main() {
    let mut xs = vec![1];
    xs[0] = 42;
    let ys = xs.clone();
    let snapshot = move || ys;
    xs[0] = 100;
    let reset = snapshot();
    assert_eq!(&reset, &vec![42]);
    assert_eq!(xs, vec![100]);
    xs = reset;
    assert_eq!(xs, vec![42]);
}