fn main() {
let mut xs=vec![-3_i64,-2,0,1,4];
let evens: Vec<i64> = xs.iter().copied().filter(|it| it.rem_euclid(2) == 0).collect();
let squares: Vec<i64> = xs.iter().map(|&it| it * it).collect();
let total = xs.iter().fold(0, |acc, &x| acc + x);
xs.sort_by(|a, b| b.cmp(a));

assert_eq!(evens,[-2,0,4]);assert_eq!(squares,[9,4,0,1,16]);assert_eq!(total,0);assert_eq!(xs,[4,1,0,-2,-3]);
}