Shared via Rust Playground

playground.rs

fn main() {
    use std::borrow::Cow;
    
    #[allow(dead_code)]
    fn abs_all(input: &mut Cow<[i32]>) {
        for i in 0..input.len() {
            let v = input[i];
            if v < 0 {
                // clones into a vector the first time (if not already owned)
                input.to_mut()[i] = -v;
            }
        }
    }
    
    let v : Cow<[i32]> = Cow::Owned(vec![1,-4,5]);
    
    let mut v2 : Cow<[i32]> = v.clone();
    abs_all(&mut v2);
    println!("v: {:?}, v2: {:?}", v, v2);
}