How do I shove a slice into an array?

Question

let mut foo: [u8; 6] = &[0, 0, 0, 0, 0, 0]
let mut bar: &[u8] = &[1, 2, 3]

I want the desired result:

&[1, 2, 3, 0, 0, 0]

The obvious way:

let foo: [u8; 6] = [bar, vec![0; 6 - bar.len()].as_slice()].concat().try_into()...

1. It causes a lot of overhead.
2. It's not practical

Perhaps there are some other ways?

Answer 1

Use copy_from_slice:

fn main() {
    let mut foo: [u8; 6] = [0, 0, 0, 0, 0, 0];
    let mut bar: &[u8] = &[1, 2, 3];
    
    println!("before: {:?}", foo); // [0, 0, 0, 0, 0, 0]
    
    foo[..bar.len()].copy_from_slice(bar);
    
    println!("after: {:?}", foo); // [1, 2, 3, 0, 0, 0]
}

Answer 2

Like so:

fn main() {

  let mut foo: [u8; 6] = [0, 0, 0, 0, 0, 0];
  let mut bar: &[u8] = &[1, 2, 3];

  foo[..3].clone_from_slice(bar);

  println!("{:?}", foo);
}