In Go, copying slices is standard-fare and looks like this:
# It will figure out the details to match slice sizes
dst = copy(dst[n:], src[:m])
In Rust, I couldn't find a similar method as replacement. Something I came up with looks like this:
fn copy_slice(dst: &mut [u8], src: &[u8]) -> usize {
let mut c = 0;
for (&mut d, &s) in dst.iter_mut().zip(src.iter()) {
d = s;
c += 1;
}
c
}
Unfortunately, I get this compile-error that I am unable to solve:
error[E0384]: re-assignment of immutable variable `d`
--> src/main.rs:4:9
|
3 | for (&mut d, &s) in dst.iter_mut().zip(src.iter()) {
| - first assignment to `d`
4 | d = s;
| ^^^^^ re-assignment of immutable variable
How can I set d
? Is there a better way to copy a slice?
Yes, use the method clone_from_slice()
, it is generic over any element type that implements Clone
.
fn main() {
let mut x = vec![0; 8];
let y = [1, 2, 3];
x[..3].clone_from_slice(&y);
println!("{:?}", x);
// Output:
// [1, 2, 3, 0, 0, 0, 0, 0]
}
The destination x
is either a &mut [T]
slice, or anything that derefs to that, like a mutable Vec<T>
vector. You need to slice the destination and source so that their lengths match.
As of Rust 1.9, you can also use copy_from_slice()
. This works the same way but uses the Copy
trait instead of Clone
, and is a direct wrapper of memcpy
. The compiler can optimize clone_from_slice
to be equivalent to copy_from_slice
when applicable, but it can still be useful.