How are elements of a vector left-shifted in Rust?

Question

Is there a safe way to left-shift elements of a vector in Rust? (vec![1, 2, 3] becomes vec![3] when left-shifted two places). I'm dealing with Copy types, and I don't want to pay a penalty higher than what I would with a memmove.

The only solution I've found is unsafe: use memmove directly via ptr::copy.

score 15 · Accepted Answer · edited Jul 06 '16 at 15:56

I would use Vec::drain.

You can call it with a range of the elements you want to remove, and it'll shift them over afterwards. Example: (playpen)

fn main() {
    let mut v = vec![1, 2, 3];

    v.drain(0..2);

    assert_eq!(vec![3], v);
}

One other note:

I'm dealing with Copy types, and I don't want to pay a penalty higher than what I would with a memmove.

Worth noting that moving is always a memcpy in Rust, so the Copy vs non-Copy distinction doesn't matter here. It'd be the same if the types weren't Copy.

How are elements of a vector left-shifted in Rust?

1 Answers1