mut reborrow?

[Rudxain]

Does the following qualify? (Edition 2021)

pub fn xor_hasher<'a, T>(inp: &'a [T], sbox: &mut [T])
where
    T: core::ops::BitXorAssign<&'a T>,
{
    let len = sbox.len();
    if len == 0 {
        return;
    };
    for chunk in inp.chunks(len) {
        chunk.iter().zip(sbox).for_each(|(i, s)| *s ^= i);
    }
}

Doesn't compile because sbox moves into zip, so &mut *sbox must be used instead. I find this silly, but "silly" isn't enough to be considered "obscure"

[Rudxain]

I've been experimenting with this. The results are weirder...

// error
fn xor0<'a, T: 'a, I: IntoIterator<Item = &'a T>>(inp: I, sbox: &mut [T])
where
    T: core::ops::BitXorAssign<&'a T>,
{
    for _ in 0..3 {
        inp.into_iter().zip(sbox).for_each(|(i, s)| *s ^= i);
    }
}

// error
fn xor1<I: Iterator<Item = u8> + Copy>(inp: I, sbox: &mut [u8]) {
    for _ in 0..3 {
        inp.zip(sbox).for_each(|(i, s)| *s ^= i);
    }
}

fn drop_ref(sbox: &mut [u8]) {}
// works???
fn drop_multi(sbox: &mut [u8]) {
    for _ in 0..3 {
        // if sbox isn't `Copy`, then why does this compile?
        // it should move into `drop_ref`, requiring a fresh reborrow
        drop_ref(sbox); // replace by `drop` to trigger error
    }
}

[dtolnay]

Thank you for the suggestion! "Does it compile or not" flavor of questions do not tend to make good quiz questions so I would prefer not to include a question on this topic, but I appreciate the contribution.

[Rudxain]

To anyone with the same confusion as me, I've found this blog which explains really well what's happening. See also. Related: rust-lang/reference#788