use std::mem;


fn main() {
    // Right now:
    let a = [&[1,2,3][..], &[4,5,6]];
    prepare_hash_multiple(&a);
    // I want this to also work:
    let b = &[&[5,6,7][..], &a[..]];
    prepare_hash_multiple(&b);
}


fn prepare_hash_multiple(messages: &[&[u8]]) -> Vec<u8> {
    let mut res = Vec::with_capacity(messages.len() * mem::size_of::<usize>());
    for msg in messages {
        let len = msg.len().to_be_bytes();
        res.extend_from_slice(&len);
        res.extend_from_slice(&msg);
    }
    res
}