pub fn copy_slice<T,S,D>(mut dst: D, src: S) -> usize
where S: AsRef<[T]>,
      D: AsMut<[T]>,
T: Clone
{
    let mut sz=0;
    for (d,s) in dst.as_mut().iter_mut().zip(src.as_ref().iter())
    {
	*d = s.clone();
	sz+=1;
    }
    sz
}