Function expand 

pub fn expand<C: CubePrimitive>(
    scope: &mut Scope,
    from: SliceExpand<C, ReadOnly>,
    from_index: ExpandElementTyped<u32>,
    to: SliceExpand<C, ReadWrite>,
    to_index: ExpandElementTyped<u32>,
    length: u32,
)

The expand function for copy_bulk()