Hi Richard,My example was about having a collection of bits. So, #do: and #select: do continue to have the very same semantics.The whole point is to save memory behind the scenes, while keeping the same API.Consider a very large matrix of booleans. It would save memory to store booleans as bits.There is of course the "normal" way of doing it, by changing the implementation.But, with slots, it should be possible to use an instance 2DArray