I was going to ask about this as well. It seems like there's a lot of wasted space in how things are represented. The first field already tells you what type of object you're dealing with. Since you're using 64-bit integers, you could represent pointers, bools, ints and floats all in the same memory space. I guess there might be some types that use more than one field, but certainly a bool is not going to.

There's also the issue of alignment with the usage of 1-bit and 1-byte types...