PeanoCell is another GhostCell alternative.
It is inspired by TCell and frankencell.
Like TCell, PeanoCell also uses type marker to identify token <-> cell connection.
However, new owners (or tokens) can be easily created via owner_builder.new_owner(), there is no need to declare new type markers.
The main advantage over frankencell is that PeanoCell does not use unstable generic const exprs.
This was possible by replacing const generics with structs Zero, Suc<Zero>, and Suc<Suc<...>>
which correspond to the concept of peano numbers
Creating new owner builder is the only place which is not statically checked. Everything else including
- owner creating,
- Aliasing Xor Mutability check when accessing a cell with one owner,
- owner <-> cell correspondence,
are checked statically.
To my knowledge, this is on of the closest cell we currently have to GhostCell, which does everything at compile-time. The difference between PeanoCell and GhostCell is that PeanoCell doesn't require tokens to live inside closure. You can pass tokens and even token builder wherever you want, see owner_builder_passing example.
Currently, PeanoCell relies on qcell's TCell. This results in additional dynamic check when creating new owners.
Potentially, it can be implemented using UnsafeCell instead which will make everything except owner builder creation zero-cost.