I think the fundamental problem with that approach is that even in single threaded code rust makes it illegal to have to have two pointers where at least one is mutable to the same state. So I can pass in a `&mut State` pointer, but then I can't also pass in a `&mut AnElementInSomeListInState` pointer. Nor can I really have `AnElementInSomeListInState` just have a parent pointer to the rest of the state, because someone has to have a `&mut State` pointer, and they would conflict (also because doubly linked lists are hard in rust).
