One trick I found is to gate mutable access to state behind a "transaction object" which sets a flag for each object mutated, then once the transaction object's destructor is called, recomputes all derived state based on which flags were set. Using a destructor might not be the best idea since I ended up not marking it noexcept, it may be better to add an explicit "recompute" function called at the end, but this breaks the convenience of `state().cursor_mut() = new_cursor;` automatically recomputing derived state once the state() object is destroyed.