Question

I want to test for transition from one state to another. I have defined my states in an enum like this:

enum FingerStatus {
FINGERS_UP,
MOVING,
FINGERS_STILL
};

I have a “currentState” and a “newState” variable. I know that enums are just integers, and if they’re 16-bit integers, which I think they are, it’s possible to represent two enums as a single 32-bit integer.

I feel like I ought to be able to do something along the lines of

switch ({currentStatus, newFingerStatus}) {
    case {FINGERS_STILL, MOVING}:
        NSLog(@"fingers starting to move");
        break;
    case {MOVING, FINGERS_STILL}:
        NSLog(@"fingers stopped moving");
        break;
    default:
        break;
}

I realize the syntax is all wrong, but I think the basic idea is sound. Is there another nice, clean way to do this?

Answer 1

If you can guarantee your enums are less than 16 bits, this will work:

switch ((currentStatus<<16) + newFingerStatus) {
    case (FINGERS_STILL<<16) + MOVING:
        NSLog(@"fingers starting to move");
        break;
    case (MOVING<<16) + FINGERS_STILL:
        NSLog(@"fingers stopped moving");
        break;
    default:
        break;
}