compare an array of enums in (Objective) C

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

Since switches are just a fancy way to write gotos, you can't use them to do what you want to do. Use ifs instead:

if(currentStatus == FINGERS_STILL && newFingerStatus == MOVING)
{
    NSLog(@"fingers starting to move");
}
else if(currentStatus == MOVING && newFingerStatus == FINGERS_STILL)
{
    NSLog(@"fingers stopped moving");
}

Answer 2

Ints can be more than 16bits, and usually 32bits on computers( not sure about iPhone), but your idea would still work.

You can use (intOne + ( intTwo << 4 )) to put the two ints together, for comparison and evaluation.

Answer 3

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;
}

Answer 4

well for one it would probably wise to give the enums different unique values: 1,2,4 and not 0,1,2 then you can bitwise or them. Then you can do labels like:

case FINGERS_STILL|MOVING: