Is it possible to loop through enum values in Objective-C?
+1
A:
If you enum is defined as follows:
enum Direction { East, West, North, South};
You can loop through it this way:
for ( int direction = East; direction <= South; ++direction)
{
/* Do something with Direction
}
ennuikiller
2009-11-02 18:02:11
The for-loop body won't run with `direction == South`. You are missing one iteration.
notnoop
2009-11-02 18:24:21
@notnoop thanks, corrected
ennuikiller
2009-11-02 18:26:12
I've never done this, so I have some questions. Shouldn't it be Direction.East and Direction.South? Also shouldn't the condition be direction <= Direction.South? Again I've never done this, I'm not trying to correct you, just would like to learn.
Jorge Israel Peña
2009-11-02 18:28:18
Is there a better way to do this? Just curious, but it seems like depending on the declaration order of the enum values is fragile at best.
Ed Swangren
2009-11-02 18:34:36
@blaenk: i think you're confusing structs with enums.
pxl
2009-11-02 18:37:03
The test statement in your for loop is incorrect.
Barry Wark
2009-11-02 19:13:19
@Ed: Yes this is fragile, and no there's not a better way. It's not advisable to do this at all.
Chuck
2009-11-02 19:23:43
One could be more explicit as in enum Direction { East =1, West=2, North=3, South=4}; or even enum Direction { East =313, West, North, South}; but it all comes down to the same thing, except that numbering each element leaves more room for programmer error. In the end it seems to me to be as fragile or non-fragile as any const declaration.
Elise van Looij
2009-11-03 14:01:44
+4
A:
Given
enum Foo {Bar=0,Baz,...,Last};
you can iterate the elements like:
for(int i=Bar; i<=Last; i++) {
...
}
Note that this exposes the really-just-an-int nature of a C enum. In particular, you can see that a C enum doesn't really provide type safety, as you can use an int in place of an enum value and visa versa. In addition, this depends on the declaration order of the enum values: fragile to say the least. In addition, please see Chuck's comment; if the enum items are non-contiguous (e.g. because you specified explicit, non-sequential values for some items), this won't work at all. Yikes.
Barry Wark
2009-11-02 19:15:40
It also requires that all the items in the enum be contiguous. But it's the best you'll get.
Chuck
2009-11-02 19:23:09
+2
A:
It's a bit of a kludge (as is the entire concept so... eh...) but if you're going to do this multiple times, and you want to be able to deal with the possibility of non-contiguous enums, you can create a (global constant) array, and have (to use ennukiller's example) Directions directions[4] = {East, West, North, South}; and then in your loop you can talk about directions[i] rather than iterating directly over the directions themselves...
As I said, it's ugly, but it's slightly less fragile I think...
Brian Postow
2009-11-02 19:43:11