Is there a concise way to map a string to an enum in Objective-C? - objective-c

Question

I have a string I want to parse and return an equivalent enum. I need to use the enum type elsewhere, and I think I like how I'm defining it. The problem is that I don't know a good way to check the string against the enum values without being redundant about the order of the enums.
Is there no option other than a big if/else?
typedef enum {
ZZColorRed,
ZZColorGreen,
ZZColorBlue,
} ZZColorType;
- (ZZColorType)parseColor:(NSString *)inputString {
// inputString will be #"red", #"green", or #"blue" (trust me)
// how can I turn that into ZZColorRed, etc. without
// redefining their order like this?
NSArray *colors = [NSArray arrayWithObjects:#"red", #"green", #"blue", nil];
return [colors indexOfObject:inputString];
}
In Python, I'd probably do something like the following, although to be honest I'm not in love with that either.
## maps url text -> constant string
RED_CONSTANT = 1
BLUE_CONSTANT = 2
GREEN_CONSTANT = 3
TYPES = {
'red': RED_CONSTANT,
'green': GREEN_CONSTANT,
'blue': BLUE_CONSTANT,
}
def parseColor(inputString):
return TYPES.get(inputString)
ps. I know there are color constants in Cocoa, this is just an example.

Answer 1

try this: Map enum to char array
Pseudo code.. untested.
int lookup(const char* str) {
for(name = one; name < NUMBER_OF_INPUTS; name++) {
if(strcmp(str, stats[name]) == 0) return name;
}
return -1;
}
A more objective-c'ish version of the code could be:
// build dictionary
NSMutableDictionary* dict = [[NSMutableDictionary alloc] init];
for(i=0; i<number_of_strings; i++) {
[dict setObject:[NSNumber numberWithInteger:i] forKey:[NSString stringWithUTF8String:names[i]]];
}
// elsewhere... lookup in dictionary
id obj = [dict objectForKey:name];
if(obj) return [obj intValue];
return -1;

Answer 2

This has already been answered: Converting between C enum and XML
Basically, you wind up defining corresponding strings when you define your enum, and then you use a category on NSArray so that you can do this:
static NSArray* colorNamesArray = [[NSArray alloc] initWithObjects:colorNames];
//colorNames is a nil-terminated list of string literals #defined near your enum
NSString* colorName = [colorNamesArray stringWithEnum:color];
//stringWithEnum: is defined with a category
Sure, the #define is a little ugly, but the code above, which is what you'll work with most of the time, is actually pretty clean.

Answer 3

I was never satisfied with any of the suggestions. (But I appreciate the effort that went into them.) I tried a few of them but they didn't feel good or were error-prone in practice.
I ended up created a custom dictionary to map integers to strings which feels a lot better because it's Cocoa through and through. (I didn't subclass NSDictionary in order to make it harder to misuse.)
#interface ZZEnumDictionary : NSObject {
NSMutableDictionary *dictionary;
}
+ (id)dictionary;
+ (id)dictionaryWithStrings:(id)firstString, ...;
- (NSString *)stringForInt:(NSInteger)intEnum;
- (NSInteger)intForString:(NSString *)stringEnum;
- (BOOL)isValidInt:(NSInteger)intEnum;
- (BOOL)isValidString:(NSString *)stringEnum;
- (BOOL)stringEquals:(NSString *)stringEnum intEnum:(NSInteger)intEnum;
- (BOOL)setContainsString:(NSSet *)set forInt:(NSInteger)intEnum;
- (NSArray *)allStrings;
#end
#interface ZZEnumDictionary ()
- (void)setInt:(NSInteger)integer forString:(NSString *)string;
#end