Get debug descriptions for enums in Objective-C via terrible terrible macro hackery.

gistfile1.m

/* Get strings descriptions for enum values for debugging.

 Usage:
 With enum 
 
     typedef enum {
         AppleFruit = 0,
         BlueberryFruit = 1,
         BlackberryFruit = -1
     } Fruit;

 This declares a function DescriptionOfFruit:
     IMPLEMENT_DESCRIPTION_OF_ENUM(Fruit, AppleFruit, BlueberryFruit, BlackberryFruit)

 This:
     for (int fruit = -1; fruit < 2; fruit++) {
         NSLog(@"fruit:%@", DescriptionOfFruit(fruit));
     }
 Prints @"fruit:BlackberryFruit", @"fruit:AppleFruit", @"fruit:BlueberryFruit"
 */
 


#define IMPLEMENT_DESCRIPTION_OF_ENUM(type, ...) \
static NSString *DescriptionOf##type(type val) { \
    return _DescriptionForEnumValue(val, @""#type, @""#__VA_ARGS__, ## __VA_ARGS__); \
}

static NSString *_DescriptionForEnumValue(long enumVal, NSString *descriptionOfEnumeration, NSString *commaSeparatedEnumValueDescriptions, int firstEnumValue, ...) {
    NSString *enumValueDescription = nil;
    NSScanner *enumValueDescriptionScanner = [[NSScanner alloc] initWithString:commaSeparatedEnumValueDescriptions];
    NSCharacterSet *commaAndWhitespaceCharacterSet = [NSCharacterSet characterSetWithCharactersInString:@", \t\n\r\v"];
    NSCharacterSet *commaAndWhitespaceInvertedCharacterSet = [commaAndWhitespaceCharacterSet invertedSet];
    
    if (firstEnumValue == enumVal) {
        [enumValueDescriptionScanner scanUpToCharactersFromSet:commaAndWhitespaceCharacterSet intoString:&enumValueDescription];
    } else {
        [enumValueDescriptionScanner scanUpToCharactersFromSet:commaAndWhitespaceCharacterSet intoString:NULL];
        [enumValueDescriptionScanner scanUpToCharactersFromSet:commaAndWhitespaceInvertedCharacterSet intoString:NULL];
        va_list args;
        va_start(args, firstEnumValue);
        while (![enumValueDescriptionScanner isAtEnd]) {
            NSInteger candidateEnumVal;
            candidateEnumVal = va_arg(args, int);  // by my read of C99 6.7.2.2, enum values are always representable as int.  Thus they'll always get promoted to int bit-width if smaller for a varargs call, and unsigned and signed ints are bit-compatible on the range representable by ints (6.2.6.2)
            
            if (candidateEnumVal == enumVal) {
                [enumValueDescriptionScanner scanUpToCharactersFromSet:commaAndWhitespaceCharacterSet intoString:&enumValueDescription];
                break;
            } else {
                [enumValueDescriptionScanner scanUpToCharactersFromSet:commaAndWhitespaceCharacterSet intoString:NULL];
                [enumValueDescriptionScanner scanUpToCharactersFromSet:commaAndWhitespaceInvertedCharacterSet intoString:NULL];
            }
        }
        va_end(args);
    }
    enumValueDescription = enumValueDescription ?: [NSString stringWithFormat:@"<unknown value %ld in enumeration %@>", (long)enumVal, descriptionOfEnumeration];
    return enumValueDescription;
}