Remove Emoji in NSString

gistfile1.m

// XCode 4.2.1

@implementation NSString(EmojiExtension)

- (NSString*)removeEmoji {
    __block NSMutableString* temp = [NSMutableString string];
    
    [self enumerateSubstringsInRange: NSMakeRange(0, [self length]) options:NSStringEnumerationByComposedCharacterSequences usingBlock:
     ^(NSString *substring, NSRange substringRange, NSRange enclosingRange, BOOL *stop){
         
         const unichar hs = [substring characterAtIndex: 0];
         
         // surrogate pair
         if (0xd800 <= hs && hs <= 0xdbff) {
             const unichar ls = [substring characterAtIndex: 1];
             const int uc = ((hs - 0xd800) * 0x400) + (ls - 0xdc00) + 0x10000;
             
             [temp appendString: (0x1d000 <= uc && uc <= 0x1f77f)? @"": substring]; // U+1D000-1F77F
             
         // non surrogate
         } else {
             [temp appendString: (0x2100 <= hs && hs <= 0x26ff)? @"": substring]; // U+2100-26FF
         }
     }];
    
    return temp;
}

@end

just to followup. -- apparently the [:emoji:] property used in the ICU transform includes digits, some punctuation, other things not generally though to be emoji.

I am finding this method on an NSString category working better

- (NSString *)stringByRemovingEmoji {
    static NSRegularExpression * regex = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        // remove all emoji less those that are digits, punctuation, letters, latin 1 supplement or letter like symbols
        // or BIDI Non-Spacing Mark
        NSError * error = nil;
        regex = [NSRegularExpression regularExpressionWithPattern:@"([[:emoji:]--[:digit:]--[:punctuation:]--[:letter:]--[:block=Latin-1_sup:]--[:block=letter-like-symbols:]]|\\uFE0F)" options: 0 error:&error];
        if (error){
            NSLog(@"Error forming regex");
        }
    });
    
    return [regex stringByReplacingMatchesInString:self options:0 range:NSMakeRange(0, self.length) withTemplate:@""];
}