Iterate over all characters of a NSString as NSStrings.

NSString+CharacterEnumeration.m

typedef void(^StringEnumerationBlock)(NSString *characterString, NSUInteger index, BOOL *stop);

- (void)enumerateCharactersUsingBlock:(StringEnumerationBlock)block {
    NSParameterAssert(block);
    BOOL stop = NO;
    for (NSUInteger i = 0; i < self.length; i++) {
        const unichar character = [self characterAtIndex:i];
        NSString *characterString = [NSString stringWithCharacters:&character length:1];
        block(characterString, i, &stop);
        if (stop) {
            break;
        }
    }
}