gistfile1.txt

-(NSArray*)objectForKeyedSubscript:(NSString*)pattern
{
	NSError *error;
	NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:pattern options:0 error:&error];
    NSAssert( ! error, @"regex processing error");

	NSMutableArray *strings = [NSMutableArray new];
	NSArray *matches = [regex matchesInString:self options:0 range:self.fullRange];
	for(NSTextCheckingResult *match in matches) {
		for (NSInteger i = 0; i < match.numberOfRanges; i++) {
			NSRange range = [match rangeAtIndex: i];
			NSString *substring = [self substringWithRange: range];
			[strings addObject: substring];
		}
	}

	return strings.count == 0  ?  nil  :  strings;
}




-(id)setObject:(NSString*)newPattern forKeyedSubscript:(NSString*)oldPattern
{
	NSError *error;
	NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:oldPattern options:0 error:&error];
	NSAssert(! error, @"Regex processing error");

	NSString *newString = [regex stringByReplacingMatchesInString:self options:0 range:self.fullRange withTemplate: newPattern];
	return newString;
}

One of the most creative ways to use subscript on strings .)