Replaces all matches of a given regular expression in a given string using a given block

RRReplaceRegularExpressionMatchesInString.m

/*!
 * Replaces all matches of a given regular expression in a given string using a
 * given block to compute the replacement string for each match. The block
 * accepts the match result, the progressively replaced string along with its
 * progressive offset.
 */
NSString *RRReplaceRegularExpressionMatchesInString(NSRegularExpression *regex, NSString *string, NSString *(^replacementStringForResult)(NSTextCheckingResult *result, NSString *inString, NSInteger offset))
{
	NSMutableString *mutableString = [string mutableCopy];
	
	NSInteger offset = 0;
	for (NSTextCheckingResult *result in [regex matchesInString:string options:0 range:NSMakeRange(0, [string length])])
	{
		// Replaces the entire result range. However the results after matching
		// have ranges in the index space of the original string. Offset the
		// range to correct for progressive replacements.
		NSRange resultRange = [result range];
		resultRange.location += offset;
		
		NSString *replacementString = replacementStringForResult(result, mutableString, offset);
		[mutableString replaceCharactersInRange:resultRange withString:replacementString];
		offset += [replacementString length] - resultRange.length;
	}
	
	return [mutableString copy];
}