How do you use NSRegularExpression's replacementStringForResult:inString:offset:template:

Question

I have a series of characters that I want to match with a regular expression, and replace them with specific strings depending on what they are.

Example:

In

Answer 1

I was looking for something similar, but didn't like most of the answers here, so I wrote something inspired by how PHP does string replacement:

@implementation NSString (preg_replace)

- (instancetype)stringByReplacingMatchesFromRegularExpression:(NSRegularExpression *)regularExpression replacementBlock:(NSString * (^)(NSArray *matches))replacementBlock
{
    NSMutableString *finalString = self.mutableCopy;
    NSUInteger offset = 0;

    for (NSTextCheckingResult *match in [regularExpression matchesInString:self options:0 range:NSMakeRange(0, self.length)]) {
        NSMutableArray *matches = [NSMutableArray array];
        for (NSUInteger index = 0; index < match.numberOfRanges; ++index) {
            [matches addObject:[self substringWithRange:[match rangeAtIndex:index]]];
        }
        NSString *replacementString = replacementBlock(matches.copy);

        [finalString replaceCharactersInRange:NSMakeRange(match.range.location + offset, match.range.length) withString:replacementString];
        offset += replacementString.length - match.range.length;
    }

    return finalString;
}

@end

To use it:

NSRegularExpression *expression = [[NSRegularExpression alloc] initWithPattern:@"[0-9A-F]{2}" options:0 error:nil];
NSString *string = @"AB-DE-EF";
NSString *result = [string stringByReplacingMatchesFromRegularExpression:expression replacementBlock:^NSString *(NSArray *matches) {
    return [NSString stringWithFormat:@"(%@)", [matches[0] lowercaseString]];
}];
NSLog(@"Result = %@", result); // "(ab)-(de)-(ef)"