JSのString.prototype.replace()で関数を渡すのと同等の処理

NSString+Replacement.m

- (NSString *)stringByReplacingPattern:(NSString *)patternString usingBlock:(NSString *(^)(NSTextCheckingResult *match))replacer {
  if (!replacer) {
    return nil;
  }

  NSRegularExpression *regex = [NSRegularExpression
                                regularExpressionWithPattern:patternString
                                options:NSRegularExpressionAnchorsMatchLines
                                error:NULL];
  
  __block NSMutableString *converted = [NSMutableString string];
  __block NSUInteger position = 0;
  [regex enumerateMatchesInString:self
                          options:0
                            range:NSMakeRange(0, self.length)
                       usingBlock:^(NSTextCheckingResult *match, NSMatchingFlags flags, BOOL *stop) {
                         NSRange range = [match rangeAtIndex:0];
                         // マッチした部分までの文字列を追加
                         [converted appendString:[self substringWithRange:NSMakeRange(position, range.location - position)]];
                         // マッチした部分は変換
                         [converted appendString:replacer(match)];
                         position = range.location + range.length;
                       }];
  
  if (position < self.length) {
    [converted appendString:[self substringFromIndex:position]];
  }
  return converted;
}