code: func (fs *Filters) getWatchersByTopic(topic TopicType) []*Filter {
  	res := make([]*Filter, 0, len(fs.allTopicsMatcher))
  	for watcher := range fs.allTopicsMatcher {
  		res = append(res, watcher)
  	}
  	for watcher := range fs.topicMatcher[topic] {
  		res = append(res, watcher)
  	}
  	return res
  }
docs: // getWatchersByTopic returns a slice containing the filters that
  // match a specific topic