code: func (t *Filter) Init() {
  	t.catNames = make(map[string]bool, 0)
  	t.catPrefixes = make([]string, 0)
  	for _, cat := range t.Categories {
  		if strings.HasSuffix(cat, "*") {
  			t.catPrefixes = append(t.catPrefixes, cat[:len(cat)-1])
  		} else {
  			t.catNames[cat] = true
  		}
  	}
  }
docs: // Init initializes the filter.
  // Init must be called before Allow is called.