sclass CCI_Choice extends CharacterClassIterator {
  bool canEndHere;
  
  // can be a HashMap or TreeMap (e.g. with special comparator)
  Map<Char, CharacterClassIterator> map;
  
  // computed on demand
  CharRange acceptedCharRange;

  *() {}
  *(bool canEndHere, Map<Char, CharacterClassIterator> *map) {}
  
  CharacterClassIterator acceptChar(char c) {
    ret assertNotNull(map.get(c));
  }

  bool canEndHere() {
    ret canEndHere;
  }
  
  bool canAcceptChar(char c) {
    ret map.containsKey(c);
  }

  Cl<Char> acceptedChars() { ret keys(map); }

  CharRange acceptedCharRange() {
    if (empty(map)) null;
    if (acceptedCharRange == null)
      acceptedCharRange = calcAcceptedCharRange();
    ret acceptedCharRange;
  }
  
  CharRange calcAcceptedCharRange() {
    if (map instanceof TreeMap) {
      ret CharRange(firstKey(map), lastKey((TreeMap<Char, CharacterClassIterator>) map));
    } else {
      char min = 0xFFFF, max = 0;
      for (char c : keys(map)) {
        if (c < min) min = c;
        if (c > max) max = c;
      }
      ret CharRange(min, max); 
    }
  }
  
  // object is immutable, so no cloning necessary
  CharacterClassIterator cloneCCI() {
    this;
  }
}  

Began life as a copy of #1029558