persistable sclass AutoCreateList<A> extends RandomAccessAbstractList<A> {
  new L<A> list;
  IF1<Int, A> createElement; // optional, takes index and produces element
  
  *(IF1<Int, A> *createElement) {}
  *(IF0<A> createElement) { this(if0ToIF1(createElement)); }
  *(Class<? extends A> elementClass) { this(classToIF0(elementClass)); }
  
  public int size() { ret list.size(); }
  public A get(int i) {
    while (i >= size())
      list.add(createElement?.get(i));
    ret list.get(i);
  }
  
  public A set(int i, A a) {
    ret list.set(i, a);
  };
  
  public bool add(A a) { ret list.add(a); }
}

Began life as a copy of #1031197