sclass HashedByteArray {
  byte[] data;
  int hashCode;
  
  public int hashCode() {
    if (hashCode == 0)
      hashCode = oneIfZero(arrayHashCode(data));
    ret hashCode;
  }
  
  public bool equals(O o) {
    if (o cast HashedByteArray)
      ret this == o || hashCode == o.hashCode && arraysEqual(data, o.data);
    false;
  }
}