persistable asclass AbstractMatrix<A> is Matrix<A> {
  int w, h;

  *(int *w, int *h) {}

  public int getWidth() { ret w; }
  public int getHeight() { ret h; }
  
  toString {
    ret flexLines(
      roundBracket(w+"x"+h),
      countIteratorToList(y -> str(getLine(y)), getHeight()));
  }
  
  public void set(int x, int y, A a) { unimplemented(); }
}