persistable sclass ArrayMatrix<A> implements Matrix<A> {
  int w, h;
  A[] data;
  
  *(int *w, int *h) {}
  *(int *w, int *h, A[] *data) {}
  
  public int getWidth() { ret w; }
  public int getHeight() { ret h; }
  
  public A get(int x, int y) { ret data[y*w+x]; }
  public void set(int x, int y, A a) { data[y*w+x] = a; }
}