persistable sclass ListToMatrix<A> extends AbstractMatrix<A> {
  L<A> data;
  
  *(int w, int h, L<A> *data) { super(w, h); }
  
  int xyToIndex(int x, int y) {
    ret y*w+x;
  }

  public A get(int x, int y) { ret data.get(xyToIndex(x, y)); }
  public void set(int x, int y, A a) { data.set(xyToIndex(x, y), a); }
}

Began life as a copy of #1033239