program tb_top;

// here is a shape class, defining that there will be

// some shapes to draw, and they all must have

// a shape method to be used by the "BFM"

 virtual class Shapes;

    // every shape must have a total size, and a start coordinate

    int total_size;

    int start_x, start_y;

    bit[7:0] color;

    // every shape must implement draw and color actions

    virtual task draw();

    endtask

    // by defining code here, it becomes optional for

    // derived methods to define it there.

    // because it is virtual, the derived object method

    // will override this call, unless super is used by

    // the derived object to call this one

    virtual task setcolor (bit [7:0] color);

       this.color = color;

    endtask

 endclass

class Circle extends Shapes;

  bit [30:0] circle_d_data;

  function new(int size = 4);

      total_size = size * 3;

  endfunction

  // here is how I would draw a circle

  // I keep it virtual so that one someone

  // can create a 3D circle and build upon

  // this example

  virtual task draw();

     // do the actual draw here

     $display("drawing a circle...\n");

  endtask

endclass

class Square extends Shapes;

  int drawn = 0;

  function new(int sizex = 1, int sizey = 1);

      total_size = sizex * sizey;

  endfunction

  virtual task draw();

     // do the actual draw here

     $display("drawing a square...\n");

     drawn = 1;

  endtask

  virtual task setcolor(bit [7:0] color);

     // here I need to do the base class stuff, but then

     // the work of updating the color of the square

     super.setcolor(color);

     if (drawn == 1) begin

     $display("updating drawing...\n");

  end

endtask

Shapes s[2];

Circle c1;

Square s1;

initial

begin

   // initialize the objects, let base class handles

   // point to them also

   c1 = new(); // create a circle object

   s[0] = c1; // s[0] also points to that circle

   s1 = new(); // create a square object

   s[1] = s1; // watch out for sharp edges

   //s0.draw(); is the same as calling c1.draw(), but

   // the neat thing here is that a BFM only needs the

   // base class handle, and doesn't need to be modified

   // if the functionality or data features change!!

   s[0].draw();

   s[0].setcolor(22);

   // is the same as

   c1.draw();

   c1.setcolor(22);

   // but the base methods didn't need to be changed

end

endprogram