program example_classes();

// here is the same house blueprint from example1

   class House_Blueprint;

   // first we declare variables that define general properities
   // of all houses even though a specific house will
   // have unique data

   int number_of_rooms;
   bit family_room_lightswitch;
   static string street_name; // all homes here share the same street name


   // on building a house, initialize defaults
   // and build the house based on argument liss

   function new(int rooms, string street = "");
       if (street != "")
          street_name = street;
          number_of_rooms = rooms;
          family_room_lightswitch = 0;
   endfunction


   // we can flip the lights of a specific house with
   // a method call
   task hit_the_switch() ;
       family_room_lightswitch = !family_room_lightswitch;
   endtask


   // we can return values in function calls
   function bit lights() ;
        lights = family_room_lightswitch;
   endfunction


endclass


// now we are going to create a subclass which uses all
// the existing functionality, but adds a second floor


class Monster_House_Blueprint extends House_Blueprint;

   // add in a second floor number of rooms
   int second_story_rooms;
   int first_story_rooms;

   //change the lightswitch functionality
   bit [1:0] family_room_lightswitch;

   function new(int rooms, string street = "");

      // super is used to access the base class
      // methods and data. If new has an arg list,
      // you MUST call super.new for it.
      super.new(rooms, street);

      // here we can access data of both the derived and base class
      second_story_rooms = number_of_rooms /2 ;
      first_story_rooms = number_of_rooms - second_story_rooms ;


      // since I have redefined family_room_lightswitch,
      // I need to take data out of the super class
      // and put it here, since the super.new used it.

      // note the use of this and super

      this.family_room_lightswitch = super.family_room_lightswitch;


   endfunction

   // since I changed the family_room_lightswitch, the methods
   // have to be changed too, to access the derived data

   task hit_the_switch() ;
      case (family_room_lightswitch)
         2'b11: family_room_lightswitch = 2'b00;
         2'b00: family_room_lightswitch = 2'b11;
         default: family_room_lightswitch = 2'b00;
      endcase

   endtask

   // we can return values in function calls
   function bit[1:0] lights() ;
          lights = family_room_lightswitch;
   endfunction

endclass


Monster_House_Blueprint red, blue, yellow, green;
// here we declare handles pointing to the Monster House.
// now we can immediately take advantage of the new
//functionality


int result;

initial

   begin

        // red now points to a home with 4 rooms,
        //2 on floor 0, and 2 on floor 1
        red = new(4, "middlefield");

        // green now points to a home with 6 rooms
        // 3 on floor 0 and 3 on floor 1
        // note the second arg is missing!
        // Don't worry: Its a default arguement, so its optional
        green = new(6);


        // here we turn on the light switch in the red house
        // by accessing the method
        red.hit_the_switch();


        // we can do the same thing by directly accessing the variable,
        // as long as it is a public variable
        // note that while this is less coding, the purpose of
        // methods is to check the input and do the calculations
        // to prevent introduction of incorrect data
        // (i.e. -1 rooms wouldn't make sense )
        red.family_room_lightswitch = 1;


        // here we can get the results of the lights being on or off
        // in the room. Note the red house and the green house
        // are based on the same blueprint, but have different
        // values
        result = red.lights();
        result = green.lights();

    end

endprogram