program Virtual_2;

{ ******************** class definitions **********************}
{$R+}
type

   Vehicle = object

      Wheels : integer;

      Weight : real;

      constructor Init(In_Wheels : integer; In_Weight : real);

      procedure Message; virtual;

   end;
   Car = object(Vehicle)

      Passenger_Load : integer;

      constructor Init(In_Wheels : integer;

                       In_Weight : real;

                       People    : integer);

      procedure Message; virtual;

   end;
   Truck = Object(Vehicle)

      Passenger_Load : integer;

      Payload        : real;

      constructor Init(People : integer;

                       Max_Load : real;

                       In_Wheels : integer;

                       In_Weight : real);

      procedure Message; virtual;

   end;
{ ********************* class implementations ******************** }
   constructor Vehicle.Init(In_Wheels : integer; In_Weight : real);

   begin

      Wheels := In_Wheels;

      Weight := In_Weight;

   end;
   procedure Vehicle.Message;

   begin

      WriteLn('This message is from the vehicle.');

   end;
   constructor Car.Init(In_Wheels : integer;

                        In_Weight : real;

                        People    : integer);

   begin

      Wheels := In_Wheels;

      Weight := In_Weight;

      Passenger_Load := People;

   end;
   procedure Car.Message;

   begin

      WriteLn('This message is from the car.');

   end;
   constructor Truck.Init(People : integer;

                          Max_Load : real;

                          In_Wheels : integer;

                          In_Weight : real);

   begin

      Passenger_Load := People;

      Payload := Max_Load;

      Wheels := In_Wheels;

      Weight := In_Weight;

   end;
   procedure Truck.Message;

   begin

      WriteLn('This message is from the truck.');

   end;
   procedure Output_A_Message(VAR Machine : Vehicle);

   begin

      Write('This is from Output_A_message; ');

      Machine.Message;

   end;
{ ************************ main program ************************** }
var Unicycle : Vehicle;

    Sedan    : Car;

    Semi     : Truck;
begin
   Unicycle.Init(1, 12.0);

   Sedan.Init(4, 2100.0, 5);

   Semi.Init(1, 25000.0, 18, 5000.0);
   WriteLn;

   Unicycle.Message;

   Sedan.Message;

   Semi.Message;
   WriteLn;

   Output_A_Message(Unicycle);

   Output_A_Message(Sedan);

   Output_A_Message(Semi);
end.


Result of execution

This message is from the vehicle.

This message is from the car.

This message is from the truck.
This is from Output_A_Message; This message is from the vehicle.

This is from Output_A_Message; This message is from the car.

This is from Output_A_Message; This message is from the truck.