program interfacetest;

type
  IUpgradable = interface
    procedure Upgrade;
  end;

  TEgg = class(TInterfacedObject, IUpgradable)
    public
      constructor Create;
      destructor Destroy; override;
      procedure Upgrade;
  end;

constructor TEgg.Create;
begin
  WriteLn('Egg built');
end;

destructor TEgg.Destroy;
begin
  WriteLn('Egg destroyed');
  inherited;
end;

procedure TEgg.Upgrade;
begin
  WriteLn('Egg now produces better aliens');
end;

procedure Test;
var
  Egg: IUpgradable;
begin
  Egg := TEgg.Create;
end;

begin
  Test;
end.