Project Structure

• Protection.dpr
• ProtForm.pas
• TestClass.pas
• ProtForm.dfm

program Protection;

uses
  Forms,
  ProtForm in 'ProtForm.pas' {Form1},
  TestClass in 'TestClass.pas';

{$R *.RES}

begin
  Application.Initialize;
  Application.CreateForm(TForm1, Form1);
  Application.Run;
end.

unit ProtForm;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

uses
  TestClass;

procedure TForm1.Button1Click(Sender: TObject);
var
  Obj: TTest;
begin
  Obj := TTest.Create;
  Obj.PublicData := 10;
//  Obj.ProtectedData := 20;  //won't compile
  ShowMessage (Obj.GetValue);
  Obj.Free;
end;

type
  TFake = class (TTest);

procedure TForm1.Button2Click(Sender: TObject);
var
  Obj: TTest;
begin
  Obj := TTest.Create;
  Obj.PublicData := 10;
  TFake (Obj).ProtectedData := 20; // compiles!
  ShowMessage (Obj.GetValue);
  Obj.Free;
end;

end.

unit TestClass;

interface

type
  TTest = class
  protected
    ProtectedData: Integer;
  public
    PublicData: Integer;
    function GetValue: string;
  end;

implementation

uses
  SysUtils;

function TTest.GetValue: string;
begin
  Result := Format ('Public: %d, Protected: %d',
    [PublicData, ProtectedData]);
end;

end.

object Form1: TForm1
  Left = 266
  Top = 126
  Width = 285
  Height = 129
  Caption = 'Protection'
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'MS Sans Serif'
  Font.Style = []
  PixelsPerInch = 96
  TextHeight = 13
  object Button1: TButton
    Left = 48
    Top = 32
    Width = 75
    Height = 25
    Caption = 'Run Test'
    TabOrder = 0
    OnClick = Button1Click
  end
  object Button2: TButton
    Left = 136
    Top = 32
    Width = 75
    Height = 25
    Caption = 'Hack'
    TabOrder = 1
    OnClick = Button2Click
  end
end