unit Unit1;

interface

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

type
TForm1 = class(TForm)
procedure FormCreate(Sender: TObject);
private
FBool:boolean;
property
bool:boolean read FBool write FBool;
end;

var
Form1: TForm1;

implementation

{$R *.DFM}

procedure TForm1.FormCreate(Sender: TObject);
begin
self.bool := true; //работает
end;

end.