Out parameter

unit Unit1;

interface

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

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

var
  Form1: TForm1;

implementation

{$R *.dfm}

type
  TFoo = class
  private
    FBar: string;
  public
    property Bar: string read FBar write FBar;
  end;

procedure DoSomething(const AString: string; out AFoo: TFoo);
begin
  AFoo.Bar := AFoo.Bar + AString;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  LFoo: TFoo;
begin
  LFoo := TFoo.Create();
  try
    LFoo.Bar := 'Hello World';
//    ShowMessage(LFoo.Bar);
    DoSomething('a', LFoo);
//    ShowMessage(LFoo.Bar);
  finally
    LFoo.Free();
  end;
end;

end.