Delphi：對TMemoryStream.Memory錯誤的理解

TMemoryStream 的 Position 變化後, 我曾經認為它的 Memory 屬性也會變化; 只怪不看源碼, 只想當然!

procedure TForm1.FormCreate(Sender: TObject);
var
  Stream1,Stream2: TMemoryStream;
  pw: TPtrWrapper;
begin
  Stream1 := TStringStream.Create('1234567890');
  Stream2 := TStringStream.Create('ABCDEFGHIJ');
 
  //想把 Stream1 變成 123DEFG890
  pw := TPtrWrapper.Create(Stream2.Memory);
  pw := TPtrWrapper.Create(pw.ToInteger + 3);
 
  Stream1.Position := 3;
  Stream1.Write(pw.ToPointer^, 4);
 
  ShowMessage(TStringStream(Stream1).DataString); //123DEFG890
 
  Stream1.Free;
  Stream2.Free;
end;