這是延續上一個 TObjectList 的問題，但上串已經結案了，所以另起爐灶，若造成閱讀不便，歹勢。     

 
  PAA=^TAA;
  TAA= class(TObject)
    。。。
    procedure show;
  end;    procedure TForm1.FormCreate(Sender: TObject);
begin
  a:= TAA.Create(1);
  List1.Add(a);
end;    procedure TForm1.Button1Click(Sender: TObject);
begin
  (List1.Items[0] as TAA).show;      //這樣會Error
  TAA(List1.Items[0]).show;          //這樣OK
end;

The as operator makes use of the RTTI before typecasting and it can work on interfaces, too. Typecast using Txxx() is much faster than the as operator since there will be no checking. According to my experience, the as operator sometimes behave strangely (e.g. D6 ok while D5 error???) and personally I would only use as when typecasting interface, for objects I always use the direct typecast.