On Tue, 11 Dec 2018 22:19:11 +0100
Vojtěch Čihák <vojtech.ci...@atlas.cz> wrote:
> Hi,
>
> why this code gives EInvalidCast at runtime (but compiles well):w
>
> program Project1;
> {$mode objfpc}{$H+}
>
> uses
> {$IFDEF UNIX}{$IFDEF UseCThreads}
> cthreads,
> {$ENDIF}{$ENDIF}
> Classes, fgl
> { you can add units after this };
>
> {$R *.res}
> type
> TMyClass = class
> procedure Output1;
> end;
>
> TMyList = class (specialize TFPGObjectList<TMyClass>)
>
> end;
>
> TMyDescClass = class(TMyClass)
> procedure Output2;
> end;
>
> var MyList: TMyList;
> MyClass: TMyClass;
>
> procedure TMyClass.Output1;
> begin
> WriteLn('Output1');
> end;
>
> procedure TMyDescClass.Output2;
> begin
> WriteLn('Output2');
> end;
>
> begin
> MyList:=TMyList.Create(True);
> MyClass:=TMyClass.Create;
> MyList.Add(MyClass);
> MyList[0].Output1;
> TMyDescClass(MyList[0]); // EInvalidCast
because MyClass is not TMyDescClass
Mattias
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