Once in a while I run into this problem and every single time it takes me forever to remember the cause: Say, you have got an interface and a class implementing that interface: type IMyInterface = interface function asMyInterface: IMyInterface; end; type TMyClass = class(TInterfacedObject, IMyInterface) private function asMyInterface: IMyInterface; end; [...] function TMyClass.asMyInterface: IMyInterface; … Continue reading class as interface: Operator not applicable to this operand →