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type IMyInterface = class(IInterface)
     ...

     TMyControl = class(TCheckBox,IInterface);


var
 MyControl : TMyControl;
 MyInterface : IMyInterface;

...

 MyInterface := MyControl;

 if (MyInterface is??? TMyControl) then ...                    

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if (Parent is TEdit) then ...                    

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type
  IMyInterface = interface
   ['{0B4E2DA5-EFC8-49ED-8928-9ADD1E7D030D}']
  end;

  TMyObject = class(TInterfacedObject,IMyInterface)
    destructor Destroy; override;
  end;

destructor TMyObject.Destroy;
begin
  ShowMessage('Destroyed');
end;

procedure TForm1.FormCreate(Sender: TObject);
var
  MyInterface: IMyInterface;
  MyObject: TMyObject;
begin
  MyObject := TMyObject.Create;
  MyInterface := MyObject;

  if MyObject is TMyObject then
   ShowMessage('MyObject is TMyObject');

  if Supports(MyInterface, IMyInterface) then
   ShowMessage('MyInterface supports IMyInterface');

  // automatische Freigabe
end;