How to implements a interface to a controller?

I trying to implements a interface to a controller but when i try that, the request is converted into a string. Here is the code of the controller:

class FilesController extends Controller implements Repository
{
    function __construct()
    {
        $this->factory = new RepositoryFactoryImp();
    }


    public function index($request)
    {
        $repository = $this->factory->createRepository($request->type_repository);

        return $repository->getFilesList($request);
    }
}

Here is the code of the interface:

interface Repository
{
    public function index(GetFileListRequest $request);
}

Then the error that i get is:

ErrorException: Trying to get property 'type_repository' of non-object in file C:\xampp\htdocs\pocs\repository\app\Http\Controllers\FilesController.php on line 31

I do a dd($request); and the result is a string, the string is the content of type_repository variable of the route:

Route::get('files/{type_repository}', 'filesController@index');

What can be the problem? Is possible to implements a interface to a controller?

via Chebli Mohamed