how to write a Polymorphism action in controller

//支付定金协议确认
public function depositAction($incart,$car){

    $this->view->pick('pay/deposit');
}

public function depositAction(){

    $this->view->pick('pay/deposit');
}
edited Sep '15
public function depositAction($incart = "default", $car = null) {

   $this->view->pick('pay/deposit');
}