question about using $this as a method in a function argument

I have a question about using $this as an argument in a method. I have a simple class called privatemsg and have another data class which it cals for doing the actual insert. Basically, I want the privatemsg class to pass itself as a parameter. I thought using self would do it but nothing seemed to happen. I passed $this as the arg (and am using type-hinting on the privatemsg_data class) and it works. To be totally honest, I have never used $this way and it looks a little strange / inelegant. Should I be doing this another way? Ultimately, I'd like to use a Domain / Mapper model but even then when I look at examples, I see that this takes place. thanks, jonathan class PrivateMsg{ private $msg_recipient_id; private $headline; private $body; //removed get's / set's for brevity public function insertPrivateMsg() {

        $privatemsg_data=new Privatemsg_Data();
        $privatemsg_data->insertMsg($this);

}