删除PHP方法中的引用传递

我想在此方法中删除引用传递，我该如何做到这一点?

    public function insertFirst($data)
    {
        $link = New Node($data);
        $link->next = $this->first;
        $this->first =& $link;
        if(null === $this->last)
            $this->last = &$link;
        $this->count++;
        return $this;
    }