在php中实现链表 - 这是安全的构造吗？

Question

Here is an implementation of linked list. It's OK, it's working. But there are few lines that bother me (comments inside method are mine):

//insertion at the start of linklist
public function insertFirst($data)
{
    $link = new ListNode($data);     // create local variable
    $link->next = $this->firstNode;
    $this->firstNode = &$link;       // and remember the reference to it in $this->firstNode

Edit: Let me analyse this method line by line: L1. We create a local variable: $link. L2. Doesn't matter. L3. In 'firstNode' property we save the reference to local variable.

OK, all clear. But at the end of this method the local variable ($link) will be destroyed. So in 'firstNode' we have a reference to non-existent variable. The place in memory where $link variable was stored is free now. PHP can store there something new. Isn't it?