problems with references

poison

hi there
I' fairly new to PHP (not to programming 😉 and I'm having a little trouble with a class I wrote to store tree-like structures...
the method I'm trying to get to work for about 2 days is Node::getParentCount() ...
if the object isn't the root element...the result is always 1 .... regardless on what 'level' it is...and I fail to undestand the reason...
the code is below (really cut down)
maybe you guys can give me a little help ?
thanks =D

class Node {
	var $_elements;
	var $_parent;


/**
* @return Node
* @desc class for Tree-like structures
*/
function Node () {
	$this->_data=array();
}


/**
* @return void
* @param mixed $data
* @desc add data
*/
function add ($data) {
	$index=$this->elements();

	// crashes PHP if I don't assign by reference here (o_O)
	$this->_elements[$index]=&$data;

	// if added element is a Node Object, set parent node reference to this object...
	if (is_a($this->_elements[$index], 'Node')) {
		$this->_elements[$index]->_setParentNode__($this);
	}

}

/**
* @return mixed
* @param int $index
* @desc get element at index
*/
function &get ($index) {
	return $this->_elements[$index];
}


/**
* @return int
* @desc get number of elements
*/
function elements () {
	return count ($this->_elements);
}



/**
* @return Node
* @desc get reference to parent node
*/
function &getParentNode () {
	return $this->_parent;
}


/**
* @return void
* @param Node $parent_node
* @desc set reference to 'parent' node
*/
function _setParentNode__ (&$parent_node) {
	$this->_parent=&$parent_node;
}


/**
* @return bool
* @desc check for a parent node
*/
function hasParentNode () {
	return (!is_null($this->_parent));
}


/**
* @return int
* @desc <defunct> get number of 'parents' node has 
*/
function getParentCount () {
	$parents=0;
	$tmp=&$this;
	while ($tmp->hasParentNode ()) {
		$tmp=&$tmp->getParentNode();
		++$parents;
	}
	return $parents;
}


}

Weedpacket

Um, works for me...

// Your code, verbatim

$t1 = new Node();
$t2 = new Node();
$t3 = new Node();
$t4 = new Node();
$t5 = new Node();
$t6 = new Node();

$t1->add($t2);
$t1->add($t3);
$t2->add($t4);
$t4->add($t5);
$t4->add($t6);

echo $t1->getParentCount();
echo $t2->getParentCount();
echo $t3->getParentCount();
echo $t4->getParentCount();
echo $t5->getParentCount();
echo $t6->getParentCount();

Output:

poison

thanks for your answer =)
now things are getting really strange...
may I ask you what PHP version you are running ?
I've tested with 4.3.2 and 4.3.5, and it doesn't work....

Weedpacket

Originally posted by poison
thanks for your answer =)
now things are getting really strange...
may I ask you what PHP version you are running ?
I've tested with 4.3.2 and 4.3.5, and it doesn't work....

Oh, good point; I'm using 5.0.0RC1 at the moment. Hang on a tick; I'll install - ah, 4.3.0 - and try that.

Okay. I see. $this->parent is always ending up null. setParentNode() is working (parents can be added by hand á là $t2->_setParentNode($t1);), so it must be add() that's choking.

It is recognising that those $data which are Nodes are in fact Nodes (and wouldn't it be better to distinguish between nodes and data?) and they are being set with their parents there, but they're not surviving beyond that.

Ah, but $data is not being passed by reference but by value - it's a copy, and $this->_elements[$index] is being made a reference to that copy, not the original. It's the copy that's having its parent set, not the original - whose parent remains null.

So the parameter passed to ->add() has to be by reference; i.e., declared as function add(&$data) so that modifications to $data work on the original object and not a copy; that's why it works in PHP5 - objects are automatically passed by reference.

Of course doing this means that $foo->add('forty-two'); won't work, because PHP4 needs the argument to ->add() to be something it can make a reference to. It means either $forty_two = 'forty-two'; $foo->add($forty_two); or separating the tasks of "adding children" from "adding data".

poison

thank you
now I understand =D