Problems with Parent Child References

Anon

I've designed an architecture in PHP which is dependent on a class hierarchy
which has a parent class with a member variable which is a child object.
That child object contains a reference back to the parent. The problem I'm
running into is changes to the parent's member variables are not reflected
in the child's reference to the parent. Let me use a code example to
illustrate my point.

Class Parent {
var $sTest = "apple";
var $pChild;
function Parent() {
$this->pChild = new Child();
$this->pChild->SetParent($this);
}
}

Class Child {
var $pParent;

function SetParent(&$pParent) {
$this->pParent = &$pParent;
}
function PrintParentData() {
echo "Parents Test data: ".$this->pParent->sTest." \n";
}
}

$pParent = new Parent();
$pParent->sTest = "orange";
echo "pParent->sTest = ".$pParent->sTest." \n";
$pParent->pChild->PrintParentData();

// Prints:
// pParent->sTest = orange
// Parents Test data: apple

// Instead of :
// pParent->sTest = orange
// Parents Test data: orange

I think I've coded this correctly as per the docs on references. I'm using
PHP4.1.1. My conclusions are :

This is not possible in PHP due to safety mechanisms built into the
language to safeguard against circular references (and infinite recursion).
I'm doing something wrong.

Thanks to anyone willing to take a stab...

Kevin Morris

tomhath

Taking a reference to $this desn't seem to work right (at least inside the constructor). Setting the parent after the object is created works okay.

class Parent {
var $sTest = "apple";
var $pChild;
function Parent() {
$this->pChild = new Child();
//$this->pChild->SetParent($this);
}
}

class Child {
var $pParent;

function SetParent(&$pParent) {
$this->pParent = &$pParent;
}

function PrintParentData() {
echo "Parents Test data: ".$this->pParent->sTest." \n";
}
}

$pParent = new Parent();
$pParent->pChild->pParent = &$pParent;

echo "pParent->sTest = " . $pParent->sTest . " \n";
$pParent->pChild->PrintParentData();

$pParent->sTest = "orange";

echo "pParent->sTest = " . $pParent->sTest . " \n";
$pParent->pChild->PrintParentData();

tomhath

Must be a constructor thing, your code works in other functions inside the class:

class Parent {
var $sTest = "apple";
var $pChild;

function Parent() {
$this->pChild = new Child();
}
function SetChildParent () {
$this->pChild->SetParent ($this);
}
}

class Child {
var $pParent;

function SetParent(&$pParent) {
$this->pParent = &$pParent;
}
function PrintParentData() {
echo "Parents Test data: ".$this->pParent->sTest." \n";
}
}

$pParent = new Parent();
$pParent->SetChildParent();

echo "pParent->sTest = " . $pParent->sTest . " \n";
$pParent->pChild->PrintParentData();

$pParent->sTest = "orange";

echo "pParent->sTest = " . $pParent->sTest . " \n";
$pParent->pChild->PrintParentData();

Anon

Tom,

Must be a constructor thing, your code works in other functions inside the class:

I independently made the same conclusion. My guess is the reference 'address' isn't finalized until the constructor has exited. Only then can you get a useful reference to the constructed object.

While not incredibly elegant I can live with the "Set parent after instantiation" workaround.

Thanks for your input by the way.

-Kevin