Can't modify variable in parent class from child class

[bulletseed]

Hi.  I'm kinda new at extending classes.  I have tried searching all over this and other forums about this problem and I just haven't been able to figure it out. I have one class extending another and I'm trying to modify the value of a variable in the parent class. The problem is that once the function in the child class ends, the parent's variable that I just changed turns back into what it was before.

 

<?php
class _parent
{
public $var;

public function __construct()
{
	$this->var = 'OLD';
}

public function show()
{
	$child = new _child();
	$child->change();
	echo $this->var;
}
}

class _child extends _parent
{
public function change()
{
	$this->var = 'NEW';
}	
}

$parent = new _parent();
$parent->show();

/* Why is output not NEW ??? */
?>

 

What am I doing wrong? Or am I trying something that is not possible?

 

Thanks for your feedback.

 

-BulletSeed

[Jessica]

You never call the function

$parent->change()

[bulletseed]

Huh? But there is no change() function in the parent class. There is a change() function in the child class which I am calling from within the parent's show() function.

[Jessica]

Ah right.

You create a new child. The variable that gets changed is the one in child, not the parent. If you want to change $parent's variable, you need to pass $parent to the function or have it return a value which you can then assign.

 

You have like this:

$a is parent.

$b is a variable inside $a;

make a change to $b, it doesn't affect $a.

 

Why do all your classes start with _? that's going to get annoying to type all the time.

[bulletseed]

(The underscore is just there because in this example i wanted to use the 'parent' and 'child' names for the classes for clarity but parent is a reserved word in PHP. I don't use them in my real project.)

 

Well the thing is that i cant return that value in that function because in my real project I'm already returning something else there. I just wanted to know if what I am trying to do here (modifying a variable in a parent class from WITHIN a child class) was actually possible at all. I thought it would be.

[Jessica]

No because what you end up modifying is the $child, not the $parent

[bulletseed]

but... but... but... it EXTENDS! isnt that what that keyword is supposed to be for?  :'(

[Jessica]

No, extends means the class includes all the variables and functions of the parent. It doesn't mean the $child is a pointer to $parent, which is how you're trying to use it, as if $child was $parent, so any changes you make to $child would apply to $parent. That's not what extends means.

[bulletseed]

ahh, gotcha. hmmm... if that's how it works.. then...

 

...ok... i just tried doing the same thing by declaring the $var as static and referencing it with the '::' operator on both classes and it seems to work exactly like I wanted originally. I guess that's the correct way of doing what I was thinking.