Object Oriented PHP5 and referencing the object that contains the object

MacWorks

I've built a number of data-driven PHP sites. But with the advent of PHP5, I'm migrating much of my code to be completely object-oriented and I really like the approach.

I'm stumbling on one key thing. It seems to me that the PHP language is missing a solution for referencing the object that CONTAINS the current object (not extends).

So here's my example ...

<?php

class myFoot
	{
		private $has_warts = "many!";
		private $toe;

	public function __construct()
		{
			echo "CREATING FOOT<br />" . "\n";
			$this->toe = new myToe();
		}

	public function Warts()
		{
			return $this->has_warts;
		}
}

class myToe
	{
		public function __construct()
			{
				echo "CREATING TOE<br />" . "\n";
				echo $GLOBALS['foot']->Warts(); /* Doesn't work! */
			}
	}


$GLOBALS['foot'] = new myFoot();
echo "FOOT IS " . (( is_object( $GLOBALS['foot'] )) ? '' : 'NOT ' ) . ' AN OBJECT!';

?>

[INDENT]
RESULT ...

CREATING FOOT
CREATING TOE

Fatal error: Call to a member function Warts() on a non-object in /Library/WebServer/Documents/warts.php on line 25
[/INDENT]

Here's where I'm stuck: How to I reference the myFoot object from myToe to find out if it has warts? parent:: doesn't work because myToe doesn't EXTEND myFoot -- which is exactly what I want in this case. It's not appropriate for myToe to extend myFoot because while myFoot might have warts, that doesn't mean that myToe does.

HOW DO I POINT TO myFoot from myToe ???

Where am I going wrong? I've tried using the $GLOBALS approach, but it seams that $GLOBALS isn't always in scope. Further it seems weird to use $GLOBALS to reference the object that contains the object you're calling $GLOBALS from.

Why isn't there a way to access the "parent" object -- parent in the sense that it's the object that contains the object -- not extends!

laserlight

I find your use of $GLOBALS with OOP disturbing. Here is my example:

<?php
class myFoot
{
    private $has_warts = "many!";
    private $toe;

public function __construct()
{
    echo "CREATING FOOT<br />\n";
    $this->toe = new myToe($this);
}

public function Warts()
{
    return $this->has_warts;
}
}

class myToe
{
    private $foot;

public function __construct($foot)
{
    echo "CREATING TOE<br />\n";
    $this->foot = $foot;
    echo 'How many warts? ' . $this->foot->Warts() . "<br />\n";
}
}

$foot = new myFoot();
echo '$foot is ' . (is_object($foot) ? '' : 'NOT') . ' an object!';

?>

EDIT:
In case you did not see the idea, it is basically for the myToe object to hold a reference (a pointer, really) to a myFoot object. So when the myFoot object creates its myToe object member variable, it passes a reference to itself (i.e., $this) to the constructor for the myToe object.

NogDog

Being simple-minded, I'd probably do something explicit like:

<?php

class Foot
{
   private $hasWarts;
   private $toe;

   public function __construct($hasWarts = false)
   {
      $this->hasWarts = $hasWarts;
      $this->toe = new Toe();
   }

   public function setWarts($bool)
   {
      $this->hasWarts = (bool)$bool;
      if(!empty($this->toe))
      {
         $this->toe->setFootWarts($this->hasWarts);
      }
   }

   public function test()
   {
      printf("<p>This foot %s warts.</p>\n",
            ($this->hasWarts) ? "has" : "does not have");
      $this->toe->test();
   }
}

class Toe
{
   private $footHasWarts;

   public function setFootWarts($bool)
   {
      $this->footHasWarts = (bool)$bool;
   }

   public function test()
   {
      printf("This toe's foot %s warts",
            ($this->footHasWarts) ? "has" : "does not have");
   }
}

$test = new Foot();
$test->test();
$test->setWarts(true);
$test->test();

laserlight

Being simple-minded, I'd probably do something explicit like:

That would be better, since the toe should not need to know about the foot that contains it. However, if we want to take that attempt at loose coupling to its logical conclusion, the toe should not be storing $footHasWarts either, though it might model the fact that it has warts, upon which the question of whether a foot has warts would be decided by checking whether itself or any of its toes have warts.

NogDog

While presumably this is an abstract scenario, perhaps we need to step back and ask, "why does a toe need to know if the foot has warts?" How does the fact that there is a wart on the heal, the instep, or another toe affect how any given toe object functions?

laserlight

While presumably this is an abstract scenario, perhaps we need to step back and ask, "why does a toe need to know if the foot has warts?"

Yes, that is what I mean by "the toe should not be storing $footHasWarts either, though it might model the fact that it has warts". A toe can know that it has warts, and a foot can know that it has toes that have warts (and maybe also has warts on itself), but a toe does not need to know anything about a foot.

MacWorks

Thanks laserlight! I was able to rework my code and get it working. What I'm doing is actually much more complicated than the example.

I just wish there was a way to have PHP objects point to their "owner" objects without having to pass reference. But passing $this will have to do for now.

laserlight

Thanks laserlight! I was able to rework my code and get it working.

You're welcome 🙂
Remember to mark this thread as resolved using the thread tools.

I just wish there was a way to have PHP objects point to their "owner" objects without having to pass reference. But passing $this will have to do for now.

From what I gather, PHP has borrowed syntax and concepts from C++ and Java, and both these languages support object oriented programming natively and yet still require an association relationship between objects to be established by maintaining pointers or references.