[PHP-DEV] Using $this-Pointer in the constructor From: Klaus Reimer (k.reimer <email protected>)
Date: 08/31/00

Hi,

Currently we are in great trouble with PHP4. We are heavily using references
to objects in our current project and we need to create a reference from a
class in the constructor of the class itself. But it is not working. I have
tested it with PHP 4.0.1 and the new PHP 4.0.2.
But finally I managed to write a short example script where it is not
working. Before I open a bug report, I want to be sure, that I am doing it
the right way. Here is the code that is refusing to work correctly:

<?php
  class CParent {
    var $Ref;
 
    function setRef(&$Child) {
      $this->Ref=&$Child;
    }
 
    function drawRef() {
      printf(":%s:<br>\n",$this->Ref->Value);
    }
  }
 
  class CChild {
    var $Value;
 
    function CChild(&$Parent) {
      $Parent->setRef($this);
    }
  }
 
  $Parent=new CParent;
  $Child=new CChild($Parent);
  $Child->Value="Test";
  $Parent->drawRef();
?>

This script creates a Parent-Class and a Child-Class. The constructor of the
child class connects itself to the Parent class by passing its reference to
the Parent. Then I change its property $Value to "Test" and call the Parents
drawRef()-function. The drawRef-Function is printing the Value of the
referenced object. Well, finally it is NOT printing the Value. The value
seems to be empty. But the reference is working. If a add some methods to
CChild, the Parent can call these methods through the reference. But all
properties of CChild are empty. It looks like $Parent is working with a COPY
of $Child and not with a reference. I thought there is something wrong with
the setRef()-method, where I store the Reference in the $Ref-Variable, but...

...if I do the same in another way (Not using the constructor, instead
writing the reference from Child to Parent manually) it is working. Here is
the working code:

<?php
  class CParent {
    var $Ref;
 
    function setRef(&$Child) {
      $this->Ref=&$Child;
    }
 
    function drawRef() {
      printf(":%s:<br>\n",$this->Ref->Value);
    }
  }
 
  class CChild {
    var $Value;
 
    // In this example I don't use the constructor to connect this
    // class to CParent
  }
 
  $Parent=new CParent;
 
  // Instead I call the setRef()-method manually to do it
  $Child=new CChild;
  $Parent->setRef($Child);
 
  $Child->Value="Test";
  $Parent->drawRef();
?>

This script is working perfectly. So I wonder why is the first script not
working? What is wrong about making a reference to $this in the constructor
of $this? And to create just more confusion: If I assign a value to
$this->Value in the constructor, this value is printed by drawRef() and
values assigned later are ignored.

Any hints? Is this a bug in PHP, a not implemented feature, or a bug in my
script? 

-- 
MfG
Klaus Reimer
twisd AG i.G.
http://www.twisd.de

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