OOP and References in PHP

Object Oriented Programming in PHP – Part 7

Forward: In this part of the series, we look at object references.

By: Chrysanthus Date Published: 9 Aug 2012

Introduction

This is part 7 of my series, Object Oriented Programming in PHP. Understanding references in any language is generally a headache: You need to know what a reference means in a language and then know how to use it in that language. Just knowing what it means is normally not enough to know how to use it. So, we have to learn how to use references in Object Oriented Programming of PHP. The word, object, below refers to an instantiated object. In this part of the series, we look at object references.

Note: If you cannot see the code or if you think anything is missing (broken link, image absent), just contact me at forchatrans@yahoo.com. That is, contact me for the slightest problem you have about what you are reading.

Assigning an Object Variable to another Variable
When you assign an object variable to a new variable, as object $a is assigned to $b below, both variables still refer to the same region (object) in memory; no copy of the region content is made to another region. Read and try the following code:

<?php

 class A
 {
 public $var = 1;
 }

 $a = new A;
 $b = $a;

 $b->var= 2;
 echo $a->var." ";
 echo $b->var." ";

?>

Assigning an Object Reference to a Variable
When you assign an object reference to a new variable, as &$c is assigned to $d below, the results are the same as copying an object variable to another; no memory region content is copied to another memory region. Read and try the following code:

<?php

 class A
 {
 public $var = 1;
 }

 $c = new A;
 $d = &$c;

 $d->var= 2;
 echo $c->var." ";
 echo $d->var." ";

?>

Passing an Object as Ordinary Argument to a Function
When you pass an object as argument to a function, both the parameter object and the object outside the function, refer to the same region (object) in memory. Read and try the following code:

<?php

 class A
 {
 public $var = 1;
 }

 $e = new A;
 echo $e->var . " ";

 function fn($obj)
 {
 $obj->var = 2;
 echo $obj->var . " ";
 }

 fn($e);

 echo $e->var . " ";

?>

Passing an Object by Reference
When you pass an object by reference to a function, the results are the same as passing the object ordinarily. Read and try the following code:

<?php

 class A
 {
 public $var = 1;
 }

 $e = new A;
 echo $e->var . " ";

 function fn(&$obj)
 {
 $obj->var = 2;
 echo $obj->var . " ";
 }

 fn($e);

 echo $e->var . " ";

?>

Let us stop here for this part of the series and continue in the next part.

Chrys

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