PHP Comparing Objects

Introduction

PHP has a comparison operator == using which a simple comarison of two objecs variables can be performed. It returns true if both belong to same class and values of corresponding properties are are same.

PHP's === operator compares two object variables and returns true if and only if they refer to same instance of same class

We use following two classes for comparison of objects with these oprators

Example

<?php
class test1{
   private $x;
   private $y;
   function __construct($arg1, $arg2){
      $this->x=$arg1;
      $this->y=$arg2;
   }
}
class test2{
   private $x;
   private $y;
   function __construct($arg1, $arg2){
      $this->x=$arg1;
      $this->y=$arg2;
   }
}
?>

two objects of same class

Example

$a=new test1(10,20);
$b=new test1(10,20);
echo "two objects of same class\n";
echo "using == operator : ";
var_dump($a==$b);
echo "using === operator : ";
var_dump($a===$b);

Output

two objects of same class
using == operator : bool(true)
using === operator : bool(false)

two references of same object

Example

$a=new test1(10,20);
$c=$a;
echo "two references of same object\n";
echo "using == operator : ";
var_dump($a==$c);
echo "using === operator : ";
var_dump($a===$c);

Output

two references of same object
using == operator : bool(true)
using === operator : bool(true)

two objects of different classes

Example

$a=new test1(10,20);
$d=new test2(10,20);
echo "two objects of different classes\n";
echo "using == operator : ";
var_dump($a==$d);
echo "using === operator : ";
var_dump($a===$d);

Output

Output shows following result

two objects of different classes
using == operator : bool(false)
using === operator : bool(false)