Php/docs/language.oop5.object-comparison
Comparing Objects
When using the comparison operator (==),
object variables are compared in a simple manner, namely: Two object
instances are equal if they have the same attributes and values (values are compared with ==), and are
instances of the same class.
When using the identity operator (===),
object variables are identical if and only if they refer to the same
instance of the same class.
An example will clarify these rules.
Example #1 Example of object comparison in PHP 5
<?phpfunction bool2str($bool){ if ($bool === false) { return 'FALSE'; } else { return 'TRUE'; }}function compareObjects(&$o1, &$o2){ echo 'o1 == o2 : ' . bool2str($o1 == $o2) . "\n"; echo 'o1 != o2 : ' . bool2str($o1 != $o2) . "\n"; echo 'o1 === o2 : ' . bool2str($o1 === $o2) . "\n"; echo 'o1 !== o2 : ' . bool2str($o1 !== $o2) . "\n";}class Flag{ public $flag; function __construct($flag = true) { $this->flag = $flag; }}class OtherFlag{ public $flag; function __construct($flag = true) { $this->flag = $flag; }}$o = new Flag();$p = new Flag();$q = $o;$r = new OtherFlag();echo "Two instances of the same class\n";compareObjects($o, $p);echo "\nTwo references to the same instance\n";compareObjects($o, $q);echo "\nInstances of two different classes\n";compareObjects($o, $r);?>
The above example will output:
Two instances of the same class o1 == o2 : TRUE o1 != o2 : FALSE o1 === o2 : FALSE o1 !== o2 : TRUE Two references to the same instance o1 == o2 : TRUE o1 != o2 : FALSE o1 === o2 : TRUE o1 !== o2 : FALSE Instances of two different classes o1 == o2 : FALSE o1 != o2 : TRUE o1 === o2 : FALSE o1 !== o2 : TRUE
Note:
Extensions can define own rules for their objects comparison (
==).
