对象的比较

在 PHP 5 中，object comparison is a more complicated than in PHP 4 and more in accordance to what one will expect from an Object Oriented Language (not that PHP 5 is such a language).

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, and are instances of the same class.

另外一点，when using the identity operator (===), object variables are identical if and only if they refer to the same instance of the same class.

下面的例子会清楚的说明上面的规则。

例子 19-8. PHP 5中对象比较的例子 <?php function 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 {     var $flag;     function Flag($flag=true) {             $this->flag = $flag;     } } class OtherFlag {     var $flag;     function OtherFlag($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); ?>

上面例子的输出结果：

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