note 45570 deleted from language.operators.type by colder
| From: | colder@php.net | Date: | Sat, 24 Feb 2007 10:01:23 +0000 |
| Subject: | note 45570 deleted from language.operators.type by colder | ||
| References: | 1 | Groups: | php.notes |
| Request: | Send a blank email to php-notes+get-123808@lists.php.net to get a copy of this message | ||
Note Submitter: glen at arkadia-systems dot com
----
If you are updating code to replace 'is_a()' with the PHP5 compliant
'instanceof' operator, you may find it necessary to change the basic
architecture of your code to make this work.
'instanceof' will throw a fatal error if the object being checked for does not
exist.
'is_a()' will simply return false under this condition.
In the example below, 'is_a()' would effectively detect the need to create an
instance of class 'A', but in this case 'instanceof' will crash your program
with a fatal error.
<?php
// define classes
// Commenting this class will cause an error when 'instanceof' looks for 'A'
// class A {}
class B {}
// create a new object
// $thing = new A();
$thing = new B();
if (is_a($thing, 'A')) {
echo 'Yes, $thing is_a A<br>';
} else {
echo 'No, $thing is not is_a A<br>';
}
if ($thing instanceof A) {
echo 'Yes, $thing is an instaceof A<br>';
} else {
echo 'No, $thing is not an instaceof A<br>';
}
?>
>>> Output:
No, $thing is not is_a A
Fatal error: Class 'A' not found in is_a-instanceof.php on line 19
>>>
A suitable work-around for this situation is to check for the existence of the
class before performing the 'instanceof' comparison:
<?php
/* ... */
if (class_exists('A') && $thing instanceof A) {
echo 'Yes, $thing is an instaceof A<br>';
} else {
echo 'No, $thing is not an instaceof A<br>';
}
?>