The type operator instanceof does not seem to be mentioned in some PHP books. In the detailed description of PHP, it is only mentioned without going into details. I will excerpt it from the manual for notes.
The instanceof operator was introduced in PHP 5. Before this, was_a() was used, but is_a() is obsolete. It is better to use instanceof.
1. Used to determine whether a variable belongs to an instance of a certain class;
2. Used to determine whether a variable is an instance of a subclass inherited from a certain parent class;
3. Used to determine whether a variable is an instance of an object that implements a certain interface.
Prior to PHP 5.1.0, instanceof would call __autoload() if the class name to be checked did not exist. Additionally, a fatal error is generated if the class is not loaded. You can get around this problem by using a dynamic class reference or a string variable containing the class name:
Example #6 Avoid class name lookup and fatal errors caused by instanceof in PHP 5.0
$d = 'NotMyClass';
var_dump($a instanceof $d); // no fatal error here
?>
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