php type operator

instanceof is used to determine whether a PHP variable belongs to an instance of a certain class:

Example #1 Using instanceof

<?php
    class MyClass
    {
    }
    class NotMyClass
    {
    }
    $a = new MyClass;
    var_dump($a instanceof MyClass);
    var_dump($a instanceof NotMyClass);
?>

on a class The above routine will output:

bool(true)
bool(false)

instanceof also Can be used to determine whether a variable is an instance of a subclass inherited from a certain parent class:

Example #2 Use instanceof

<?php
    class ParentClass
    {
    }
    class MyClass extends ParentClass
    {
    }
    $a = new MyClass;
    var_dump($a instanceof MyClass);
    var_dump($a instanceof ParentClass);
?>

on the inherited class The above routine will output:

bool(true)
bool(true)

To check whether an object is not an instance of a class, you can use the logical operator not.

Example #3 Use instanceof to check that the object is not an instance of a certain class

<?php
    class MyClass
    {
    }
    $a = new MyClass;
    var_dump(!($a instanceof stdClass));
?>

The above routine will output:

bool(true)

Finally, instanceof can also be used to determine whether a variable is an object that implements a certain interface Example of:

Example #4 Using instanceof

<?php
    interface MyInterface
    {
    }
    class MyClass implements MyInterface
    {
    }
    $a = new MyClass;
    var_dump($a instanceof MyClass);
    var_dump($a instanceof MyInterface);
?>

on an interface The above routine will output:
bool(true)
bool(true)

Although instanceof is usually used directly with the class name, it can also use objects or characters String variable:

<?php
    interface MyInterface
    {
    }
    class MyClass implements MyInterface
    {
    }
    $a = new MyClass;
    $b = new MyClass;
    $c = &#39;MyClass&#39;;
    $d = &#39;NotMyClass&#39;;
    var_dump($a instanceof $b); // $b is an object of class MyClass
    var_dump($a instanceof $c); // $c is a string &#39;MyClass&#39;
    var_dump($a instanceof $d); // $d is a string &#39;NotMyClass&#39;
?>

The above routine will output:

bool(true)
bool(true)
bool(false)

If the variable being detected is not an object, instanceof does not issue any error message but returns FALSE. Not allowed to detect constants.
Example #6 Use instanceof to detect other variables

<?php
    $a = 1;
    $b = NULL;
    $c = imagecreate(5, 5);
    var_dump($a instanceof stdClass); // $a is an integer
    var_dump($b instanceof stdClass); // $b is NULL
    var_dump($c instanceof stdClass); // $c is a resource
    var_dump(FALSE instanceof stdClass);
?>

The above routine will output:

bool(false)
bool(false)
bool(false)
PHP Fatal error: instanceof expects an object instance, constant given

However There are some pitfalls when using instanceof that you must be aware of. 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 avoid this problem by using a dynamic class reference or a string variable containing the class name:

Example #7 Avoid the class name lookup and fatal error problems caused by instanceof in PHP 5.0

<?php
    $d = &#39;NotMyClass&#39;;
    var_dump($a instanceof $d); // no fatal error here
?>

The above routine will output :

bool(false)

instanceof operator was introduced in PHP 5. Before this, is_a() was used, but later is_a() was abandoned and replaced by instanceof. Note that as of PHP 5.3.0, the use of is_a() is restored.