instanceof

instanceof is used to determine whether a PHP variable is an instantiated object of a certain class:

Example #1 Using instanceof with classes

<?php
class?MyClass
{
}

class?NotMyClass
{
}
$a?=?new?MyClass;

var_dump($a?instanceof?MyClass);
var_dump($a?instanceof?NotMyClass);
?>

The above example will output:

bool(true)
bool(false)

instanceof can also be used to determine whether a variable is an instantiated object of a class that inherits from a parent class:

Example #2 Using instanceof with inherited classes

<?php
class?ParentClass
{
}

class?MyClass?extends?ParentClass
{
}

$a?=?new?MyClass;

var_dump($a?instanceof?MyClass);
var_dump($a?instanceof?ParentClass);
?>

The above example will output:

bool(true)
bool(true)

To check if an object is not an instanceof a class, the logical not operator can be used.

Example #3 Using instanceof to check if object is not an instanceof a class

<?php
class?MyClass
{
}

$a?=?new?MyClass;
var_dump(!($a?instanceof?stdClass));
?>

The above example will output:

bool(true)

Lastly, instanceof can also be used to determine whether a variable is an instantiated object of a class that implements an interface:

Example #4 Using instanceof for class

<?php
interface?MyInterface
{
}

class?MyClass?implements?MyInterface
{
}

$a?=?new?MyClass;

var_dump($a?instanceof?MyClass);
var_dump($a?instanceof?MyInterface);
?>

The above example will output:

bool(true)
bool(true)

Although instanceof is usually used with a literal classname, it can also be used with another object or a string variable:

Example #5 Using instanceof with other variables

<?php
interface?MyInterface
{
}

class?MyClass?implements?MyInterface
{
}

$a?=?new?MyClass;
$b?=?new?MyClass;
$c?=?'MyClass';
$d?=?'NotMyClass';

var_dump($a?instanceof?$b);?//?$b?is?an?object?of?class?MyClass
var_dump($a?instanceof?$c);?//?$c?is?a?string?'MyClass'
var_dump($a?instanceof?$d);?//?$d?is?a?string?'NotMyClass'
?>

The above example will output:

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

instanceof does not throw any error if the variable being tested is not an object, it simply returns FALSE. Constants, however, are not allowed.

Example #6 Using instanceof to test 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 example will output:

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

There are a few pitfalls to be aware of. Before PHP version 5.1.0, instanceof would call __autoload() if the class name did not exist. In addition, if the class was not loaded, a fatal error would occur. This can be worked around by using a dynamic class reference, or a string variable containing the class name:

Example #7 Avoiding classname lookups and fatal errors with instanceof in PHP 5.0

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

The above example will output:

bool(false)

The instanceof operator was introduced in PHP 5. Before this time is_a() was used but is_a() has since been deprecated in favor of instanceof. Note that as of PHP 5.3.0, is_a() is no longer deprecated.