instanceof is used to determine whether a PHP variable is an instantiated object of a certain class:
<?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:
<?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.
<?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:
<?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:
<?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.
<?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:
<?php $d = 'NotMyClass'; var_dump($a instanceof $d); // no fatal error here ?>
The above example will output:
bool(false)
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