Type Operators

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

Example 15-8. 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 15-9. 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)

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

Example 15-10. 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 15-11. 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)

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 15-12. 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.

See also get_class() and is_a().