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Type Operators

Examples:
Using instanceof with classes

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

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<?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)
Using instanceof with inherited classes

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

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<?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)
Using instanceof to check if object is not an instanceof a class

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

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

The above example will output:

bool(true)
Using instanceof for class

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

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<?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)
Using instanceof with other variables

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

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<?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)
Using instanceof to test other variables

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

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<?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
Avoiding classname lookups and fatal errors with instanceof in PHP 5.0

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:

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

The above example will output:

bool(false)
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doc_php
2025-01-10 15:47:30
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