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PHP

Type Operators


Type Operators

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) 

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 #6 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.

See also get_class() and is_a().



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