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 with interfaces
<?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, were not allowed prior to PHP 7.3.0.
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
As of PHP 7.3.0, constants are allowed on the left-hand-side of the instanceof operator.
Example #7 Using instanceof to test constants
<?php
var_dump(FALSE instanceof stdClass);
?>Output of the above example in PHP 7.3:
bool(false)
As of PHP 8.0.0, instanceof can now be used with arbitrary expressions. The expression must be wrapped in parentheses and produce a string.
Example #8 Using instanceof with an arbitrary expression
<?php
class ClassA extends \stdClass {}
class ClassB extends \stdClass {}
class ClassC extends ClassB {}
class ClassD extends ClassA {}
function getSomeClass(): string
{
return ClassA::class;
}
var_dump(new ClassA instanceof ('std' . 'Class'));
var_dump(new ClassB instanceof ('Class' . 'B'));
var_dump(new ClassC instanceof ('Class' . 'A'));
var_dump(new ClassD instanceof (getSomeClass()));
?>Output of the above example in PHP 8:
bool(true) bool(true) bool(false) bool(true)
The instanceof operator has a functional variant with the is_a() function.