Type Operators
instanceof is used to determine whether a PHP variable is an instantiated object of a certain class:
Using instanceof with classes
<?php
class MyClass
{
}
class NotMyClass
{
}
$a = new MyClass;
var_dump($a instanceof MyClass);
var_dump($a instanceof NotMyClass);
?>
ENTITY
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:
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);
?>
ENTITY
bool(true)
bool(true)
To check if an object is not an instanceof a class, the logical not operator can be used.
Using instanceof to check if object is not an instanceof a class
<?php
class MyClass
{
}
$a = new MyClass;
var_dump(!($a instanceof stdClass));
?>
ENTITY
bool(true)
Lastly, instanceof can also be used to determine whether a variable is an instantiated object of a class that implements an interface:
Using instanceof with interfaces
<?php
interface MyInterface
{
}
class MyClass implements MyInterface
{
}
$a = new MyClass;
var_dump($a instanceof MyClass);
var_dump($a instanceof MyInterface);
?>
ENTITY
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:
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'
?>
ENTITY
bool(true)
bool(true)
bool(false)
instanceof does not throw any error if the variable being tested is not an object, it simply returns ENTITY. Constants, however, were not allowed prior to PHP 7.3.0.
Using instanceof to test other variables
<?php
$a = 1;
$b = NULL;
$c = fopen('/tmp/', 'r');
var_dump($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);
?>
ENTITY
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.
Using instanceof to test constants
<?php
var_dump(FALSE instanceof stdClass);
?>
ENTITY
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.
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()));
?>
ENTITY
bool(true)
bool(true)
bool(false)
bool(true)
The instanceof operator has a functional variant with the is_a function.
ENTITY
get_class, is_a
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