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Type Operators

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The instanceof operator has a functional variant with the is_a function.

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

Using instanceof with classes

php

<?php
class MyClass
{
}

class NotMyClass
{
}
$a = new MyClass;

var_dump($a instanceof MyClass);
var_dump($a instanceof NotMyClass);
?>

The above example will output:

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:

Using instanceof with inherited classes

php

<?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:

output

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

<?php
class MyClass
{
}

$a = new MyClass;
var_dump(!($a instanceof stdClass));
?>

The above example will output:

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:

Using instanceof with interfaces

php

<?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:

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:

Using instanceof with other variables

php

<?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:

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.

Using instanceof to test other variables

php

<?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);
?>

The above example will output:

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.

Using instanceof to test constants

php

<?php
var_dump(FALSE instanceof stdClass);
?>

output

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

<?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

bool(true)
bool(true)
bool(false)
bool(true)

The instanceof operator has a functional variant with the is_a() function.