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instanceof is used to determine whether a PHP variable is an instantiated object of a certain class.
Example: instanceof operator and conversions
<?php
$i = 3;
$d = 2.5;
$s = "abc";
$c = new stdClass;
class dClass extends stdClass {}
$e = new dClass;
class nClass {}
$n = new nClass;
echo "\$i: ";
var_dump($i);
$is_stdclass = ($i instanceof stdClass);
print("\$i instanceof stdClass: " . ($is_stdclass ? "true" : "false") . "\n\n");
echo "\$d: ";
var_dump($d);
$is_stdclass = ($d instanceof stdClass);
print("\$d instanceof stdClass: " . ($is_stdclass ? "true" : "false") . "\n\n");
echo "\$s: ";
var_dump($s);
$is_stdclass = ($s instanceof stdClass);
print("\$s instanceof stdClass: " . ($is_stdclass ? "true" : "false") . "\n\n");
echo "\$c: ";
var_dump($c);
$is_stdclass = ($c instanceof stdClass);
print("\$c instanceof stdClass: " . ($is_stdclass ? "true" : "false") . "\n\n");
echo "\$e: ";
var_dump($e);
$is_stdclass = ($e instanceof stdClass);
print("\$e instanceof stdClass: " . ($is_stdclass ? "true" : "false") . "\n\n");
echo "\$n: ";
var_dump($n);
$is_stdclass = ($n instanceof stdClass);
print("\$n instanceof stdClass: " . ($is_stdclass ? "true" : "false") . "\n\n");
View: Example
Execute:
Result:
$i: int(3)
$i instanceof stdClass: false
$d: float(2.5)
$d instanceof stdClass: false
$s: string(3) "abc"
$s instanceof stdClass: false
$c: object(stdClass)#1 (0) {
}
$c instanceof stdClass: true
$e: object(dClass)#2 (0) {
}
$e instanceof stdClass: true
$n: object(nClass)#3 (0) {
}
$n instanceof stdClass: false
Example: 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: 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: 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: 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: 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)
[The interface and its implementation in the above example is useless. – KK]
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: 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);
?>
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: 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: 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.
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