Php/docs/language.operators.type
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
<?phpclass MyClass{}class NotMyClass{}$a = new MyClass;var_dump($a instanceof MyClass);var_dump($a instanceof NotMyClass);?>
The above example will output:
bool(true) bool(false)
instanceof can also be used to determine whether a variable
is an instantiated object of a class that inherits from a parent class:
Example #2 Using instanceof with inherited classes
<?phpclass ParentClass{}class MyClass extends ParentClass{}$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
<?phpclass 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
<?phpinterface MyInterface{}class MyClass implements MyInterface{}$a = new MyClass;var_dump($a instanceof MyClass);var_dump($a instanceof MyInterface);?>
The above example will output:
bool(true) bool(true)
Although instanceof is usually used with a literal classname,
it can also be used with another object or a string variable:
Example #5 Using instanceof with other variables
<?phpinterface MyInterface{}class MyClass implements MyInterface{}$a = new MyClass;$b = new MyClass;$c = 'MyClass';$d = 'NotMyClass';var_dump($a instanceof $b); // $b is an object of class MyClassvar_dump($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); // $a is an integervar_dump($b instanceof stdClass); // $b is NULLvar_dump($c instanceof stdClass); // $c is a resourcevar_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
<?phpvar_dump(FALSE instanceof stdClass);?>
Output of the above example in PHP 7.3:
bool(false)
The instanceof operator has a functional variant
with the is_a() function.
