Array Operators
SIMPLE, CLEAN, CLEAR use of the instanceof OPERATOR
First, define a couple of simple PHP Objects to work on -- I'll introduce Circle and Point. Here's the class definitions for both:
<?php
class Circle
{
protected $radius = 1.0;
/*
* This function is the reason we are going to use the
* instanceof operator below.
*/
public function setRadius($r)
{
$this->radius = $r;
}
public function __toString()
{
return 'Circle [radius=' . $this->radius . ']';
}
}
class Point
{
protected $x = 0;
protected $y = 0;
/*
* This function is the reason we are going to use the
* instanceof operator below.
*/
public function setLocation($x, $y)
{
$this->x = $x;
$this->y = $y;
}
public function __toString()
{
return 'Point [x=' . $this->x . ', y=' . $this->y . ']';
}
}
?>
Now instantiate a few instances of these types. Note, I will put them in an array (collection) so we can iterate through them quickly.
<?php
$myCollection = array(123, 'abc', 'Hello World!',
new Circle(), new Circle(), new Circle(),
new Point(), new Point(), new Point());
$i = 0;
foreach($myCollection AS $item)
{
/*
* The setRadius() function is written in the Circle class
* definition above, so make sure $item is an instance of
* type Circle BEFORE calling it AND to avoid PHP PMS!
*/
if($item instanceof Circle)
{
$item->setRadius($i);
}
/*
* The setLocation() function is written in the Point class
* definition above, so make sure $item is an instance of
* type Point BEFORE calling it AND to stay out of the ER!
*/
if($item instanceof Point)
{
$item->setLocation($i, $i);
}
echo '$myCollection[' . $i++ . '] = ' . $item . '<br>';
}
?>
$myCollection[0] = 123
$myCollection[1] = abc
$myCollection[2] = Hello World!
$myCollection[3] = Circle [radius=3]
$myCollection[4] = Circle [radius=4]
$myCollection[5] = Circle [radius=5]
$myCollection[6] = Point [x=6, y=6]
$myCollection[7] = Point [x=7, y=7]
$myCollection[8] = Point [x=8, y=8]
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
<?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 for class
<?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)
There are a few pitfalls to be aware of. Before PHP version 5.1.0, instanceof would call __autoload() if the class name did not exist. In addition, if the class was not loaded, a fatal error would occur. This can be worked around by using a dynamic class reference, or a string variable containing the class name:
Example #6 Avoiding classname lookups and fatal errors with instanceof in PHP 5.0
<?php
$d = 'NotMyClass';
var_dump($a instanceof $d); // no fatal error here
?>
The above example will output:
bool(false)
The instanceof operator was introduced in PHP 5. Before this time is_a() was used but is_a() has since been deprecated in favor of instanceof. Note that as of PHP 5.3.0, is_a() is no longer deprecated.
See also get_class() and is_a().
add a note
User Contributed Notes
Type Operators
wbcarts at juno dot com
18-May-2012 02:14
Sudarshan Wadkar
15-Dec-2011 04:34
I don't see any mention of "namespaces" on this page so I thought I would chime in. The instanceof operator takes FQCN as second operator when you pass it as string and not a simple class name. It will not resolve it even if you have a `use MyNamespace\Bar;` at the top level. Here is what I am trying to say:
## testinclude.php ##
<?php
namespace Bar1;
{
class Foo1{ }
}
namespace Bar2;
{
class Foo2{ }
}
?>
## test.php ##
<?php
include('testinclude.php');
use Bar1Foo1 as Foo;
$foo1 = new Foo(); $className = 'Bar1\Foo1';
var_dump($foo1 instanceof Bar1Foo1);
var_dump($foo1 instanceof $className);
$className = 'Foo';
var_dump($foo1 instanceof $className);
use Bar2Foo2;
$foo2 = new Foo2(); $className = 'Bar2\Foo2';
var_dump($foo2 instanceof Bar2Foo2);
var_dump($foo2 instanceof $className);
$className = 'Foo2';
var_dump($foo2 instanceof $className);
?>
## stdout ##
bool(true)
bool(true)
bool(false)
bool(true)
bool(true)
bool(false)
jmullee at yahoo dot com
14-Apr-2011 06:29
returns true for any ancestor class, not just immediate superclasses.
php -r "class Mammal{}; class Primate extends Mammal {}; class Human extends Primate{}; \$h=new Human(); echo (\$h instanceof Mammal)?'Yes':'no';"
Yes
Jennifer
31-Mar-2011 06:40
I was getting frustrated by instanceof not taking a string for its first argument so I wrote this function that takes strings or objects for both args and deals with both classes and interfaces. I hope it's useful to someone.
<?php
/**
* @desc: replacement for instanceof that accept strings or objects for both args
* @param: Mixed $object- string or Object
* @param: Mixed $class- string or Object
* @return: Boolean
*/
function oneof($object, $class){
if(is_object($object)) return $object instanceof $class;
if(is_string($object)){
if(is_object($class)) $class=get_class($class);
if(class_exists($class)) return is_subclass_of($object, $class) || $object==$class;
if(interface_exists($class)) {
$reflect = new ReflectionClass($object);
return !$reflect->implementsInterface($class);
}
}
return false;
}
?>
fbableus
18-Mar-2011 06:05
If you want to test if a classname is an instance of a class, the instanceof operator won't work.
<?php
$classname = 'MyClass';
if( $classname instanceof MyParentClass) echo 'Child of it';
else echo 'Not child of it';
?>
Will always output
Not child of it
You must use a ReflectionClass :
<?php
$classname = 'MyClass';
$myReflection = new ReflectionClass($classname);
if( $myReflection->isSubclassOf('MyParentClass')) echo 'Child of it';
else echo 'Not child of it';
?>
Will output the good result.
If you're testing an interface, use implementsInterface() instead of isSublassOf().
mauritsdajong at gmail dot com
13-Aug-2010 03:38
Sometimes you want to typehint objects INSIDE an array, but I think you can't.
Instead, you can use this function to check the classes inside this array:
<?php
public checkObjectsArray(array $array, $classname, $strict = false) {
if (!$strict) {
foreach ($array as $element) {
if (!($element instanceof $classname)) {
return false;
}
}
}
else {
foreach ($array as $element) {
if (get_class($element) != $classname) {
return false;
}
}
}
return true;
}
?>
phil dot taylor at gmail dot com
15-Jul-2010 04:13
It seems like instanceOf is using a string comparison. Longer class names take longer to check in conditional statements
eg.
if ($f instanceOf HelloWorldTestClass)
is much slower than
if ($f instanceOf HWT)
jtaal at eljakim dot nl
17-Nov-2008 05:37
You can use "self" to reference to the current class:
<?php
class myclass {
function mymethod($otherObject) {
if ($otherObject instanceof self) {
$otherObject->mymethod(null);
}
return 'works!';
}
}
$a = new myclass();
print $a->mymethod($a);
?>
kevin dot benton at beatport dot com
21-Aug-2008 09:31
Example #5 could also be extended to include...
var_dump($a instanceof MyInterface);
The new result would be
bool(true)
So - instanceof is smart enough to know that a class that implements an interface is an instance of the interface, not just the class. I didn't see that point made clearly enough in the explanation at the top.
ejohnson82 at gmail dot com
18-Jan-2008 01:59
The PHP parser generates a parse error on either of the two lines that are commented out here.
Apparently the 'instanceof' construct will take a string variable in the second spot, but it will NOT take a string... lame
class Bar {}
$b = new Bar;
$b_class = "Bar";
var_export($b instanceof Bar); // this is ok
var_export($b instanceof $b_class); // this is ok
//var_export($f instanceof "Bar"); // this is syntactically illegal
//var_export($f instanceof 'Bar'); // this is syntactically illegal
julien plee using g mail dot com
20-Jul-2007 06:56
Response to vinyanov at poczta dot onet dot pl:
You mentionned "the instanceof operator will not accept a string as its first operand". However, this behavior is absolutely right and therefore, you're misleading the meaning of an instance.
<?php 'ClassA' instanceof 'ClassB'; ?> means "the class named ClassA is an instance of the class named ClassB". This is a nonsense sentence because when you instanciate a class, you ALWAYS obtain an object. Consequently, you only can ask if an object is an instance of a class.
I believe asking if "a ClassA belongs to a ClassB" (or "a ClassA is a class of (type) ClassB") or even "a ClassA is (also) a ClassB" is more appropriate. But the first is not implemented and the second only works with objects, just like the instanceof operator.
Plus, I just have tested your code and it does absolutely NOT do the same as instanceof (extended to classes)! I can't advise anyone to reuse it. The use of <?php is_instance_of ($instanceOfA, 'ClassB'); ?> raises a warning "include_once(Object id #1.php) …" when using __autoload (trying to look for $instanceOfA as if it was a class name).
Finally, here is a fast (to me) sample function code to verify if an object or class:
<?php
function kind_of (&$object_or_class, $class)
{
return is_object ($object_or_class) ?
$object_or_class instanceof $class
: (is_subclass_of ($object_or_class $class)
|| strtolower ($object_or_class) == strtolower ($class));
}
?>
jphaas at gmail dot com
11-Jul-2007 10:50
Posting this so the word typeof appears on this page, so that this page will show up when you google 'php typeof'. ...yeah, former Java user.
vinyanov at poczta dot onet dot pl
19-Jun-2007 03:57
Unfortunately the instanceof operator will not accept a string as its first operand. So I wrote this function. It does exactly the same (ie, successively checks identicalness, inheritance and implementation). Just on strings.
<?php
function is_instance_of($sub, $super)
{
$sub = (string)$sub;
$super = is_object($super) ? get_class($super) : (string)$super;
switch(true)
{
case $sub === $super; // well ... conformity
case is_subclass_of($sub, $super):
case in_array($super, class_implements($sub)):
return true;
default:
return false;
}
}
// testing
interface X {}
class A {}
class B extends A {}
class C extends B {}
class D implements X {}
$i = 'is_instance_of';
var_dump($i('A', 'A'), $i('B', 'A'), $i('C', 'A'), $i('D', 'X'));
?>
jeanyves dot terrien at orange-ftgroup dot com
13-Mar-2007 12:34
Cross version function even if you are working in php4
(instanceof is an undefined operator for php4)
function isMemberOf($classename) {
$ver = floor(phpversion());
if($ver > 4) {
$instanceof = create_function ('$obj,$classname','return $obj instanceof $classname;');
return $instanceof($this,$classname);
} else {
// Php4 uses lowercase for classname.
return is_a($this, strtolower($classname));
}
} // end function isMemberOf
soletan at toxa dot de
03-Mar-2007 04:04
Please note: != is a separate operator with separate semantics. Thinking about language grammar it's kind of ridicilous to negate an operator. Of course, it's possible to negate the result of a function (like is_a()), since it isn't negating the function itself or its semantics.
instanceof is a binary operator, and so used in binary terms like this
terma instanceof termb
while ! (negation) is a unary operator and so may be applied to a single term like this
!term
And a term never consists of an operator, only! There is no such construct in any language (please correct me!). However, instanceof doesn't finally support nested terms in every operand position ("terma" or "termb" above) as negation does:
!!!!!!!!!!!!!!term == term
So back again, did you ever write
a !!!!!!!!!!!!= b
to test equivalence?
mikael dot knutsson at gmail dot com
05-Dec-2006 08:34
I can confirm what thisbizness at gmail dot com said just below in PHP 5.2, furthermore, people looking to use this as a "if $a is not instance of A" for error throwing purposes or other, just type it like this:
<?php
if( !$a instanceof A ) {
throw new Exception( '$a is not instance of A.' );
}
?>
This also works if $a is not an object, or not even set (you will get an E_NOTICE if it isn't set though).
A note worth making is that if you are unsure of if class A is present when making this comparison, and you don't want to trigger the __autoload() magic method, scroll down for examples of how to get around this.
I was unsure about it at first since most other operators have their own negative (like !=) or they are/can be used as function calls (like !is_a()) but it is this simple. Hope it helps someone.
Until again!
archanglmr at yahoo dot com
17-Feb-2005 06:37
Negated instanceof doesn't seem to be documented. When I read instanceof I think of it as a compairson operator (which I suppose it's not).
<?php
class A {}
class X {}
//parse error from !
if (new X !instanceof A) {
throw new Exception('X is not an A');
}
//proper way to negate instanceof ?
if (!(new X instanceof A)) {
throw new Exception('X is not an A');
}
?>
d dot schneider at 24you dot de
18-Dec-2004 12:42
use this for cross-version development...
<?php
function is_instance_of($IIO_INSTANCE, $IIO_CLASS){
if(floor(phpversion()) > 4){
if($IIO_INSTANCE instanceof $IIO_CLASS){
return true;
}
else{
return false;
}
}
elseif(floor(phpversion()) > 3){
return is_a($IIO_INSTANCE, $IIO_CLASS);
}
else{
return false;
}
}
?>