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is_subclass_of

(PHP 4, PHP 5, PHP 7, PHP 8)

is_subclass_ofChecks if the object has this class as one of its parents or implements it

Description

is_subclass_of(mixed $object_or_class, string $class, bool $allow_string = true): bool

Checks if the given object_or_class has the class class as one of its parents or implements it.

Parameters

object_or_class

A class name or an object instance. No error is generated if the class does not exist.

class

The class name

allow_string

If this parameter set to false, string class name as object_or_class is not allowed. This also prevents from calling autoloader if the class doesn't exist.

Return Values

This function returns true if the object object_or_class, belongs to a class which is a subclass of class, false otherwise.

Examples

Example #1 is_subclass_of() example

<?php
// define a class
class WidgetFactory
{
  var 
$oink 'moo';
}

// define a child class
class WidgetFactory_Child extends WidgetFactory
{
  var 
$oink 'oink';
}

// create a new object
$WF = new WidgetFactory();
$WFC = new WidgetFactory_Child();

if (
is_subclass_of($WFC'WidgetFactory')) {
  echo 
"yes, \$WFC is a subclass of WidgetFactory\n";
} else {
  echo 
"no, \$WFC is not a subclass of WidgetFactory\n";
}


if (
is_subclass_of($WF'WidgetFactory')) {
  echo 
"yes, \$WF is a subclass of WidgetFactory\n";
} else {
  echo 
"no, \$WF is not a subclass of WidgetFactory\n";
}


if (
is_subclass_of('WidgetFactory_Child''WidgetFactory')) {
  echo 
"yes, WidgetFactory_Child is a subclass of WidgetFactory\n";
} else {
  echo 
"no, WidgetFactory_Child is not a subclass of WidgetFactory\n";
}
?>

The above example will output:

yes, $WFC is a subclass of WidgetFactory
no, $WF is not a subclass of WidgetFactory
yes, WidgetFactory_Child is a subclass of WidgetFactory

Example #2 is_subclass_of() using interface example

<?php
// Define the Interface
interface MyInterface
{
  public function 
MyFunction();
}

// Define the class implementation of the interface
class MyClass implements MyInterface
{
  public function 
MyFunction()
  {
    return 
"MyClass Implements MyInterface!";
  }
}

// Instantiate the object
$my_object = new MyClass;

// Works since 5.3.7

// Test using the object instance of the class
if (is_subclass_of($my_object'MyInterface')) {
  echo 
"Yes, \$my_object is a subclass of MyInterface\n";
} else {
  echo 
"No, \$my_object is not a subclass of MyInterface\n";
}

// Test using a string of the class name
if (is_subclass_of('MyClass''MyInterface')) {
  echo 
"Yes, MyClass is a subclass of MyInterface\n";
} else {
  echo 
"No, MyClass is not a subclass of MyInterface\n";
}
?>

The above example will output:

Yes, $my_object is a subclass of MyInterface
Yes, MyClass is a subclass of MyInterface

Notes

Note:

Using this function will use any registered autoloaders if the class is not already known.

See Also

  • get_class() - Returns the name of the class of an object
  • get_parent_class() - Retrieves the parent class name for object or class
  • is_a() - Checks if the object is of this class or has this class as one of its parents
  • class_parents() - Return the parent classes of the given class

add a note add a note

User Contributed Notes 7 notes

up
14
gunniboyh at web dot de
15 years ago
is_subclass_of() works also with classes between the class of obj and the superclass.

example:
<?php
class A {};
class
B extends A {};
class
C extends B {};

$foo=new C();
echo ((
is_subclass_of($foo,'A')) ? 'true' : 'false');
?>

echoes 'true' .
up
9
nicholas at aquarionics dot com
12 years ago
This might be useful to someone, so:

If you're using Autoload, you should be aware that this will attempt to autoload $classname if it isn't already loaded. I discovered this when I had something using is_subclass_of inside an error thrown by autoload, which then recursed until it ran out of memory.
up
1
alan at jynxy.net
3 years ago
The $allow_string parameter is not very clearly documented. When true, it simply allows the first parameter to be the name of a class, instead of an object whose class we are interested in.

Some usage examples:

class parent_class {
    // objects and methods ...
}

$possible_child_object = new possible_child_class(); // might be an extension of parent_class

$result = is_subclass_of($possible_child_object, 'parent_class'); //  valid
$result = is_subclass_of($possible_child_object, 'parent_class', false); //  valid
$result = is_subclass_of('possible_child_class', 'parent_class', true); // valid
$result = is_subclass_of('possible_child_class', 'parent_class', false); // not valid
up
0
Damien Bezborodov
12 years ago
If you need something similar to is_subclass_of() to determine if a class implements an interface before instantiating it, use reflection:

<?php

interface A_Interface {}
class
A implements A_Interface {}

$reflectionA = new ReflectionClass('A');
var_dump(
   
$reflectionA->implementsInterface('A_Interface')
);

?>
bool(true)
up
-2
jm
12 years ago
It would appear that is_subclass_of is case insensitive unlike get_class in php5.
i.e.

<?php
class fooBar {}
class
bar extends fooBar {}

assert(get_class(new fooBar()) == "fooBar");
assert(is_subclass_of(new bar(), "foobar") == true);
?>

i run across this while migrating some code from php4 to php5 and the code would only half-the-time break.
up
-5
kostyl_kostyl gav-gav mail point ru
12 years ago
<?php
interface I {
}
class
A implements I {
}
class
B extends {
}
if (
is_subclass_of('A', 'I')) {
    echo
'good<br>';
}
else {
    echo
'bad<br>';
}
if (
is_subclass_of('B', 'I')) {
    echo
'good<br>';
}
else {
    echo
'bad<br>';
}
if (
is_subclass_of('B', 'A')) {
    echo
'good<br>';
}
else {
    echo
'bad<br>';
}
?>

result:
bad <- you must to describe intermediate class B to be good
good
good
up
-6
Ondra Zizka
14 years ago
For PHP4:

<?php
/** Returns whether specified class is subclass of the other class. */
function is_subclass($sClass, $sExpectedParentClass){
    do if(
$sExpectedParentClass === $sClass ) return true;
    while(
false != ($sClass = get_parent_class($sClass)) );
    return
false;
}
// Test:
class A {} class B extends A {} class C extends B {} echo (int) is_subclass('C', 'A');
?>
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