is_subclass_of

(PHP 4, PHP 5)

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

Description

bool is_subclass_of ( mixed $object , string $class_name [, bool $allow_string = TRUE ] )

Checks if the given object has the class class_name as one of its parents.

Parameters

object

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

class_name

The class name

allow_string

If this parameter set to false, string class name as object 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, belongs to a class which is a subclass of class_name, FALSE otherwise.

Changelog

Version Description
5.3.9 Added allow_string parameter
5.3.7 Added support for class_name to work with interfaces
5.0.3 You may also specify the object parameter as a string (the name of the class)

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";
}


// usable only since PHP 5.0.3
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

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User Contributed Notes 6 notes

up
2
gunniboyh at web dot de
8 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
1
nicholas at aquarionics dot com
5 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
kostyl_kostyl gav-gav mail point ru
5 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
0
Damien Bezborodov
5 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
0
jm
6 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
0
Ondra Zizka
8 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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