PHP is_subclass_of() Function

The PHP is_subclass_of() function is used to check if the given object_or_class has the specified class as one of its parents or implements it.

Syntax

is_subclass_of(object_or_class, class, allow_string)

Parameters

`object_or_class`	`Required.` Specify a class name or an object instance. No error is generated if the class does not exist.
`class`	`Required.` Specify the class name.
`allow_string`	`Optional.` If set to false, string class name as object_or_class is not allowed. This also prevents from calling autoloader if the class does not exist.

Return Value

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

Example: is_subclass_of() example

The example below shows the usage of is_subclass_of() function.

<?php
//defining a class
class WidgetFactory {
  //codes
}

//defining a child class
class WidgetFactory_Child extends WidgetFactory {
  //codes
}

//creating new objects
$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 output of the above code will be:

Yes, $WFC is a subclass of WidgetFactory
No, $WF is not a subclass of WidgetFactory
Yes, WidgetFactory_Child is a subclass of WidgetFactory

Example: is_subclass_of() using interface example

Consider the example below where this function is used with interface.

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

//defining the class implementation of the interface
class MyClass implements MyInterface {
  public function MyFunction() {
    //codes
  }
}

//creating new object
$myObj = new MyClass();

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

//checking 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 output of the above code will be:

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

❮ PHP Classes/Objects Reference