is_subclass_of

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

    is_subclass_of — Checks 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 whether the object is of a given type or subtype
    • class_parents() - Return the parent classes of the given class

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    User Contributed Notes 3 notes

    up
    17
    gunniboyh at web dot de
    18 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
    10
    nicholas at aquarionics dot com
    15 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
    2
    alan at jynxy.net
    6 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
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