PHP 8.1.28 Released!

    is_subclass_of

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

    is_subclass_of — 检查对象是否继承或者实现（implement）此类

    说明

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

    检查指定的 object_or_class 是否继承或者实现（implement） class。

    参数

    object_or_class

    类名或者对象实例。如果类不存在，也不会报错。

    class

    类名

    allow_string

    如果此参数设置为 false，将不允许将字符串类名传递给 object_or_class。如果类不存在，这也可以防止调用自动加载器。

    返回值

    如果对象 object_or_class 属于 class 的子类，则返回 true，否则返回 false。

    示例

    示例 #1 is_subclass_of() 示例

    <?php
    // 定义类
    class WidgetFactory
    {
    var     $oink = 'moo';
    }

    // 定义子类
    class WidgetFactory_Child extends WidgetFactory
    {
    var     $oink = 'oink';
    }

    // 创建新对象
    $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";
    }
    ?>

    以上示例会输出：

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

    示例 #2 is_subclass_of() 使用接口示例

    <?php
    // 定义接口
    interface MyInterface
    {
    public function     MyFunction();
    }

    // 定义实现了接口的类
    class MyClass implements MyInterface
    {
    public function     MyFunction()
    {
    return     "MyClass Implements MyInterface!";
    }
    }

    // 实例化对象
    $my_object = new MyClass;

    // 自 5.3.7 起可用

    // 使用类的对象实例进行检查
    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";
    }

    // 使用字符串类名进行检查
    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";
    }
    ?>

    以上示例会输出：

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

    注释

    注意:

    如果此类不是已知类，使用此函数会使用任何已注册的 autoloader。

    参见

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    User Contributed Notes 3 notes

    up
    17
    gunniboyh at web dot de
    17 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
    5 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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