is_subclass_of()

(PHP 4, PHP 5, PHP 7)

如果此对象是该类的子类，则返回TRUE

说明

如果对象$object所属类是类$class_name的子类，则返回TRUE，否则返回FALSE。

自 PHP 5.0.3 起也可以用一个字符串来指定$object参数（类名）。

Example #1is_subclass_of()例子

以上例程会输出：

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

参见get_class()、get_parent_class()和is_a()。

参数

A class name or an object instance

The class name

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

返回值

This function returnsTRUEif the object$object, belongs to a class which is a subclass of$class_name,FALSEotherwise.

更新日志

范例

Example #2is_subclass_of()example

以上例程会输出：

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

注释

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

• get_class() 返回对象的类名
• get_parent_class() 返回对象或类的父类名
• is_a() 如果对象属于该类或该类是此对象的父类则返回 TRUE
• class_parents() 返回指定类的父类。

is_subclass_of() works also with classes between the class of obj and the superclass.
example:

echoes 'true' .

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.

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

It would appear that is_subclass_of is case insensitive unlike get_class in php5.
i.e.

i run across this while migrating some code from php4 to php5 and the code would only half-the-time break.

If you need something similar to is_subclass_of() to determine if a class implements an interface before instantiating it, use reflection:

bool(true)

For PHP4: 

result:
bad 

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