is_subclass_of

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

is_subclass_of — 如果此对象是该类的子类，则返回 true

说明

is_subclass_of ( object $object , string $class_name ) : bool

如果对象 object 所属类是类 class_name 的子类，则返回 true，否则返回 false。

Note:

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

Example #1 is_subclass_of() 例子

<?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";
}
?>

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

object

A class name or an object instance

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.

返回值

This function returns true if the object object, belongs to a class which is a subclass of class_name, false otherwise.

范例

Example #2 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";
}
?>

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

Note:

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

User Contributed Notes

alan at jynxy.net 21-Jun-2018 06:56
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
nicholas at aquarionics dot com 17-Mar-2009 01:02
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.
Damien Bezborodov 16-Mar-2009 04:55
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)
kostyl_kostyl gav-gav mail point ru 07-Mar-2009 03:08
<?php
interface I {
}
class A implements I {
}
class B extends A  {
}
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
jm 30-Sep-2008 08:02
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.
Ondra Zizka 13-Oct-2006 05:31
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');
?>
gunniboyh at web dot de 20-May-2006 06:16
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' .
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