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

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 #1is_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$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

<?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

• 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:
<?php
class A {};
class B extends A {};
class C extends B {};
$foo=new C();
echo ((is_subclass_of($foo,'A')) ? 'true' : 'false');
?>
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.
<?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.

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)

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');
?>

<?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