is_a

(PHP 4 >= 4.2.0, PHP 5, PHP 7)

is_a — 如果对象属于该类或该类是此对象的父类则返回 TRUE

说明

bool is_a ( object $object , string $class_name [, bool $allow_string = FALSE ] )

如果 object 是该类或该类是此对象的父类。

参数

object: The tested object
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

Returns TRUE if the object is of this class or has this class as one of its parents, FALSE otherwise.

更新日志

版本	说明
5.3.9	Added `allow_string` parameter
5.3.0	This function is no longer deprecated, and will therefore no longer throw `E_STRICT` warnings.
5.0.0	This function became deprecated in favour of the instanceof operator. Calling this function will result in an `E_STRICT` warning.

范例

Example #1 is_a() 例子

  <?php
 // define a class
 class  WidgetFactory
 {
  var  $oink  =  'moo' ;
}

 // create a new object
 $WF  = new  WidgetFactory ();

if ( is_a ( $WF ,  'WidgetFactory' )) {
  echo  "yes, \$WF is still a WidgetFactory\n" ;
}
 ?>

Example #2 在 PHP 5 中使用 instanceof 运算符

  <?php
 if ( $WF  instanceof  WidgetFactory ) {
    echo  'Yes, $WF is a WidgetFactory' ;
}
 ?>

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_subclass_of() - 如果此对象是该类的子类，则返回 TRUE

用户评论:

[#1] portugal {at} jawira {dot} com [2015-06-12 21:32:03]

I just want to point out that you can replace "is_a()" function with the "instanceof" operator, BUT you must use a variable to pass the class name string.

This will work:
<?php $object = new \stdClass(); $class_name = '\stdClass'; var_dump(is_a($object, $class_name)); // bool(true) var_dump(is_a($object, '\stdClass')); // bool(true) var_dump($object instanceof $class_name); // bool(true) ?>

While this don't:
<?php $object = new \stdClass(); var_dump($object instanceof '\stdClass'); // Parse error: syntax error, unexpected ''\stdClass'' (T_CONSTANT_ENCAPSED_STRING) ?>

[#2] eitan at mosenkis dot net [2012-01-12 13:09:26]

As of PHP 5.3.9, is_a() seems to return false when passed a string for the first argument. Instead, use is_subclass_of() and, if necessary for your purposes, also check if the two arguments are equal, since is_subclass_of('foo', 'foo') will return false, while is_a('foo', 'foo') used to return true.

[#3] Aron Budinszky [2011-09-07 04:21:55]

Be careful! Starting in PHP 5.3.7 the behavior of is_a() has changed slightly: when calling is_a() with a first argument that is not an object, __autoload() is triggered!

In practice, this means that calling is_a('23', 'User'); will trigger __autoload() on "23". Previously, the above statement simply returned 'false'.

More info can be found here:
https://bugs.php.net/bug.php?id=55475

Whether this change is considered a bug and whether it will be reverted or kept in future versions is yet to be determined, but nevertheless it is how it is, for now...

[#4] p dot scheit at zweipol dot net [2007-01-16 01:44:48]

At least in PHP 5.1.6 this works as well with Interfaces.

<?php interface test { public function A(); } class TestImplementor implements test { public function A () { print "A"; } } $testImpl = new TestImplementor(); var_dump(is_a($testImpl,'test')); ?>

will return true

[#5] cesoid at yahoo dot com [2005-10-05 19:01:04]

is_a returns TRUE for instances of children of the class.

For example:

class Animal
{}

class Dog extends Animal
{}

$test = new Dog();

In this example is_a($test, "Animal") would evaluate to TRUE as well as is_a($test, "Dog").

This seemed intuitive to me, but did not seem to be documented.