is_a

(PHP 4 >= 4.2.0, PHP 5)

is_a — Checks if the object is of this class or has this class as one of its parents

Description

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

Checks if the given object is of this class or has this class as one of its parents.

Parameters

object: The tested object
class_name: The class name
allow_string: Whether to call autoloader if the class doesn't exist.

Return Values

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

Changelog

Version	Description
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.

Examples

Example #1 is_a() example


<?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 Using the instanceof operator in PHP 5


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


What a farce, I must say. :)



PHP 5.3.9 adds an $allow_string parameter in order to handle strings being passed in, but controls the auto-loading behavior? Talk about confusing. Not sure if there's a committee discussing changes to core functions like this, but I feel that's a poor design. Don't get me wrong, I greatly appreciate the voluntary efforts of PHP developers, but this loosy-goosy approach to function prototypes is a recipe for disaster over the long term.

eitan at mosenkis dot net 12-Jan-2012 01:09


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.

Aron Budinszky 07-Sep-2011 04:21


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...

p dot scheit at zweipol dot net 16-Jan-2007 01:44


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

martin dunisch 13-Feb-2006 12:02


Workaround for older PHP-Versions:



function is_a($anObject, $aClass) {

   return get_class($anObject) == strtolower($aClass)

     or is_subclass_of($anObject, $aClass);

}

dead dot screamer at seznam dot cz 06-Feb-2006 11:44


Why I test if class `A` inherit class `B` or implements interface `C` before I create class `A`?



<?

//That isn't work:



//1. function is_A()

if(is_A('A','B'))$a=new A;

if(is_A('A','C'))$a=new A;



//2. operator instanceOf

if(A instanceOf B)$a=new A;

if(A instanceOf C)$a=new A;

?>

zabmilenko at hotmail dot com 07-Oct-2005 05:18


Lazy Instantiation using is_a() and php5





<?php





class ObjectA


{


    public function print_line($text)


    {


        print $text . "\n";


    }


}





class ObjectB


{


    public function ObjectA()


    {


        static $objecta;





        if (!is_a($objecta, 'ObjectA'))


        {


            $objecta = new ObjectA;


        }





        return $objecta;


    }


}





$obj = new ObjectB;


$obj->ObjectA()->print_line('testing, 1 2 3');





?>





In the above example, ObjectA is not instantiated until needed by ObjectB.  Then ObjectB can continually use it's creation as needed without reinstantiating it.  





There are other ways, but I like this one :-)

cesoid at yahoo dot com 05-Oct-2005 07:01


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.

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