Type Operators

PHP has a single type operator: instanceof. instanceof is used to determine whether a given object is of a specified object class.

The instanceof operator was introduced in PHP 5. Before this time is_a() was used but is_a() has since been deprecated in favor of instanceof.

<?php
class A { }
class B { }

$thing = new A;

if ($thing instanceof A) {
    echo 'A';
}
if ($thing instanceof B) {
    echo 'B';
}
?>

As $thing is an object of type A, but not B, only the block dependent on the A type will be executed:

See also get_class() and is_a().

User Contributed Notes
Type Operators

archanglmr at yahoo dot com
17-Feb-2005 08:37


Negated instanceof doesn't seem to be documented. When I read instanceof I think of it as a compairson operator (which I suppose it's not).



<?php

class A {}

class X {}



//parse error from !

if (new X !instanceof A) {

    throw new Exception('X is not an A');

}

//proper way to negate instanceof ?

if (!(new X instanceof A)) {

    throw new Exception('X is not an A');

}

?>

d dot schneider at 24you dot de
18-Dec-2004 02:42


use this for cross-version development...



<?php



function is_instance_of($IIO_INSTANCE, $IIO_CLASS){

    if(floor(phpversion()) > 4){

        if($IIO_INSTANCE instanceof $IIO_CLASS){

            return true;

            }

        else{

            return false;

            }

        }

    elseif(floor(phpversion()) > 3){

        return is_a($IIO_INSTANCE, $IIO_CLASS);

        }

    else{

        return false;

        }

    }



?>

glen at arkadia-systems dot com
11-Sep-2004 12:00


If you are updating code to replace 'is_a()' with the PHP5 compliant

'instanceof' operator, you may find it necessary to change the basic

architecture of your code to make this work.



'instanceof' will throw a fatal error if the object being checked for does not

exist.



'is_a()' will simply return false under this condition.



In the example below, 'is_a()' would effectively detect the need to create an

instance of class 'A', but in this case 'instanceof' will crash your program

with a fatal error.



<?php

// define classes



// Commenting this class will cause an error when 'instanceof' looks for 'A'

// class A {}



class B {}



// create a new object

// $thing = new A();

$thing = new B();



if (is_a($thing, 'A')) {

    echo 'Yes, $thing is_a A<br>';

} else {

    echo 'No, $thing is not is_a A<br>';

}



if ($thing instanceof A) {

    echo 'Yes, $thing is an instaceof A<br>';

} else {

    echo 'No, $thing is not an instaceof A<br>';

}



?>



>>> Output:

No, $thing is not is_a A

Fatal error: Class 'A' not found in is_a-instanceof.php on line 19

>>>



A suitable work-around for this situation is to check for the existence of the

class before performing the 'instanceof' comparison:



<?php



/* ... */



if (class_exists('A') && $thing instanceof A) {

    echo 'Yes, $thing is an instaceof A<br>';

} else {

    echo 'No, $thing is not an instaceof A<br>';

}



?>

zimba dot spam at gmail dot com
10-Sep-2004 02:17


instanceof cannot use a string for the comparison like is_a.

Instead, you can use a class instance (not documented)

Example :

<?

$x = new myClass();

$y = new myClass();



echo is_a($x, get_class($y));   // Returns true/1



echo $x instanceof get_class($y);   // Doesn't work, instead use :



echo $x instanceof $y;

?>



Cheers,

zimba

"Leo Pedretti" <lpedretti at suserver dot com>
24-Aug-2004 10:59


The instanceof operator also checks the interface tree. For example, the following code:



<?



interface Human {

    public function say($var);

    public function gender();

}



class man implements Human {

    public function say($var) {

    "Oh yeah, $var\n"

    }



    public function gender() {

    return "male";

    }

}



class woman implements Human {

    public function say($var) {

    "Oh dear, $var\n"

    }



    public function gender() {

    return "female";

    }

}



$m = new man;

$w = new woman;

if ($p instanceof Human) {

    print "\$p is Human.\n";

} else {

    print "\$p is not Human.\n";

}

print "\$m is of gender ".$m->gender()."\n";



if ($w instanceof Human) {

    print "\$w is Human.\n";

} else {

    print "\$w is not Human.\n";

}

print "\$w is of gender ".$w->gender()."\n";

?>



Will produce the output



$m is Human.

$m is of gender male

$w is Human.

$w is of gender female

Jesse Scott (scotje at wwc dot edu)
06-Jul-2004 08:52


Since it's not stated authoritatively here, I'll add that instanceof *does* check all the way up the inheritence tree.



So in this code:



<?php

    class A

    {

        var $someProp;

    }

    

    class B extends A

    {

        function showProp()

        {

            echo $someProp;

        }

    }

    

    $obj1 = new B;



    if ($obj1 instanceof A)

        echo "Instanceof checks inheritence tree!";

    else

        echo "Instanceof does not check inheritence tree!";

?>



The first branch of the if/else block is executed since ($obj1 instanceof A) evaulates to TRUE.