类型运算符

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julien plee using g mail dot com
21-Jul-2007 01:56


Response to vinyanov at poczta dot onet dot pl:



You mentionned "the instanceof operator will not accept a string as its first operand". However, this behavior is absolutely right and therefore, you're misleading the meaning of an instance.



<?php 'ClassA' instanceof 'ClassB'; ?> means "the class named ClassA is an instance of the class named ClassB". This is a nonsense sentence because when you instanciate a class, you ALWAYS obtain an object. Consequently, you only can ask if an object is an instance of a class.



I believe asking if "a ClassA belongs to a ClassB" (or "a ClassA is a class of (type) ClassB") or even "a ClassA is (also) a ClassB" is more appropriate. But the first is not implemented and the second only works with objects, just like the instanceof operator.



Plus, I just have tested your code and it does absolutely NOT do the same as instanceof (extended to classes)! I can't advise anyone to reuse it. The use of <?php is_instance_of ($instanceOfA, 'ClassB'); ?> raises a warning "include_once(Object id #1.php) " when using __autoload (trying to look for $instanceOfA as if it was a class name).



Finally, here is a fast (to me) sample function code to verify if an object or class:



<?php

function kind_of (&$object_or_class, $class)

{

    return is_object ($object_or_class) ? 

        $object_or_class instanceof $class

        : (is_subclass_of ($object_or_class $class)

           || strtolower ($object_or_class) == strtolower ($class));

} 

?>

jphaas at gmail dot com
11-Jul-2007 05:50


Posting this so the word typeof appears on this page, so that this page will show up when you google 'php typeof'.  ...yeah, former Java user.

vinyanov at poczta dot onet dot pl
19-Jun-2007 10:57


Unfortunately the instanceof operator will not accept a string as its first operand. So I wrote this function. It does exactly the same (ie, successively checks identicalness, inheritance and implementation). Just on strings.



<?php



function is_instance_of($sub, $super)

{

    $sub = (string)$sub;

    $super = is_object($super) ? get_class($super) : (string)$super;

    

    switch(true)

    {

        case $sub === $super; // well ... conformity

        case is_subclass_of($sub, $super):

        case in_array($super, class_implements($sub)):

            return true;

        default:

            return false;

    }

}



// testing



interface X {}

class A {}

class B extends A {}

class C extends B {}

class D implements X {}



$i = 'is_instance_of';

var_dump($i('A', 'A'), $i('B', 'A'), $i('C', 'A'), $i('D', 'X'));



?>

jeanyves dot terrien at orange-ftgroup dot com
13-Mar-2007 08:34


Cross version function even if you are working in php4

(instanceof is an undefined operator for php4)



   function isMemberOf($classename) {

      $ver = floor(phpversion());

      if($ver > 4) {

         $instanceof = create_function ('$obj,$classname','return $obj instanceof $classname;');

         return $instanceof($this,$classname);

      } else {

         // Php4 uses lowercase for classname.

         return is_a($this, strtolower($classname));

      }

   } // end function isMemberOf

soletan at toxa dot de
03-Mar-2007 12:04


Please note: != is a separate operator with separate semantics. Thinking about language grammar it's kind of ridicilous to negate an operator. Of course, it's possible to negate the result of a function (like is_a()), since it isn't negating the function itself or its semantics.



instanceof is a binary operator, and so used in binary terms like this



terma instanceof termb



while ! (negation) is a unary operator and so may be applied to a single term like this



!term



And a term never consists of an operator, only! There is no such construct in any language (please correct me!). However, instanceof doesn't finally support nested terms in every operand position ("terma" or "termb" above) as negation does:



!!!!!!!!!!!!!!term == term



So back again, did you ever write



a !!!!!!!!!!!!= b



to test equivalence?

mikael dot knutsson at gmail dot com
06-Dec-2006 04:34


I can confirm what thisbizness at gmail dot com said just below in PHP 5.2, furthermore, people looking to use this as a "if $a is not instance of A" for error throwing purposes or other, just type it like this: 

<?php

if( !$a instanceof A ) {

    throw new Exception( '$a is not instance of A.' );

}

?>



This also works if $a is not an object, or not even set (you will get an E_NOTICE if it isn't set though).

A note worth making is that if you are unsure of if class A is present when making this comparison, and you don't want to trigger the __autoload() magic method, scroll down for examples of how to get around this.



I was unsure about it at first since most other operators have their own negative (like !=) or they are/can be used as function calls (like !is_a()) but it is this simple. Hope it helps someone.



Until again!

archanglmr at yahoo dot com
18-Feb-2005 02:37


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 08:42


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;

        }

    }



?>

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