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[2004-08-18 16:31 UTC] hans at velum dot net
Description:
------------
[pasted from messages on internals@ list]
I like the new $obj instanceof ClassName way of checking class / interface types, .... but this method does have one major drawback compared to the old is_a() approach:
The class must be loaded in order to perform an instanceof check!
There are many situations where you do not want to have to load every class to see whether a returned object is a class of that type. In particular for driver classes, the current model requires loading *every* possible driver in order to check to see which type of class was returned.
is_a() works great, but has been deprecated and is now generating E_STRICT errors.
Reproduce code:
---------------
[conributed by Sean Coates on internals@ list]
<?php
class Foo {}
$foo = unserialize('O:3:"Foo":0:{}');
echo '$foo is_a Foo? '. (is_a($foo, 'Foo') ? 'yes' : 'no') ."\n";
echo '$foo instanceof Foo? '. ($foo instanceof Foo ? 'yes' : 'no') ."\n";
?>
---- and ----
<?php
//class Foo {}
$foo = unserialize('O:3:"Foo":0:{}');
echo '$foo is_a Foo? '. (is_a($foo, 'Foo') ? 'yes' : 'no') ."\n";
echo '$foo instanceof Foo? '. ($foo instanceof Foo ? 'yes' : 'no') ."\n";
?>
Expected result:
----------------
$foo is_a Foo? yes
$foo instanceof Foo? yes
---- and ----
$foo is_a Foo? no
$foo instanceof Foo? no
Actual result:
--------------
$foo is_a Foo? yes
$foo instanceof Foo? yes
---- and ----
$foo is_a Foo? no
Fatal error: Class 'Foo' not found in
/home/sean/phpdoc/scripts/tmp/is_a.php on line 8
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Last updated: Tue Aug 26 07:00:02 2025 UTC |
Can't reproduce: marcus@frodo /usr/src/PHP_5_0 $ php -r 'function __autoload($name) { var_dump($name); } $x = NULL; var_dump($x instanceof test);' make: `sapi/cli/php' is up to date. string(4) "test" Fatal error: Class 'test' not found in Command line code on line 1 marcus@frodo /usr/src/PHP_5_0 $ php -r 'function __autoload($name) { var_dump($name); eval("class $name {}");} $x = NULL; var_dump($x instanceof test);' make: `sapi/cli/php' is up to date. string(4) "test" bool(false) So the problem lies in unserialize() -> other bugThe example was buggy, but the bug exists :) php5 -r 'class Foo{} $f = unserialize("O:3:\"Foo\":0:{}"); var_dump(!($foo instanceof Bar));' Bar could be a huge class, I dont want to load it just to check $f wasnt a instance of it?I'll try to summarize: there is no easy way to check if class implements some interface. This is needed, when, for example, php-application has support for loading external classes. external classes have to implement some interface. And check for this should happen BEFORE object creation. (for example, there might be a need for some specific constructor syntax). PHP 5.0 allows to do the following things: 1). $parent = get_parent_class("SomeClassName"). This would be sufficient, if plugins _extend_ some base class. that's not our case - wouldn't work for interfaces 2). if ($obj instanceof "SomeInterfaceName") {}. This would work, if we could create object before the interface check. Wouldn't work for non-existen objects 3). reflection API. it can do the thing, but overhead (both in code and in resources) is too big