Edit report at http://bugs.php.net/bug.php?id=52318&edit=1
ID: 52318
Comment by: bastard dot internets at gmail dot com
Reported by: brendel at krumedia dot de
Summary: Weak references for PHP
Status: Open
Type: Feature/Change Request
Package: Scripting Engine problem
PHP Version: Irrelevant
Block user comment: N
New Comment:
brendel at krumedia dot de - Good call: "$user now contains a new user
object"
When looking at it from a security perspective, I do believe you just
killed all my arguments against. Not because you've proven it
impossible, but because unless the developer explicitly wants that
functionality, their code will have a thousand holes.
Previous Comments:
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[2010-08-09 08:21:48] brendel at krumedia dot de
Hi bastard dot internets at gmail dot com,
see how variable references are no solution:
<?php
$repository = new SplWeakArrayValues();
$user = $dbTable->getUserById(1);
$repository[$user->id] = $user;
// Now two variables hold object references to one user object
$user = new User();
// $user now contains a new user object and the old one should have
// been removed from the repository. This time i do not assign null
// but another (transient) user object.
// count($repository) should equal 0.
?>
------------------------------------------------------------------------
[2010-08-09 08:08:26] bastard dot internets at gmail dot com
brendel at krumedia dot de - You got me at "Also count($repository)
should equal 0"
As I said earlier, "Registry::$Collection[$a->id] = null;" will set all
variables referring to this object handle to null globally. However,
count(Registry::$Collection) is still 1.
I'd still argue this is possible using existing language features.
However, it means juggling so many references, forced implementing
spaghetti code to get a solution, and a single missing "&" symbol
anywhere leading to hours of debugging. And, I just found myself
needing just such a solution.
So, I'd have to vote for a built-in interface or class like you
describe.
------------------------------------------------------------------------
[2010-08-03 16:43:39] brendel at krumedia dot de
Sample code use case:
<?php
$repository = new SplWeakArrayValues(); // assume it implements
// ArrayAccess and others
$user = $this->userObjectFromSomewhere();
$repository[$user->id] = $user;
// Now two variables hold object references to one user object
$user = null;
// Since $repository is weak, the destructor of the class of $user
should have been called now
// Also count($repository) should equal 0
?>
------------------------------------------------------------------------
[2010-08-03 16:32:36] brendel at krumedia dot de
bastard dot internets at gmail dot com, please see the constructor
parameter "weakKeys" of
http://livedocs.adobe.com/flex/3/langref/flash/utils/Dictionary.html to
get an idea. This is not about variable references.
------------------------------------------------------------------------
[2010-07-30 20:43:47] bastard dot internets at gmail dot com
brendel at krumedia dot de - I was confused by your description,
interpreting your example as describing a problem where you still need
access to data within repository objects that were unexpectedly emptied,
while your reference to weak references could mean this is actually
expected and desired behavior.
Which was why I brought up a dual solution to get mostly to that point
by using an already existing feature. For example:
<?php
class Registry
{
public static $Collection = array();
static function &Enlist($obj)
{
$obj->id = count(self::$Collection);
self::$Collection[$obj->id] =& $obj;
return $obj;
}
}
// Both $a and Registry::$Collection[$a->id] will show same object
$a =& Registry::Enlist(new stdClass);
// "Global Free"
Registry::$Collection[$a->id] = null; // or $a = null; for same effect
?>
This should free the object, even though I think it means you still have
a 3-ref_count 'null' valued zval out there. But, in order to work
consistently for a certain object, it requires you to always assign your
working variables this way everywhere, and set one of them to "= null"
to truly free the object. Otherwise, unsetting one will leave all
others intact - if that's what you want.
I was thinking you were describing a language enhancement which should
automatically handle all that. Perhaps something simply like
"unset($this)" instead to enforce virtual global freeing.
Hopefully this isn't a red herring. I'm more or less new to alternative
reference types, so I may be misunderstanding how you want this to
apply. As far as I can tell, "Registry" above can be made to somewhat
act like a combination of a "WeakHashMap" and a reference list. Can you
add a code example to show how your idea can be implemented?
------------------------------------------------------------------------
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