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Date: Wed, 7 Dec 2005 23:15:55 -0500
To: internals@lists.php.net
Subject: Re: [PHP-DEV] $this->this and avoiding circular references
From: apinstein@mac.com (Alan Pinstein)

My question is closely related to the one discussed on this php-dev  
thread:

http://thread.gmane.org/gmane.comp.php.devel/32430

Someone just sent me this link, which I didn't find myself when  
searching b/c the searches strip "this" from queries.

Anyway, the question is related to reference counting of objects when  
assigned by value and by reference. It is a very important OO topic  
as the ability to have a non-ref-counted object "handle" is basically  
requisite to prevent circular reference deadlocks in OO projects.

If the way I have proposed doesn't work, then what is the official  
way? And there *must* be one, otherwise, there is no way to avoid  
huge memory leaks (deferred release until end-of-script, I know, but  
it's a memory leak in the context of the script while it's running)  
with this kind of OO arrangement.

In particular what confuses me is, why does, at least on PHP 5.0.4,  
this:

$obj = &$this->this;	// doesn't seem to increment the refcount of the  
object

behaves differently from:

$obj = &$this;		// does seem to increment the refcount to the object

References to $this should not only be valid, but are pretty much  
required for proper memory management in an OO environment, unless  
there is some other sanctioned way to get a weak reference... now I  
am not sure if the fact that making a & reference to an object  
doesn't increment the refcount is intended behavior, or an unintended  
side effect that may change. This is one of my major questions.

Also, in regards to the thread linked above, I'd say that making & 
$this an error is not desirable behavior; but maybe changing the  
value of $this should be (ie in C terms, $this is not an lvalue).  
Although, in C++/Obj-C you *can* even change this/self... in fact  
it's common in Obj-C:

- (id) init
{
     if (self = [super init]) { /* etc */ }
     return self;
}

Of course PHP is not Obj-C, but it's OO and garbage collected in a  
similar way, so PHP has the same need for manipulating $this; that  
is, creating weak references.

Alan


On Dec 7, 2005, at 11:27 AM, Antony Dovgal wrote:

> On 07.12.2005 18:40, Alan Pinstein wrote:
>> Hi all-
> <skip>
>
> Please use php-general@lists.php.net for questions regarding  
> development *in* PHP.
> -- 
> Wbr, Antony Dovgal