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Date: Thu, 08 Jul 2004 00:22:26 +0300
To: "Rob Richards" <rrichards@ctindustries.net>
Cc: "Marcus Boerger" <helly@php.net>,<internals@lists.php.net>
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Subject: Re: [PHP-DEV] extended objects with read_property and 
  get_property_ptr_ptr
From: zeev@zend.com (Zeev Suraski)

At 22:27 07/07/2004, Rob Richards wrote:
>  From: Zeev Suraski
>
> > It's not a correct fix :I  get_ptr_ptr must return the address of an
> > allocated zval *, one which can later be separated,
> > etc.  T(result->u.var).var.ptr doesn't fall into that category - it can be
> > gone in the next opcode...
> >
> > The only safe way to return a zval ** is for the underlying object model
>to
> > implement get_ptr_ptr...
>
>What is this then a catch 22? If get_ptr_ptr is implemented and returns an
>allocated zval **, then you can run into problems using pre/post_incdec if
>you need to rely on the read_property and write_property of those functions,
>which are only hit if you return NULL from get_ptr_ptr, which then brings
>one back full circle to getting an error in
>zend_fetch_property_address_inner when returning a NULL zval **.

I guess so, yes, it's a bit of a catch 22.  get_ptr_ptr is used in very 
rare cases - assign-by-reference is one of them, and pre/post incdec is 
another.  The assumption is that if you provide get_ptr_ptr, the engine can 
perform incdec on its own, without calling read_/write_property.  It's 
basically an optimization for standard PHP objects.  So if you want to 
support assign-by-ref and also override incdec, I guess it cannot be done 
right now.

The correct solution, I think, would be adding a boolean function (or even 
just a bit) to the handlers structure, that instructs the engine whether it 
should use get_ptr_ptr for incdec or not, since it's an 
optimization.  Maybe we can just check whether we're dealing with PHP 
objects and perform this optimization only then.  I need to look into it.

Zeev