Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:22999
Mailing-List: contact internals-help@lists.php.net; run by ezmlm
Message-ID: <445136A7.3000801@lerdorf.com>
Date: Thu, 27 Apr 2006 17:24:55 -0400
User-Agent: Thunderbird 3.0a1 (Macintosh/20060413)
MIME-Version: 1.0
To: Brion Vibber <brion@pobox.com>
CC: Brian Moon <brianm@dealnews.com>, internals@lists.php.net
References: <444FF5CD.2010805@dealnews.com> <444FF716.6070201@lerdorf.com> <44512305.90207@pobox.com>
In-Reply-To: <44512305.90207@pobox.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Subject: Re: [PHP-DEV] Passing functions to function by reference
From: rasmus@lerdorf.com (Rasmus Lerdorf)

Brion Vibber wrote:
> Rasmus Lerdorf wrote:
>>> PHP 5.0 broke this.  There was a fatal error on the array_shift that
>>> only variables could be passed by reference.  There was a good
>>> argument for it.  So, we started migrating our code.
>>>
>>> Well, seems this works in 5.1.  So, my question is, was it an
>>> intentional "fix" or will this break again and we need to continue to
>>> watch for this?
>> In 5.1 this now throws an E_STRICT instead of a warning.  It is still a
>> bad idea to pass a tempvar by reference, so yes, you should strive to
>> write E_STRICT clean code.
> 
> Stupid question: why is it a bad idea?

Well, the original reason was because it caused weird and wonderful 
memory corruption in PHP 4.3.x, so if your code is ever going to run on 
that version you really need to not do that.

It also tends to be a bug.  Most functions that take an argument by 
reference do so for a reason.  There are of course exceptions to this as 
you have pointed out and in those cases assuming your code will never 
run under PHP 4.3.x it can be valid.  I would still say it is a better 
idea to something like:

   func_taking_reference($quiet=some_func());  // throw away ref mod

and document the fact that you are intentionally throwing away the 
reference modification that func_taking_reference is making.  That way 
you avoid the E_STRICT and make it very clear what you are doing.

You could make the same argument for using undefined variables.  Often 
that indicates a bug so the E_NOTICE can be really helpful, but other 
times it just gets in the way.  I don't think that means we should do 
away with the E_NOTICE on that and I also don't think it means you 
shouldn't try to write E_NOTICE clean code.

-Rasmus