Fwd: Re: [PHP-DEV] References - good or bad

[Chuck Hagenbuch]

Maybe someone can add a note on this to CODING_STANDARDS?

----- Forwarded message from Andi Gutmans <andi@zend.com> -----
    Date: Fri, 28 Dec 2001 18:31:23 +0200
    From: Andi Gutmans <andi@zend.com>
Reply-To: Andi Gutmans <andi@zend.com>
 Subject: Re: [PHP-DEV] References - good or bad
      To: Brian Moon <brianm@dealnews.com>, PHP Development <php-
dev@lists.php.net>

As I mentioned on the ZE2 mailing list there general rule of thumb is:
a) Objects should be passed by reference.
b) Everything else including arrays should be used by value whenever 
possible semantically.

In the ZE2 objects will join b).

Basically what this means, as long as you're not changing the data passing 
it by value will take the full advantage of reference counting.

Andi

At 10:28 AM 12/28/2001 -0600, Brian Moon wrote:
>Ok, there has been some discussion on the ZE2 list about returning
>references from functions and it has gotten me looking at references in
>general.  Phorum deals with some pretty large arrays and so far that has
>made us faster than other BB's.  I want to keep it that way.
>
>First, the question: When is it a good idea to use references for
>performance reasons?
>
>Now, some things I tried (PHP 4.0.6):
>
>     $arr=array();
>     $arr=array_pad($arr, 10000, md5(microtime()));
>
>     function test($arr){
>         $newvar=$arr;
>         return $newvar;
>     }
>
>     $newvar=test($arr);
>
>This code takes 2.6MB of ram to run. Changing the function to any of these:
>
>     function test(&$arr){
>         $newvar=$arr;
>         return $newvar;
>     }
>
>     function test(&$arr){
>         $newvar=&$arr;
>         return $newvar;
>     }
>
>     function test($arr){
>         $newvar=&$arr;
>         return $newvar;
>     }
>
>it now takes 4.4MB to run. That is not what I expected.
>
>Now, this function:
>
>     function test($arr){
>         foreach($arr as $key => $var){
>             $newvar[$key]=$var;
>         }
>         return $newvar;
>     }
>
>takes 4.4MB also.  I would expect that.  However, changing it to:
>
>     function test($arr){
>         foreach($arr as $key => $var){
>             $newvar[$key]=&$arr[$key];
>         }
>         return $newvar;
>     }
>
>It now takes 6.8MB of ram.
>
>Last, this code:
>
>     $arr=array();
>     $arr=array_pad($arr, 10000, md5(microtime()));
>
>     $arr2=$arr;
>
>uses 2.6MB where:
>
>     $arr=array();
>     $arr=array_pad($arr, 10000, md5(microtime()));
>
>     $arr2=&$arr;
>
>uses 3.5MB.
>
>
>So, my conclusion is that references are bad in all cases on memory and
>should only be used when you have to know you are using the same exact data
>in two places, or a variable needs to be modified by a function.  If this is
>the case, shouldn't this be documented?
>
>Am I missing something?
>
>Brian Moon
>------------------------------------------
>dealnews.com, Inc.
>Makers of dealnews & dealmac
>http://dealnews.com/ | http://dealmac.com/
>
>
>
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----- End forwarded message -----


-chuck

--
Charles Hagenbuch, <chuck@horde.org>
"What was and what may be, lie, like children whose faces we cannot see, in the
arms of silence. All we ever have is here, now." - Ursula K. Le Guin