[Documentation bug] theme function doesn't allow variables to be passed by reference in php4

Issue status update for 
http://drupal.org/node/58714
Post a follow up: 
http://drupal.org/project/comments/add/58714

-Project:      Drupal
+Project:      Documentation
Version:      <none>
-Component:    theme system
+Component:    Developer Guide
Category:     bug reports
Priority:     normal
Assigned to:  Anonymous
Reported by:  simon rawson
Updated by:   pwolanin
-Status:       by design
+Status:       active

I certainly agree that it's not a Drupal problem, except that the theme
function documentation should mention it.  I came across this when
looking at a theme function in organic groups that is called under
og_nodeapi (hook_nodeapi).  The API for hook_nodeapi /does/ specify
passing by reference, and so I was trying to carry this
pass-by-reference down to the function that actually made a change to
the node.




pwolanin



Previous comments:
------------------------------------------------------------------------

Fri, 14 Apr 2006 09:34:19 +0000 : simon rawson

The theme function uses the func_get_args function.  In php5 this gets
the arguments by reference.  In php4 this gets a copy of the arguments.
So if I want to pass a variable by reference to a theme function and
I'm using php4... I can't, because it gets a copy of the original
variable.


e.g. calling theme('my_theme_func',$variable)


and defining  function theme_my_theme_func(&$passed) { 


will mean that changes which are made to $passed /will/ affect
$variable in php5 but /won't/ in php4.


Not sure what the design is supposed to be.  My guess is that you don't
want to be able to alter original variables in theme functions.  But it
seems unsatisfactory that the functions behave differently in php4  and
php5.




------------------------------------------------------------------------

Wed, 03 May 2006 00:24:28 +0000 : pwolanin

Yes, I just stumbled upon the same behavior.  I've been looking into the
way the organic groups module themes nodes and have been perplexed by
the fact that passing the node object by reference does not work as I
expect. 


This version works to modify the node body:


<?php
function og_view_group(&$node, $teaser = FALSE, $page = FALSE) {    
  $node=theme('og_view', &$node, $teaser, $page);
  return;
}


function theme_og_view(&$node, $teaser, $page){
  $node->body .= '<p>helllo world</p>';
  return node;
}
?>
This version doesn't:


<?php
function og_view_group(&$node, $teaser = FALSE, $page = FALSE) {    
  theme('og_view', &$node, $teaser, $page);
  return;
}


function theme_og_view(&$node, $teaser, $page){
  $node->body .= '<p>helllo world</p>';
  return;
}
?>
In the first case, passing in the pointer to $node /is/ enough that all
the contents of $node are present in theme_og_view() and can be modified
and returned.   It's very odd if different versions of PHP are so
divergent.   It /should/ work.  The webserver is running PHP Version
4.3.10.


Looking at the theme() function documentation:
http://drupaldocs.org/api/head/function/theme
doesn't suggest anything to me.




------------------------------------------------------------------------

Wed, 03 May 2006 01:20:33 +0000 : pwolanin

some comments about this issue are posted here:


http://us3.php.net/manual/en/function.func-get-arg.php
http://us3.php.net/manual/en/function.func-get-args.php


It also seems the same value/reference problem applies to
call-user-func-array():


http://us3.php.net/manual/en/function.call-user-func-array.php
http://us3.php.net/manual/en/function.call-user-func.php


It seems there may be ways around this problem, though I haven't gotten
anything to work yet.  At the least, I'd think this should be mentioned
in the theme() function documentation.




------------------------------------------------------------------------

Sat, 06 May 2006 08:57:06 +0000 : Heine

I don't think theme functions should go about and modify the data that's
passed to them. IMO they should only generate output.




------------------------------------------------------------------------

Sat, 06 May 2006 13:16:26 +0000 : Crell

Agreed.  If your theme function needs to modify something, then you're
doing something wrong.  The only reason why you'd want to then would be
for performance reasons if you're passing in a particularly large data
structure.  It's too bad PHP doesn't have a const keyword for such
things. :-)


You are correct about there being by-ref issues in PHP 4's
call_user_func() family of functions.  That's not a Drupal issue,
though, but a PHP 4 issue.  The fix is to upgrade to PHP 5, where
objects are always passed by reference, period.  That's one of the
reasons why PHP 5 does that.  


Marking this by design, since Drupal is behaving exactly as a PHP app
is expected to behave under PHP 4.  That the rules changed for PHP 5 is
PHP's problem, not Drupal's. :-)




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