The PHP manual contains the following note about 'array_walk()':

   Note: 
   If func needs to be working with the actual values of the array, specify 
	that the first parameter of func should be passed by reference. Then any 
	changes made to those elements will be made in the array itself. 

So if you want to let 'array_walk()' pass the third parameter by reference, 
you're inclined to specify that the third parameter of func should be passed by 
reference.  In the example underneath, the notation '&$userData' is used to 
specify so:

   function PrepareBowl($value, $key, &$userData) {
     print 'Mixed so far... ' . ($userData .= "$value ") . "<br>\n";
   }
 
   $ingredients = array('peach', 'cherry', 'alchohol');
   $bowl = '';
   array_walk($ingredients, 'PrepareBowl', $bowl);
   print "Bowl: $bowl";

This doesn't work however; '$assembly' will not be passed by reference and the 
output will be an empty 'bowl':

   Mixed so far... peach 
   Mixed so far... peach cherry 
   Mixed so far... peach cherry alchohol 
   Bowl: 

Only when you use the '&' notation within 'array_walk()' to specify that the 
third parameter should be passed by reference:

   array_walk($ingredients, 'PrepareBowl', &$bowl);

the output will be as expected:

   Mixed so far... peach 
   Mixed so far... peach cherry 
   Mixed so far... peach cherry alchohol 
   Bowl: peach cherry alchohol 

but, using the recommended php.ini setting 'allow_call_time_pass_reference=Off',
you'll receive the warning:

   Warning: Call-time pass-by-reference has been deprecated - argument
	passed by value; If you would like to pass it by reference, modify the 
	declaration of array_walk(). If you would like to enable call-time 
	pass-by-reference, you can set allow_call_time_pass_reference to true in 
	your INI file. However, future versions may not support this any longer.

This looks the same like bug 4116 (http://bugs.php.net/bug.php?id=4116), posted Apr 12, 2000.  Although this bug is closed with a reply that it works like the 
replier think it should work, this doesn't seem logic to me because the first 
parameter *is* passed by reference without specifying; try:

   array_walk(array('peach', 'cherry', 'alchohol'), 'PrepareBowl', &$bowl);

and you'll receive:

   Fatal error: Only variables can be passed by reference ...

Furthermore, I can't see much use of passing a third variable to 'array_walk()'
by value, modify it by passing it to func by reference ... without receiving 
back the modified variable.

Would it be a suggestion to let 'array_walk()' receive the third parameter by 
reference if specified so in the receiving func?  This would be in line with
the behaviour of the first parameter to func.


Freddy Vulto