Thank you for taking the time to write to us, but this is not
a bug. Please double-check the documentation available at
http://www.php.net/manual/ and the instructions on how to report
a bug at http://bugs.php.net/how-to-report.php

$id is modified because the original $id passed to  call_user_func() is not being passed by reference.

Hi Ilia,

your wrong, because:
$ cat test1.php
<?PHP

function nextId( &$id )
{
  $id += 1;
}

$id = 1;
echo "before call_user_func id=$id\n";
call_user_func( "nextId", &$id );
echo "after call_user_func id=$id\n";
call_user_func_array( "nextId", array( &$id ) );
echo "after call_user_func_array id=$id\n";

?>

$ php test1.php

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 call_
user_func().  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.  in /var/www/data/trevor/flexpage/test/php-bugs/test1.php on line 10
before call_user_func id=1
after call_user_func id=2
after call_user_func_array id=3

This gives the wanted result but prints out a warning.
By the way, I don't want to discus whether call_user_func is implemented as described neither it's not working as designed. I want to tell you (as php team), that the design
might be wrong.

Either, if you (as php team) don't have any plans to extend
the design (what shouldn't be to complicated), I consider you update the documentation that way, that you describe
that call_user_func will duplicate the given argument.

call_user_func is not an intelligent function (what it
could be), it's a dumb one (this is not an offending but
it is like a dumb terminal as some old unix ones).

I want to consider by this bug report to rewrite call_user_func becomes intelligent (looks what kind of
argument is required and calls that way).

Otherwise I had to open a documentation bug, because this
behaviour should be documented explicitely.

Thank you for taking the time to write to us, but this is not
a bug. Please double-check the documentation available at
http://www.php.net/manual/ and the instructions on how to report
a bug at http://bugs.php.net/how-to-report.php

I admit that the error is misleading, because it cannot tell that function was not executed directly but rather via call_user_func(). However, the actual functionality of the code is correct. The variable is not passed by reference to call_user_func(), hence making it pass a copy to nextID(). The documentation does not mention that you can pass variables by reference and that's because in this case you cannot.

Documentation says:

call_user_func

(PHP 3>= 3.0.3, PHP 4 )
call_user_func --  Call a user function given by the first parameter
Description
mixed call_user_func ( callback function [, mixed parameter [, mixed ...]])

Call a user defined function given by the function parameter. Take the following: 
 ...

I consider update the documentation by directly writing:

"This method doesn't take care about using parameters
as references as long as you specify the at calltime, which
should be enabled via php.ini even if it's deprecated, because there's no other way to call this method using
references.<br />
We consider to use call_user_func_array( func_name, array( &$param ) ) if you want to use references."

This bug has been fixed in the documentation's XML sources. Since the
online and downloadable versions of the documentation need some time
to get updated, we would like to ask you to be a bit patient.

Thank you for the report, and for helping us make our documentation better.

"Note that the parameters for call_user_func are not passed by reference." + example:

<?php
function increment(&$var)
{
    $var++;
}

$a = 0;
call_user_func('increment', $a);
echo $a; // 0

call_user_func_array('increment', array(&$a)); // You can use this instead
echo $a; // 1
?>