PHP - call_user_func reference

PHP function call_user_func() does not pass parameter variable as reference. the code below won't work as expected.

From PHP documentation:

Note that the parameters for call_user_func() are not passed by reference.

<?php

function increment(&$var)
{
    $var++;
}

$a = 0;
call_user_func('increment', $a);
echo $a."\n"; // $a is equals to 0

In order to solve this problem call_user_func_array() must be used instead.

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

$a = 0;

call_user_func_array('increment', array(&$a));
echo $a."\n"; // $a is equals to 1