<?php
class Log
{
    function doLog($msg)
    {
        echo $msg . "\n";
    }
}

$log = new Log();
$cb = array($log, 'doLog');
call_user_func($cb, 'hi');

$cb2 = &$cb;
call_user_func($cb2, 'hi2');

$cb3 = &$cb2;
call_user_func($cb3, 'hi3');

$cb4 = &$cb3;
call_user_func($cb4, 'hi4');
?>