Autoload PHP namespace

autoloader.php

<?php
function __autoload($classname) {
    $dir = dirname(__FILE__);
    $include_dir = $dir.DIRECTORY_SEPARATOR."includes".DIRECTORY_SEPARATOR."classes".DIRECTORY_SEPARATOR;
    $filename = $include_dir.str_replace('\\', DIRECTORY_SEPARATOR, $classname) . '.class.php';
    require_once($filename);
}