iflrandevu/autoload.php

<?php 

/* ----------------------------------------------------------------------------
 * Easy!Appointments - Open Source Web Scheduler
 *
 * @package     EasyAppointments
 * @author      A.Tselegidis <alextselegidis@gmail.com>
 * @copyright   Copyright (c) 2013 - 2020, Alex Tselegidis
 * @license     http://opensource.org/licenses/GPL-3.0 - GPLv3
 * @link        http://easyappointments.org
 * @since       v1.2.0
 * ---------------------------------------------------------------------------- */

function register($namespace, $path) { 
    spl_autoload_register(function ($class) use ($namespace, $path) {
        // project-specific namespace prefix
        $prefix = 'EA\\' . $namespace . '\\';

        // does the class use the namespace prefix?
        $len = strlen($prefix);
        if (strncmp($prefix, $class, $len) !== 0) {
            // no, move to the next registered autoloader
            return;
        }

        // get the relative class name
        $relative_class = substr($class, $len);

        // replace the namespace prefix with the base directory, replace namespace
        // separators with directory separators in the relative class name, append
        // with .php
        $file = $path . '/' . str_replace('\\', '/', $relative_class) . '.php';

        // if the file exists, require it
        if (file_exists($file)) {
            require $file;
        }
    });
}

register('Engine', __DIR__ . '/engine'); 
register('Themes', __DIR__ . '/themes');
register('Plugins', __DIR__ . '/plugins');