autoload.php

<?php
namespace Core3;


spl_autoload_register(function ($class) {

    if (strpos($class, __NAMESPACE__) !== 0) {
        return false;
    }

    $class_explode   = explode("\\", $class);
    $class_path      = [];
    $count_namespace = count(explode("\\", __NAMESPACE__));


    if (empty($class_explode[1]) || ! in_array($class_explode[1], ['Classes', 'Interfaces', 'Exceptions'])) {
        return false;
    }

    foreach ($class_explode as $key => $item) {
        if ($key >= $count_namespace && $key < (count($class_explode) - 1)) {
            $class_path[] = $item;
        }
    }

    $class_path[0] = lcfirst($class_path[0]);

    $class_path_implode = implode('/', $class_path);
    $class_path_implode = $class_path_implode ? "/{$class_path_implode}" : '';
    $class_name         = end($class_explode);


    $file_path = __DIR__ . "{$class_path_implode}/{$class_name}.php";

    if (file_exists($file_path)) {
        require_once $file_path;
    }
});