App.php

<?php

namespace App;

class App
{
    public function __construct()
    {
        $controller = new Controller\Example;
    }
}

Controller.php

<?php

namespace App\Controller;

//use App\Model\Example as Model;

class Example
{
    public function __construct()
    {
        $model = new \App\Model\Example();
    }
}

index.php

<?php

//spl_autoload_extensions('.php');
spl_autoload_register();

/*
 * spl_autoload_register(
 *     function ($class) {
 *         spl_autoload(str_replace('\\', DIRECTORY_SEPARATOR, $class));
 *     }
 * );
 */

$app = new \App\App;

Model.php

<?php

namespace App\Model;

class Example
{
    public function __construct()
    {
        echo 'Hello World!';
    }
}