Wordpress class autoloder with PSR4 standart.

wp-autoloader-psr4.php

spl_autoload_register(function ($className){
    if ( strpos( $className, __NAMESPACE__  ) !== 0 ) {
        return;
    }
    $className = str_replace(__NAMESPACE__ . '\\', 'includes\\', $className);
    $path = realpath(__DIR__) . DIRECTORY_SEPARATOR . strtr($className, '\\', DIRECTORY_SEPARATOR) . '.php';
    if (is_readable($path)) {
        require_once $path;
    }
});