GravTheme/four-creative.php

<?php
namespace Grav\Theme;

use Grav\Common\Theme;

class FourCreative extends Theme
{
    public static function getSubscribedEvents()
    {
        return ['onTwigExtensions' => ['onTwigExtensions', 0]];
    }

    public function onTwigExtensions()
    {
        require_once __DIR__.DIRECTORY_SEPARATOR.'php'.DIRECTORY_SEPARATOR.'DirFilesExtension.php';
        $this->grav['twig']->twig->addExtension(new DirFilesExtension());
    }
}