private function addPath(& $list, $path, $namespace)
    {
        if ($namespace !== null) {
            $paths = [$namespace => $path];
        } else {
            $paths = is_array($path) ? $path : ['' => $path];
        }

        foreach ($paths as $ns => $directories) {
            $this->addNamespacePaths($list, ltrim($ns, '0..9'), $directories);
        }
    }