protected static function createDirectory( $dir )
	{
		$perm = 0755;

		if( !is_dir( $dir ) && !mkdir( $dir, $perm, true ) )
		{
			$msg = 'Unable to create directory "%1$s" with permission "%2$s"';
			throw new \RuntimeException( sprintf( $msg, $dir, $perm ) );
		}
	}