public function cache_driver()
	{
		if ( ! $this->_cache)
		{
			$adapter = new DCache_Adapter\File(
				realpath(__DIR__.'../../../'.static::CACHE_DIR)
			);
			$adapter->setOption('ttl', static::CACHE_LIFETIME);
			$this->_cache = new DCache\Cache($adapter);
		}

		return $this->_cache;
	}