public function fromCache($cacheKey)
    {

        // query whether or not a value for the cache key is available
        if (isset($this->cache[$resolvedCacheKey = $this->resolveReference($cacheKey)])) {
            return $this->cache[$resolvedCacheKey];
        }

        // throw an exception if not
        throw new \Exception(sprintf('Can\'t find cached value for key "%s"', $cacheKey));
    }