class MemoryCache

class MemoryCache extends MemoryBackend implements MemoryCacheInterface {
    
    /**
     * Prepares a cached item.
     *
     * Checks that items are either permanent or did not expire, and returns data
     * as appropriate.
     *
     * @param object $cache
     *   An item loaded from self::get() or self::getMultiple().
     * @param bool $allow_invalid
     *   (optional) If TRUE, cache items may be returned even if they have expired
     *   or been invalidated. Defaults to FALSE.
     *
     * @return mixed
     *   The item with data as appropriate or FALSE if there is no
     *   valid item to load.
     */
    protected function prepareItem($cache, $allow_invalid = FALSE) {
        if (!isset($cache->data)) {
            return FALSE;
        }
        // Check expire time.
        $cache->valid = $cache->expire == static::CACHE_PERMANENT || $cache->expire >= $this->getRequestTime();
        if (!$allow_invalid && !$cache->valid) {
            return FALSE;
        }
        return $cache;
    }
    
    /**
     * {@inheritdoc}
     */
    public function set($cid, $data, $expire = MemoryCacheInterface::CACHE_PERMANENT, array $tags = []) {
        assert(Inspector::assertAllStrings($tags), 'Cache tags must be strings.');
        $tags = array_unique($tags);
        $this->cache[$cid] = (object) [
            'cid' => $cid,
            'data' => $data,
            'created' => $this->getRequestTime(),
            'expire' => $expire,
            'tags' => $tags,
        ];
    }

}