code: public function set($key, \DateTime $time)
      {
          $key = $this->prefix.$key;
          if (!($old_time = $this->memcache->get($key)) || $old_time < $time->getTimestamp()) {
              return $this->memcache->set($key, $time->getTimestamp());
          }
  
          return true;
      }
docs: @param string $key
  @param \DateTime $time
  
  @return bool