code: protected function set($key, $value)
      {
          $cache = apc_fetch($this->getKey());
  
          $cache[$key] = $value;
  
          apc_store($this->getKey(), $cache);
      }
docs: persists given value in cache
  
  @param string $key   the cache category (array key)
  @param mixed  $value the value to be cached
  
  @return void