code: func (c *cache) record(key string) *list.Element {
  	if item, ok := c.items[key]; ok {
  		c.keyList.MoveToFront(item.element)
  		return item.element
  	}
  	return c.keyList.PushFront(key)
  }
docs: // A function to record the given key and mark it as last to be evicted