code: func (c *LRU) RemoveOldest() (key string, value uint64, ok bool) {
  	ent := c.evictList.Back()
  	if ent != nil {
  		c.removeElement(ent)
  		kv := ent.Value.(*entry)
  		return kv.key, kv.value, true
  	}
  	return "", 0, false
  }
docs: // RemoveOldest removes the oldest item from the cache.