code: func NewLRUExpireCacheWithClock(maxSize int, clock Clock) *LRUExpireCache {
  	cache, err := lru.New(maxSize)
  	if err != nil {
  		// if called with an invalid size
  		panic(err)
  	}
  	return &LRUExpireCache{clock: clock, cache: cache}
  }
docs: // NewLRUExpireCacheWithClock creates an expiring cache with the given size, using the specified clock to obtain the current time.