https://github.com/golang/groupcache/blob/master/lru/lru.go

type Cache struct {
// MaxEntries is the maximum number of cache entries before
// an item is evicted. Zero means no limit.
MaxEntries int

// OnEvicted optionally specifies a callback function to be
// executed when an entry is purged from the cache.
OnEvicted func(key Key, value interface{})

ll    *list.List
cache map[interface{}]*list.Element

}
这里的代码为什么不能直接使用ll, 而不省去cache, 是因为get的时候好拿吗？虽然这里cache field是指针