LRU golang实现

type Cache struct {
   maxBytes int64
   nbytes   int64
    //用于排序的双向链表
   ll       *list.List
    //用于查找的哈希表，K是字符串，V是链表中的元素
   cache    map[string]*list.Element
   // optional and executed when an entry is purged.
   OnEvicted func(key string, value Value)
}

type entry struct {
   key   string
   value Value
}

// Value use Len to count how many bytes it takes
type Value interface {
   Len() int
}

func New(maxBytes int64, onEvicted func(string, Value)) *Cache {
   return &Cache{
      maxBytes:  maxBytes,
      ll:        list.New(),
      cache:     make(map[string]*list.Element),
      OnEvicted: onEvicted,
   }
}

func (c *Cache) Get(key string) (value Value, ok bool) {
   if ele, ok := c.cache[key]; ok {
      c.ll.MoveToFront(ele)
      kv := ele.Value.(*entry)
      return kv.value, true
   }
   return
}
func (c *Cache) RemoveOldest() {
   ele := c.ll.Back()
   if ele != nil {
      c.ll.Remove(ele)
      kv := ele.Value.(*entry)
      delete(c.cache, kv.key)
      c.nbytes -= int64(len(kv.key)) + int64(kv.value.Len())
      if c.OnEvicted != nil {
         c.OnEvicted(kv.key, kv.value)
      }
   }
}
func (c *Cache) Add(key string, value Value) {
   if ele, ok := c.cache[key]; ok {
      c.ll.MoveToFront(ele)
      kv := ele.Value.(*entry)
      c.nbytes += int64(value.Len()) - int64(kv.value.Len())
      kv.value = value
   } else {
      ele := c.ll.PushFront(&entry{key, value})
      c.cache[key] = ele
      c.nbytes += int64(len(key)) + int64(value.Len())
   }
   for c.maxBytes != 0 && c.maxBytes < c.nbytes {
      c.RemoveOldest()
   }
}
func (c *Cache) Len() int {
   return c.ll.Len()
}