--- /dev/null
+package simplelru
+
+import (
+ "container/list"
+ "errors"
+)
+
+// EvictCallback is used to get a callback when a cache entry is evicted
+type EvictCallback func(key interface{}, value interface{})
+
+// LRU implements a non-thread safe fixed size LRU cache
+type LRU struct {
+ size int
+ evictList *list.List
+ items map[interface{}]*list.Element
+ onEvict EvictCallback
+}
+
+// entry is used to hold a value in the evictList
+type entry struct {
+ key interface{}
+ value interface{}
+}
+
+// NewLRU constructs an LRU of the given size
+func NewLRU(size int, onEvict EvictCallback) (*LRU, error) {
+ if size <= 0 {
+ return nil, errors.New("Must provide a positive size")
+ }
+ c := &LRU{
+ size: size,
+ evictList: list.New(),
+ items: make(map[interface{}]*list.Element),
+ onEvict: onEvict,
+ }
+ return c, nil
+}
+
+// Purge is used to completely clear the cache.
+func (c *LRU) Purge() {
+ for k, v := range c.items {
+ if c.onEvict != nil {
+ c.onEvict(k, v.Value.(*entry).value)
+ }
+ delete(c.items, k)
+ }
+ c.evictList.Init()
+}
+
+// Add adds a value to the cache. Returns true if an eviction occurred.
+func (c *LRU) Add(key, value interface{}) (evicted bool) {
+ // Check for existing item
+ if ent, ok := c.items[key]; ok {
+ c.evictList.MoveToFront(ent)
+ ent.Value.(*entry).value = value
+ return false
+ }
+
+ // Add new item
+ ent := &entry{key, value}
+ entry := c.evictList.PushFront(ent)
+ c.items[key] = entry
+
+ evict := c.evictList.Len() > c.size
+ // Verify size not exceeded
+ if evict {
+ c.removeOldest()
+ }
+ return evict
+}
+
+// Get looks up a key's value from the cache.
+func (c *LRU) Get(key interface{}) (value interface{}, ok bool) {
+ if ent, ok := c.items[key]; ok {
+ c.evictList.MoveToFront(ent)
+ return ent.Value.(*entry).value, true
+ }
+ return
+}
+
+// Contains checks if a key is in the cache, without updating the recent-ness
+// or deleting it for being stale.
+func (c *LRU) Contains(key interface{}) (ok bool) {
+ _, ok = c.items[key]
+ return ok
+}
+
+// Peek returns the key value (or undefined if not found) without updating
+// the "recently used"-ness of the key.
+func (c *LRU) Peek(key interface{}) (value interface{}, ok bool) {
+ var ent *list.Element
+ if ent, ok = c.items[key]; ok {
+ return ent.Value.(*entry).value, true
+ }
+ return nil, ok
+}
+
+// Remove removes the provided key from the cache, returning if the
+// key was contained.
+func (c *LRU) Remove(key interface{}) (present bool) {
+ if ent, ok := c.items[key]; ok {
+ c.removeElement(ent)
+ return true
+ }
+ return false
+}
+
+// RemoveOldest removes the oldest item from the cache.
+func (c *LRU) RemoveOldest() (key interface{}, value interface{}, ok bool) {
+ ent := c.evictList.Back()
+ if ent != nil {
+ c.removeElement(ent)
+ kv := ent.Value.(*entry)
+ return kv.key, kv.value, true
+ }
+ return nil, nil, false
+}
+
+// GetOldest returns the oldest entry
+func (c *LRU) GetOldest() (key interface{}, value interface{}, ok bool) {
+ ent := c.evictList.Back()
+ if ent != nil {
+ kv := ent.Value.(*entry)
+ return kv.key, kv.value, true
+ }
+ return nil, nil, false
+}
+
+// Keys returns a slice of the keys in the cache, from oldest to newest.
+func (c *LRU) Keys() []interface{} {
+ keys := make([]interface{}, len(c.items))
+ i := 0
+ for ent := c.evictList.Back(); ent != nil; ent = ent.Prev() {
+ keys[i] = ent.Value.(*entry).key
+ i++
+ }
+ return keys
+}
+
+// Len returns the number of items in the cache.
+func (c *LRU) Len() int {
+ return c.evictList.Len()
+}
+
+// removeOldest removes the oldest item from the cache.
+func (c *LRU) removeOldest() {
+ ent := c.evictList.Back()
+ if ent != nil {
+ c.removeElement(ent)
+ }
+}
+
+// removeElement is used to remove a given list element from the cache
+func (c *LRU) removeElement(e *list.Element) {
+ c.evictList.Remove(e)
+ kv := e.Value.(*entry)
+ delete(c.items, kv.key)
+ if c.onEvict != nil {
+ c.onEvict(kv.key, kv.value)
+ }
+}
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