added replace method

bucket.go

@@ -30,6 +30,17 @@ func (b *Bucket) set(key string, value interface{}, duration time.Duration) (*It
 	return item, true
 }
 
+func (b *Bucket) replace(key string, value interface{}) bool {
+	b.Lock()
+	defer b.Unlock()
+	existing, exists := b.lookup[key]
+	if exists == false {
+		return false
+	}
+	existing.value = value
+	return true
+}
+
 func (b *Bucket) delete(key string) *Item {
 	b.Lock()
 	defer b.Unlock()

bucket_test.go

@@ -48,6 +48,18 @@ func (b *BucketTests) SetsAnExistingItem() {
 	Expect(new).To.Equal(false)
 }
 
+func (b *BucketTests) ReplaceDoesNothingIfKeyDoesNotExist() {
+	bucket := testBucket()
+	item, _ := bucket.set("power", TestValue("9002"), time.Minute)
+	Expect(bucket.replace("power", TestValue("9004"))).To.Equal(true)
+	Expect(item.Value().(string)).To.Equal("9004")
+}
+
+func (b *BucketTests) ReplaceReplacesThevalue() {
+	bucket := testBucket()
+	Expect(bucket.replace("power", TestValue("9002"))).To.Equal(false)
+}
+
 func testBucket() *Bucket {
 	b := &Bucket{lookup: make(map[string]*Item)}
 	b.lookup["power"] = &Item{

cache.go

@@ -65,6 +65,10 @@ func (c *Cache) Set(key string, value interface{}, duration time.Duration) {
 	}
 }
 
+func (c *Cache) Replace(key string, value interface{}) bool {
+	return c.bucket(key).replace(key, value)
+}
+
 func (c *Cache) Fetch(key string, duration time.Duration, fetch func() (interface{}, error)) (interface{}, error) {
 	item := c.Get(key)
 	if item != nil {

readme.md

@@ -92,6 +92,15 @@ cache.Delete("user:4")
 ### Extend
 The life of an item can be changed via the `Extend` method. This will change the expiry of the item by the specified duration relative to the current time.
 
+### Replace
+The value of an item can be updated to a new value without renewing the item's TTL or it's position in the LRU:
+
+```go
+cache.Replace("user:4", user)
+```
+
+`Replace` returns true if the item existed (and thus was replaced). In the case where the key was not in the cache, the value *is not* inserted and false is returned.
+
 ## Tracking
 CCache supports a special tracking mode which is meant to be used in conjunction with other pieces of your code that maintains a long-lived reference to data.