Update item with same expiry

cache.go

@@ -109,6 +109,22 @@ func (c *cache) Replace(k string, x interface{}, d time.Duration) error {
 	return nil
 }
 
+// Update only if it is already existing, keep same ttl
+// Set new expiry time which is now - its expiration
+func (c *cache) Update(k string, x interface{}) error {
+	c.mu.Lock()
+	_, found := c.get(k)
+	if !found {
+		c.mu.Unlock()
+		return fmt.Errorf("Item %s doesn't exist", k)
+	}
+	newTtl := time.Unix(0, c.items[k].Expiration)
+	c.set(k, x, newTtl.Sub(time.Now()))
+	c.mu.Unlock()
+	return nil
+}
+
+
 // Get an item from the cache. Returns the item or nil, and a bool indicating
 // whether the key was found.
 func (c *cache) Get(k string) (interface{}, bool) {

cache_test.go

@@ -1137,6 +1137,25 @@ func TestReplace(t *testing.T) {
 	}
 }
 
+func TestUpdate(t *testing.T) {
+	tc := New(75*time.Millisecond, 1*time.Millisecond)
+	tc.Set("a", 1, DefaultExpiration)
+
+	<-time.After(50 * time.Millisecond)
+	_, found := tc.Get("a")
+	if !found {
+		t.Error("error in update; didnt find value that was expected")
+	}
+
+	tc.Update("a", 2)
+	<-time.After(26 * time.Millisecond)
+
+	a, found := tc.Get("a")
+	if found || a != nil {
+		t.Error("Getting A found value that shouldn't exist:", a)
+	}
+}
+
 func TestDelete(t *testing.T) {
 	tc := New(DefaultExpiration, 0)
 	tc.Set("foo", "bar", DefaultExpiration)