Delete expired items before setting

cache.go

@@ -57,14 +57,27 @@ func (c *cache) Set(k string, x interface{}, d time.Duration) {
 	if d > 0 {
 		e = time.Now().Add(d).UnixNano()
 	}
+
+	var item Item
+	var evicted bool
+
 	c.mu.Lock()
+	if c.onEvicted != nil {
+		item, evicted = c.items[k]
+	}
+
 	c.items[k] = Item{
 		Object:     x,
 		Expiration: e,
 	}
 	// TODO: Calls to mu.Unlock are currently not deferred because defer
 	// adds ~200 ns (as of go1.)
 	c.mu.Unlock()
+
+	// try to call onEvicted if key existed before but the item is different
+	if evicted && item.Object != x {
+		c.onEvicted(k, item.Object)
+	}
 }
 
 func (c *cache) set(k string, x interface{}, d time.Duration) {

cache_test.go

@@ -1247,6 +1247,37 @@ func TestOnEvicted(t *testing.T) {
 	}
 }
 
+func TestOnEvictedCalledBeforeSet(t *testing.T) {
+	tc := New(DefaultExpiration, 0)
+	expiry := 1 * time.Nanosecond
+
+	works := false
+	tc.OnEvicted(func(k string, v interface{}) {
+		if k == "foo" && v.(int) == 3 {
+
+			works = true
+		}
+		tc.Set("bar", 4, DefaultExpiration)
+	})
+
+	tc.Set("foo", 3, expiry)
+	if tc.onEvicted == nil {
+		t.Fatal("tc.onEvicted is nil")
+	}
+
+	// calling Set again with the same key should evict
+	// the item if different
+	tc.Set("foo", 5, DefaultExpiration)
+
+	x, _ := tc.Get("bar")
+	if !works {
+		t.Fatal("works bool not true")
+	}
+	if x.(int) != 4 {
+		t.Error("bar was not 4")
+	}
+}
+
 func TestCacheSerialization(t *testing.T) {
 	tc := New(DefaultExpiration, 0)
 	testFillAndSerialize(t, tc)