Add O(1) ItemCount method to retrieve items currently in the cache map (whether expired and not cleaned up or not)

cache.go

@@ -49,6 +49,7 @@ type unexportedInterface interface {
 	DecrementFloat64(string, float64) (float64, error)
 	Delete(string)
 	DeleteExpired()
+	ItemCount() int
 	Flush()
 	Save(io.Writer) error
 	SaveFile(string) error
@@ -933,6 +934,15 @@ func (c *cache) LoadFile(fname string) error {
 	return fp.Close()
 }
 
+// Returns the number of items in the cache. This may include items that have
+// expired, but have not yet been cleaned up.
+func (c *cache) ItemCount() int {
+	c.Lock()
+	n := len(c.items)
+	c.Unlock()
+	return n
+}
+
 // Delete all items from the cache.
 func (c *cache) Flush() {
 	c.Lock()

cache_test.go

@@ -1122,6 +1122,16 @@ func TestDelete(t *testing.T) {
 	}
 }
 
+func TestItemCount(t *testing.T) {
+	tc := New(0, 0)
+	tc.Set("foo", "1", 0)
+	tc.Set("bar", "2", 0)
+	tc.Set("baz", "3", 0)
+	if n := tc.ItemCount(); n != 3 {
+		t.Errorf("Item count is not 3: %d", n)
+	}
+}
+
 func TestFlush(t *testing.T) {
 	tc := New(0, 0)
 	tc.Set("foo", "bar", 0)