Off return nil

goevent.go

@@ -61,19 +61,26 @@ func (p *Event) On(f interface{}) error {
 	return nil
 }
 
-func (p *Event) Off(f interface{}) {
+func (p *Event) Off(f interface{}) error {
 	fn := reflect.ValueOf(f)
 
 	p.lmu.Lock()
 	defer p.lmu.Unlock()
 	l := len(p.listeners)
+	m := l // for error check
 	for i := 0; i < l; i++ {
 		if fn == p.listeners[i] {
+			// XXX: GC Ref: http://jxck.hatenablog.com/entry/golang-slice-internals
 			p.listeners = append(p.listeners[:i], p.listeners[i+1:]...)
 			l--
 			i--
 		}
 	}
+
+	if l == m {
+		return fmt.Errorf("Listener does't exists")
+	}
+	return nil
 }
 
 func (p *Event) checkFuncSignature(f interface{}) (*reflect.Value, error) {

goevent_test.go

@@ -115,7 +115,10 @@ func TestOff(t *testing.T) {
 		t.Errorf("k expected 1, but got %d", k)
 	}
 
-	p.Off(f)
+	err := p.Off(f)
+	if err != nil {
+		t.Error(err)
+	}
 	p.Trigger()
 	if i != 1 {
 		t.Errorf("i expected 1, but got %d", i)
@@ -126,4 +129,9 @@ func TestOff(t *testing.T) {
 	if k != 2 {
 		t.Errorf("k expected 2, but got %d", k)
 	}
+
+	err = p.Off(f)
+	if err == nil {
+		t.Errorf("should return error when Listener doesn't exists. but got nil")
+	}
 }

table.go

@@ -8,7 +8,7 @@ import (
 type Table interface {
 	On(string, interface{}) error
 	Trigger(string, ...interface{}) error
-	Off(string, interface{})
+	Off(string, interface{}) error
 	Destroy(string) error
 }
 
@@ -47,16 +47,16 @@ func (t *table) On(name string, f interface{}) error {
 	return ev.On(f)
 }
 
-// XXX: return error?
-func (t *table) Off(name string, f interface{}) {
+func (t *table) Off(name string, f interface{}) error {
 	t.mu.Lock()
 	defer t.mu.Unlock()
 
 	e, ok := t.events[name]
 	if !ok {
-		return
+		return fmt.Errorf("%s event has not been defined yet.", name)
 	}
-	e.Off(f)
+
+	return e.Off(f)
 }
 
 func (t *table) Destroy(name string) error {

table_test.go

@@ -44,7 +44,10 @@ func TestTableOff(t *testing.T) {
 	f := func() { i++ }
 	ta.On("foo", f)
 	ta.Trigger("foo")
-	ta.Off("foo", f)
+	err := ta.Off("foo", f)
+	if err != nil {
+		t.Error(err)
+	}
 	ta.Trigger("foo")
 	if i != 1 {
 		t.Errorf("i expected 1, but got %d", i)