Implemented ExtendFront/Back functions to insert a list of elements into a list.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/181151

src/pkg/container/list/list.go

@@ -191,3 +191,25 @@ func (l *List) Iter() <-chan interface{} {
 	go l.iterate(c)
 	return c
 }
+
+// PushBackList inserts each element of ol at the back of the list.
+func (l *List) PushBackList(ol *List) {
+	last := ol.Back()
+	for e := ol.Front(); e != nil; e = e.Next() {
+		l.PushBack(e.Value)
+		if e == last {
+			break
+		}
+	}
+}
+
+// PushFrontList inserts each element of ol at the front of the list. The ordering of the passed list is preserved.
+func (l *List) PushFrontList(ol *List) {
+	first := ol.Front()
+	for e := ol.Back(); e != nil; e = e.Prev() {
+		l.PushFront(e.Value)
+		if e == first {
+			break
+		}
+	}
+}

src/pkg/container/list/list_test.go

@@ -134,3 +134,62 @@ func TestList(t *testing.T) {
 	checkListPointers(t, l, []*Element{})
 	checkListLen(t, l, 0)
 }
+
+func checkList(t *testing.T, l *List, es []interface{}) {
+	if l.Len() != len(es) {
+		t.Errorf("list has len=%v, want %v", l.Len(), len(es))
+		return
+	}
+	i := 0
+	for le := range l.Iter() {
+		if le != es[i] {
+			t.Errorf("elt #%d has value=%v, want %v", i, le, es[i])
+		}
+		i++
+	}
+}
+
+func TestExtending(t *testing.T) {
+	l1 := New()
+	l2 := New()
+
+	l1.PushBack(1)
+	l1.PushBack(2)
+	l1.PushBack(3)
+
+	l2.PushBack(4)
+	l2.PushBack(5)
+
+	l3 := New()
+	l3.PushBackList(l1)
+	checkList(t, l3, []interface{}{1, 2, 3})
+	l3.PushBackList(l2)
+	checkList(t, l3, []interface{}{1, 2, 3, 4, 5})
+
+	l3 = New()
+	l3.PushFrontList(l2)
+	checkList(t, l3, []interface{}{4, 5})
+	l3.PushFrontList(l1)
+	checkList(t, l3, []interface{}{1, 2, 3, 4, 5})
+
+	checkList(t, l1, []interface{}{1, 2, 3})
+	checkList(t, l2, []interface{}{4, 5})
+
+	l3 = New()
+	l3.PushBackList(l1)
+	checkList(t, l3, []interface{}{1, 2, 3})
+	l3.PushBackList(l3)
+	checkList(t, l3, []interface{}{1, 2, 3, 1, 2, 3})
+
+	l3 = New()
+	l3.PushFrontList(l1)
+	checkList(t, l3, []interface{}{1, 2, 3})
+	l3.PushFrontList(l3)
+	checkList(t, l3, []interface{}{1, 2, 3, 1, 2, 3})
+
+	l3 = New()
+	l1.PushBackList(l3)
+	checkList(t, l1, []interface{}{1, 2, 3})
+	l1.PushFrontList(l3)
+	checkList(t, l1, []interface{}{1, 2, 3})
+}