container/list: Add Len() method to List.

R=r
APPROVED=gri
DELTA=23  (23 added, 0 deleted, 0 changed)
OCL=32106
CL=32189

src/pkg/container/list/list.go

@@ -18,12 +18,14 @@ type Element struct {
 // List represents a doubly linked list.
 type List struct {
 	front, back *Element;
+	len int;
 }
 
 // Init initializes or clears a List.
 func (l *List) Init() *List {
 	l.front = nil;
 	l.back = nil;
+	l.len = 0;
 	return l
 }
 
@@ -57,6 +59,7 @@ func (l *List) Remove(e *Element) {
 
 	e.prev = nil;
 	e.next = nil;
+	l.len--;
 }
 
 func (l *List) insertFront(e *Element) {
@@ -68,6 +71,7 @@ func (l *List) insertFront(e *Element) {
 	} else {
 		l.back = e;
 	}
+	l.len++;
 }
 
 func (l *List) insertBack(e *Element) {
@@ -79,6 +83,7 @@ func (l *List) insertBack(e *Element) {
 	} else {
 		l.front = e;
 	}
+	l.len++;
 }
 
 // PushFront inserts the value at the front of the list, and returns a new Element containing it.
@@ -113,6 +118,11 @@ func (l *List) MoveToBack(e *Element) {
 	l.insertBack(e);
 }
 
+// Len returns the number of elements in the list.
+func (l *List) Len() int {
+	return l.len
+}
+
 func (l *List) iterate(c chan <- *Element) {
 	var next *Element;
 	for e := l.front; e != nil; e = next {

src/pkg/container/list/list_test.go

@@ -42,19 +42,29 @@ func checkListPointers(t *testing.T, l *List, es []*Element) {
 	}
 }
 
+func checkListLen(t *testing.T, l *List, n int) {
+	if an := l.Len(); an != n {
+		t.Errorf("l.Len() = %d, want %d", an, n);
+	}
+}
+
 func TestList(t *testing.T) {
 	l := New();
 	checkListPointers(t, l, []*Element{});
+	checkListLen(t, l, 0);
 
 	// Single element list
 	e := l.PushFront("a");
+	checkListLen(t, l, 1);
 	checkListPointers(t, l, []*Element{ e });
 	l.MoveToFront(e);
 	checkListPointers(t, l, []*Element{ e });
 	l.MoveToBack(e);
 	checkListPointers(t, l, []*Element{ e });
+	checkListLen(t, l, 1);
 	l.Remove(e);
 	checkListPointers(t, l, []*Element{});
+	checkListLen(t, l, 0);
 
 	// Bigger list
 	e2 := l.PushFront(2);
@@ -62,9 +72,11 @@ func TestList(t *testing.T) {
 	e3 := l.PushBack(3);
 	e4 := l.PushBack("banana");
 	checkListPointers(t, l, []*Element{ e1, e2, e3, e4 });
+	checkListLen(t, l, 4);
 
 	l.Remove(e2);
 	checkListPointers(t, l, []*Element{ e1, e3, e4 });
+	checkListLen(t, l, 3);
 
 	l.MoveToFront(e3);  // move from middle
 	checkListPointers(t, l, []*Element{ e3, e1, e4 });
@@ -88,4 +100,5 @@ func TestList(t *testing.T) {
 		l.Remove(e);
 	}
 	checkListPointers(t, l, []*Element{});
+	checkListLen(t, l, 0);
 }