make Len() == 0 for nil vector.Vector

(mimic behavior of slices)

R=r
DELTA=12  (12 added, 0 deleted, 0 changed)
OCL=28960
CL=28962

src/lib/container/vector/vector.go

@@ -84,7 +84,11 @@ func New(len int) *Vector {
 
 
 // Len returns the number of elements in the vector.
+// Len is 0 if p == nil.
 func (p *Vector) Len() int {
+	if p == nil {
+		return 0;
+	}
 	return len(p.a)
 }
 

src/lib/container/vector/vector_test.go

@@ -10,6 +10,14 @@ import "sort"
 import "fmt"
 
 
+func TestZeroLen(t *testing.T) {
+	var a *vector.Vector;
+	if a.Len() != 0 { t.Errorf("A) expected 0, got %d", a.Len()); }
+	a = vector.New(0);
+	if a.Len() != 0 { t.Errorf("B) expected 0, got %d", a.Len()); }
+}
+
+
 func TestInit(t *testing.T) {
 	var a vector.Vector;
 	if a.Init(0).Len() != 0 { t.Error("A") }