Extract counter value from vector

vector.go

@@ -103,3 +103,13 @@ func (a Vector) Concurrent(b Vector) bool {
 	comp := a.Compare(b)
 	return comp == ConcurrentGreater || comp == ConcurrentLesser
 }
+
+// Counter returns the current value of the given counter ID.
+func (v Vector) Counter(id uint64) uint64 {
+	for _, c := range v {
+		if c.ID == id {
+			return c.Value
+		}
+	}
+	return 0
+}

vector_test.go

@@ -118,5 +118,17 @@ func TestMerge(t *testing.T) {
 			t.Errorf("%d: %+v.Merge(%+v) == %+v (expected %+v)", i, tc.a, tc.b, m, tc.m)
 		}
 	}
-
+}
+
+func TestCounterValue(t *testing.T) {
+	v0 := Vector{Counter{42, 1}, Counter{64, 5}}
+	if v0.Counter(42) != 1 {
+		t.Error("Counter error, %d != %d", v0.Counter(42), 1)
+	}
+	if v0.Counter(64) != 5 {
+		t.Error("Counter error, %d != %d", v0.Counter(64), 5)
+	}
+	if v0.Counter(72) != 0 {
+		t.Error("Counter error, %d != %d", v0.Counter(72), 0)
+	}
 }