set minimum capacity at anytime

deque.go

@@ -13,17 +13,6 @@ type Deque struct {
 	minCap int
 }
 
-// New creates a new Deque that has a minimum capacity of 2^minCapacityExp.  If
-// the value of the minimum capacity is less than or equal to the minimum
-// allowed, then New returns the same as new(Deque).
-func New(minCapacityExp uint) *Deque {
-	q := new(Deque)
-	if 1<<minCapacityExp > minCapacity {
-		q.minCap = 1 << minCapacityExp
-	}
-	return q
-}
-
 // Len returns the number of elements currently stored in the queue.
 func (q *Deque) Len() int {
 	return q.count
@@ -190,6 +179,21 @@ func (q *Deque) Rotate(n int) {
 	}
 }
 
+// SetMinCapacity sets a minimum capacity of 2^minCapacityExp.  If the value of
+// the minimum capacity is less than or equal to the minimum allowed, then
+// capacity is set to the minimum allowed.  This may be called at anytime to
+// set a new minimum capacity.
+//
+// Setting a larger minimum capacity may be used to prevent resizing when the
+// number of stored items changes frequently across a wide range.
+func (q *Deque) SetMinCapacity(minCapacityExp uint) {
+	if 1<<minCapacityExp > minCapacity {
+		q.minCap = 1 << minCapacityExp
+	} else {
+		q.minCap = minCapacity
+	}
+}
+
 // prev returns the previous buffer position wrapping around buffer.
 func (q *Deque) prev(i int) int {
 	return (i - 1) & (len(q.buf) - 1) // bitwise modulus

deque_test.go

@@ -480,9 +480,10 @@ func TestRemoveOutOfRangePanics(t *testing.T) {
 	})
 }
 
-func TestNew(t *testing.T) {
+func TestSetMinCapacity(t *testing.T) {
+	var q Deque
 	exp := uint(8)
-	q := New(8)
+	q.SetMinCapacity(exp)
 	q.PushBack("A")
 	if q.minCap != 1<<exp {
 		t.Fatal("wrong minimum capacity")
@@ -497,6 +498,10 @@ func TestNew(t *testing.T) {
 	if len(q.buf) != 1<<exp {
 		t.Fatal("wrong buffer size")
 	}
+	q.SetMinCapacity(0)
+	if q.minCap != minCapacity {
+		t.Fatal("wrong minimum capacity")
+	}
 }
 
 func assertPanics(t *testing.T, name string, f func()) {
@@ -590,7 +595,8 @@ func BenchmarkYoyo(b *testing.B) {
 }
 
 func BenchmarkYoyoFixed(b *testing.B) {
-	q := New(16)
+	var q Deque
+	q.SetMinCapacity(16)
 	for i := 0; i < b.N; i++ {
 		for j := 0; j < 65536; j++ {
 			q.PushBack(j)