Add more methods

2 files changed, 70 insertions, 5 deletions

diff --git a/vecdeque.go b/vecdeque.go
index 94d64da..5d6cc92 100644
--- a/vecdeque.go
+++ b/vecdeque.go
@@ -100,6 +100,23 @@ func (q *DQ[T]) PushBack(values ...T) {
 	q.buf = q.buf[:len(q.buf)+len(values)]
 }
 
+// Reset empties the deque, retaining the underlying storage for use by
+// future pushes.
+func (q *DQ[T]) Reset() {
+	q.buf = q.buf[:0]
+}
+
+// AvailableBuffer returns an empty slice with q.Cap()-q.Len() capacity. This
+// slice is intended to be appended to and passed to an immediately succeeding
+// DQ.PushBack call. The slice is only valid until the next push operation on q.
+func (q *DQ[T]) AvailableBuffer() []T {
+	endIdx := q.toPhysicalIdx(len(q.buf))
+	if endIdx <= q.head {
+		return q.buf[endIdx:endIdx:q.head]
+	}
+	return q.buf[endIdx:endIdx]
+}
+
 // Grow makes space for at least n more elements to be inserted in the given
 // deque without reallocation.
 func (q *DQ[T]) Grow(n int) {
@@ -151,7 +168,7 @@ func (q *DQ[T]) Grow(n int) {
 // any elements.
 func (q *DQ[T]) All() func(func(int, T) bool) {
 	return func(yield func(int, T) bool) {
-		for i := range q.Len() {
+		for i := range len(q.buf) {
 			if !yield(i, q.Get(i)) {
 				return
 			}
@@ -159,14 +176,21 @@ func (q *DQ[T]) All() func(func(int, T) bool) {
 	}
 }
 
-// PopAll returns an iterator that consumes all the values in the deque, leaving
-// it empty.
+// PopAll empties the deque and returns an iterator over the popped elements.
+// It's not safe to modify the deque while iterating using PopAll.
 func (q *DQ[T]) PopAll() func(func(T) bool) {
+	n := len(q.buf)
+	q.buf = q.buf[:0]
 	return func(yield func(T) bool) {
-		for val, ok := q.PopFront(); ok; val, ok = q.PopFront() {
-			if !yield(val) {
+		endIdx := q.toPhysicalIdx(n)
+		for i := q.head; ; {
+			if !yield(q.buf[:cap(q.buf)][i]) {
 				return
 			}
+			i = q.wrapAdd(i, 1)
+			if i == endIdx {
+				break
+			}
 		}
 	}
 }
diff --git a/vecdeque_test.go b/vecdeque_test.go
index 527c46c..a66fff4 100644
--- a/vecdeque_test.go
+++ b/vecdeque_test.go
@@ -1,6 +1,8 @@
 package vecdeque
 
 import (
+	"bytes"
+	"fmt"
 	"slices"
 	"testing"
 )
@@ -242,7 +244,22 @@ func TestPopFrontPushFront(t *testing.T) {
 	}
 }
 
+func TestReset(t *testing.T) {
+	t.Parallel()
+
+	q := From([]int{1, 2, 3, 4, 5})
+	q.Reset()
+	if got, want := q.Len(), 0; got != want {
+		t.Errorf("After Reset() Len() = %d, want %d", got, want)
+	}
+	if got, want := q.Cap(), 5; got != want {
+		t.Errorf("After Reset() Cap() = %d, want %d", got, want)
+	}
+}
+
 func TestPopAll(t *testing.T) {
+	t.Parallel()
+
 	q := From([]int{1, 2, 3})
 	got := make([]int, 0, q.Len())
 	for x := range q.PopAll() {
@@ -256,3 +273,27 @@ func TestPopAll(t *testing.T) {
 		t.Errorf("PopAll() returned values %d, want %d", got, want)
 	}
 }
+
+func TestAvailableBuffer(t *testing.T) {
+	t.Parallel()
+
+	const cap = 10
+	q := WithCapacity[byte](cap)
+	q.PushBack(append(q.AvailableBuffer(), []byte("     ")...)...)
+	q.PushBack(fmt.Appendf(q.AvailableBuffer(), "%d", 12345)...)
+	for range 5 {
+		q.PopFront()
+	}
+	q.PushBack(fmt.Appendf(q.AvailableBuffer(), "%d", 67890)...)
+	if got, want := q.Cap(), cap; got != want {
+		t.Errorf("Cap() = %d, want %d", got, want)
+	}
+	got := make([]byte, q.Len())
+	for i, x := range q.All() {
+		got[i] = x
+	}
+	want := []byte("1234567890")
+	if !bytes.Equal(got, want) {
+		t.Errorf("Incorrect content after appending to AvailableBuffer, got %d want %d", got, want)
+	}
+}