diff --git a/list/copy_on_write_array_list.go b/list/copy_on_write_array_list.go
index c069ad3..c5f6e79 100644
--- a/list/copy_on_write_array_list.go
+++ b/list/copy_on_write_array_list.go
@@ -1,127 +1,148 @@
-package list
-
-import (
-	"sync"
-
-	"github.com/ecodeclub/ekit/internal/errs"
-	"github.com/ecodeclub/ekit/internal/slice"
-)
-
-var (
-	_ List[any] = &CopyOnWriteArrayList[any]{}
-)
-
-// CopyOnWriteArrayList 基于切片的简单封装 写时加锁，读不加锁，适合于读多写少场景
-type CopyOnWriteArrayList[T any] struct {
-	vals  []T
-	mutex *sync.Mutex
-}
-
-// NewCopyOnWriteArrayList
-func NewCopyOnWriteArrayList[T any]() *CopyOnWriteArrayList[T] {
-	m := &sync.Mutex{}
-	return &CopyOnWriteArrayList[T]{
-		vals:  make([]T, 0),
-		mutex: m,
-	}
-}
-
-// NewCopyOnWriteArrayListOf 直接使用 ts，会执行复制
-func NewCopyOnWriteArrayListOf[T any](ts []T) *CopyOnWriteArrayList[T] {
-	items := make([]T, len(ts))
-	copy(items, ts)
-	m := &sync.Mutex{}
-	return &CopyOnWriteArrayList[T]{
-		vals:  items,
-		mutex: m,
-	}
-}
-
-func (a *CopyOnWriteArrayList[T]) Get(index int) (t T, e error) {
-	l := a.Len()
-	if index < 0 || index >= l {
-		return t, errs.NewErrIndexOutOfRange(l, index)
-	}
-	return a.vals[index], e
-}
-
-// Append 往CopyOnWriteArrayList里追加数据
-func (a *CopyOnWriteArrayList[T]) Append(ts ...T) error {
-	a.mutex.Lock()
-	defer a.mutex.Unlock()
-	n := len(a.vals)
-	newItems := make([]T, n, n+len(ts))
-	copy(newItems, a.vals)
-	newItems = append(newItems, ts...)
-	a.vals = newItems
-	return nil
-}
-
-// Add 在CopyOnWriteArrayList下标为index的位置插入一个元素
-// 当index等于CopyOnWriteArrayList长度等同于append
-func (a *CopyOnWriteArrayList[T]) Add(index int, t T) (err error) {
-	a.mutex.Lock()
-	defer a.mutex.Unlock()
-	n := len(a.vals)
-	newItems := make([]T, n, n+1)
-	copy(newItems, a.vals)
-	newItems, err = slice.Add(newItems, t, index)
-	a.vals = newItems
-	return
-}
-
-// Set 设置CopyOnWriteArrayList里index位置的值为t
-func (a *CopyOnWriteArrayList[T]) Set(index int, t T) error {
-	a.mutex.Lock()
-	defer a.mutex.Unlock()
-	n := len(a.vals)
-	if index >= n || index < 0 {
-		return errs.NewErrIndexOutOfRange(n, index)
-	}
-	newItems := make([]T, n)
-	copy(newItems, a.vals)
-	newItems[index] = t
-	a.vals = newItems
-	return nil
-}
-
-// 这里不涉及缩容，每次都是当前内容长度申请的数组容量
-func (a *CopyOnWriteArrayList[T]) Delete(index int) (T, error) {
-	a.mutex.Lock()
-	defer a.mutex.Unlock()
-	newItems := make([]T, len(a.vals))
-	copy(newItems, a.vals)
-	res, t, err := slice.Delete(newItems, index)
-	if err != nil {
-		return t, err
-	}
-	newItems = res
-	a.vals = newItems
-	return t, nil
-}
-
-func (a *CopyOnWriteArrayList[T]) Len() int {
-	return len(a.vals)
-}
-
-func (a *CopyOnWriteArrayList[T]) Cap() int {
-	return cap(a.vals)
-}
-
-func (a *CopyOnWriteArrayList[T]) Range(fn func(index int, t T) error) error {
-	for key, value := range a.vals {
-		e := fn(key, value)
-		if e != nil {
-			return e
-		}
-	}
-	return nil
-}
-
-func (a *CopyOnWriteArrayList[T]) AsSlice() []T {
-	a.mutex.Lock()
-	defer a.mutex.Unlock()
-	res := make([]T, len(a.vals))
-	copy(res, a.vals)
-	return res
-}
+// Copyright 2021 ecodeclub
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package list
+
+import (
+	"sync"
+
+	"github.com/ecodeclub/ekit/internal/errs"
+	"github.com/ecodeclub/ekit/internal/slice"
+)
+
+var (
+	_ List[any] = &CopyOnWriteArrayList[any]{}
+)
+
+// CopyOnWriteArrayList 基于切片的简单封装 写时加锁，读不加锁，适合于读多写少场景
+type CopyOnWriteArrayList[T any] struct {
+	vals  []T
+	mutex *sync.Mutex
+}
+
+// NewCopyOnWriteArrayList
+func NewCopyOnWriteArrayList[T any]() *CopyOnWriteArrayList[T] {
+	m := &sync.Mutex{}
+	return &CopyOnWriteArrayList[T]{
+		vals:  make([]T, 0),
+		mutex: m,
+	}
+}
+
+// NewCopyOnWriteArrayListOf 直接使用 ts，会执行复制
+func NewCopyOnWriteArrayListOf[T any](ts []T) *CopyOnWriteArrayList[T] {
+	items := make([]T, len(ts))
+	copy(items, ts)
+	m := &sync.Mutex{}
+	return &CopyOnWriteArrayList[T]{
+		vals:  items,
+		mutex: m,
+	}
+}
+
+func (a *CopyOnWriteArrayList[T]) Get(index int) (t T, e error) {
+	l := a.Len()
+	if index < 0 || index >= l {
+		return t, errs.NewErrIndexOutOfRange(l, index)
+	}
+	return a.vals[index], e
+}
+
+// Append 往CopyOnWriteArrayList里追加数据
+func (a *CopyOnWriteArrayList[T]) Append(ts ...T) error {
+	a.mutex.Lock()
+	defer a.mutex.Unlock()
+	n := len(a.vals)
+	newItems := make([]T, n, n+len(ts))
+	copy(newItems, a.vals)
+	newItems = append(newItems, ts...)
+	a.vals = newItems
+	return nil
+}
+
+// Add 在CopyOnWriteArrayList下标为index的位置插入一个元素
+// 当index等于CopyOnWriteArrayList长度等同于append
+func (a *CopyOnWriteArrayList[T]) Add(index int, t T) (err error) {
+	a.mutex.Lock()
+	defer a.mutex.Unlock()
+	n := len(a.vals)
+	newItems := make([]T, n, n+1)
+	copy(newItems, a.vals)
+	newItems, err = slice.Add(newItems, t, index)
+	a.vals = newItems
+	return
+}
+
+// Set 设置CopyOnWriteArrayList里index位置的值为t
+func (a *CopyOnWriteArrayList[T]) Set(index int, t T) error {
+	a.mutex.Lock()
+	defer a.mutex.Unlock()
+	n := len(a.vals)
+	if index >= n || index < 0 {
+		return errs.NewErrIndexOutOfRange(n, index)
+	}
+	newItems := make([]T, n)
+	copy(newItems, a.vals)
+	newItems[index] = t
+	a.vals = newItems
+	return nil
+}
+
+// 这里不涉及缩容，每次都是当前内容长度申请的数组容量
+func (a *CopyOnWriteArrayList[T]) Delete(index int) (T, error) {
+	a.mutex.Lock()
+	defer a.mutex.Unlock()
+	var ret T
+	n := len(a.vals)
+	if index >= n || index < 0 {
+		return ret, errs.NewErrIndexOutOfRange(n, index)
+	}
+	newItems := make([]T, len(a.vals)-1)
+	item := 0
+	for i, v := range a.vals {
+		if i == index {
+			ret = v
+			continue
+		}
+		newItems[item] = v
+		item++
+	}
+	a.vals = newItems
+	return ret, nil
+}
+
+func (a *CopyOnWriteArrayList[T]) Len() int {
+	return len(a.vals)
+}
+
+func (a *CopyOnWriteArrayList[T]) Cap() int {
+	return cap(a.vals)
+}
+
+func (a *CopyOnWriteArrayList[T]) Range(fn func(index int, t T) error) error {
+	for key, value := range a.vals {
+		e := fn(key, value)
+		if e != nil {
+			return e
+		}
+	}
+	return nil
+}
+
+func (a *CopyOnWriteArrayList[T]) AsSlice() []T {
+	a.mutex.Lock()
+	defer a.mutex.Unlock()
+	res := make([]T, len(a.vals))
+	copy(res, a.vals)
+	return res
+}
diff --git a/list/copy_on_write_array_list_test.go b/list/copy_on_write_array_list_test.go
index 58b7c6b..0f99b23 100644
--- a/list/copy_on_write_array_list_test.go
+++ b/list/copy_on_write_array_list_test.go
@@ -1,3 +1,16 @@
+// Copyright 2021 ecodeclub
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
 package list
 
 import (