Go编程模式 - 3.继承与嵌入

// 定义了两种interface
type Painter interface {
 Paint()
}

type Clicker interface {
 Click()
}

// 标准组件，用于嵌入
type Widget struct {
 X, Y int
}

// Label 实现了 Painter
type Label struct {
 Widget        // Embedding (delegation)
 Text   string // Aggregation
}

func (label Label) Paint() {
 fmt.Printf("%p:Label.Paint(%q)\n", &label, label.Text)
}

// ListBox声明了Paint和Click，所以实现了Painter和Clicker
type ListBox struct {
 Widget          // Embedding (delegation)
 Texts  []string // Aggregation
 Index  int      // Aggregation
}

func (listBox ListBox) Paint() {
 fmt.Printf("ListBox.Paint(%q)\n", listBox.Texts)
}

func (listBox ListBox) Click() {
 fmt.Printf("ListBox.Click(%q)\n", listBox.Texts)
}

// Button 继承了Label，所以直接实现了Painter
// 接下来，Button又声明了Paint和Click，所以实现了Painter和Clicker，其中Paint方法被覆
type Button struct {
 Label // Embedding (delegation)
}

func (button Button) Paint() { // Override
 fmt.Printf("Button.Paint(%s)\n", button.Text)
}

func (button Button) Click() {
 fmt.Printf("Button.Click(%s)\n", button.Text)
}

func main() {
 label := Label{Widget{10, 70}, "Label"}
 button1 := Button{Label{Widget{10, 70}, "OK"}}
 button2 := Button{Label{Widget{50, 70}, "Cancel"}}
 listBox := ListBox{Widget{10, 40},
  []string{"AL", "AK", "AZ", "AR"}, 0}

 for _, painter := range []Painter{label, listBox, button1, button2} {
  painter.Paint()
 }

 for _, widget := range []interface{}{label, listBox, button1, button2} {
  // 默认都实现了Painter接口，可以直接调用
  widget.(Painter).Paint()
  if clicker, ok := widget.(Clicker); ok {
   clicker.Click()
  }
 }
}

// 定义两种方法的组合
type PaintClicker interface {
 Painter
 Clicker
}

func main() {
 // 在上面的例子中，interface传参其实不太优雅，有没有更优雅的实现呢？那就用组合的interface
 for _, widget := range []PaintClicker{listBox, button1, button2} {
  widget.Paint()
  widget.Click()
 }
}

// Int集合，用于最基础的增删查
type IntSet struct {
 data map[int]bool
}

func NewIntSet() IntSet {
 return IntSet{make(map[int]bool)}
}

func (set *IntSet) Add(x int) { set.data[x] = true }

func (set *IntSet) Delete(x int) { delete(set.data, x) }

func (set *IntSet) Contains(x int) bool { return set.data[x] }

// 可撤销的Int集合，依赖于IntSet，我们看看基本实现
type UndoableIntSet struct { // Poor style
 IntSet    // Embedding (delegation)
 functions []func()
}

func NewUndoableIntSet() UndoableIntSet {
 return UndoableIntSet{NewIntSet(), nil}
}

// 新增
// 不存在元素时：添加元素，并新增撤销函数：删除
// 存在元素时：不做任何操作，并新增撤销函数：空
func (set *UndoableIntSet) Add(x int) { // Override
 if !set.Contains(x) {
  set.data[x] = true
  set.functions = append(set.functions, func() { set.Delete(x) })
 } else {
  set.functions = append(set.functions, nil)
 }
}

// 删除，与新增相反
// 存在元素时：删除元素，并新增撤销函数：新增
// 不存在元素时：不做任何操作，并新增撤销函数：空
func (set *UndoableIntSet) Delete(x int) { // Override
 if set.Contains(x) {
  delete(set.data, x)
  set.functions = append(set.functions, func() { set.Add(x) })
 } else {
  set.functions = append(set.functions, nil)
 }
}

// 撤销：执行最后一个撤销函数function
func (set *UndoableIntSet) Undo() error {
 if len(set.functions) == 0 {
  return errors.New("No functions to undo")
 }
 index := len(set.functions) - 1
 if function := set.functions[index]; function != nil {
  function()
  set.functions[index] = nil // For garbage collection
 }
 set.functions = set.functions[:index]
 return nil
}

type Undo []func()

func (undo *Undo) Add(function func()) {
 *undo = append(*undo, function)
}

func (undo *Undo) Undo() error {
 functions := *undo
 if len(functions) == 0 {
  return errors.New("No functions to undo")
 }
 index := len(functions) - 1
 if function := functions[index]; function != nil {
  function()
  functions[index] = nil // For garbage collection
 }
 *undo = functions[:index]
 return nil
}

type IntSet2 struct {
 data map[int]bool
 undo Undo
}

func NewIntSet2() IntSet2 {
 return IntSet2{data: make(map[int]bool)}
}

func (set *IntSet2) Undo() error {
 return set.undo.Undo()
}

func (set *IntSet2) Contains(x int) bool {
 return set.data[x]
}

func (set *IntSet2) Add(x int) {
 if !set.Contains(x) {
  set.data[x] = true
  set.undo.Add(func() { set.Delete(x) })
 } else {
  set.undo.Add(nil)
 }
}

func (set *IntSet2) Delete(x int) {
 if set.Contains(x) {
  delete(set.data, x)
  set.undo.Add(func() { set.Add(x) })
 } else {
  set.undo.Add(nil)
 }
}