编程范式游记（8）- Go语言的委托模式 [2026重制版]

// 原文中的简单示例
type Widget struct {
    X, Y int
}

type Label struct {
    Widget        // Embedding (delegation)
    Text   string // Aggregation
    X int         // Override
}

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

package main

import (
	"fmt"
	"strings"
)

// ==================== 基础组件 ====================

// Point 表示二维坐标
type Point struct {
	X, Y int
}

func (p Point) String() string {
	return fmt.Sprintf("(%d,%d)", p.X, p.Y)
}

// Size 表示尺寸
type Size struct {
	Width, Height int
}

func (s Size) String() string {
	return fmt.Sprintf("%dx%d", s.Width, s.Height)
}

// ==================== 基础Widget ====================

// Widget 基础控件接口
type Widget interface {
	Paint()
	GetPosition() Point
	GetSize() Size
	SetVisible(bool)
	IsVisible() bool
}

// BaseWidget 基础控件实现（可嵌入）
type BaseWidget struct {
	Position Point
	Size     Size
	visible  bool
	ID       string
}

func NewBaseWidget(id string, pos Point, size Size) *BaseWidget {
	return &BaseWidget{
		Position: pos,
		Size:     size,
		visible:  true,
		ID:       id,
	}
}

func (w *BaseWidget) GetPosition() Point { return w.Position }
func (w *BaseWidget) GetSize() Size     { return w.Size }
func (w *BaseWidget) SetVisible(v bool)  { w.visible = v }
func (w *BaseWidget) IsVisible() bool    { return w.visible }
func (w *BaseWidget) Paint() {
	fmt.Printf("  [%s] at %s size %s\n", w.ID, w.Position, w.Size)
}

// ==================== 具体组件 ====================

// Label 标签控件（嵌入BaseWidget）
type Label struct {
	*BaseWidget          // 嵌入基础控件
	Text        string
	FontSize    int
	TextColor   string // "#RRGGBB"
	Alignment   string // "left"|"center"|"right"
}

func NewLabel(id string, pos Point, text string) *Label {
	return &Label{
		BaseWidget: NewBaseWidget(id, pos, Size{Width: len(text) * 8, Height: 16}),
		Text:       text,
		FontSize:   12,
		TextColor:  "#000000",
		Alignment:  "left",
	}
}

func (l *Label) Paint() {
	if !l.IsVisible() {
		return
	}
	padding := strings.Repeat(" ", l.Position.X)
	fmt.Printf("%s📝 Label[%s]: \"%s\" (font:%dpx, color:%s)\n",
		padding, l.ID, l.Text, l.FontSize, l.TextColor)
}

// Button 按钮控件（嵌入Label）
type Button struct {
	*Label                // 嵌入标签（间接嵌入了BaseWidget)
	OnClick     func()    // 回调函数
	IsDisabled  bool
	HoverStyle  bool
}

func NewButton(id string, pos Point, text string, onClick func()) *Button {
	return &Button{
		Label:    NewLabel(id, pos, text),
		OnClick:  onClick,
	}
}

func (b *Button) Paint() {
	if !b.IsVisible() {
		return
	}
	state := "🔘"
	if b.IsDisabled {
		state = "🚫"
	} else if b.HoverStyle {
		state = "🔳"
	}
	padding := strings.Repeat(" ", b.GetPosition().X)
	fmt.Printf("%s%s Button[%s]: \"%s\"\n", padding, state, b.ID, b.Text)
}

func (b *Button) Click() {
	if b.IsDisabled || b.OnClick == nil {
		return
	}
	b.OnClick()
}

// ListBox 列表框控件
type ListBox struct {
	*BaseWidget
	Items    []string
	Selected int // -1表示未选中
	MultiSelect bool
}

func NewListBox(id string, pos Point, items []string) *ListBox {
	height := len(items) * 24
	if height > 200 {
		height = 200
	}
	return &ListBox{
		BaseWidget: NewBaseWidget(id, pos, Size{Width: 200, Height: height}),
		Items:      items,
		Selected:   -1,
	}
}

func (lb *ListBox) Paint() {
	if !lb.IsVisible() {
		return
	}
	padding := strings.Repeat(" ", lb.GetPosition().X)
	fmt.Printf("%s📋 ListBox[%s]:\n", padding, lb.ID)
	for i, item := range lb.Items {
		marker := "  "
		if i == lb.Selected {
			marker = "▶ "
		}
		fmt.Printf("%s  %s%s\n", padding, marker, item)
	}
}

func (lb *ListBox) Select(index int) error {
	if index < -1 || index >= len(lb.Items) {
		return fmt.Errorf("index out of range")
	}
	lb.Selected = index
	return nil
}

// ==================== 接口多态演示 ====================

// Painter 可绘制接口
type Painter interface {
	Paint()
}

// Clicker 可点击接口
type Clicker interface {
	Click()
}

// 渲染一组控件
func RenderWidgets(widgets []Painter) {
	fmt.Println("\n=== 渲染控件 ===")
	for _, w := range widgets {
		w.Paint()
	}
}

// 处理点击事件
func HandleClicks(widgets []Clicker) {
	fmt.Println("\n=== 处理点击 ===")
	for _, w := range widgets {
		if clicker, ok := w.(Clicker); ok {
			clicker.Click()
		}
	}
}

// ==================== 使用示例 ====================

func main() {
	// 创建各种控件
	title := NewLabel("title", Point{10, 10}, "用户管理系统 v2.0")
	nameInput := NewLabel("name_label", Point{50, 60}, "用户名:")

	submitBtn := NewButton("submit_btn", Point{200, 100}, "登录", func() {
		fmt.Println("  ✅ 登录按钮被点击！验证凭据...")
	})

	cancelBtn := NewButton("cancel_btn", Point{300, 100}, "取消", func() {
		fmt.Println("  ❌ 取消操作")
	})
	cancelBtn.IsDisabled = true // 禁用取消按钮

	userList := NewListBox(
		"user_list",
		Point{50, 150},
		[]string{"管理员-张三", "编辑-李四", "访客-王五", "运维-赵六"},
	)
	userList.Select(0) // 默认选中第一项

	// 多态容器
	var widgets []Painter = []Painter{title, nameInput, submitBtn, cancelBtn, userList}

	// 渲染所有控件
	RenderWidgets(widgets)

	// 处理可点击的控件
	var clickable []Clicker
	for _, w := range widgets {
		if c, ok := w.(Clicker); ok {
			clickable = append(clickable, c)
		}
	}
	HandleClicks(clickable)

	// 类型断言获取具体功能
	fmt.Println("\n=== 特定操作 ===")
	if listBox, ok := widgets[4].(*ListBox); ok {
		listBox.Select(2)
		listBox.Paint()
	}
}

// 原文中的特定类型实现
type UndoableIntSet struct {
    IntSet    // Embedding
    functions []func()
}

package main

import (
	"errors"
	"fmt"
	"time"
)

// ==================== 泛型Undo框架 ====================

// UndoAction 表示一个撤销动作
type UndoAction func()

// UndoStack 泛型撤销栈
type UndoStack struct {
	actions []UndoAction
	maxSize int
}

func NewUndoStack(maxSize int) *UndoStack {
	if maxSize <= 0 {
		maxSize = 100 // 默认最大100步
	}
	return &UndoStack{
		actions: make([]UndoAction, 0, maxSize),
		maxSize: maxSize,
	}
}

// Push 添加撤销动作
func (u *UndoStack) Push(action UndoAction) error {
	if len(u.actions) >= u.maxSize {
		return errors.New("undo stack overflow")
	}
	u.actions = append(u.actions, action)
	return nil
}

// Undo 执行撤销
func (u *UndoStack) Undo() error {
	if len(u.actions) == 0 {
		return errors.New("nothing to undo")
	}

	// 弹出最后一个动作
	index := len(u.actions) - 1
	action := u.actions[index]

	// 执行撤销
	action()

	// 从栈中移除
	u.actions = u.actions[:index]
	return nil
}

// CanUndo 是否可以撤销
func (u *UndoStack) CanUndo() bool {
	return len(u.actions) > 0
}

// Count 待撤销的操作数
func (u *UndoStack) Count() int {
	return len(u.actions)
}

// Clear 清空撤销栈
func (u *UndoStack) Clear() {
	u.actions = u.actions[:0]
}

// ==================== 泛型集合接口 ====================

// Collection 泛型集合接口（约束）
type Collection[T any] interface {
	Add(item T)
	Remove(item T) bool
	Contains(item T) bool
	Len() int
	Clear()
	ForEach(fn func(T))
}

// ==================== 具体集合实现 ====================

// IntSet 整数集合
type IntSet struct {
	data map[int]bool
	undo *UndoStack
}

func NewIntSet() *IntSet {
	return &IntSet{
		data: make(map[int]bool),
		undo: NewUndoStack(50),
	}
}

func (s *IntSet) Add(x int) {
	if s.Contains(x) {
		s.undo.Push(func() {}) // 空操作，已存在
		return
	}
	s.data[x] = true
	s.undo.Push(func() { delete(s.data, x) })
}

func (s *IntSet) Remove(x int) bool {
	if !s.Contains(x) {
		s.undo.Push(func() {})
		return false
	}
	delete(s.data, x)
	s.undo.Push(func() { s.data[x] = true })
	return true
}

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

func (s *IntSet) Len() int {
	return len(s.data)
}

func (s *IntSet) Clear() {
	s.data = make(map[int]bool)
}

func (s *IntSet) ForEach(fn func(int)) {
	for k := range s.data {
		fn(k)
	}
}

func (s *IntSet) Undo() error {
	return s.undo.Undo()
}

func (s *IntSet) String() string {
	items := make([]int, 0, len(s.data))
	for k := range s.data {
		items = append(items, k)
	}
	return fmt.Sprintf("{%v}", items)
}

// StringSet 字符串集合（展示泛型的威力）
type StringSet struct {
	data map[string]bool
	undo *UndoStack
}

func NewStringSet() *StringSet {
	return &StringSet{
		data: make(map[string]bool),
		undo: NewUndoStack(50),
	}
}

func (s *StringSet) Add(x string) {
	if s.Contains(x) {
		s.undo.Push(func() {})
		return
	}
	s.data[x] = true
	s.undo.Push(func() { delete(s.data, x) })
}

func (s *StringSet) Remove(x string) bool {
	if !s.Contains(x) {
		s.undo.Push(func() {})
		return false
	}
	delete(s.data, x)
	s.undo.Push(func() { s.data[x] = true })
	return true
}

func (s *StringSet) Contains(x string) bool {
	return s.data[x]
}

func (s *StringSet) Len() int           { return len(s.data) }
func (s *StringSet) Clear()            { s.data = make(map[string]bool) }
func (s *StringSet) ForEach(fn func(string)) {
	for k := range s.data {
		fn(k)
	}
}
func (s *StringSet) Undo() error         { return s.undo.Undo() }
func (s *StringSet) String() string {
	items := make([]string, 0, len(s.data))
	for k := range s.data {
		items = append(items, k)
	}
	return fmt.Sprintf("{%v}", items)
}

// ==================== 泛型事务管理器 ====================

// TransactionalCollection 支持事务的集合装饰器
type TransactionalCollection[T comparable] struct {
	collection Collection[T]
	undo        *UndoStack
	inTxn       bool
	txnActions  []UndoAction
}

func NewTransactionalCollection[T comparable](c Collection[T]) *TransactionalCollection[T] {
	return &TransactionalCollection[T]{
		collection: c,
		undo:       NewUndoStack(100),
		inTxn:      false,
		txnActions: make([]UndoAction, 0),
	}
}

func (tc *TransactionalCollection[T]) Add(item T) {
	action := func() { tc.collection.Remove(item) }

	tc.collection.Add(item)

	if tc.inTxn {
		tc.txnActions = append(tc.txnActions, action)
	} else {
		tc.undo.Push(action)
	}
}

func (tc *TransactionalCollection[T]) Remove(item T) bool {
	if !tc.collection.Contains(item) {
		return false
	}

	action := func() { tc.collection.Add(item) }
	tc.collection.Remove(item)

	if tc.inTxn {
		tc.txnActions = append(tc.txnActions, action)
	} else {
		tc.undo.Push(action)
	}
	return true
}

func (tc *TransactionalCollection[T]) BeginTransaction() {
	tc.inTxn = true
	tc.txnActions = tc.txnActions[:0]
	fmt.Println("📝 开始事务...")
}

func (tc *TransactionalCollection[T]) CommitTransaction() {
	if !tc.inTxn {
		return
	}

	// 将事务内的所有动作推入全局撤销栈
	for i := len(tc.txnActions) - 1; i >= 0; i-- {
		tc.undo.Push(tc.txnActions[i])
	}

	tc.inTxn = false
	tc.txnActions = tc.txnActions[:0]
	fmt.Println("✅ 事务提交成功")
}

func (tc *TransactionalCollection[T]) RollbackTransaction() {
	if !tc.inTxn {
		return
	}

	// 反向执行所有事务内操作
	for i := len(tc.txnActions) - 1; i >= 0; i-- {
		tc.txnActions[i]()
	}

	tc.inTxn = false
	tc.txnActions = tc.txnActions[:0]
	fmt.Println("❌ 事务已回滚")
}

func (tc *TransactionalCollection[T]) Undo() error {
	return tc.undo.Undo()
}

func (tc *TransactionalCollection[T]) Contains(item T) bool {
	return tc.collection.Contains(item)
}

func (tc *TransactionalCollection[T]) Len() int {
	return tc.collection.Len()
}

func (tc *TransactionalCollection[T]) ForEach(fn func(T)) {
	tc.collection.ForEach(fn)
}

// ==================== 使用示例 ====================

func main() {
	fmt.Println("===== 整数集合 Undo 演示 =====")

	intSet := NewIntSet()

	// 添加元素
	fmt.Println("\n添加元素:")
	for _, n := range []int{1, 3, 5, 7, 9} {
		intSet.Add(n)
		fmt.Printf("  Add(%d) → %s\n", n, intSet)
	}

	// 删除元素
	fmt.println("\n删除元素:")
	for _, n := range []int{3, 7} {
		intSet.Remove(n)
		fmt.Printf("  Remove(%d) → %s\n", n, intSet)
	}

	// Undo操作
	fmt.println("\n执行 Undo:")
	for i := 0; i < 3; i++ {
		if err := intSet.Undo(); err != nil {
			fmt.Printf("  Undo #%d: %v\n", i+1, err)
			break
		}
		fmt.Printf("  Undo #%d → %s\n", i+1, intSet)
	}

	// 继续Undo到清空
	fmt.println("\n全部 Undo:")
	for intSet.Undo() == nil {
		fmt.Printf("  ... → %s\n", intSet)
	}

	// ========== 字符串集合 ==========
	fmt.Println("\n===== 字符串集合 Undo 演示 =====")

	strSet := NewStringSet()
	strings := []string{"apple", "banana", "cherry", "date", "elderberry"}

	fmt.Println("\n添加水果:")
	for _, s := range strings {
		strSet.Add(s)
		fmt.Printf("  Add(%q) → %s\n", s, strSet)
	}

	// 移除一些
	fmt.Println("\n移除水果:")
	strSet.Remove("banana")
	strSet.Remove("date")
	fmt.Printf("  当前状态: %s\n", strSet)

	// Undo
	fmt.Println("\nUndo 两次:")
	strSet.Undo()
	fmt.Printf("  After Undo #1: %s\n", strSet)
	strSet.Undo()
	fmt.Printf("  After Undo #2: %s\n", strSet)

	// ========== 事务演示 ==========
	fmt.Println("\n===== 事务演示 =====")

	txIntSet := NewTransactionalCollection[int](NewIntSet())

	txIntSet.BeginTransaction()
	fmt.Println("\n事务中操作:")
	txIntSet.Add(10)
	txIntSet.Add(20)
	txIntSet.Add(30)
	txIntSet.Remove(20)
	fmt.Printf("  事务内状态: 元素数=%d\n", txIntSet.Len())

	// 提交事务
	fmt.Println("\n提交事务:")
	txIntSet.CommitTransaction()
	fmt.Printf("  提交后状态: 元素数=%d\n", txIntSet.Len())

	// 可以Undo整个事务
	fmt.Println("\nUndo事务:")
	txIntSet.Undo()
	txIntSet.Undo()
	txIntSet.Undo()
	fmt.Printf("  Undo后状态: 元素数=%d\n", txIntSet.Len())

	// ========== 回滚演示 ==========
	fmt.Println("\n===== 回滚演示 =====")

	txStrSet := NewTransactionalCollection[string](NewStringSet())
	txStrSet.BeginTransaction()

	txStrSet.Add("red")
	txStrSet.Add("green")
	txStrSet.Add("blue")
	fmt.Printf("  事务内: %s\n", txStrSet.Len()) // 3个

	fmt.Println("回滚事务:")
	txStrSet.RollbackTransaction()
	fmt.Printf("  回滚后: %s\n", txStrSet.Len()) // 0个
}

// ❌ 依赖具体类型
func ProcessUser(db *MySQLDB) { ... }

// ✅ 依赖接口
type UserRepository interface {
    GetUser(id string) (*User, error)
    SaveUser(user *User) error
}

func ProcessUser(repo UserRepository) { ... }

// ❌ 大接口（违反ISP）
type Manager interface {
    Manage()
    Lead()
    Code()
    Design()
    Test()
    Deploy()
}

// ✅ 小接口组合
type Coder interface { Code() }
type Leader interface { Lead() }
type Manager interface {
    Coder
    Leader
}

// Go 1.18+: 泛型函数
func First[T any](items []T) (T, bool) {
    var zero T
    if len(items) == 0 {
        return zero, false
    }
    return items[0], true
}

// 使用
nums := []int{1, 2, 3}
firstNum, ok := First(nums)

strs := []string{"a", "b"}
firstStr, ok := First(strs)

// ❌ 过深的嵌入层次
type UltraButton struct {
    *AdvancedButton // 嵌入
}
type AdvancedButton struct {
    *StyledButton // 嵌入
}
type StyledButton struct {
    *BaseButton // 嵌入
}
// 维护噩梦！

// ✅ 扁平化 + 组合
type Button struct {
    base    *BaseWidget
    actions ActionHandlers
}