Add Chapter 4: Functions and Interfaces - Closures, Defer, Panic/Recover, and Interfaces (Deep Dive)

2026-03-23 23:30:20 +00:00
parent 67e47dd5dd
commit aa46d006a8
3 changed files with 1327 additions and 0 deletions
--- a/chapters/chapter-4/main.go
+++ b/chapters/chapter-4/main.go
@@ -0,0 +1,429 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"time"
+)
+
+// 4.1 函数基础
+func add(a, b int) int {
+	return a + b
+}
+
+func divide(a, b float64) (float64, error) {
+	if b == 0 {
+		return 0, fmt.Errorf("除数不能为零")
+	}
+	return a / b, nil
+}
+
+func divideNamed(a, b float64) (result float64, err error) {
+	if b == 0 {
+		err = fmt.Errorf("除数不能为零")
+		return
+	}
+	result = a / b
+	return
+}
+
+func sum(nums ...int) int {
+	total := 0
+	for _, n := range nums {
+		total += n
+	}
+	return total
+}
+
+func functionBasics() {
+	fmt.Println("=== 函数基础 ===")
+	fmt.Println("add(3, 4):", add(3, 4))
+	
+	result, err := divide(10, 2)
+	if err != nil {
+		fmt.Println("错误:", err)
+	} else {
+		fmt.Printf("10 / 2 = %.2f\n", result)
+	}
+	
+	result2, _ := divideNamed(20, 4)
+	fmt.Printf("20 / 4 = %.2f\n", result2)
+	
+	fmt.Println("sum(1,2,3,4,5):", sum(1, 2, 3, 4, 5))
+	nums := []int{10, 20, 30}
+	fmt.Println("sum(nums...):", sum(nums...))
+}
+
+// 4.2 闭包
+func createCounter() func() int {
+	count := 0
+	return func() int {
+		count++
+		return count
+	}
+}
+
+func createMultiplier(factor int) func(int) int {
+	return func(x int) int {
+		return x * factor
+	}
+}
+
+func closureLoopBug() {
+	funcs := make([]func(), 3)
+	for i := 0; i < 3; i++ {
+		funcs[i] = func() {
+			fmt.Print(i, " ")
+		}
+	}
+	fmt.Print("Bug: ")
+	for _, f := range funcs {
+		f()
+	}
+	fmt.Println()
+}
+
+func closureLoopFix() {
+	funcs := make([]func(), 3)
+	for i := 0; i < 3; i++ {
+		i := i
+		funcs[i] = func() {
+			fmt.Print(i, " ")
+		}
+	}
+	fmt.Print("Fix: ")
+	for _, f := range funcs {
+		f()
+	}
+	fmt.Println()
+}
+
+func closureDemo() {
+	fmt.Println("\n=== 闭包示例 ===")
+	
+	counter := createCounter()
+	fmt.Println("counter():", counter()) // 1
+	fmt.Println("counter():", counter()) // 2
+	fmt.Println("counter():", counter()) // 3
+	
+	double := createMultiplier(2)
+	triple := createMultiplier(3)
+	fmt.Println("double(5):", double(5))  // 10
+	fmt.Println("triple(5):", triple(5))  // 15
+	
+	closureLoopBug()
+	closureLoopFix()
+}
+
+// 4.3 defer
+func deferDemo() {
+	fmt.Println("\n=== defer 示例 ===")
+	
+	defer fmt.Println("延迟 1")
+	defer fmt.Println("延迟 2")
+	fmt.Println("立即执行")
+	
+	// defer 参数求值
+	i := 0
+	defer fmt.Println("defer 时求值 i =", i)
+	i = 10
+	
+	// 闭包 defer
+	defer func() {
+		fmt.Println("执行时求值 i =", i)
+	}()
+	
+	fmt.Println("defer 结束")
+}
+
+func deferLoopDemo() {
+	fmt.Println("\n=== defer 循环陷阱 ===")
+	
+	// 错误：循环中 defer
+	for i := 0; i < 3; i++ {
+		f, err := os.Create(fmt.Sprintf("temp%d.txt", i))
+		if err != nil {
+			fmt.Println("创建文件失败:", err)
+			continue
+		}
+		defer f.Close() // 所有 defer 在函数结束时执行
+		f.WriteString("test")
+	}
+	
+	// 正确：立即执行
+	for i := 0; i < 3; i++ {
+		func() {
+			f, err := os.Create(fmt.Sprintf("temp2_%d.txt", i))
+			if err != nil {
+				return
+			}
+			defer f.Close()
+			f.WriteString("test")
+		}()
+	}
+	
+	fmt.Println("文件操作完成")
+}
+
+// 4.4 panic 和 recover
+func panicDemo() {
+	fmt.Println("\n=== panic 和 recover ===")
+	
+	defer func() {
+		if r := recover(); r != nil {
+			fmt.Println("捕获 panic:", r)
+		}
+	}()
+	
+	fmt.Println("开始")
+	panic("发生错误")
+	fmt.Println("不会执行")
+}
+
+type MyError struct {
+	Code    int
+	Message string
+}
+
+func (e MyError) Error() string {
+	return fmt.Sprintf("错误码 %d: %s", e.Code, e.Message)
+}
+
+func safeDivide(a, b int) int {
+	if b == 0 {
+		panic(MyError{Code: 1001, Message: "除数不能为零"})
+	}
+	return a / b
+}
+
+func handlePanic() {
+	defer func() {
+		if r := recover(); r != nil {
+			if err, ok := r.(MyError); ok {
+				fmt.Printf("自定义错误：代码=%d, 消息=%s\n", err.Code, err.Message)
+			} else {
+				fmt.Printf("未知 panic: %v\n", r)
+			}
+		}
+	}()
+	
+	safeDivide(10, 0)
+}
+
+func panicRecoverDemo() {
+	panicDemo()
+	handlePanic()
+}
+
+// 4.5 接口
+type Speaker interface {
+	Speak() string
+}
+
+type Dog struct {
+	Name string
+}
+
+func (d Dog) Speak() string {
+	return d.Name + " 汪汪叫"
+}
+
+type Cat struct {
+	Name string
+}
+
+func (c Cat) Speak() string {
+	return c.Name + " 喵喵叫"
+}
+
+func makeSound(s Speaker) {
+	fmt.Println(s.Speak())
+}
+
+func typeAssertionDemo() {
+	fmt.Println("\n=== 类型断言 ===")
+	
+	var v interface{} = "hello"
+	
+	// 基本断言
+	if s, ok := v.(string); ok {
+		fmt.Println("是字符串:", s)
+	}
+	
+	// 类型开关
+	switch t := v.(type) {
+	case int:
+		fmt.Printf("整数：%d\n", t)
+	case string:
+		fmt.Printf("字符串：%s\n", t)
+	default:
+		fmt.Printf("未知类型：%T\n", t)
+	}
+}
+
+func interfaceDemo() {
+	dog := Dog{Name: "旺财"}
+	cat := Cat{Name: "咪咪"}
+	
+	makeSound(dog)
+	makeSound(cat)
+	
+	typeAssertionDemo()
+}
+
+// 4.6 综合案例：插件系统
+type Plugin interface {
+	Name() string
+	Run() error
+}
+
+type HelloPlugin struct{}
+
+func (h HelloPlugin) Name() string {
+	return "HelloPlugin"
+}
+
+func (h HelloPlugin) Run() error {
+	fmt.Println("Hello from plugin!")
+	return nil
+}
+
+type MathPlugin struct{}
+
+func (m MathPlugin) Name() string {
+	return "MathPlugin"
+}
+
+func (m MathPlugin) Run() error {
+	fmt.Printf("2 + 2 = %d\n", 2+2)
+	return nil
+}
+
+func pluginDemo() {
+	fmt.Println("\n=== 插件系统 ===")
+	
+	plugins := []Plugin{
+		HelloPlugin{},
+		MathPlugin{},
+	}
+	
+	for _, p := range plugins {
+		fmt.Printf("加载插件：%s\n", p.Name())
+		if err := p.Run(); err != nil {
+			fmt.Println("插件运行失败:", err)
+		}
+	}
+}
+
+// 4.6 综合案例：中间件链
+type Middleware func(Handler) Handler
+type Handler func(string) string
+
+func logging(next Handler) Handler {
+	return func(input string) string {
+		fmt.Printf("[LOG] 输入：%s\n", input)
+		result := next(input)
+		fmt.Printf("[LOG] 输出：%s\n", result)
+		return result
+	}
+}
+
+func timing(next Handler) Handler {
+	return func(input string) string {
+		start := time.Now()
+		result := next(input)
+		fmt.Printf("[TIME] 耗时：%v\n", time.Since(start))
+		return result
+	}
+}
+
+func auth(next Handler) Handler {
+	return func(input string) string {
+		if input == "" {
+			return "错误：空输入"
+		}
+		return next(input)
+	}
+}
+
+func businessLogic(input string) string {
+	return "处理结果：" + input
+}
+
+func middlewareDemo() {
+	fmt.Println("\n=== 中间件链 ===")
+	
+	handler := auth(timing(logging(businessLogic)))
+	result := handler("测试数据")
+	fmt.Println("最终结果:", result)
+}
+
+// 4.6 综合案例：错误包装
+type AppError struct {
+	Code    int
+	Message string
+	Cause   error
+}
+
+func (e *AppError) Error() string {
+	if e.Cause != nil {
+		return fmt.Sprintf("错误码 %d: %s (原因：%v)", e.Code, e.Message, e.Cause)
+	}
+	return fmt.Sprintf("错误码 %d: %s", e.Code, e.Message)
+}
+
+func wrapError(err error, code int, message string) error {
+	if err == nil {
+		return nil
+	}
+	return &AppError{
+		Code:    code,
+		Message: message,
+		Cause:   err,
+	}
+}
+
+func readFile(path string) ([]byte, error) {
+	return nil, fmt.Errorf("文件不存在")
+}
+
+func processFile(path string) error {
+	data, err := readFile(path)
+	if err != nil {
+		return wrapError(err, 1001, "读取文件失败")
+	}
+	
+	if len(data) == 0 {
+		return wrapError(nil, 1002, "文件为空")
+	}
+	
+	return nil
+}
+
+func errorHandlingDemo() {
+	fmt.Println("\n=== 错误处理链 ===")
+	
+	err := processFile("test.txt")
+	if err != nil {
+		if appErr, ok := err.(*AppError); ok {
+			fmt.Printf("应用错误：代码=%d, 消息=%s\n", appErr.Code, appErr.Message)
+			if appErr.Cause != nil {
+				fmt.Printf("根本原因：%v\n", appErr.Cause)
+			}
+		} else {
+			fmt.Println("未知错误:", err)
+		}
+	}
+}
+
+func main() {
+	functionBasics()
+	closureDemo()
+	deferDemo()
+	deferLoopDemo()
+	panicRecoverDemo()
+	interfaceDemo()
+	pluginDemo()
+	middlewareDemo()
+	errorHandlingDemo()
+}