Add Chapter 3: Data Structures - Arrays, Slices, Maps, and Structs (Deep Dive)

chapters/chapter-3/go.mod

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+module go-tutorial
+
+go 1.21

chapters/chapter-3/main.go

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+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"sort"
+	"sync"
+	"time"
+)
+
+// 3.1 数组示例
+func arrayExamples() {
+	fmt.Println("=== 数组示例 ===")
+	
+	// 声明数组
+	var arr1 [5]int
+	arr2 := [3]string{"A", "B", "C"}
+	arr3 := [4]int{10, 20, 30, 40}
+	arr4 := [5]int{1, 2}  // 部分初始化
+	arr5 := [...]int{1, 2, 3, 4, 5}
+	
+	fmt.Printf("arr1: %v\n", arr1)
+	fmt.Printf("arr2: %v\n", arr2)
+	fmt.Printf("arr3: %v\n", arr3)
+	fmt.Printf("arr4: %v\n", arr4)
+	fmt.Printf("arr5: %v\n", arr5)
+	
+	// 访问和修改
+	arr1[0] = 99
+	fmt.Printf("修改后 arr1: %v\n", arr1)
+	
+	// 多维数组
+	matrix := [2][3]int{
+		{1, 2, 3},
+		{4, 5, 6},
+	}
+	fmt.Printf("matrix[0][1]: %d\n", matrix[0][1])
+}
+
+// 3.2 切片示例
+func sliceExamples() {
+	fmt.Println("\n=== 切片示例 ===")
+	
+	// 从数组创建
+	arr := [5]int{1, 2, 3, 4, 5}
+	s1 := arr[0:3]
+	s2 := arr[1:]
+	s3 := arr[:3]
+	s4 := arr[:]
+	
+	fmt.Printf("s1: %v, len=%d, cap=%d\n", s1, len(s1), cap(s1))
+	fmt.Printf("s2: %v, len=%d, cap=%d\n", s2, len(s2), cap(s2))
+	fmt.Printf("s3: %v, len=%d, cap=%d\n", s3, len(s3), cap(s3))
+	fmt.Printf("s4: %v, len=%d, cap=%d\n", s4, len(s4), cap(s4))
+	
+	// make 创建
+	s5 := make([]int, 5)
+	s6 := make([]int, 3, 10)
+	fmt.Printf("s5: %v, len=%d, cap=%d\n", s5, len(s5), cap(s5))
+	fmt.Printf("s6: %v, len=%d, cap=%d\n", s6, len(s6), cap(s6))
+	
+	// append
+	s7 := []int{1, 2, 3}
+	s7 = append(s7, 4)
+	s7 = append(s7, 5, 6, 7)
+	s8 := []int{8, 9, 10}
+	s7 = append(s7, s8...)
+	fmt.Printf("s7 after append: %v\n", s7)
+	
+	// 容量变化演示
+	fmt.Println("\n容量变化:")
+	s9 := make([]int, 0, 5)
+	for i := 1; i <= 10; i++ {
+		s9 = append(s9, i)
+		fmt.Printf("追加 %d: len=%d, cap=%d\n", i, len(s9), cap(s9))
+	}
+	
+	// copy
+	src := []int{1, 2, 3, 4, 5}
+	dst := make([]int, 3)
+	n := copy(dst, src)
+	fmt.Printf("\n复制了 %d 个元素，dst: %v\n", n, dst)
+	
+	// 共享底层数组陷阱
+	s10 := []int{1, 2, 3, 4, 5}
+	s11 := s10[1:3]
+	s11[0] = 99
+	fmt.Printf("\n共享数组陷阱:\n")
+	fmt.Printf("s10: %v\n", s10)
+	fmt.Printf("s11: %v\n", s11)
+	
+	// 释放内存的正确方式
+	fmt.Println("\n释放内存:")
+	data := make([]int, 1000)
+	small := append([]int(nil), data[:10]...)
+	fmt.Printf("small cap: %d (原 data cap: %d)\n", cap(small), cap(data))
+}
+
+// 3.3 映射示例
+func mapExamples() {
+	fmt.Println("\n=== 映射示例 ===")
+	
+	// 创建映射
+	m1 := make(map[string]int)
+	m1["one"] = 1
+	m1["two"] = 2
+	
+	m2 := map[string]int{
+		"one":   1,
+		"two":   2,
+		"three": 3,
+	}
+	
+	fmt.Printf("m1: %v\n", m1)
+	fmt.Printf("m2: %v\n", m2)
+	
+	// 读取和检查存在
+	value, exists := m2["two"]
+	fmt.Printf("two 存在： %v, 值： %d\n", exists, value)
+	
+	value, exists = m2["four"]
+	fmt.Printf("four 存在： %v, 值： %d\n", exists, value)
+	
+	// 删除
+	delete(m2, "one")
+	fmt.Printf("删除 one 后： %v\n", m2)
+	
+	// 遍历（无序）
+	fmt.Println("\n遍历映射:")
+	for k, v := range m2 {
+		fmt.Printf("%s: %d\n", k, v)
+	}
+	
+	// nil 映射
+	var m3 map[string]int
+	fmt.Printf("\nnil 映射读取： %d\n", m3["key"])
+	// m3["key"] = 1  // panic!
+	
+	// 嵌套映射
+	scores := map[string]map[string]int{
+		"Alice": {"math": 95, "english": 88},
+		"Bob":   {"math": 92, "english": 90},
+	}
+	fmt.Printf("\nAlice 数学成绩： %d\n", scores["Alice"]["math"])
+	
+	// 动态创建
+	if scores["Charlie"] == nil {
+		scores["Charlie"] = make(map[string]int)
+	}
+	scores["Charlie"]["math"] = 85
+	fmt.Printf("Charlie 数学成绩： %d\n", scores["Charlie"]["math"])
+}
+
+// 3.4 结构体示例
+func structExamples() {
+	fmt.Println("\n=== 结构体示例 ===")
+	
+	// 定义结构体
+	type Person struct {
+		Name  string
+		Age   int
+		Email string
+	}
+	
+	// 初始化
+	p1 := Person{Name: "Alice", Age: 25, Email: "alice@example.com"}
+	p2 := Person{"Bob", 30, "bob@example.com"}
+	p3 := Person{Name: "Charlie"}
+	p4 := &Person{Name: "David", Age: 28}
+	
+	fmt.Printf("p1: %+v\n", p1)
+	fmt.Printf("p2: %+v\n", p2)
+	fmt.Printf("p3: %+v\n", p3)
+	fmt.Printf("p4: %+v\n", *p4)
+	
+	// 方法
+	type Rectangle struct {
+		Width  float64
+		Height float64
+	}
+	
+	rect := Rectangle{Width: 10, Height: 5}
+	
+	// 定义方法（在函数外定义）
+	area := rect.Width * rect.Height
+	fmt.Printf("矩形面积： %.2f\n", area)
+	
+	// 嵌入
+	type Employee struct {
+		Person
+		ID     int
+		Salary float64
+	}
+	
+	e := Employee{
+		Person: Person{Name: "Eve", Age: 35},
+		ID:     1001,
+		Salary: 50000,
+	}
+	
+	fmt.Printf("员工姓名： %s\n", e.Name)  // 直接访问嵌入字段
+	fmt.Printf("员工 ID: %d\n", e.ID)
+	
+	// 结构体标签
+	type User struct {
+		ID       int    `json:"id"`
+		Name     string `json:"name"`
+		Email    string `json:"email,omitempty"`
+		Password string `json:"-"`
+	}
+	
+	user := User{ID: 1, Name: "Alice", Email: "alice@example.com", Password: "secret"}
+	jsonData, _ := json.Marshal(user)
+	fmt.Printf("JSON: %s\n", jsonData)
+}
+
+// 3.5 学生管理系统
+type Student struct {
+	ID    int     `json:"id"`
+	Name  string  `json:"name"`
+	Age   int     `json:"age"`
+	Score float64 `json:"score"`
+}
+
+type StudentManager struct {
+	students map[int]*Student
+	nextID   int
+}
+
+func NewStudentManager() *StudentManager {
+	return &StudentManager{
+		students: make(map[int]*Student),
+		nextID:   1,
+	}
+}
+
+func (sm *StudentManager) AddStudent(name string, age int, score float64) int {
+	id := sm.nextID
+	sm.nextID++
+	sm.students[id] = &Student{ID: id, Name: name, Age: age, Score: score}
+	return id
+}
+
+func (sm *StudentManager) GetStudent(id int) *Student {
+	return sm.students[id]
+}
+
+func (sm *StudentManager) UpdateStudent(id int, name string, age int, score float64) bool {
+	if student, exists := sm.students[id]; exists {
+		student.Name = name
+		student.Age = age
+		student.Score = score
+		return true
+	}
+	return false
+}
+
+func (sm *StudentManager) DeleteStudent(id int) bool {
+	if _, exists := sm.students[id]; exists {
+		delete(sm.students, id)
+		return true
+	}
+	return false
+}
+
+func (sm *StudentManager) GetAllStudents() []*Student {
+	students := make([]*Student, 0, len(sm.students))
+	for _, s := range sm.students {
+		students = append(students, s)
+	}
+	return students
+}
+
+func (sm *StudentManager) SortByScore(descending bool) []*Student {
+	students := sm.GetAllStudents()
+	sort.Slice(students, func(i, j int) bool {
+		if descending {
+			return students[i].Score > students[j].Score
+		}
+		return students[i].Score < students[j].Score
+	})
+	return students
+}
+
+func studentManagerDemo() {
+	fmt.Println("\n=== 学生管理系统 ===")
+	
+	manager := NewStudentManager()
+	
+	id1 := manager.AddStudent("Alice", 20, 95.5)
+	id2 := manager.AddStudent("Bob", 22, 88.0)
+	id3 := manager.AddStudent("Charlie", 21, 92.5)
+	
+	fmt.Printf("添加学生 ID: %d, %d, %d\n", id1, id2, id3)
+	
+	manager.UpdateStudent(id1, "Alice", 21, 97.0)
+	fmt.Printf("更新后 Alice: %+v\n", manager.GetStudent(id1))
+	
+	manager.DeleteStudent(id2)
+	fmt.Printf("删除后学生数量： %d\n", len(manager.GetAllStudents()))
+	
+	sorted := manager.SortByScore(true)
+	fmt.Println("\n按分数降序排列:")
+	for _, s := range sorted {
+		fmt.Printf("  %s: %.1f\n", s.Name, s.Score)
+	}
+	
+	jsonStr, _ := json.MarshalIndent(manager.students, "", "  ")
+	fmt.Println("\nJSON 导出:")
+	fmt.Println(string(jsonStr))
+}
+
+// 3.6 性能对比
+func slicePerformance() {
+	fmt.Println("\n=== 切片性能对比 ===")
+	
+	// 预分配容量
+	start := time.Now()
+	s1 := make([]int, 0, 10000)
+	for i := 0; i < 10000; i++ {
+		s1 = append(s1, i)
+	}
+	fmt.Printf("预分配容量耗时： %v\n", time.Since(start))
+	
+	// 不预分配容量
+	start = time.Now()
+	s2 := make([]int, 0)
+	for i := 0; i < 10000; i++ {
+		s2 = append(s2, i)
+	}
+	fmt.Printf("不预分配容量耗时： %v\n", time.Since(start))
+}
+
+// 3.7 并发安全映射
+func concurrentMapDemo() {
+	fmt.Println("\n=== 并发安全映射 ===")
+	
+	var m = make(map[string]int)
+	var mu sync.RWMutex
+	
+	var wg sync.WaitGroup
+	
+	// 写操作
+	for i := 0; i < 100; i++ {
+		wg.Add(1)
+		go func(id int) {
+			defer wg.Done()
+			mu.Lock()
+			m[fmt.Sprintf("key%d", id%10)] = id
+			mu.Unlock()
+		}(i)
+	}
+	
+	wg.Wait()
+	fmt.Printf("最终映射大小： %d\n", len(m))
+}
+
+func main() {
+	arrayExamples()
+	sliceExamples()
+	mapExamples()
+	structExamples()
+	studentManagerDemo()
+	slicePerformance()
+	concurrentMapDemo()
+}