Go语言中避免空指针解引用错误的策略与实践

package main

import "fmt"

type Astruct struct {
    Number int
    Letter string
}

type Bstruct struct {
    foo int
    AStructList *[]Astruct // 指向Astruct切片的指针
}

type Cstruct struct {
    Bstruct
}

func (a *Astruct) String() string {
    return fmt.Sprintf("Number = %d, Letter = %s", a.Number, a.Letter)
}

func main() {
    c := new(Cstruct) // c.Bstruct.AStructList 此时为 nil
    // 如果此处不进行初始化，直接访问 c.Bstruct.AStructList 将导致 panic
    // for _, x := range(*c.Bstruct.AStructList) { // 错误：解引用 nil 指针
    //     fmt.Printf("%s\n", &x)
    // }

    // 正确的初始化方式（避免 panic）
    astructlist := make([]Astruct, 3)
    for i := range astructlist {
        astructlist[i] = Astruct{i, "a"}
    }
    c.Bstruct = Bstruct{100, &astructlist} // 将指针赋给 AStructList

    for _, x := range(*c.Bstruct.AStructList) {
        fmt.Printf("%s\n", &x)
    }
}

package main

import "fmt"

type Astruct struct {
    Number int
    Letter string
}

type Bstruct struct {
    foo         int
    AStructList []*Astruct // 存储Astruct指针的切片
}

type Cstruct struct {
    Bstruct
}

func (a *Astruct) String() string {
    return fmt.Sprintf("Number = %d, Letter = %s", a.Number, a.Letter)
}

func main() {
    // 初始化一个存储Astruct指针的切片
    astructlist := make([]*Astruct, 3)
    for i := range astructlist {
        astructlist[i] = &Astruct{i, "a"} // 将Astruct实例的地址赋给切片元素
    }

    c := new(Cstruct)
    c.Bstruct = Bstruct{100, astructlist} // 直接将切片赋给 AStructList

    // 遍历时直接使用切片元素（已经是指针）
    for _, x := range c.Bstruct.AStructList {
        fmt.Printf("%s\n", x) // x 已经是 *Astruct 类型，fmt.Printf 会自动解引用
    }

    // 演示 AStructList 为 nil 的情况（不会 panic）
    c2 := new(Cstruct)
    // c2.Bstruct.AStructList 保持零值 nil
    fmt.Println("\n--- c2 示例 ---")
    if c2.Bstruct.AStructList == nil {
        fmt.Println("c2.Bstruct.AStructList is nil (but won't panic on range)")
    }
    for _, x := range c2.Bstruct.AStructList { // 对 nil 切片进行 range 不会 panic
        fmt.Printf("%s\n", x)
    }
    fmt.Println("c2.Bstruct.AStructList range finished without panic.")
}

type User struct {
    Name    string
    Profile *UserProfile // 指向 UserProfile 的指针
}

type UserProfile struct {
    Age     int
    Address string
}

func main() {
    user := User{Name: "Alice"} // user.Profile 此时为 nil

    // 错误：直接访问 user.Profile.Age 会 panic
    // user.Profile.Age = 30

    // 正确：显式初始化 Profile 字段
    user.Profile = &UserProfile{Age: 30, Address: "123 Main St"}
    fmt.Printf("User: %s, Age: %d\n", user.Name, user.Profile.Age)

    // 或者使用 new()
    user2 := User{Name: "Bob"}
    user2.Profile = new(UserProfile)
    user2.Profile.Age = 25
    user2.Profile.Address = "456 Oak Ave"
    fmt.Printf("User: %s, Age: %d\n", user2.Name, user2.Profile.Age)
}

func GetOptionalData() *string {
    // 模拟有时返回数据，有时返回 nil
    if time.Now().Second()%2 == 0 {
        data := "Some data"
        return &data
    }
    return nil
}

func main() {
    dataPtr := GetOptionalData()

    if dataPtr != nil { // 检查指针是否为 nil
        fmt.Printf("Retrieved data: %s\n", *dataPtr)
    } else {
        fmt.Println("No data available.")
    }

    // 对于结构体内部的指针字段
    user := User{Name: "Charlie"}
    // user.Profile 保持 nil

    if user.Profile != nil {
        fmt.Printf("Charlie's age: %d\n", user.Profile.Age)
    } else {
        fmt.Println("Charlie has no profile.")
    }
}