Golang指针和结构体嵌套使用注意事项

type Address struct {
    City string
}

type User struct {
    Name    string
    Addr    *Address  // 指针字段
}

var u User
u.Addr.City = "Beijing"  // panic: runtime error: invalid memory address

u.Addr = &Address{City: "Beijing"}
// 或
u.Addr = new(Address)
u.Addr.City = "Shanghai"

type Config struct {
    Timeout int
}

func (c Config) SetTimeout(t int) {
    c.Timeout = t  // 修改的是副本
}

type Server struct {
    Conf *Config
}

s := &Server{Conf: &Config{}}
s.Conf.SetTimeout(30)  // 不生效

func (c *Config) SetTimeout(t int) {
    c.Timeout = t  // 修改原始实例
}

type Log struct {
    Level string
}

type App struct {
    Name string
    Log  *Log
}

a1 := App{Name: "app1", Log: &Log{Level: "info"}}
a2 := a1  // 浅拷贝：Log 指针被复制，指向同一对象
a2.Log.Level = "debug"

fmt.Println(a1.Log.Level) // 输出 "debug"，被意外修改

type Engine struct {
    Power int
}

type Car struct {
    *Engine  // 匿名指针字段
    Brand string
}

c := Car{Brand: "Tesla"}
fmt.Println(c.Power) // panic: nil pointer dereference

if c.Engine != nil {
    fmt.Println(c.Engine.Power)
}