Go结构体的基本使用详解

type 类型名 struct {
    字段名 字段类型
    …
}

//示例：
type Animal struct {
  Name string
  Age  int
}

//结构体实例化
//写法1
//var a Animal 
//a.Name = "aaa"
//a.Age = 18
//写法2
a := Animal{ 
  Name: "dog",
  Age:  18,
}
fmt.Println(fmt.Sprintf("%T - %v", a, a)) //main.Animal - {dog 18}

//结构体指针实例化
//写法1
var b *Animal 
b = new(Animal)
//写法2
//b := new(Animal)  
//写法3
//b := &Animal{}    
b.Name = "cat"                            //在底层是(*b).Name = "cat"，这是Go语言帮我们实现的语法糖
fmt.Println(fmt.Sprintf("%T - %v", b, b)) //*main.Animal - &{cat 0}

var v struct {
  Name string
  Age  int
}
fmt.Println(v)

var v struct{}
fmt.Println(unsafe.Sizeof(v)) //0

v1 := struct{}{}
fmt.Println(unsafe.Sizeof(v1)) //0

func NewPerson(name string, age int8) Person {
  return Person{
    name: name,
    age:  age,
  }
}

func NewPerson(name string, age int8) *Person {
  return &Person{
    name: name,
    age:  age,
  }
}

func (接收者变量 接收者类型) 方法名(参数列表) (返回参数) {
    函数体
}

func NewPerson(name string, age int8) *Person {
  return &Person{
    name: name,
    age:  age,
  }
}

func (p *Person) Dream() {
  p.name = "aaa"
  fmt.Printf("%s的梦想是学好Go语言\n", p.name)  //aaa的梦想是学好Go语言
}

func main() {
  p1 := NewPerson("小王子", 25)
  p1.Dream()
  fmt.Println(p1) //&{aaa 25}
}

type MyInt int

func (i MyInt) SayInt() {
  fmt.Println("my type is MyInt")
}

func main() {
  var i1 MyInt
  i2 := MyInt(10)
  i1.SayInt()
  i2.SayInt()
}

输出结果：
my type is MyInt
my type is MyInt

type User struct {
  Name    string
  Gender  string
  Address //匿名字段
}

type Address struct {
  Province   string
  City       string
  CreateTime string
}

func main() {
  var u1 User
  u1.Name = "张三"
  u1.Gender = "男"
  u1.Address.City = "北京" //匿名字段默认使用类型名作为字段名
  u1.CreateTime = "2019" //匿名字段可以省略，但注意多个匿名字段下有相同字段名，会编译失败，所以建议不采用省略写法
  fmt.Println(u1)
}

type Animal struct {
  Name string
  Age  int
}

func (a Animal) Say() {
  fmt.Println(fmt.Sprintf("1-my name is %s and age is %d", a.Name, a.Age))
}

type Cat struct {
  Animal //嵌套结构体实现继承
}

func main() {
  c1 := Cat{}
  c1.Name = "加菲猫"
  c1.Age = 5
  c1.Say()

  //输出结果：
  //1-my name is 加菲猫 and age is 5
}

func (c Cat) Say() {
  fmt.Println(fmt.Sprintf("2-my name is %s and age is %d", c.Name, c.Age))
}

func (c Cat) Run() {
  fmt.Println(fmt.Sprintf("my name is %s，还是跑步高手", c.Name))
}

func main() {
  c1 := Cat{}
  c1.Name = "加菲猫"
  c1.Age = 5
  c1.Say()
  c1.Run()

  //输出结果：
  //2-my name is 加菲猫 and age is 5
  //my name is 加菲猫，还是跑步高手
}

`key1:"value1" key2:"value2"`

type CardInfo struct {
  Title  string `json:"title"`
  Desc   string
  height int `json:"height"`
}

func main() {
  c1 := CardInfo{
    Title:  "成长之星",
    Desc:   "balabala",
    height: 100,
  }
  data, _ := json.Marshal(c1)
  fmt.Println(string(data)) //{"title":"成长之星","Desc":"balabala"}

  str := "{"title":"title111", "desc":"desc222", "height":20}"
  c2 := CardInfo{}
  _ = json.Unmarshal([]byte(str), &c2)
  fmt.Println(c2) //{title111 desc222 0}
}