go-poiter-new-make-nil

go-poiter-new-make-nil.go

package main

import "fmt"

func main() {
	// 声明一个变量 aVar 类型为 string
	var aVar string
	fmt.Printf("aVar: %p %#v\n", &aVar, aVar) // 输出 aVar: 0xc42000e240 ""

	aVar = "This is a aVar"
	fmt.Printf("aVar: %p %#v\n", &aVar, aVar) // 输出 aVar: 0xc42000e240 ""

	// 声明一个指针变量 aPot 其类型也是 string
	var aPot *string
	fmt.Printf("aPot: %p %#v\n", &aPot, aPot) // 输出 aPot: 0xc42000c030 (*string)(nil)

	aPot = &aVar
	*aPot = "This is a Pointer"
	fmt.Printf("aVar: %p %#v \n", &aVar, aVar) // 输出 aVar: 0xc42000e240 "This is a Pointer"
	fmt.Printf("aPot: %p %#v %#v \n", &aPot, aPot, *aPot) // 输出 aPot: 0xc42000c030 (*string)(0xc42000e240) "This is a Pointer"

	// 声明另外一个指针变量
	var aNewPot *int
	// 使用new开辟一块内存
	aNewPot = new(int)
	*aNewPot = 217
	fmt.Printf("aNewPot: %p %#v %#v \n", &aNewPot, aNewPot, *aNewPot) // 输出 aNewPot: 0xc42007a028 (*int)(0xc42006e1f0) 217

	// 声明一个数组
	var arr [5]int
	fmt.Printf("arr: %p %#v \n", &arr, arr) // arr: 0xc420014180 [5]int{0, 0, 0, 0, 0}
	arr[0], arr[1] = 1, 2
	fmt.Printf("arr: %p %#v \n", &arr, arr) // arr: 0xc420014180 [5]int{1, 2, 0, 0, 0}

	// 声明一个指针数组
	var arrPot *[5]int
	fmt.Printf("arrPot: %p %#v \n", &arrPot, arrPot) // arrPot: 0xc42000c040 (*[5]int)(nil)
	// 给指针数组初始化其值，即开辟一个内存并返回地址
	arrPot = new([5]int)
	fmt.Printf("arrPot: %p %#v \n", &arrPot, arrPot) // arrPot: 0xc42000c040 &[5]int{0, 0, 0, 0, 0}
	(*arrPot)[0] = 11
	fmt.Printf("arrPot: %p %#v \n", &arrPot, arrPot) // arrPot: 0xc42000c040 &[5]int{11, 0, 0, 0, 0}

	// 声明一个map
	var aMap map[string]string
	fmt.Printf("aMap: %p %#v \n", &aMap, aMap)  // aMap: 0xc42000c048 map[string]string(nil)

	//&aMap = new(map[string]string) // 报错： cannot assign to &aMap
	// 使用make初始化一个map内存，并返回该map
	aMap = make(map[string]string)
	aMap["name"] = "Golang"
	fmt.Printf("aMap: %p %#v \n", &aMap, aMap) // aMap: 0xc420078038 map[string]string{"name":"Golang"}

	// 声明一个map类型的指针
	var mapPot *map[string]int

	fmt.Printf("mapPot: %p %#v \n", &mapPot, mapPot) //  mapPot: 0xc42000c050 (*map[string]int)(nil)
	// 初始化map指针的地址
	mapPot = new(map[string]int)

	fmt.Printf("mapPot: %p %#v \n", &mapPot, mapPot) // mapPot: 0xc42000c050 &map[string]int(nil)

	 //(*mapPot)["age"] = 21 // 报错
	// 初始化map指针指向的map
	(*mapPot) = make(map[string]int)
	(*mapPot)["age"] = 21
	fmt.Printf("mapPot: %p %#v \n", &mapPot, mapPot) // mapPot: 0xc42000c050 &map[string]int{"age":21}

	// 定义一个基于map的自定义类型
	type User map[string]string

	// 初始化，其零值为nil
	var user User

	fmt.Printf("user: %p %#v \n", &user, user)  // user: 0xc42000c060 main.User(nil)
	user = make(User)
	user["name"] = "Golang"
	fmt.Printf("user: %p %#v \n", &user, user) // user: 0xc42007a050 main.User{"name":"Golang"}


	var userPot *User

	fmt.Printf("userPot: %p %#v \n", &userPot, userPot) // userPot: 0xc42000c068 (*main.User)(nil)

	userPot = new(User)
	fmt.Printf("userPot: %p %#v \n", &userPot, userPot) // userPot: 0xc42000c068 &main.User(nil)

	(*userPot) = make(User)
	fmt.Printf("userPot: %p %#v \n", &userPot, userPot) // userPot: 0xc42000c068 &main.User{}

	(*userPot)["name"] = "Golang"
	fmt.Printf("userPot: %p %#v \n", &userPot, userPot) // userPot: 0xc42000c068 &main.User{"name":"Golang"}


	person := Person{"vanyar", 21}
	fmt.Printf("person<%s:%d>\n", person.name, person.age)
	person.sayHi()
	// 值接受者
	person.ModifyAge(210)
	person.sayHi()
	// 指针接受者
	person.ChangeAge(210)
	person.sayHi()

	personPot := &Person{"noldor", 27}
	fmt.Printf("personPot<%s:%d>\n", personPot.name, personPot.age)
	personPot.sayHi()
	personPot.ModifyAge(270)
	personPot.sayHi()
	personPot.ChangeAge(270)
	personPot.sayHi()
}

type Person struct {
	name string
	age int
}

func (p Person) sayHi() {
	fmt.Printf("SayHi -- This is %s, my age is %d\n",p.name, p.age)
}

func (p Person) ModifyAge(age int) {
	fmt.Printf("ModifyAge")
	p.age = age
}

func (p *Person) ChangeAge(age int)  {
	fmt.Printf("ModifyAge")
	p.age = age
}