Catatan Pointer Go Lang

p01.go

// You can edit this code!
// Click here and start typing.
package main

import "fmt"

type User struct {
  Name string
  Age  int
}

func changeNameByValue(u User) {
  u.Name = "Andi"
}

func changeNameByPointer(u *User) {
  u.Name = "Andi"
}

func resetAge(age *int) {
  *age = 0
}

func (u *User) Rename(name string) {
  u.Name = name
}

func main() {
  user := User{
    Name: "Budi",
    Age:  25,
  }

  // Awal: {Budi 25}
  fmt.Println("Awal:", user)

  changeNameByValue(user)

  // Setelah changeNameByValue: {Budi 25}
  fmt.Println("Setelah changeNameByValue:", user)

  changeNameByPointer(&user)

  // Setelah changeNameByPointer: {Andi 25}
  fmt.Println("Setelah changeNameByPointer:", user)

  resetAge(&user.Age)

  // Setelah resetAge: {Andi 0}
  fmt.Println("Setelah resetAge:", user)

  user.Rename("Joko")

  // Setelah Rename: {Joko 0}
  fmt.Println("Setelah Rename:", user)

  // Bikin struct langsung dalam bentuk pointer
  userPtr := &User{
    Name: "Siti",
    Age:  30,
  }

  // Ga usah lagi pake *
  changeNameByPointer(userPtr)

  fmt.Println("User pointer:", userPtr.Name, userPtr.Age)
}

p02.go

package main

import "fmt"

// =====================
// INT
// =====================

// value (ga ngaruh)
func addByValue(x int) {
  x = x + 10
}

// pointer (ngaruh)
func addByPointer(x *int) {
  *x = *x + 10
}

// =====================
// STRING
// =====================

// value
func changeNameByValue(name string) {
  name = "Andi"
}

// pointer
func changeNameByPointer(name *string) {
  *name = "Andi"
}

// =====================
// BOOL
// =====================

// value
func setActiveByValue(active bool) {
  active = true
}

// pointer
func setActiveByPointer(active *bool) {
  *active = true
}

// =====================
// MAIN
// =====================

func main() {

  // ---- INT
  age := 20
  addByValue(age)
  fmt.Println("INT value:", age) // 20

  addByPointer(&age)
  fmt.Println("INT pointer:", age) // 30

  // ---- STRING
  name := "Budi"
  changeNameByValue(name)
  fmt.Println("STRING value:", name) // Budi

  changeNameByPointer(&name)
  fmt.Println("STRING pointer:", name) // Andi

  // ---- BOOL
  isActive := false
  setActiveByValue(isActive)
  fmt.Println("BOOL value:", isActive) // false

  setActiveByPointer(&isActive)
  fmt.Println("BOOL pointer:", isActive) // true
}

p03.go

package main

import "fmt"

func main() {

  // =====================
  // STRING
  // =====================

  name := "Budi"

  x := &name       // x pegang alamat name
  fmt.Println(*x)  // buka isi alamat -> "Budi"

  *x = "Andi"      // ubah isi alamat
  fmt.Println(name) // name ikut berubah -> "Andi"

  // =====================
  // INT
  // =====================

  age := 25

  y := &age        // y pegang alamat age
  fmt.Println(*y)  // 25

  *y = 30          // ubah isi alamat
  fmt.Println(age) // 30
}