Pointers

• Pointers
• Creating Pointers
• Dereferencing Pointers
• The new Function
• Working with nil
• Types With Internal Pointers

Creating Pointers

package main

import ("fmt")

func main() {
    var a int = 42

  // *int is a pointer to int type
    // & gets the address of a
  var b *int = &a
  fmt.Println(&a, b)     
}

Dereferencing Pointers

package main

import ("fmt")

func main() {
    var a int = 42
    var b *int = &a
  fmt.Println(&a, b)

  // precede pointer with * to dereference the pointer
    fmt.Println(a, *b)

}

The new Function

package main

import ("fmt")


func main() {
    var ms *myStruct
  // initializing a variable to a pointer to an object
  ms = &myStruct{foo: 21}
    fmt.Println(ms)
}

type myStruct struct {
    foo int
}

- another way to create pointers to an object - can't initialize the fields at the same time

package main

import ("fmt")

func main() {
    var ms *myStruct
    ms = new(myStruct)

    // go dereference object pointers automatically
    ms.foo = 32 // (*ms).foo = 32
    fmt.Println(ms.foo) // fmt.Println((*ms).foo)
}

type myStruct struct {
    foo int
    bar string
}

Working with nil

package main

import ("fmt")


func main() {
    var ms *myStruct

  // print uninitialized pointer: <nil>
  fmt.Println(ms)

  // initializing a variable to a pointer to an object
  ms = &myStruct{foo: 21}
    fmt.Println(ms)
}

type myStruct struct {
    foo int
}

Types With Internal Pointers

• all assignment operations in Go are copy operations
• slices and maps contain internal pointers, so copies point to same underlying data

package main

import ("fmt")

func main() {
  // since slices are made up of pointers, bot a, b change
    a := []int{1, 2, 3}
    b := a
    fmt.Println(a, b)
    a[1] = 31
    fmt.Println(a, b)

  // [1 2 3] [1 2 3]
  // [1 31 3] [1 31 3]
}

package main

import ("fmt")

func main() {
    a := map[string]string{"foo": "bar", "baz": "buz"}
    b := a
    fmt.Println(a, b)
    a["foo"] = "qux "
    fmt.Println(a, b)

  // map[baz:buz foo:bar] map[baz:buz foo:bar]
  // map[baz:buz foo:qux ] map[baz:buz foo:qux ]
}