Pointer #

package main

import (
	"fmt"
)

func noPointer() string {
	return "string"
}
func pointerReturnNil() *string {
	return nil // You cannot return nil from a function that returns a string
	// but you can return nil from a function that returns a pointer to a string!
	// The zero value of a pointer is nil
}
func pointerReturnAndOpt() *string {
	s := "string" // &"string" doesn't work.
	return &s
}
func main() {
	fmt.Println(">>> noPointer() return a string >>> ")
	fmt.Println(noPointer()) // prints string
	fmt.Println("")

	fmt.Println(">>> pointerReturnNil() return nil (*string) >>> ")
	fmt.Println(pointerReturnNil()) // prints <nil>
	fmt.Println("")

	fmt.Println(">>> pointerReturnAndOpt() return &s >>> ")
	fmt.Println(pointerReturnAndOpt()) // prints something like 0x40c158 (an address in memory)
	fmt.Println("")

	fmt.Println(">>> s holds an address im memeory, return &s >>> ")
	s := pointerReturnAndOpt() // now s holds an address in memory for a variable
	fmt.Println(s)             // something like 0x40c138
	fmt.Println(*s)
	fmt.Println("")

	fmt.Println(">>> sp holds the value >>> ")
	sp := *s        // now sp holds the value found at the address s holds
	fmt.Println(sp) // string
	fmt.Println(&sp) // sp's address
	fmt.Println("")
}

package main

import (
	"fmt"
)

type User struct {
	Name string
	Pet  []string
}

func (p2 *User) newPet() {
	fmt.Println(*p2, "underlying value of p2 before")
	p2.Pet = append(p2.Pet, "Lucy")
	fmt.Println(*p2, "underlying value of p2 after")
}
func main() {
	u := User{Name: "Anna", Pet: []string{"Bailey"}} // this time we'll generate a pointer!
	fmt.Println(u, "u before")
	p := &u // Let's make a pointer to u!
	p.newPet()
	fmt.Println(u, "u after")
	// Does Anna have a new pet now? Yes!
}