package main

import "fmt"

type dog struct {
	name   string
	friend *dog
}

func newDog(name string) *dog {
	return &dog{name: name}
}

func (d *dog) describe() {
	if d.friend == nil {
		fmt.Printf("%s has no friend.\n", d.name)
		return
	}
	fmt.Printf("%s is friends with %s.\n", d.name, d.friend.name)
}

func main() {
	rex := newDog("Rex")
	lassie := newDog("Lassie")
	rex.describe()
	lassie.describe()

	rex.friend = lassie
	rex.describe()
	lassie.describe()

	rex.friend.name = "Lady"
	rex.describe()
	lassie.describe()
}