Basic interface example in Go

interface-ex.go

package main

import (
	"fmt"
	"strings"
)

func write(msg string) {
	fmt.Println(msg)
}

type M interface {
	save()
}

type U interface {
	M
	setSlug() User
}

type User struct {
	id int
	name string
	slug string
}

func (u User) save() {
	write("Saving to the users table!")
	fmt.Print(u)
}

func (u User) setSlug() User {
	u.slug = strings.ToLower(u.name)
	return u
}

func main() {
	var u U = User{id: 1, name: "David"}
	u = u.setSlug()
	u.save()
}