OnJava8-Examples/staticchecking/petspeak.go

// staticchecking/petspeak.go
// <20>2016 MindView LLC: see Copyright.txt
package main
import "fmt"

type Cat struct {}
func (this Cat) speak() { fmt.Printf("meow!\n")}

type Dog struct {}
func (this Dog) speak() { fmt.Printf("woof!\n")}

type Bob struct {}
func (this Bob) bow() { fmt.Printf("thank you, thank you!\n") }
func (this Bob) speak() { fmt.Printf("Welcome to the neighborhood!\n") }
func (this Bob) drive() { fmt.Printf("beep, beep!\n") }

type Speaker interface {
  speak()
}

func command(s Speaker) { s.speak() }

// If "Speaker" is never used anywhere else, it can be anonymous:
func command2(s interface { speak() }) { s.speak() }

func main() {
  command(Cat{})
  command(Dog{})
  command(Bob{})
  command2(Cat{})
  command2(Dog{})
  command2(Bob{})
}