// Chapter 29 example: this file does not compile, on purpose. A rock has no
// describe method, so it cannot be used as a describer. Run it and read the
// error, then add the missing method.
//
// Run with: go run exercises/29/04-missing-method.go

package main

import "fmt"

type describer interface {
	describe()
}

type animal struct {
	name string
}

func (a animal) describe() {
	fmt.Printf("%s is an animal.\n", a.name)
}

type rock struct {
	weight int
}

func introduce(d describer) {
	d.describe()
}

func main() {
	introduce(animal{name: "Bug"})
	introduce(rock{weight: 5})
}