Chapter 11 - Interfaces

Exercise 2: Type Assertions

Here are updated Fan and CoffeePot types, both of which satisfy an Appliance interface. We’ve also added a Use method that accepts an Appliance. Currently, Use only calls the TurnOn method on the Appliance…

Update Use so that it calls Oscillate on the Appliance if (and only if) it’s a Fan. Use should also call Brew on the Appliance if (and only if) it’s a CoffeePot.

Solution

package main

import "fmt"

type Appliance interface {
	TurnOn()
}

type Fan string

func (f Fan) TurnOn() {
	fmt.Println("Spinning")
}
func (f Fan) Oscillate() {
	fmt.Println("Rotating on base")
}

type CoffeePot string

func (c CoffeePot) TurnOn() {
	fmt.Println("Powering up")
}
func (c CoffeePot) Brew() {
	fmt.Println("Heating Up")
}

func Use(appliance Appliance) {
	fmt.Println(appliance)
	appliance.TurnOn()
	// YOUR CODE HERE: If the appliance is a
	// Fan, call its Oscillate method.
	fan, ok := appliance.(Fan)
	if ok {
		fan.Oscillate()
	}
	// If the appliance is a CoffeePot, call
	// its Brew method.
	coffeePot, ok := appliance.(CoffeePot)
	if ok {
		coffeePot.Brew()
	}
}

func main() {
	Use(Fan("Windco Breeze"))
	Use(CoffeePot("LuxBrew"))
}

Output:

Windco Breeze
Spinning
Rotating on base
LuxBrew
Powering up
Heating Up