Multiple Interfaces

A type can implement any number of interfaces in Go. For example, the empty interface, interface{}, is always implemented by every type because it has no requirements.

Assignment

Complete the required methods so that the email type implements both the expense and formatter interfaces.

1

Complete the cost() method

• If the email is not "subscribed", then the cost is 5 cents for each character in the body.

• If it is, then the cost is 2 cents per character.

• Return the total cost of the entire email in cents.

2

Complete the format() method

• It should return a string in this format:

'CONTENT' | Subscribed

• If the email is not subscribed, change the second part to "Not Subscribed":

'CONTENT' | Not Subscribed

The single quotes are included in the string, and CONTENT is the email's body. For example:

'Hello, World!' | Subscribed

You may want to import the fmt package and use Sprintf.

Code (starter)

package main

func (e email) cost() int {
	// ?
}

func (e email) format() string {
	// ?
}

type expense interface {
	cost() int
}

type formatter interface {
	format() string
}

type email struct {
	isSubscribed bool
	body         string
}

Solution

package main

import (
	"fmt"
)

func (e email) cost() int {
	if !e.isSubscribed {
		return len(e.body) * 5
	}
	return len(e.body) * 2
}

func (e email) format() string {
	subscribedText := "Subscribed"
	if !e.isSubscribed {
		subscribedText = "Not Subscribed"
	}
	return fmt.Sprintf("'%s' | %s", e.body, subscribedText)
}

type expense interface {
	cost() int
}

type formatter interface {
	format() string
}

type email struct {
	isSubscribed bool
	body         string
}