Anonymous Functions

Anonymous functions are true to form in that they have no name. They're useful when defining a function that will only be used once or to create a quick closure.

Let's say we have a function conversions that accepts another function, converter as input:

func conversions(converter func(int) int, x, y, z int) (int, int, int) {
	convertedX := converter(x)
	convertedY := converter(y)
	convertedZ := converter(z)
	return convertedX, convertedY, convertedZ
}

We could define a function normally and then pass it in by name... but it's usually easier to just define it anonymously:

func double(a int) int {
    return a + a
}

func main() {
    // using a named function
	newX, newY, newZ := conversions(double, 1, 2, 3)
	// newX is 2, newY is 4, newZ is 6

    // using an anonymous function
	newX, newY, newZ = conversions(func(a int) int {
	    return a + a
	}, 1, 2, 3)
	// newX is 2, newY is 4, newZ is 6
}

Assignment

Complete the printReports function. It takes as input a sequence of messages, intro, body, outro. It should call printCostReport once for each message.

For each call of printCostReport, give it an anonymous function that returns the cost of a message as an integer. Here are the costs:

• Intro: 2x the message length

• Body: 3x the message length

• Outro: 4x the message length

Use the built-in len() function to get the length of a string:

helloLen := len("hello")
// helloLen = 5

Solution

main.go

package main

import "fmt"

// Solution below

func printReports(intro, body, outro string) {
	printCostReport(func(i string) int {
		return 2 * len(i)
	}, intro)

	printCostReport(func(b string) int {
		return 3 * len(b)
	}, body)

	printCostReport(func(o string) int {
		return 4 * len(o)
	}, outro)
}

// don't touch below this line

func main() {
	printReports(
		"Welcome to the Hotel California",
		"Such a lovely place",
		"Plenty of room at the Hotel California",
	)
}

func printCostReport(costCalculator func(string) int, message string) {
	cost := costCalculator(message)
	fmt.Printf(`Message: "%s" Cost: %v cents`, message, cost)
	fmt.Println()
}