Practice Time: Extension Functions

 

Practice Time

It can be useful to know the weight of a book, for example, for shipping. The weight of a book can change because sometimes pages get torn, and the page count changes. While calculating the weight could be defined as a method, it’s more like a helper function. Besides, it would hurt a book's feelings to have a method that tears up its pages.

1. Add a mutable property pages to Book.
2. Create an extension function on Book that returns the weight of a book as the page count multiplied by 1.5 grams.
3. Create another extension, tornPages(), that takes the number of torn pages as an argument and changes the page count of the book.
4. Write a class Puppy with a method playWithBook() that takes a book as an argument, and removes a random number of pages from the book.
5. Create a puppy and give it a book to play with, until there are no more pages.

Main File

// File:            Main.kt
// Programmer:      Engineer Nolverto Urias Obeso
// Creation Date:   06/24/2023
// Email:           nolvertou@gmail.com
// Description:     Using extension functions 

fun main() {
    // TODO 5: Create a puppy and give it a book to play with, until there are no more pages.
    val puppy = Puppy()
    val book = Book("A Practical Guide to Adopting UVM", "Sharon Rosenberg", 2011, 320)

    while(book.pages > 0){
        puppy.playWithBook(book)
        println("${book.pages} left in ${book.title}")
    }
    println("Sad puppy, no more pages in ${book.title}. ")
}

// TODO 2: Create an extension function on Book that returns the weight
//  of a book as the page count multiplied by 1.5 grams.
fun Book.weight(): Double = pages * 1.5

// TODO 3: Create another extension, tornPages(), that takes the number of torn pages as
//  an argument and changes the page count of the book.
fun Book.tornPages(tornPages: Int) = if (pages >= tornPages) pages -= tornPages else pages = 0

Book Class

// TODO 1: Add a mutable property pages to Book.
class Book(val title: String, val author: String, val year:Int, var pages: Int) {
}

Puppy Class
import java.util.Random

// TODO 4: Write a class Puppy with a method playWithBook() that takes a book as an argument,
//  and removes a random number of pages from the book.
class Puppy {

    fun playWithBook(book: Book){
        book.tornPages(Random().nextInt(8))
    }
}