Scala for the Impatient: Chapter 6 exercises solutions

sfti_ch06_exercises.scala

//1. Write an object Conversions with methods inchesToCentimeters, gallonsToLiters, and
//milesToKilometers.

object Conversions {
	def inchesToCentimeters(inches: Double) = inches * 2.54
	
	def gallonsToLiters(gallons: Double) = gallons * 3.78541
	
	def milesToKilometers(miles: Double) = miles * 1.60934
}

//2. The preceding problem wasn't very object-oriented. Provide a general superclass
//UnitConversion and define objects InchesToCentimeters, GallonsToLiters, and
//MilesToKilometers that extend it.

class UnitConversion(val conversionFactor: Double) {
	private def convert(value: Double) = value * conversionFactor
	
	def apply(value: Double) = convert(value)
}

object InchesToCentimeters extends UnitConversion(2.54) {}
object GallonsToLiters extends UnitConversion(3.78541) {}
object MilesToKilometers extends UnitConversion(1.60934) {}

//3. Define an Origin object that extends java.awt.Point. Why is this not actually a
//good idea? (Have a close look at the methods of the Point class.)
// Maybe because Point class has a move() etc. methods and origin shouldn't move??

object Origin extends java.awt.Point {}

//4. Define a Point class with a companion object so that you can construct Point
//instances as Point(3, 4), without using new.

class Point(val x: Int, val y: Int) {
	override def toString = "(" + x + ", " + y + ")"
}

object Point {
  def apply(x: Int, y: Int) = new Point(x, y)
}

//5. Write a Scala application, using the App trait, that prints the command-line
//arguments in reverse order, separated by spaces. For example, scala Reverse
//Hello World should print World Hello.

object Reverse extends App {
	for(s <- args.reverse) print(s + " ")
	println()
}

//6. Write an enumeration describing the four playing card suits so that the toString
//method returns ♣, ♦, ♥, or ♠.

object CardSuite extends Enumeration {
	type CardSuite = Value
	val Club = Value("♣")
	val Diamond = Value("♦")
	val Heart = Value("♥")
	val Spade = Value("♠")
}

//7. Implement a function that checks whether a card suit value from the preceding exercise is red.
import CardSuite._
def isRed(card: CardSuite) = card == Diamond || card == Heart

//8. Write an enumeration describing the eight corners of the RGB color cube. As
//IDs, use the color values (for example, 0xff0000 for Red).

object RGBCube extends Enumeration {
	val Black = Value(0x000000, "Black")
	val Red = Value(0xff0000, "Red")
	val Green = Value(0x00ff00, "Green")
	val Yellow = Value(0xffff00, "Yellow")
	val Blue = Value(0x0000ff, "Blue")
	val Cyan = Value(0x00ffff, "Cyan")
	val Magenta = Value(0xff00ff, "Magenta")
	val White = Value(0xffffff, "White")
}

For answer 7, Spade should be Heart.

My 6:

object Reverse extends App {
  print(args.reverse.mkString(" "))
}