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3 Next Steps in Scala

// In file next-steps-in-scala/Ex1.scala

  val big = new java.math.BigInteger("12345")


// In file next-steps-in-scala/Ex1.scala

  val greetStrings = new Array[String](3)
  
  greetStrings(0) = "Hello"
  greetStrings(1) = ", "
  greetStrings(2) = "world!\n"

  for i <- 0 to 2 do
    print(greetStrings(i))


// In file next-steps-in-scala/Ex2.scala

  val greetStrings: Array[String] = new Array[String](3)


// In file next-steps-in-scala/Ex2.scala

  greetStrings(0) = "Hello"
  greetStrings(1) = ", "
  greetStrings(2) = "world!\n"


// In file next-steps-in-scala/Ex2.scala

  for i <- 0 to 2 do
    print(greetStrings(i))


  greetStrings(0) = "Hello" 


  greetStrings.update(0, "Hello")


// In file next-steps-in-scala/Ex3.scala

  val greetStrings = new Array[String](3)

  greetStrings.update(0, "Hello")
  greetStrings.update(1, ", ")
  greetStrings.update(2, "world!\n")

  for i <- 0.to(2) do
    print(greetStrings.apply(i))


// In file next-steps-in-scala/Ex3.scala

  val numNames = Array("zero", "one", "two")


// In file next-steps-in-scala/Ex3.scala

  val numNames2 = Array.apply("zero", "one", "two")


  

Step 1. Use lists

// In file next-steps-in-scala/Ex3.scala

  val oneTwoThree = List(1, 2, 3)


// In file next-steps-in-scala/Ex3.scala

  val oneTwo = List(1, 2)
  val threeFour = List(3, 4)
  val oneTwoThreeFour = oneTwo ::: threeFour


// In file next-steps-in-scala/Ex3.scala

  val twoThree = List(2, 3)
  val oneTwoThree = 1 :: twoThree


// In file next-steps-in-scala/Ex3.scala

  val oneTwoThree = 1 :: 2 :: 3 :: Nil


  

Step 2. Use tuples

// In file next-steps-in-scala/Ex3.scala

  val pair = (99, "Luftballons")
  val num = pair(0)  // type Int, value 99
  val what = pair(1) // type String, value "Luftballons"


  

Step 3. Use sets and maps

// In file next-steps-in-scala/Ex3.scala

  var jetSet = Set("Boeing", "Airbus")
  jetSet += "Lear"
  val query = jetSet.contains("Cessna") // false


// In file next-steps-in-scala/Ex3.scala

  jetSet = jetSet + "Lear"


// In file next-steps-in-scala/Ex3.scala

  import scala.collection.mutable

  val movieSet = mutable.Set("Spotlight", "Moonlight")
  movieSet += "Parasite"
  // movieSet now contains: "Spotlight", "Moonlight", "Parasite"


// In file next-steps-in-scala/Ex3.scala

  import scala.collection.immutable.HashSet

  val hashSet = HashSet("Tomatoes", "Chilies")
  val ingredients = hashSet + "Coriander"
  // ingredients contains "Tomatoes", "Chilies", "Coriander"


// In file next-steps-in-scala/Ex3.scala

  import scala.collection.mutable

  val treasureMap = mutable.Map.empty[Int, String]
  treasureMap += (1 -> "Go to island.")
  treasureMap += (2 -> "Find big X on ground.")
  treasureMap += (3 -> "Dig.")
  val step2 = treasureMap(2) // "Find big X on ground."


// In file next-steps-in-scala/Ex3.scala

  val romanNumeral = Map(
    1 -> "I", 2 -> "II", 3 -> "III", 4 -> "IV", 5 -> "V"
  )
  val four = romanNumeral(4) // "IV"


  

Step 4. Learn to recognize the functional style

// In file next-steps-in-scala/Ex3.scala

  def printArgs(args: List[String]): Unit =
    var i = 0
    while i < args.length do
      println(args(i))
      i += 1


// In file next-steps-in-scala/Ex3.scala

  def printArgs(args: List[String]): Unit =
    for arg <- args do
      println(arg)


// In file next-steps-in-scala/Ex3.scala

  def printArgs(args: List[String]): Unit =
    args.foreach(println)


// In file next-steps-in-scala/Ex3.scala

  def formatArgs(args: List[String]) = args.mkString("\n")


// In file next-steps-in-scala/Ex3.scala

  println(formatArgs(args))


// In file next-steps-in-scala/Ex3.scala

  val res = formatArgs(List("zero", "one", "two"))
  assert(res == "zero\none\ntwo")


  

Step 5. Transform with map and for-yield

  val adjectives = List("One", "Two", "Red", "Blue")


  val nouns = adjectives.map(adj => adj + " Fish")
  // List(One Fish, Two Fish, Red Fish, Blue Fish)


  val nouns =
    for adj <- adjectives yield
      adj + " Fish"
  // List(One Fish, Two Fish, Red Fish, Blue Fish)


  val lengths = nouns.map(noun => noun.length)
  // List(8, 8, 8, 9)


  val lengths =
    for noun <- nouns yield
      noun.length
  // List(8, 8, 8, 9)


  val ques = Vector("Who", "What", "When", "Where", "Why")

  val usingMap = ques.map(q => q.toLowerCase + "?")
  // Vector(who?, what?, when?, where?, why?)

  val usingForYield =
    for q <- ques yield
      q.toLowerCase + "?"
  // Vector(who?, what?, when?, where?, why?)


  val startsW = ques.find(q => q.startsWith("W")) // Some(Who)
  val hasLen4 = ques.find(q => q.length == 4)     // Some(What)
  val hasLen5 = ques.find(q => q.length == 5)     // Some(Where)
  val startsH = ques.find(q => q.startsWith("H")) // None


  startsW.map(word => word.toUpperCase)      // Some(WHO)


  for word <- startsW yield word.toUpperCase // Some(WHO)


  startsH.map(word => word.toUpperCase)      // None


  for word <- startsH yield word.toUpperCase // None