Scala-esittelyn jäsentelyä 25.8.08

• "You know who you are. You're the developer who picked up Java years ago, maybe as a second language and better alternative to C++, maybe as your first language coming into the industry. You're comfortable with Java, you know its ins and outs, its moods. It's like an old girlfriend; you may not feel the vibe anymore, but you know just how to rub it so it smiles. In short, you're a craftsman, and Java is your workhorse tool. You're starting to to become a bit pragmatic about your language choice though. To put it mildly, the Java honeymoon is over. While you can hardly find enough fault with the language to just walk away, you're certainly open-minded enough to consider alternatives." [Daniel Spiewak blogissaan Scala for Java Refugees]

• Miksi Scala?

• Javaa Scalalla: Scala-kielelle muokattuja esimerkkejä kurssimateriaalista Ohjelmoinnin perusteita Java-kielellä

• Linkkejä Scala-sivuille

• [Scala-sivuni]

• ... yksi esimerkki vielä ...

• Funktionaalinen olio - "immutaabeli" olio:
  "Immutable objects offer several advantages over mutable objects, and one potential disadvantage. First, immutable objects are often easier to reason about than mutable ones, because they do not have complex state spaces that change over time. Second, you can pass immutable objects around quite freely, whereas you may need to make defensive copies of mutable objects before passing them to other code. Third, there is no way for two threads concurrently accessing an immutable to corrupt its state once it has been properly constructed, because no thread can change the state of an immutable. Fourth, immutable objects make safe hashtable keys. If a mutable object is mutated after it is placed into a HashSet, for example, that object may not be found the next time you look into the HashSet. The main disadvantage of immutable objects is that they sometimes require that a large object graph be copied where otherwise an update could be done in place. In some cases this can be awkward to express and might also cause a performance bottleneck. As a result, it is not uncommon for libraries to provide mutable alternatives to immutable classes. For example, class StringBuilder is a mutable alternative to the immutable String."
  [Odersky, Spoon, Venners: Programming in Scala, 4th preprint]

• Esimerkki [Scala by Example]:

  class Rational(n: Int, d: Int) {
    private def gcd(x: Int, y: Int): Int = {
      if (x == 0) y
      else if (x < 0) gcd(-x, y)
      else if (y < 0) gcd(x, -y)
      else gcd(y % x, x)
    }
    private val g = gcd(n, d)
  
    val numer: Int = n/g
    val denom: Int = d/g
    def +(that: Rational) =
      new Rational(numer * that.denom + that.numer * denom,
                   denom * that.denom)
    def -(that: Rational) =
      new Rational(numer * that.denom - that.numer * denom,
                   denom * that.denom)
    def *(that: Rational) =
      new Rational(numer * that.numer, denom * that.denom)
    def /(that: Rational) =
      new Rational(numer * that.denom, denom * that.numer)
  
    override def toString() = "(" + numer + "/" + denom +")"  // oma lisäys
                                                              // korjattu 21.10.2008!
  }
  
  //--- pää ------------------ oma lisäys 
  
  object ratio {
    def main(args: Array[String]) = {
       val a = new Rational(2,3)
       val b = new Rational(1,4)
       println(a+b)
       println(a-b)
       println(a*b)
       println(a/b)
    }
  }
  
  

  Ohjelma tulostaa:

  (11/12)
  (5/12)
  (1/6)
  (8/3)
  
  

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