After a long time here is a post about Scala again. I played around with composition of objects an classes from traits.

This post is also a reaction to Thomas Biskups post Toying around ..., where he played around with Qi4j to perhaps find a better architecture for his rogue like rpg “JADE”. We sometimes talking about this and I once mentioned Scalas traits.

So here is a little example of object and class composition with traits in Scala from the domain of role play games. I implemented some simple traits which I used to compose a class and a (singelton) object.

package de.myndian.scala.rpg

// Something that has a “name”
trait Named
{
  def name : String
}

// Something that has “power”
trait Powered
{
  def power : Int
}

// A namend thing that can be hitted 
trait Hitable
{
  this: Named =>
  
  var hitpoints : Int
  
  def hit(points : Int)
  {
    hitpoints -= points
    print(name + “ was hitted with ” + points + “ points. ”) 
    if(hitpoints <= 0)
      println(name + " is dead.")
    else
      println(name + " has " + hitpoints + " hitpoints remaining.")
  }
}

// A named thing that can use its power to hit a hittable
trait Fighter
{
  this : Named with Powered =>
  
  val rnd = new Random(System.currentTimeMillis)
  
  def hit(target : Named with Hitable)
  {
    println(name + “ hits ” + target.name)
    target.hit(rnd.nextInt(power))
  }
}

class Door(val name : String, var hitpoints : Int) 
    extends Named
    with Hitable


// In this fight the dwarf “kills” a door 
object DemoFight
    extends Application
{
  var aDoor = new Door(“a door”, 10)

  object TheDwarf
      extends Named
      with Hitable
      with Fighter
      with Powered
  {
    val name = “the dwarf”
    val power = 10
    var hitpoints = 20
  }

  while(aDoor.hitpoints > 0)
    TheDwarf.hit(aDoor)
}

Some sample output:

the dwarf hits a door
a door was hitted with 3 points. a door has 7 hitpoints remaining.
the dwarf hits a door
a door was hitted with 7 points. a door is dead.

So Thomas, what about “SADE”? ;-)