demonstrate addition of methods to existing classes, and typesafe dynamic pattern matching on baseclass references

addme.scala

class Base {
	def doit = println ("base")
}

class Sub1 extends Base {
	override def doit = println ("sub1")
	def onething = println("specific to sub1")
}

class Sub2 extends Base {
	override def doit = println ("sub2")
	def otherthing = println("specific to sub2")
}

class Sub3 extends Base {
	override def doit = println ("sub3")
}


/// extensions


// this are just helper methods for pattern-match/destructuring
object Sub1 {
	def unapply(s : Sub1) = Some("ciao from s1")
}

object Sub2 {
	def unapply(s : Sub2) = Some("ciao from s2")
}

// this one demonstrates a pattern match on subclasses of Base and destructuring assignment
case class BaseStuff(val thing: Base)  {
	def act = {
		println ("base stuff .... ")
		thing match {
			case sub1 : Sub1 => 
// the following 3 lines are equivalent
//				sub1 match {case Sub1(message) => println("acting on a sub1 " + message)}
//				val message = sub1 match { case Sub1(message) => message}
				val Sub1(message) = sub1

				println("acting on a sub1 " + message)
				sub1.onething
			case Sub2(message) => 
				println("acting on a sub2 " + message)
// By using destructuring/pattern-match in the case pattern, we don't have access to the value casted with type Sub2
//				sub2.otherthing
// but we can cast it
				(thing.asInstanceOf[Sub2]).otherthing
			case _ =>
				println("unhandled case....")
		}
	}
}

// this one adds the method "act" to instances of "Base" 
implicit def base2basestuff(x: Base) = new BaseStuff(x)

val ss = List(new Sub1, new Sub2, new Sub3)

println("-- testing")

ss.foreach(s => s.act)