Scala de Design Pattern: Visitor

　Visitorパターン。
Accepterをパターンマッチングで処理できるので、
Acceptor毎にvisitメソッドを定義しなくて良い。

package designpattern.visitor
trait Acceptor {

    def accept(visitor: Visitor) = visitor.visit(this) 

}
case class AcceptorImpl1 extends Acceptor

case class AcceptorImpl2 extends Acceptor
trait Visitor {

    val name: String

    def visit(acceptor: Acceptor): Unit =

        acceptor match {

            case a:AcceptorImpl1 => println(name + " -> " + a)

            case a:AcceptorImpl2 => println(name + " -> " + a)

            case _ => 

        }

}
class VisitorImpl1 extends Visitor {

    val name = "VisitorImpl1"

}
class VisitorImpl2 extends Visitor {

    val name = "VisitorImpl2"

}
object Main {

    def main(args: Array[String]) = {  

        val a = new AcceptorImpl1

        a.accept(new VisitorImpl1)

        a.accept(new VisitorImpl2)

    }

}