Scala de Design Pattern: Observer

Observerパターン。
　

trait Subject {

    var observerCollection = List[Observer]()

    def addObserver(o: Observer)

    def notifyObservers

}
trait Observer {

    def notify(value: Int): Unit

}
object Main {

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

        val concreteSubject = new Subject {

            var i = 0

            def addObserver(o: Observer) = observerCollection :+= o

            def notifyObservers = 

                observerCollection.foreach({ i = i + 1; _.notify(i)})

        }

        

        val observerA = new Observer {

            def notify(value: Int) = println("ObserverA "+ value)

        }

        val observerB = new Observer {

            def notify(value: Int) = println("ObserverB "+ value)

        }

        

        concreteSubject.addObserver(observerA)

        concreteSubject.addObserver(observerB)

        

        concreteSubject.notifyObservers

        concreteSubject.notifyObservers      

    }

}
// 【実行結果】

// ObserverA 1

// ObserverB 1

// ObserverA 2

// ObserverB 2