scala actors example

学习Scala已经有不少时间了，对FP还是不甚了了。现在决定把自己的点滴的进步都记录下来。

 

今天看一个写信并等待回复的场景。

Jilen写了一封信给Yision（是我的一个大学同学），现在Jilen把信投递到邮递员Jerry（另外一个大学同学），邮递员把信送给Yision

Yision收到后回复了一封信给Jilen，这封信同样给邮递员Jerry

 

现在看看我们的类型系统

类型系统分成两类对象，人和消息（信件和回复）

先来看看我们的消息系统

 

sealed trait Message {
  val from: Person
  val to: Person
  val content: String
}
case class Letter(val from: Person, val to: Person, val content: String) extends Message
case class Reply(val from: Person, val to: Person, val content: String) extends Message

 

 Letter是一封信，Reply是一封回信（这里继承体系也许不那么合理）

 

再来看看我们的邮递员

 

/**
 * 邮递员
 */
class Postmen(name: String) extends Person(name) {
  def act = {
    loop {
      reactWithin(1000) {
        case x: Message =>
          println("[postmen] a message from %s to %s".format(x.from.name, x.to.name))
          x.to ! x
        case TIMEOUT =>
          println("[postmen] have no message within 1000 ms, i am now going to have a rest")
          exit()
      }
    }
  }
  start()
}

 

 邮递员这里做两件事，

 

1. 不停查看有没有收到消息，如果有就说有一封从谁写给谁的信需要投递
2. 如果1000ms内没有任何信件，就下班了

Jerry是这里唯一的邮递员

object Jerry extends Postmen("jerry")

 

 

再看看Jilen(我)是怎么写信的，

Jilen是独一无二的，所以他是一个object

    

/* it is me
*/
object Jilen extends Person("jilen") {
  def act {
    loop {
      react {
        case (toWhom: Person, content: String) =>
          //把信件给邮递员
          Jerry ! Letter(this, toWhom, content)
          receive {
            case Reply(from, to, content) =>
              //收到回复了
              println("[Jilen] a reply from " + from.name + " received, writes \"" + content + "\"")
              exit()
          }
      }
    }
  }

  /**
   * 还不知到这是给谁的信
   */
  class NoReceiver(val content: String) {
    /**
     * 指定信给谁，然后投递给邮递员
     */
    def to(whom: Person) = Jilen ! (whom, content)
  }

  def write(content: String) = {
    new NoReceiver(content)
  }
  start()
}

Jilen有个write方法可以在信纸上写上要说的话，返回一个NoReceiver，可以理解成信封上还没写收信人

  /**
   * 还不知到这是给谁的信
   */
  class NoReceiver(val content: String) {
    /**
     * 指定信给谁，然后投递给邮递员
     */
    def to(whom: Person) = Jilen ! (whom, content)
  }

to 方法填好收信人并告诉自己把信投递出去， 投递之后Jilen开始一直等待回复(下面的receive)

 

 case (toWhom: Person, content: String) =>
          //把信件给邮递员
          Jerry ! Letter(this, toWhom, content)
          receive {
            case Reply(from, to, content) =>
              //收到回复了
              println("[Jilen] a reply from " + from.name + " received, writes \"" + content + "\"")
              exit()

 

Yision同样是一个object，他收到了Jilen的信并回复

 

object Yision extends Person("yision") {
  def act = {
    loop {
      react {
        //收到信并回复
        case Letter(from, to, content) =>
          println("[Yision] receive letter from %s, writes %s".format(from.name, to.name))
          Jerry ! Reply(this, from, "i have received a letter from you, and will reply to you soon")
          exit()
      }
    }
  }
  start()
}

 

等等！整个程序还差一个入口。

 

object App {
  def main(args: Array[String]) {
    Jilen write "hello" to Yision //
  }
}

 main方法只有一行，Jilen写了一封信给Yision，这就像一个导火线点燃了后面Jerry和Yision的所有动作。