scala - 表达相似值对象的惯用 scala/FP 方式

Question

我想知道表达类似消息(值对象)的惯用方式是什么假设我有一些想要发送的消息:UserEnter、UserLeft、UserSendGreeting 等。希望以下内容能表达我的困境

我认为有两个选项可以表达它:

trait UserAction
case class UserEnter (username:String,hour:Long,day:WeekDay,room:Int)
case class UserLeft (username:String,hour:Long,day:WeekDay,room:Int)
case class UserSendGreeting (username:String,,hour:Long,day:WeekDay,greeting:String)

def foo(userActions:List[UserAction]) = {
userActions match {
case UserEnter(userName)::tail =>
sendWelcomeMessage(userName)
handleOtherActions(tail) 

case UserLeft::tail => "must enter first"
case _ => "do something else"
}

另一种方法是:

    trait Action
    case class Enter(room:Int) extends Action
    case object Left(room:Int) extends Action
    case object Greet(msg:String) extends Action

    case class UserAction(username:String,action:Action,,hour:Long,day:WeekDay)

    def foo(userActions:List[UserAction]) = {
    userActions match {
    case head::tail if head.action == Enter =>
    sendWelcomeMessage(head.userName)    
    handleOtherActions(tail)             
    case head::tail if head.action == Left => "must enter first"
    case _ => "do something else"
    }

第一个选项更明确，更容易进行模式匹配，但代码重复性更高。另一种对操作本身更明确，但模式匹配更详细
哪种方式更好？

Answer 1

不要让事情过于复杂化。如果您需要一对User(在您的情况下是字符串名称)和Action，请使用Tuple。将所有“...其他属性”收集到相应的 Action 中也是有意义的。

type User = String

sealed trait Action

case class Enter(room:Int) extends Action

case class Left(room:Int) extends Action

case class Greet(msg:String) extends Action


def foo(userActions:List[(User, Action)]) = userActions match {
    case (username, _:Enter)::tail =>
      sendWelcomeMessage(username)
      handleOtherActions(tail)
    case (username, _:Left)::tail => "must enter first"
    case _ => "do something else"
  }

另外不要忘记，模式匹配允许您取消任意深度的层次结构:

case (username, Enter(room))::tail =>