Question

您能告诉我这个Scala代码有什么问题吗？

package com.user.common

class Notification(message: String, next: Option[Notification]) {
  def write(): String = {
    message
  }

  def getAll(): Stream[Notification] = {
    next match {
      case Some(n) => Stream.cons(n, n.getAll())
      case None => Stream.empty
    }
  }
}

case class Email(msg: String)
  extends Notification(msg, None)

case class SMS(msg: String)
  extends Notification(msg, Option(Email))

case class VoiceRecording(msg: String)
  extends Notification(msg, Option(SMS))

编译器的错误如下所示。

[error] /common/Test.scala:15: type mismatch;
[error]  found   : Some[A]
[error]  required: Option[com.user.common.Notification]
[error]       case Some(n) => Stream.cons(n, n.getAll())
[error]                ^
[error] /common/Test.scala:15: type mismatch;
[error]  found   : A
[error]  required: com.user.common.Notification
[error]       case Some(n) => Stream.cons(n, n.getAll())
[error]                                   ^
[error] /common/Test.scala:15: value getAll is not a member of type parameter A
[error]       case Some(n) => Stream.cons(n, n.getAll())
[error]                                        ^
[error] /common/Test.scala:25: type mismatch;
[error]  found   : com.user.common.Email.type
[error]  required: com.user.common.Notification
[error]   extends Notification(msg, Option(Email))
[error]                                    ^
[error] /common/Test.scala:28: type mismatch;
[error]  found   : com.user.common.SMS.type
[error]  required: com.user.common.Notification
[error]   extends Notification(msg, Option(SMS))
[error]                                    ^
[error] 5 errors found
[error] (compile:compileIncremental) Compilation failed

我无法理解这个问题。同样，我不知道如何重组代码。我的基本想法是保持一个案例类的值并迭代它们直到我达到无。从顶级案例类到低级别案例类。

Answer 1

case class SMS(msg: String)
  extends Notification(msg, Option(Email))

case class VoiceRecording(msg: String)
  extends Notification(msg, Option(SMS))`

在第二个参数中，您将在类类型上传递一个选项，而该类的实例是预期的

也许你想要的是

case class SMS(msg: String)
  extends Notification(msg, Option(Email(msg)))

case class VoiceRecording(msg: String)
  extends Notification(msg, Option(SMS(msg)))`

Scala递归参数？

1 个答案: