Scala recursive parameters? - scala

Question

Could you please tell me what is wrong with this Scala code?
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))
The errors from compiler are as below.
[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
I could not understand the problem. Similarly, I have no idea how to restructure the code. My basic idea is to keep value of one case class and iterate over them until I reach to None. From top level case class until low level one.

Answer 1

case class SMS(msg: String)
extends Notification(msg, Option(Email))
case class VoiceRecording(msg: String)
extends Notification(msg, Option(SMS))`
In your second parameter, you are passing an option on a class type whereas an instance of the class is expected
Maybe what you want is
case class SMS(msg: String)
extends Notification(msg, Option(Email(msg)))
case class VoiceRecording(msg: String)
extends Notification(msg, Option(SMS(msg)))`