Scala: Matching case classes

Question

The following code claims that Jack is employed in construction, but Jane is yet another victim of the rough economy:

abstract class Person(name: String) {

  case class Student(name: String, major: String) extends Person(name)

  override def toString(): String = this match {
    case Student(name, major) => name + " studies " + major
    case Worker(name, occupation) => name + " does " + occupation
    case _ => name + " is unemployed"
  }
}

case class Worker(name: String, job: String) extends Person(name)

object Narrator extends Person("Jake") {
  def main(args: Array[String]) {
    var friend: Person = new Student("Jane", "biology")
    println("My friend " + friend) //outputs "Jane is unemployed"
    friend = new Worker("Jack", "construction")
    println("My friend " + friend) //outputs "Jack does construction"
  }
}

Why does the match fail to recognize Jane as a Student?

Answer 1

What I believe is happening here is that the Student case class is being declared inside of Person. Hence the case Student in the toString will only match Students that are part of a particular Person instance.

If you move the case class Student to be parallel to the case class Worker (and then remove the unnecessary extends Person("Jake") from object Narrator ... which is only there so that the new Student wound up being a Person$Student specific to Jake), you will find Jane does indeed study biology.