oop - Scala:匹配案例类

Question

以下代码声称 jack 受雇于建筑业，但简是经济不景气的另一个受害者:

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"
  }
}

为什么匹配无法将 Jane 识别为学生？

Answer 1

我相信这里发生的是 Student案例类在 Person 内声明.因此 case Student在 toString只会匹配 Student s 是特定 Person 的一部分实例。

如果您移动 case class Student平行于 case class Worker (然后从 extends Person("Jake") 中删除不必要的 object Narrator ......这只是为了让 new Student 最终成为 Jake 特有的 Person$Student)，你会发现 Jane 确实研究生物学。