case class

scala编译器会自动为case class生成apply方法作为构造方法

case class的比较不是比较引用，而是比较每个字段的值。

case class的copy方法，可以改变要copy的某个字段

case class Message(sender: String, recipient: String, body: String)
val message4 = Message("A", "B", "Hello World")
val message5 = message4.copy(body="Hello Earth")

PATTERN MATCHING

scala中的模式匹配除了可以正向检查一个值是否和模式匹配，当匹配成功时，还可以逆向解析出这个值包含的元素如：

abstract class Notification

case class Email(sender: String, title: String, body: String) extends Notification

case class SMS(caller: String, message: String) extends Notification

case class VoiceRecording(contactName: String, link: String) extends Notification


def showNotification(notification: Notification): String = {
  notification match {
    case Email(sender, title, _) =>
      s"You got an email from $sender with title: $title"
    case SMS(number, message) =>
      s"You got an SMS from $number! Message: $message"
    case VoiceRecording(name, link) =>
      s"you received a Voice Recording from $name! Click the link to hear it: $link"
  }
}

模式匹配后还可以加 if <boolean expression> 如：

case Email(sender, title, _) if sender == "vip" =>
      s"You got an vip email from $sender with title: $title"