นิพจน์ match

match คืออะไร

ไวยากรณ์พื้นฐาน

object Main {
  def main(args: Array[String]): Unit = {
    val n = 2
    val word = n match {
      case 1 => "one"
      case 2 => "two"
      case 3 => "three"
    }
    println(word)
  }
}

กรณีไวลด์การ์ด

object Main {
  def main(args: Array[String]): Unit = {
    val n = 9
    val word = n match {
      case 1 => "one"
      case 2 => "two"
      case _ => "many"
    }
    println(word)
  }
}

การจับคู่สตริง

object Main {
  def main(args: Array[String]): Unit = {
    val cmd = "start"
    val msg = cmd match {
      case "start" => "Starting up"
      case "stop"  => "Shutting down"
      case _       => "Unknown command"
    }
    println(msg)
  }
}

match ส่งคืนค่า

object Main {
  def main(args: Array[String]): Unit = {
    val light = "red"
    println(s"Action: " + (light match {
      case "red"   => "stop"
      case "green" => "go"
      case _       => "caution"
    }))
  }
}

การรวมกรณี

object Main {
  def main(args: Array[String]): Unit = {
    val day = "Sat"
    val kind = day match {
      case "Sat" | "Sun" => "weekend"
      case _             => "weekday"
    }
    println(kind)
  }
}

match ในฟังก์ชัน

object Main {
  def describe(n: Int): String = n match {
    case 0 => "zero"
    case 1 => "one"
    case _ => "other"
  }
  def main(args: Array[String]): Unit = {
    println(describe(0))
    println(describe(5))
  }
}

การผูกค่าทั้งหมด

object Main {
  def main(args: Array[String]): Unit = {
    val n = 42
    val result = n match {
      case 0     => "nothing"
      case other => s"got $other"
    }
    println(result)
  }
}

ลำดับมีความสำคัญ

object Main {
  def main(args: Array[String]): Unit = {
    val n = 1
    val msg = n match {
      case 1 => "specific one"
      case _ => "anything else"
    }
    println(msg)
  }
}

เหตุใดจึงใช้ match

นำทุกอย่างมารวมกัน

object Main {
  def grade(score: Int): String = score match {
    case 10 | 9 => "excellent"
    case 8 | 7  => "good"
    case _      => "keep trying"
  }
  def main(args: Array[String]): Unit = {
    println(grade(9))
    println(grade(7))
    println(grade(3))
  }
}

ตรวจสอบอย่างรวดเร็ว

สรุปทบทวน