Case Classes and Pattern Matching

Default Cases

Handle unlisted values with a catch-all case.

default-case The `_` case matches anything the earlier cases missed. Its body can still read the original value to build a fallback result.

Default Cases

code
DefaultCase.scala
Replay: real traced execution (multi-file project)
object Main {
  def main(args: Array[String]): Unit = {
    val code = 9
    val label = code match {
      case 1 => "one"
      case 2 => "two"
      case _ => "code:" + code
    }

    println("code=" + code)
    println("label=" + label)
  }
}

object Main {
  def main(args: Array[String]): Unit = {
    val code = 1
    val label = code match {
      case 1 => "one"
      case 2 => "two"
      case _ => "code:" + code
    }

    println("code=" + code)
    println("label=" + label)
  }
}

object Main {
  def main(args: Array[String]): Unit = {
    val code = 2
    val label = code match {
      case 1 => "one"
      case 2 => "two"
      case _ => "code:" + code
    }

    println("code=" + code)
    println("label=" + label)
  }
}

  1. code ← 9, label ← code:9

    1object Main {2  def main(args: Array[String]): Unit = {3    val code→ 9 = 9 //@code=1, 24    val label→ code:9 = code9 match {5      case 1 => "one"6      case 2 => "two"7      case _ => "code:" + code98    }910    println("code=" + code9)11    println("label=" + labelcode:9)12  }13}
    outputcode=9
label=code:9

  1. code ← 1, label ← one

    1object Main {2  def main(args: Array[String]): Unit = {3    val code→ 1 = 14    val label→ one = code1 match {5      case 1 => "one"6      case 2 => "two"7      case _ => "code:" + code18    }910    println("code=" + code1)11    println("label=" + labelone)12  }13}
    outputcode=1
label=one

  1. code ← 2, label ← two

    1object Main {2  def main(args: Array[String]): Unit = {3    val code→ 2 = 24    val label→ two = code2 match {5      case 1 => "one"6      case 2 => "two"7      case _ => "code:" + code28    }910    println("code=" + code2)11    println("label=" + labeltwo)12  }13}
    outputcode=2
label=two