match式にてcase classのチェック漏れを検出 ref: http://qiita.com/items/30d02a5306514df67de0

file0.scala

sealed abstract class Season
case class Spring() extends Season
case class Summer() extends Season
case class Fall() extends Season
case class Winter() extends Season

// FallとWinterを忘れたパターンマッチ
scala> def checkSeason(s: Season) = s match {
     | case Spring() => "Spring!"
     | case Summer() => "Summer!"
     | }

file1.txt

<console>:12: warning: match is not exhaustive!
missing combination           Fall
missing combination         Winter

       def checkSeason(s: Season) = s match {
                                    ^
checkSeason: (s: Season)java.lang.String

file2.scala

scala> def checkSeason(s: Season) = (s: @unchecked) match {
     | case Spring() => "Spring!"
     | case Summer() => "Summer!"
     | }

file3.txt

scala> checkSeason(Fall())
scala.MatchError: Fall() (of class Fall)
    at .checkSeason(<console>:12)
                (以下省略)