An annotation that gets applied to a selector in a match expression. If it is present, exhaustiveness warnings for that expression will be suppressed.

For example, compiling the code:

    object test extends Application {
      def f(x: Option[int]) = x match {
        case Some(y) => y
      }
      f(None)
    }

will display the following warning:

    test.scala:2: warning: does not cover case {object None}
      def f(x: Option[int]) = x match {
                              ^
    one warning found

The above message may be suppressed by substituting the expression x with (x: @unchecked). Then the modified code will compile silently, but, in any case, a MatchError will be raised at runtime.