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scala
Match on inner type generates no compiler warning but fails at runtime
The attached sample code compiles fine in Scala 2.11.7 and Scala 2.10.3 (Scala 2.9.3 warns that "TestMain.scala:9: error: scrutinee is incompatible with pattern type") - even with -unchecked -deprecation -feature -Xfuture -Xfatal-warnings -Xlint compiler options - but prints "ChildA#InnerOne: b.InnerOne" when run, i.e. the match at TestMain:8 matches ChildA#InnerOne although x is ChildB#InnerOne (and thus I'd expect it to print "ChildB#InnerOne: b.InnerOne".
While I think the match should be possible (by type-checking the reference to the outer object) the compiler should at least generate a warning (like it does for matching things like case e:Seq[String]=> ???.
Imported From: https://issues.scala-lang.org/browse/SI-9484?orig=1 Reporter: Bernhard Messerer (messi) Affected Versions: 2.11.7 See #2, #6583 Attachments:
- TestMain.scala (created on Sep 23, 2015 9:54:01 AM UTC, 608 bytes)
At 2.13.8, still no outer checking, but compiler overcompensates by warning:
t9484.scala:9: warning: match may not be exhaustive.
It would fail on the following input: (x: Parent#InnerOne forSome x not in (ChildA#InnerOne, ChildB#InnerOne))
x match {
^
The attached test
object TestMain {
def main(args:Array[String]): Unit = {
val b=new ChildB
val x:Parent#InnerOne=new b.InnerOne("b.InnerOne")
matchInnerOne(x)
}
def matchInnerOne(x:Parent#InnerOne):Unit={
x match {
case ao:ChildA#InnerOne⇒ println("ChildA#InnerOne: "+ao.name)
case bo:ChildB#InnerOne⇒ println("ChildB#InnerOne: "+bo.name)
}
}
}
sealed trait Parent {
sealed trait Inner {
def name:String
}
final class InnerOne(val name:String) extends Inner
final class InnerTwo(val name:String) extends Inner
}
class ChildA extends Parent
class ChildB extends Parent
Oh wait, ChildX are not final. OK, same result if final.
