Aladdin - Scala Bugtracking
[#196] project: compiler priority: medium category: bug
submitter assigned to status date submitted
Matthias Burak fixed 2003-10-15 11:57:51.0
subject Empty sequence pattern yields NullPointerException
code 
object Foo with Executable {
  def test(xs: List[Any]) = xs match {
    case List(b@()) =>
    	Console.println("b = " + b);
  }
  test(List(1));
}
what happened 
Crashes at runtime:

Exception in thread "main" java.lang.ExceptionInInitializerError
        at Foo.main(K.scala)
Caused by: java.lang.NullPointerException
        at Foo$.test(K.scala:3)
        at Foo$.(K.scala:6)
        at Foo$.(K.scala)
        ... 1 more
what expected Fails at runtime with a MatchError.
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Changes of this bug report
Burak  edited on  2003-10-29 15:28:36.0

Although this pattern was generated by your code Matthias (it does not contain | or *), it is a regular expression, so I took care of it. (TestRegTraverser did not handle empty sequences).

The current hack-ish solution is to translate every Pattern that contains a sequence node by Algebraic+SequenceMatcher, where this very annoying special case can be added without major pain. That makes the 'Sequence' parts of the PatternMatcher class obsolete though... they will never be called.