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Extractor on type alias in conjunction with other pattern causes error #9190

scabug opened this Issue Feb 27, 2015 · 3 comments


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scabug commented Feb 27, 2015

The following snippet results in compilation error with scala 2.11.x (full stacktrace in attachment). Note that only two patterns together (with extractor first) in match clause brings error.

java.lang.AssertionError: assertion failed: (trait Two,type One)
trait Test {
  trait Two[A, B]
  type One[A] = Two[A, A]

  object Extract {
    def unapply(o: One[_]): Option[_] = ???

  def matcher[T](o: One[T]) = o match {
    case Extract(t) => ??? // extractor alone is ok
    case _: One[_]  => ??? // other pattern in conjunction with extractor causes error
    case _          => ??? // wildcard pattern is also ok

Scala version 2.10.4 compiles fine. This seems to be a regression introduced in 2.11.0 and affected subsequent versions.


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scabug commented Feb 27, 2015

Imported From:
Reporter: Dmitry Bushev (4e6)
Affected Versions: 2.11.0, 2.11.1, 2.11.2, 2.11.3, 2.11.4, 2.11.5

  • stacktrace.log (created on Feb 27, 2015 12:03:06 PM UTC, 16057 bytes)

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scabug commented Mar 2, 2015

@alexeyr said:
Might be related to (or a duplicate of?) #9114

@scabug scabug added the patmat label Apr 7, 2017


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xuwei-k commented Aug 16, 2018

duplicate #9114. fixed since Scala 2.11.9

@xuwei-k xuwei-k closed this Aug 16, 2018

@SethTisue SethTisue added this to the 2.11.11 milestone Aug 16, 2018

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