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Compiler incorrectly reports unreachable code after List() pattern #5029

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scabug opened this issue Sep 26, 2011 · 4 comments
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Compiler incorrectly reports unreachable code after List() pattern #5029

scabug opened this issue Sep 26, 2011 · 4 comments
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@scabug scabug commented Sep 26, 2011

I don't think the following code should produce a compiler error:

scala> (Vector(): Seq[_]) match { case List() => true; case Nil => false }}}
<console>:8: error: unreachable code
              (Vector(): Seq[_]) match { case List() => true; case Nil => false }
                                                                          ^

The following slightly modified version seems to show that the false can be reached:

scala> (Vector(): Seq[_]) match { case List() => true; case x if x == Nil => false }
warning: there were 1 unchecked warnings; re-run with -unchecked for details
res1: Boolean = false

See also this Stack Overflow question.

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@scabug scabug commented Sep 26, 2011

Imported From: https://issues.scala-lang.org/browse/SI-5029?orig=1
Reporter: Travis Brown (travisbrown)
Affected Versions: 2.9.1

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@scabug scabug commented May 12, 2012

@retronym said:
Fixed by virtpatmat in 2.10, test case pending merge:

scala/scala#539

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@scabug scabug commented May 12, 2012

@retronym said:
Needs a bit more thought, see Adriaans comments in the pull request.

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@scabug scabug commented May 12, 2012

@retronym said:
After a brief doubletake triggered by the unintuitive case Nil vs case List, I'm back in the "this ticket is closed" camp.

@scabug scabug closed this May 12, 2012
@scabug scabug added this to the 2.10.0 milestone Apr 7, 2017
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