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False match exhaustiveness warning with case class containing enum #7206

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scabug opened this issue Mar 2, 2013 · 4 comments
Closed

False match exhaustiveness warning with case class containing enum #7206

scabug opened this issue Mar 2, 2013 · 4 comments
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@adriaanm
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enum patmat

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@scabug
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scabug commented Mar 2, 2013 

object E extends Enumeration {
  val V = Value
}

sealed case class C(e: E.Value)

class Test {
  def foo(c: C) {
    c match {
      case C(E.V) => {}
    }
  }

  def foo2(e: E.Value) {
    e match {
      case E.V => {}
    }
  }
}

This code produces the following warning in Test.foo:

Test.scala:9: warning: match may not be exhaustive.
It would fail on the following input: C((x: E.Value forSome x not in V))
    c match {
    ^

Test.foo2 produces no warning (as expected), even though it's essentially the same match.
@scabug
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scabug commented Mar 2, 2013

Imported From: https://issues.scala-lang.org/browse/SI-7206?orig=1
Reporter: Роман Донченко (dpb)
Affected Versions: 2.10.0, 2.10.1-RC2, 2.10.1

@scabug
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scabug commented Mar 3, 2013

@adriaanm said:
Scala's Enumeration is implemented purely as a library that the compiler has no knowledge of. I'm reluctant to special-case it in the pattern matcher.

@scabug
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scabug commented Apr 5, 2014

Erik Allik (eallik) said (edited on Apr 5, 2014 3:00:24 AM UTC):
Would it be feasible to make Enumeration use case classes internally so as to benefit from the exhaustiveness checks performed on those?

@scabug
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scabug commented Jan 29, 2016

@retronym said:
Closing as not-a-bug. There have been some efforts to make an alternative version of scala.Enumeration that would be amenable to pattern matching analysis, but we can't really do better with the legacy one.

I recommend using sealed heirarchies of case classes rather than scala.Enumeration. Plain old Java Enums are also a good choice (the pattern matcher can analyse these.)

@scabug scabug closed this as completed Jan 29, 2016
@SethTisue SethTisue mentioned this issue Sep 10, 2022
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