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inconsistency between "non-sensible equals warning" and stable identifier pattern #7211

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scabug opened this issue Mar 3, 2013 · 3 comments
Open

inconsistency between "non-sensible equals warning" and stable identifier pattern #7211

scabug opened this issue Mar 3, 2013 · 3 comments
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fixed in Scala 3 This issue does not exist in the Scala 3 compiler (https://github.com/lampepfl/dotty/) patmat
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@scabug
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scabug commented Mar 3, 2013 

scala> class C; class D
defined class C
defined class D

scala> val c = new C
c: C = C@4acdd9ba

scala> val d = new D
d: D = D@1ee8d9a5

scala> c == d
<console>:12: warning: C and D are unrelated: they will most likely never compare equal
              c == d
                ^
res14: Boolean = false

scala> val c = new C
c: C = C@462d62d9

scala> (new D) match { case `c` => true; case _ => false }
res10: Boolean = false
@scabug
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scabug commented Mar 3, 2013

Imported From: https://issues.scala-lang.org/browse/SI-7211?orig=1
Reporter: @retronym
Affected Versions: 2.10.0
See #5897

@scabug scabug added this to the Backlog milestone Apr 7, 2017
This was referenced Apr 7, 2017
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@scala scala deleted a comment from scabug Feb 1, 2023
@SethTisue
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Scala 3 doesn't warn on c == d, but it rejects the pattern match outright:

1 |(new D) match { case `c` => true; case _ => false }
  |                     ^^^
  |                     Found:    (c : C)
  |                     Required: D
  |                     pattern type is incompatible with expected type

I'm going to chalk that up as a "fixed in Scala 3"

@SethTisue SethTisue added the fixed in Scala 3 This issue does not exist in the Scala 3 compiler (https://github.com/lampepfl/dotty/) label Feb 1, 2023
@som-snytt
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I ran out of steam trying to pin down when dotty gets it correct. Actually I wanted to go out for a run in the sun over an hour ago. I assume it's related to the linked ticket 7655, at least in spirit.

Welcome to Scala 3.2.2 (19, Java OpenJDK 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.

scala> class C; object C extends C; class D extends C; object D extends D; val c = C(); val d = D()
// defined class C
// defined object C
// defined class D
// defined object D
val c: C = C@61911947
val d: D = D@640c216b

scala> D() match { case `c` => }
scala.MatchError: rs$line$1$D@44485db (of class rs$line$1$D)
  ... 33 elided

@som-snytt som-snytt mentioned this issue Feb 4, 2023
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fixed in Scala 3 This issue does not exist in the Scala 3 compiler (https://github.com/lampepfl/dotty/) patmat
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[WIP] Enforce stable id patterns conform under Xsource:3 som-snytt/scala
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@SethTisue @som-snytt @scabug