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Lubs have lost precision since 2.9 #5302

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scabug opened this issue Dec 13, 2011 · 4 comments
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Lubs have lost precision since 2.9 #5302

scabug opened this issue Dec 13, 2011 · 4 comments
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scabug commented Dec 13, 2011 

scala> trait A { val x: A }
defined trait A

scala> trait B { val x: B }
defined trait B

scala> class C extends A with B { lazy val x = new C }
defined class C

scala> class D extends A with B { lazy val x = new D }
defined class D

scala> if (true) new C else new D
res0: ScalaObject with A with B = C@662ad0d

In 2.9 the type of res0 was ScalaObject with A with B { val x: ScalaObject with A with B }.
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scabug commented Dec 13, 2011

Imported From: https://issues.scala-lang.org/browse/SI-5302?orig=1
Reporter: @xeno-by

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scabug commented Dec 13, 2011

@paulp said:
If you run that sequence with "scala -Dscalac.debug.lub" you will see why:

Malformed lub: ScalaObject with A with B{val x: ScalaObject with A with B}
Argument C does not conform.  Falling back to ScalaObject with A with B
lub of List(C, D) is ScalaObject with A with B

So unless I'm further gone than I'm thought, the lub can't be right if one of the contributors to the lub does not conform to it. scalac thinks that !(t <:< lubRefined), in this case that C does not conform. So there is a bug somewhere, but right at this moment it looks to me like a bug in the subtyping logic. I'll open to suggestions.

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scabug commented Dec 13, 2011

@paulp said:
Assigning back to you for either your own suggestion or because you have proximity to martin.

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scabug commented Dec 16, 2011

@paulp said:
Closing as duplicate of #5317 ; see my comment there.

@scabug scabug closed this as completed Dec 16, 2011
@scabug scabug mentioned this issue Apr 7, 2017
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