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Subtle change in outer capture under -Ydelambdafy:method #9408

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scabug opened this issue Jul 18, 2015 · 6 comments
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Subtle change in outer capture under -Ydelambdafy:method #9408

scabug opened this issue Jul 18, 2015 · 6 comments
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@retronym
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backend
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2.12.0-M3

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@scabug
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scabug commented Jul 18, 2015 

// test.scala
class C {
  def test {
    println({() => class D; classOf[D].getDeclaredFields.mkString(",")}.apply())
  }
}

object Test {
  def main(args: Array[String]): Unit = {
    new C().test
  }

}
% scalac-hash v2.11.7 test.scala  && scala-hash v2.11.7 Test
public final C$$anonfun$test$1 C$$anonfun$test$1$D$1.$outer

% scalac-hash v2.11.7 -Ydelambdafy:method test.scala  && scala-hash v2.11.7 -Ydelambdafy:method Test
public final C C$D$1.$outer

This difference is observable via a change in memory retention, or a change in the serializability of D (as seen in the wild in Shapeless: milessabin/shapeless@ac12155)

I'm not really sure why we need an outer pointer at all for a local class such as D.
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scabug commented Jul 18, 2015

Imported From: https://issues.scala-lang.org/browse/SI-9408?orig=1
Reporter: @retronym
Affected Versions: 2.11.7
See #4440, #1419

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scabug commented Jul 18, 2015

@retronym said:
See also the discussion bewteen me and @milessabin on on the shapeless commit: milessabin/shapeless@ac12155

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scabug commented Jul 19, 2015

@milessabin said (edited on Jul 19, 2015 10:39:25 AM UTC):
See eventual fix in shapeless here.

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scabug commented Jul 22, 2015

@retronym said:
Here's an attempt to infer the finality of local classes with respect to the outer pointer elision optimization: scala/scala@2.12.x...retronym:ticket/9408

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scabug commented Jul 22, 2015

@retronym said:
scala/scala#4652

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scabug commented Jul 22, 2015

@milessabin said:
Awesome ... thanks :-)

@scabug scabug closed this as completed Jul 23, 2015
@scabug scabug added the backend label Apr 7, 2017
@scabug scabug added this to the 2.12.0-M3 milestone Apr 7, 2017
@scabug scabug mentioned this issue Apr 7, 2017
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@som-snytt som-snytt mentioned this issue Dec 11, 2023
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