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cycle with default arguments creates null field #5366

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scabug opened this issue Jan 11, 2012 · 2 comments
Open

cycle with default arguments creates null field #5366

scabug opened this issue Jan 11, 2012 · 2 comments

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@scabug
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@scabug scabug commented Jan 11, 2012

class IdAndMsg(val id: Int,  val msg: String = "")

case object ObjA extends IdAndMsg(1)
case object ObjB extends IdAndMsg(2)

object IdAndMsg {
  val values = List(ObjA , ObjB)
}

object Test {
  def main(args: Array[String]): Unit = {
    ObjA
    println(IdAndMsg.values)
  }
}

/*
Output:
List(null, ObjB)
*/

The cycle is that if one references ObjA first, its superclass has a default argument which is retrieved from object IdAndMsg, which has a val which refers to ObjA, which is null.

It doesn't seem necessary - IdAndMsg.init$default$2 is a static method, but it creates IdAndMsg$ and populates the MODULE$ field so it can call IdAndMsg$.init$default$2. At least in the case of constants, the static method could return it directly and avoid loading the object.

@scabug
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@scabug scabug commented Jan 11, 2012

Imported From: https://issues.scala-lang.org/browse/SI-5366?orig=1
Reporter: @paulp
Affected Versions: 2.8.1, 2.9.3, 2.10.6, 2.11.8, 2.12.0-RC1

@scabug
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@scabug scabug commented May 14, 2012

@lrytz said:
I tried once implementing constructor defaults using static methods but it was not straightforward. I don't remember the details, in principle it could most likely be done.

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