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object member variable initialization #9360

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scabug opened this issue Jun 19, 2015 · 2 comments
Closed

object member variable initialization #9360

scabug opened this issue Jun 19, 2015 · 2 comments
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@scabug
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scabug commented Jun 19, 2015

class BaseClass(s: String) {
  def print: Unit = {
    println("hashCode=" + this.hashCode + " | " + this.getClass.getSimpleName + " " + s)
    println(this.getClass.getDeclaringClass.getName)
  }
}

object Object {
  val s: String = "hello"

  object AObj extends BaseClass(s)

  object BObj extends BaseClass(s)

  val list = List(AObj, BObj)

  def print() {
    println(list)
  }
}

object ObjectInit {
  def main(args: Array[String]) {
    Object.AObj.print
    Object.BObj.print
    Object.print
  }
}

Output: AObj in list is null.
List(null, fun.Object$BObj$@28d93b30)
Expected: initialization of list should be initialized correctly independent from Object.AObj.print/Object.AObj.print.

Note: If No Object.AObj.print/Object.AObj.print be called before Object.print, the initialization is correct.

@scabug
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scabug commented Jun 19, 2015

Imported From: https://issues.scala-lang.org/browse/SI-9360?orig=1
Reporter: JIE HUANG (JIEHUANG)
Affected Versions: 2.11.6

@som-snytt
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duplicates #9115

where the nested object depends on a member of the enclosing object.

liufengyun added a commit to scala/scala3 that referenced this issue Jun 16, 2023
The problem is illustrated by the example below:

``` Scala
class Foo(val opposite: Foo)
case object A extends Foo(B)     // A -> B
case object B extends Foo(A)     // B -> A
```
The check aims to be simple for programmers to understand, expressive,
fast, and sound.

The check is centered around two design ideas: (1) initialization-time
irrelevance; (2) partial ordering.

The check enforces the principle of _initialization-time irrelevance_,
which means that the time when a static object is initialized should not
change program semantics. For that purpose, it enforces the following
rule:

> **The initialization of a static object should not directly or
indirectly read or write mutable state owned by another static object**.

This principle not only puts the initialization of static objects on a
solid foundation but also avoids whole-program analysis.

Partial ordering means that the initialization dependencies of static
objects form a directed-acyclic graph (DAG). No cycles with length
bigger than 1 allowed --- which might lead to deadlocks in the presence
of concurrency and strong coupling & subtle contracts between objects.

Related Issues:

#16152
#9176
#11262
scala/bug#9312
scala/bug#9115
scala/bug#9261
scala/bug#5366
scala/bug#9360
@som-snytt som-snytt closed this as not planned Won't fix, can't repro, duplicate, stale Aug 27, 2024
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