Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

object member variable initialization #9360

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

object member variable initialization #9360

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

Comments

@scabug
Copy link

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
Copy link
Author

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
Copy link

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
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Labels
Projects
None yet
Development

Successfully merging a pull request may close this issue.

2 participants