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lazy val reset and not re-evaluated in tail recursion #9730

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scabug opened this issue Mar 31, 2016 · 2 comments
Closed

lazy val reset and not re-evaluated in tail recursion #9730

scabug opened this issue Mar 31, 2016 · 2 comments
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backend
Milestone
2.12.0-M5

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@scabug
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scabug commented Mar 31, 2016 

import scala.annotation.tailrec

object TestLazyTail {

  def main(args: Array[String]): Unit = (() => f(true))()

  @tailrec
  private def f(next: Boolean): Unit = {
    // Should always output 5!
    lazy val x = 5
    println(x)

    if (next) f(false) else ()
  }
}

Output is:

5
0

Expected:

5
5

The necessary conditions I've found for this to show the issue:

  1. The call to the function must be in a closure
  2. The function must be tail optimized
  3. The function must be private
  4. The variable must be a lazy val

Other aspects of this snippet don't seem to impact the result.
@scabug
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scabug commented Mar 31, 2016

Imported From: https://issues.scala-lang.org/browse/SI-9730?orig=1
Reporter: Branden Visser (mrvisser)
Affected Versions: 2.11.8

@scabug
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scabug commented Aug 16, 2016

@SethTisue said:
got fixed along the way, somewhere during 2.12 development

@scabug scabug closed this as completed Aug 16, 2016
@scabug scabug added the backend label Apr 7, 2017
@scabug scabug added this to the 2.12.0-M5 milestone Apr 7, 2017
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