Re: NullPointerException for AbstractPartialFunction.orElse in 20110108 trunk (2.10)

I noticed the same problem some weeks ago and filed an issue here:

https://issues.scala-lang.org/browse/SI-5300

On Jan 9, 1:33 am, Trond Olsen wrote:
> Changed nomatchMatcher and messageMatcher to defs but still same exception.
>
> The highlighted line in AbstractPartialFunction is where the exception is
> thrown. I read the error as this.fallBackField somehow has not been set
> (null is its initial value). It is set in fallback, which in turn is only
> called from missingCase and isDefinedAt (conditionally).
>
> abstract class AbstractPartialFunction[-T1, +R]
>     extends AbstractFunction1[T1, R]
>     with PartialFunction[T1, R]
>     with Cloneable {
>
>   private var fallBackField: PartialFunction[T1 @uncheckedVariance, R
> @uncheckedVariance] = _
>
>   def fallBack: PartialFunction[T1, R] = synchronized {
>     if (fallBackField == null) fallBackField = PartialFunction.empty
>     fallBackField
>   }
>
>   override protected def missingCase(x: T1): R = fallBack(x)
>
>   // Question: Need to ensure that fallBack is overwritten before any access
>   // Is the `synchronized` here the right thing to achieve this?
>   // Is there a cheaper way?
>   override def orElse[A1 <: T1, B1 >: R](that: PartialFunction[A1, B1]) :
> PartialFunction[A1, B1] = {
>     val result = this.clone.asInstanceOf[AbstractPartialFunction[A1, B1]]
>     result.synchronized {
> *      result.fallBackField = this.fallBackField orElse that*
>       result
>     }
>   }
>
>   def isDefinedAt(x: T1): scala.Boolean = _isDefinedAt(x) ||
> fallBack.isDefinedAt(x)
>   def _isDefinedAt(x: T1): scala.Boolean
>
> }
>
> 2012/1/8 √iktor Ҡlang
>
>
>
>
>
>
>
> > Avoid using abstract vals unless you're very comfortable with
> > initialization order. Either use abstract def or lazy val.
>
> > Cheers,
> > V
> > On Jan 8, 2012 6:00 PM, "Trond Olsen" wrote:
>
> >> In the classes that mixin the Resumable trait ala:
>
> >> class A
> >>   extends Some
> >>   with Actor with Resumable {
> >>     protected val messageMatcher: PartialFunction[Any, Unit] = {
> >>         case msg =>
> >>     }
> >> }
>
> >> 2012/1/8 √iktor Ҡlang
>
> >>> Where are you assinging:
>
> >>> protected val messageMatcher: PartialFunction[Any, Unit]
>
> >>> ?
>
> >>> On Sun, Jan 8, 2012 at 4:57 PM, Trond Olsen wrote:
>
> >>>> I'm trying out the latest trunk but had some problems running my code.
> >>>> The code segment react(messageMatcher orElse nomatchMatcher) generatesNullPointerException:
>
> >>>> trait Resumable {
> >>>>   this: scala.actors.Actor =>
>
> >>>>   protected val monitor: scala.actors.Actor with Monitoring
> >>>>   protected val messageMatcher: PartialFunction[Any, Unit]
>
> >>>>   private final val nomatchMatcher: PartialFunction[Any, Unit] = {
> >>>>     case Resumable.Exit => exit()
> >>>>     case msg            => monitor.nomatchHandlers.foreach(f => f(this,
> >>>> msg))
> >>>>   }
>
> >>>>   final def act() {
> >>>>     link(monitor)
> >>>>     loop {
> >>>>       react(messageMatcher orElse nomatchMatcher)
> >>>>     }
> >>>>   }
> >>>> }
>
> >>>> with the following stack trace:
>
> >>>> Caused by: java.lang.NullPointerException
> >>>>     at
> >>>> scala.runtime.AbstractPartialFunction.orElse(AbstractPartialFunction.scala:41)
> >>>>     at
> >>>> project.ActorUtil$Resumable$$anonfun$act$1.apply(ActorUtil.scala:34)
> >>>>     at project
> >>>> .ActorUtil$Resumable$$anonfun$act$1.apply(ActorUtil.scala:34)
>
> >>>> Anyone able to spot the problem?
>
> >>>> The AbstractPartialFunction is a new optimization for 2.10:
>
> >>>> override def orElse[A1 <: T1, B1 >: R](that: PartialFunction[A1, B1]) :
> >>>> PartialFunction[A1, B1] = {
> >>>>   val result = this.clone.asInstanceOf[AbstractPartialFunction[A1, B1]]
> >>>>   result.synchronized {
> >>>>     result.fallBackField = this.fallBackField orElse that
> >>>>     result
> >>>>   }
> >>>> }
>
> >>> --
> >>> Viktor Klang
>
> >>> Akka Tech Lead
> >>> Typesafe - Enterprise-Grade Scala from the
> >>> Experts
>
> >>> Twitter: @viktorklang

I noticed the same problem some weeks ago and filed an issue here:

https://issues.scala-lang.org/browse/SI-5300


On Jan 9, 1:33 am, Trond Olsen <tr...@steinbit.org> wrote:
> Changed nomatchMatcher and messageMatcher to defs but still same exception.
>
> The highlighted line in AbstractPartialFunction is where the exception is
> thrown. I read the error as this.fallBackField somehow has not been set
> (null is its initial value). It is set in fallback, which in turn is only
> called from missingCase and isDefinedAt (conditionally).
>
> abstract class AbstractPartialFunction[-T1, +R]
>     extends AbstractFunction1[T1, R]
>     with PartialFunction[T1, R]
>     with Cloneable {
>
>   private var fallBackField: PartialFunction[T1 @uncheckedVariance, R
> @uncheckedVariance] = _
>
>   def fallBack: PartialFunction[T1, R] = synchronized {
>     if (fallBackField == null) fallBackField = PartialFunction.empty
>     fallBackField
>   }
>
>   override protected def missingCase(x: T1): R = fallBack(x)
>
>   // Question: Need to ensure that fallBack is overwritten before any access
>   // Is the `synchronized` here the right thing to achieve this?
>   // Is there a cheaper way?
>   override def orElse[A1 <: T1, B1 >: R](that: PartialFunction[A1, B1]) :
> PartialFunction[A1, B1] = {
>     val result = this.clone.asInstanceOf[AbstractPartialFunction[A1, B1]]
>     result.synchronized {
> *      result.fallBackField = this.fallBackField orElse that*
>       result
>     }
>   }
>
>   def isDefinedAt(x: T1): scala.Boolean = _isDefinedAt(x) ||
> fallBack.isDefinedAt(x)
>   def _isDefinedAt(x: T1): scala.Boolean
>
> }
>
> 2012/1/8 √iktor Ҡlang <viktor.kl...@gmail.com>
>
>
>
>
>
>
>
> > Avoid using abstract vals unless you're very comfortable with
> > initialization order. Either use abstract def or lazy val.
>
> > Cheers,
> > V
> > On Jan 8, 2012 6:00 PM, "Trond Olsen" <tr...@steinbit.org> wrote:
>
> >> In the classes that mixin the Resumable trait ala:
>
> >> class A
> >>   extends Some
> >>   with Actor with Resumable {
> >>     protected val messageMatcher: PartialFunction[Any, Unit] = {
> >>         case msg =>
> >>     }
> >> }
>
> >> 2012/1/8 √iktor Ҡlang <viktor.kl...@gmail.com>
>
> >>> Where are you assinging:
>
> >>> protected val messageMatcher: PartialFunction[Any, Unit]
>
> >>> ?
>
> >>> On Sun, Jan 8, 2012 at 4:57 PM, Trond Olsen <tr...@steinbit.org> wrote:
>
> >>>> I'm trying out the latest trunk but had some problems running my code.
> >>>> The code segment react(messageMatcher orElse nomatchMatcher) generatesNullPointerException:
>
> >>>> trait Resumable {
> >>>>   this: scala.actors.Actor =>
>
> >>>>   protected val monitor: scala.actors.Actor with Monitoring
> >>>>   protected val messageMatcher: PartialFunction[Any, Unit]
>
> >>>>   private final val nomatchMatcher: PartialFunction[Any, Unit] = {
> >>>>     case Resumable.Exit => exit()
> >>>>     case msg            => monitor.nomatchHandlers.foreach(f => f(this,
> >>>> msg))
> >>>>   }
>
> >>>>   final def act() {
> >>>>     link(monitor)
> >>>>     loop {
> >>>>       react(messageMatcher orElse nomatchMatcher)
> >>>>     }
> >>>>   }
> >>>> }
>
> >>>> with the following stack trace:
>
> >>>> Caused by: java.lang.NullPointerException
> >>>>     at
> >>>> scala.runtime.AbstractPartialFunction.orElse(AbstractPartialFunction.scala:41)
> >>>>     at
> >>>> project.ActorUtil$Resumable$$anonfun$act$1.apply(ActorUtil.scala:34)
> >>>>     at project
> >>>> .ActorUtil$Resumable$$anonfun$act$1.apply(ActorUtil.scala:34)
>
> >>>> Anyone able to spot the problem?
>
> >>>> The AbstractPartialFunction is a new optimization for 2.10:
>
> >>>> override def orElse[A1 <: T1, B1 >: R](that: PartialFunction[A1, B1]) :
> >>>> PartialFunction[A1, B1] = {
> >>>>   val result = this.clone.asInstanceOf[AbstractPartialFunction[A1, B1]]
> >>>>   result.synchronized {
> >>>>     result.fallBackField = this.fallBackField orElse that
> >>>>     result
> >>>>   }
> >>>> }
>
> >>> --
> >>> Viktor Klang
>
> >>> Akka Tech Lead
> >>> Typesafe <http://www.typesafe.com/> - Enterprise-Grade Scala from the
> >>> Experts
>
> >>> Twitter: @viktorklang