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@specialize Iterator => crash. #4123

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scabug opened this Issue Dec 31, 2010 · 7 comments

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scabug commented Dec 31, 2010

Been seeing what I can @Specialize in the library without undue difficulty.

Successes: Option, PartialFunction, List, Numeric, Ordering.

Failure:

% git diff
-trait Iterator[+A] extends TraversableOnce[A] {
+trait Iterator[@specialized +A] extends TraversableOnce[A] {

% scalac29 -d /tmp src/library/scala/collection/Iterator.scala
  Exception in thread "main" java.lang.UnsupportedOperationException
  	at ch.epfl.lamp.fjbg.JMethodType.getSize(JMethodType.java:29)
  	at ch.epfl.lamp.fjbg.JCode.emitGETFIELD(JCode.java:613)
  	at scala.tools.nsc.backend.jvm.GenJVM$$BytecodeGenerator$$$$anonfun$$genBlock$$1$$2.apply(GenJVM.scala:1131)
  	at scala.tools.nsc.backend.jvm.GenJVM$$BytecodeGenerator$$$$anonfun$$genBlock$$1$$2.apply(GenJVM.scala:1094)
  	at scala.collection.IndexedSeqOptimized$$class.foreach(IndexedSeqOptimized.scala:34)
  	at scala.collection.mutable.ArrayOps.foreach(ArrayOps.scala:38)
  	at scala.tools.nsc.backend.icode.BasicBlocks$$BasicBlock.foreach(BasicBlocks.scala:126)
  	at scala.tools.nsc.backend.jvm.GenJVM$$BytecodeGenerator.genBlock$$1(GenJVM.scala}} 

Paging Dr. Agos, Dr. Agos to the OR!

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scabug commented Dec 31, 2010

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scabug commented Feb 23, 2011

@dragos said:
This is the most spectacular failure I've seen so far in the specialization realm! I'll have a look.

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scabug commented Jun 19, 2011

@paulp said:
See also #4716 and #4717, both of which now prevent Iterator from being specialized. (I believe this bug is also still present, but those hit first.)

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scabug commented Oct 1, 2011

Jesse Eichar (jesseeichar) said:
I have specialized subclasses of Iterator but I have found a case where it crashes the compiler. Code is as follows:

trait Iter[@specialized(Byte) +A] extends Iterator[A] {
self =>
override def map[B](f: (A) => B) = super.map(f)
}

class ByteIter extends Iter[Byte] {
var i = 0
def hasNext = i<3
def next = {i += 1;i.toByte}
}

Message and top of stack trace is:

error: java.lang.UnsupportedOperationException: tail of empty list
at scala.collection.immutable.Nil$.tail(List.scala:373)
at scala.collection.immutable.Nil$.tail(List.scala:368)
at scala.tools.nsc.transform.Mixin$$anonfun$scala$tools$nsc$transform$Mixin$$rebindSuper$1.apply(Mixin.scala:96)

just compile the above code with scalac to see full trace

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scabug commented Feb 19, 2012

@paulp said:
Jesse's bug is #4012.

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scabug commented May 10, 2012

@retronym said:
Another day, another mode of failure.

Minimized:

trait Bounds[@specialized A] {
  // okay without `>: A`
  def x[B >: A]: Unit = new Bounds[B] {
    lazy val it = ???  // def or val okay
    it
  }
}

Seems in the same neck of the woods as the recently remedied #5629.

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scabug commented May 10, 2012

@paulp said:
Your test case is a near perfect duplicate of mine in #4717. I'm going to close this one then and try to make that the new hot spot for young compiler hackers on the town.

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