Compilation fails with SBT when using DenseVector(index) inside for expression and using toSet

[tburny]

Today I ran across a bug during the "specialize" phase of the Scala compiler/sbt.

The following fails to compile (with an assertion error):
def test() = {
val row = DenseVector(1,2,3,4)
for (j <- 0 until row.length if (row(j) > 3)) yield j
}

whereas the following compiles

def test() = {
val row = DenseVector(1,2,3,4)
for (j <- 0 until row.length if (5 > 3)) yield j
}

As you can see, the only difference is that row(j) has been replaced by a concrete value.
This also works:
def test() = {
val row = DenseVector(1,2,3,4)
for (j <- 0 until row.length if (row.valueAt(j) > 3)) yield j
}

I'm using SBT 12.2 with Scala 2.10.1. I also tried with Scala 2.10.0 with no difference.

Stack trace: https://gist.github.com/tburny/5650247
Source: https://github.com/tburny/bayesian-personalized-ranking/blob/8312ce8fe623ab1480b911e93beed96da6b0e0b9/src/main/scala/de/burnynet/BPRModel.scala
in methods usersWhichRatedItemPositive and positiveItemRatingsByUser

[dlwh]

Hrm, there's not much I can do about that. Can you file a bug against
Scala? You can add the flag -no-specialize---with the understanding that it
makes your code slower---in the meantime, though you have an ok workaround.

On Sat, May 25, 2013 at 11:40 AM, tburny notifications@github.com wrote:

Today I ran across a bug during the "specialize" phase of the Scala
compiler/sbt.

The following fails to compile (with an assertion error):
def test() = {
val row = DenseVector(1,2,3,4)
(for (j <- 0 until row.length if (row(j) > 3)) yield j).toSet
}

whereas the following compiles

def test() = {
val row = DenseVector(1,2,3,4)
(for (j <- 0 until row.length if (5 > 3)) yield j).toSet
}

As you can see, the only difference is that row(j) has been replaced by a
concrete value.
This also works:
def test() = {
val row = DenseVector(1,2,3,4)
(for (j <- 0 until row.length if (row.valueAt(j) > 3)) yield j).toSet
}

I'm using SBT 12.2 with Scala 2.10.1. I also tried with Scala 2.10.0 with
no difference.

Stack trace: https://gist.github.com/tburny/5650247
Project where the problem occurred:
https://github.com/tburny/bayesian-personalized-ranking

—
Reply to this email directly or view it on GitHubhttps://github.com//issues/65
.

[dlwh]

(still a problem in 2.10.2)

This is ok:

scala> class DV[@specialized(Int) T](data: Array[T]) { @inline def apply(i: Int) = data(i); def length = data.length }
defined class DV

scala> val row = new DV[Int](Array(1,2,3,4))
row: DV[Int] = DV@6eb65209

scala> (for (j <- 0 until row.length if (row(j) > 3)) yield j).toSet
res3: scala.collection.immutable.Set[Int] = Set(3)

[dlwh]

(I'm getting variants of this bug in several places, I'm going to try to sort it out soon.)

[dlwh]

https://issues.scala-lang.org/browse/SI-8572