Improbable type inference failure

scabug commented 14 years ago

I wouldn't have thought these would be particularly hard to unify, but regardless, a compilation error seems like an unlikely end? It can always be a List[Any] !

scala> List(List(1), Stream(1))            
<console>:6: error: type mismatch;
 found   : List[Int]
 required: scala.collection.immutable.LinearSeq[Int] with scala.collection.LinearSeqOptimized[Int,scala.collection.immutable.LinearSeq[Int] with scala.collection.LinearSeqOptimized[Int,scala.collection.immutable.LinearSeq[Int] with scala.collection.LinearSeqOptimized[Int,scala.collection.immutable.LinearSeq[Int] with scala.collection.LinearSeqOptimized[Any,Any]]]{def companion: scala.collection.generic.GenericCompanion[scala.collection.immutable.LinearSeq[Any] with scala.collection.LinearSeqOptimized[Any,Any]]}]{def companion: scala.collection.generic.GenericCompanion[scala.collection.immutable.LinearSeq[Any] with scala.collection.LinearSeqOptimized[Any,scala.collection.immutable.LinearSeq[Any] with scala.collection.LinearSeqOptimi...
       List(List(1), Stream(1))
                ^
<console>:6: error: type mismatch;
 found   : scala.collection.immutable.Stream[Int]
 required: scala.collection.immutable.LinearSeq[Int] with scala.collection.LinearSeqOptimized[Int,scala.collection.immutable.LinearSeq[Int] with scala.collection.LinearSeqOptimized[Int,scala.collection.immutable.LinearSeq[Int] with scala.collection.LinearSeqOptimized[Int,scala.collection.immutable.LinearSeq[Int] with scala.collection.LinearSeqOptimized[Any,Any]]]{def companion: scala.collection.generic.GenericCompanion[scala.collection.immutable.LinearSeq[Any] with scala.collection.LinearSeqOptimized[Any,Any]]}]{def companion: scala.collection.generic.GenericCompanion[scala.collection.immutable.LinearSeq[Any] with scala.collection.LinearSeqOptimized[Any,scala.collection.immutable.LinearSeq[Any] with sca...
       List(List(1), Stream(1))
                           ^

Naturally:

scala> List[Seq[Int]](List(1), Stream(1))
res9: List[Seq[Int]] = List(List(1), Stream(1, ?))

scala> List[Any](List(1), Stream(1))     
res10: List[Any] = List(List(1), Stream(1, ?))

scala> List(List(1), Stream(1): Seq[Int])   
res11: List[Seq[Int]] = List(List(1), Stream(1, ?))

Update: A smaller test case for the same sort of problem, as reported in #8882.

import scala.language.higherKinds

class A[T[_]]
object B extends A[List]
object C extends A[Option]

// This compiles
val values = Seq[Any](B, C) 
// This doesn't
val values = Seq(B, C)

scabug commented 14 years ago

Imported From: https://issues.scala-lang.org/browse/SI-3528?orig=1 Reporter: @paulp

scabug commented 14 years ago

@paulp said: This is probably a duplicate of #2322.

scabug commented 13 years ago

@SethTisue said: I hit this today.

it worked in 2.7:

Welcome to Scala version 2.7.7.final (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_22).

scala> List(Set(1,2,3), List(1,2,3))
res0: List[Collection[Int] with (Int) => AnyVal] = List(Set(1, 2, 3), List(1, 2, 3))

scabug commented 13 years ago

Commit Message Bot (anonymous) said: (extempore in r25149) Added sanity check to lub calculation to prevent invalid lubs from emerging. The underlying cause of said lubs is that higher-order type parameters are not handled correctly: this is why the issue is seen so frequently in the collections. See pending test pending/pos/those-kinds-are-high.scala for a demonstration. Until that's fixed, we can at least raise the bar a bit.

Closes #2094, #2322, #4501. Also, some test cases in neg have been promoted into working programs: #2179, #3774. (They're not in neg for the "shouldn't work" reason, but out of despair.)

In some cases, such as the original reported ticket in #3528, this only pushes the problem downfield: it still fails due to inferred type parameters not conforming to bounds. I believe a similar issue with higher-order type parameters underlies that.

Look at how far this takes us though. All kinds of stuff which did not work, now works. None of these even compiled until now:

scala> :type List(mutable.Map(1 -> 1), immutable.Map(1 -> 1)) List[scala.collection.Map[Int,Int]]

scala> :type Set(List(1), mutable.Map(1 -> 1)) scala.collection.Set[Iterable[Any] with PartialFunction[Int,Int]]

scala> :type Stream(List(1), Set(1), 1 to 5) Stream[Iterable[Int] with Int => AnyVal{def getClass(): Class[_ >: Int with Boolean <: AnyVal]}]

scala> :type Map(1 -> (1 to 10), 2 -> (1 to 10).toList) scala.collection.immutable.Map[Int,scala.collection.immutable.Seq[Int]]

PERFORMANCE: compiling quick.lib and quick.comp, this patch results in an extra 27 subtype tests. Total. Time difference too small to measure. However to be on the safe side I made it really easy to disable.

private final val verifyLubs = true // set to false

Review by moors, odersky.

scabug commented 12 years ago

@retronym said (edited on May 13, 2012 9:56:04 PM UTC): The feats of concision above don't seem to be reproducable with today's collection hierarchy + inferencer:

scala> :type Map(1 -> (1 to 10), 2 -> (1 to 10).toList)

[time passes]

scala.collection.immutable.Map[Int,scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]}; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]}; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]}; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]}; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]}; def splitAt(n: Int): (scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int], scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int])}; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]}; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]}; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]}; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]}; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]}; def splitAt(n: Int): (scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int], scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int])}; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]}; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]}; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]}; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]}; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]}; def splitAt(n: Int): (scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int], scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int])}; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]}; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]}; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]}; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]}; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]}; def splitAt(n: Int): (scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int], scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int])}; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]}; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]}; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]}; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]}; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]}; def splitAt(n: Int): (scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int], scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int])}; def splitAt(n: Int): (scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]}, scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]; def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]})}]

scabug commented 12 years ago

@paulp said: Bummer. It was still working in M2. Broken in M3. There are tests covering some cases so this must be specific to something here; probably Map's two type parameters.

Welcome to Scala version 2.10.0-M2 (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_31).
Type in expressions to have them evaluated.
Type :help for more information.

scala> :type Map(1 -> (1 to 10), 2 -> (1 to 10).toList)
scala.collection.immutable.Map[Int,scala.collection.immutable.Seq[Int]]

scabug commented 12 years ago

@paulp said: As a point of interest, one has to wonder how much CPU we burn off calculating this sort of thing:


scala.collection.immutable.Map[
  Int,scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{
    def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{
      def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{
        def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int];
        def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int];
        def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int];
        def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int];
        def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]};
        def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{
          def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int];
          def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int];
          def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int];
          def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int];
          def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]};
          def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{
            def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int];
            def dropRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int];
            def takeRight(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int];
            def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int];
            def take(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]};
            def drop(n: Int): scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int]{
              def reverse: scala.collection.immutable.Seq[Int] with scala.collection.AbstractSeq[Int];

(And on and on, that's just the beginning.)

som-snytt commented 1 year ago

Welcome to Scala 2.13.10 (OpenJDK 64-Bit Server VM, Java 19).
Type in expressions for evaluation. Or try :help.

scala> List(List(42), Set(42))
val res0: List[scala.collection.immutable.Iterable[Int] with Int => AnyVal with Equals{def iterableFactory: scala.collection.IterableFactory[[_]scala.collection.immutable.Iterable[_] with _ with Int => Any with Equals]}] = List(List(42), Set(42))

scala> Map(1 -> (1 to 10), 2 -> (1 to 10).toList)
val res1: scala.collection.immutable.Map[Int,scala.collection.immutable.AbstractSeq[Int] with scala.collection.immutable.StrictOptimizedSeqOps[Int,[_]Seq[_],Seq[Int]] with java.io.Serializable{def takeRight(n: Int): scala.collection.immutable.AbstractSeq[Int] with scala.collection.immutable.StrictOptimizedSeqOps[Int,[_]Seq[_],Seq[Int]] with java.io.Serializable{def takeRight(n: Int): scala.collection.immutable.AbstractSeq[Int] with scala.collection.immutable.StrictOptimizedSeqOps[Int,[_]Seq[_],Seq[Int]] with java.io.Serializable{def takeRight(n: Int): scala.collection.immutable.AbstractSeq[Int] with java.io.Serializable; def reverse: scala.collection.immutable.AbstractSeq[Int] with java.io.Serializable; def slice(from: Int, until: Int): scala.collection.immutable.A...

where it would be nice if it truncated the unwieldy type and showed me the representable value. It looks like the crazy refinement is on Serializable? res0 has an underscore where I'm not used to seeing one. and

Welcome to Scala 3.2.2 (19, Java OpenJDK 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.

scala> List(List(42), Set(42))
val res0: List[(Int => Int | Boolean) & Equals & scala.collection.immutable.Iterable[Int]] = List(List(42), Set(42))

scala> Map(1 -> (1 to 10), 2 -> (1 to 10).toList)
val res1: Map[Int, scala.collection.immutable.AbstractSeq[Int]] = Map(1 -> Range 1 to 10, 2 -> List(1, 2, 3, 4, 5, 6, 7, 8, 9, 10))

scala / bug

Improbable type inference failure #3528