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unresolved type constructor during implicit resolution: crash #5845

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scabug opened this Issue May 28, 2012 · 6 comments

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scabug commented May 28, 2012

The error message is similar to #4365, but this is not code or file order dependent that I have determined.

class Num[T] {
  def mkOps = new Ops
  class Ops { def +++(rhs: T) = () }
}

class A {
  implicit def infixOps[T, CC[X] <: Num[X]](lhs: T)(implicit num: CC[T]) = num.mkOps
  implicit val n1 = new Num[Int] { }
  println(5 +++ 5)
}
T in class Num cannot be instantiated from ?CC
	at scala.reflect.internal.SymbolTable.abort(SymbolTable.scala:43)
	at scala.tools.nsc.Global.abort(Global.scala:225)
	at scala.reflect.internal.Types$AsSeenFromMap.throwError$1(Types.scala:4318)
	at scala.reflect.internal.Types$AsSeenFromMap.toInstance$1(Types.scala:4372)
	at scala.reflect.internal.Types$AsSeenFromMap.apply(Types.scala:4376)
	at scala.reflect.internal.Types$TypeMap$$anonfun$noChangeToSymbols$2.apply(Types.scala:4011)
	at scala.reflect.internal.Types$TypeMap$$anonfun$noChangeToSymbols$2.apply(Types.scala:4011)
	at scala.collection.LinearSeqOptimized$class.forall(LinearSeqOptimized.scala:69)
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scabug commented May 28, 2012

Imported From: https://issues.scala-lang.org/browse/SI-5845?orig=1
Reporter: @paulp
Other Milestones: 2.10.0

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scabug commented May 28, 2012

@retronym said:
Fixing the crash is easy enough; getting the inference to work for a view is harder:

retronym/scala@82fb9a7

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scabug commented May 28, 2012

@retronym said:
This version works well (even in 2.9.x with -Ydependent-method-types).

class Num[T] {
  def mkOps = new Ops
  class Ops { def +++(rhs: T) = () }
}

class A {
  implicit def infixOps[T](lhs: T)(implicit num: Num[T]): num.Ops = num.mkOps
  implicit val n1: Num[Int] = new Num[Int] { }
  5 +++ 5
}
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scabug commented May 28, 2012

@scabug scabug closed this May 28, 2012

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scabug commented Jul 20, 2012

@odersky said:
The fix for #4881 fixes the inference for this one also.

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scabug commented Jul 20, 2012

@odersky said:
Correction: It fixes it in one of the two failing cases.

@scabug scabug added this to the 2.10.0-M3 milestone Apr 7, 2017

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