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by-name types inferred with eta-expansion #7899

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scabug opened this issue Oct 7, 2013 · 5 comments
Closed

by-name types inferred with eta-expansion #7899

scabug opened this issue Oct 7, 2013 · 5 comments
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@retronym
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byname infer
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2.11.0-M7

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@scabug
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scabug commented Oct 7, 2013 

scala> def foo[B](f: (=> Int) => B): Option[B] = ???
foo: [B](f: (=> Int) => B)Option[B]

scala> def b = foo(identity)
b: Option[=> Int]

scala> def b = foo(identity(_))
b: Option[Int]
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scabug commented Oct 7, 2013

Imported From: https://issues.scala-lang.org/browse/SI-7899?orig=1
Reporter: @retronym
Affected Versions: 2.10.0

@scabug
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scabug commented Oct 7, 2013

@retronym said (edited on Oct 7, 2013 9:09:41 AM UTC):
This leads to ClassCastExceptions:

scala> def foo[B](f: (=> Int) => B): () => B = () => f(0)
foo: [B](f: (=> Int) => B)() => B

scala> def b = foo(identity(_))
b: () => Int

scala> def b = foo(identity)
b: () => => Int

scala> foo(identity)()
java.lang.ClassCastException: $anonfun$foo$1$$anonfun$apply$1 cannot be cast to java.lang.Integer
	at scala.runtime.BoxesRunTime.unboxToInt(BoxesRunTime.java:106)

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scabug commented Oct 7, 2013

@retronym said:
WIP: https://github.com/retronym/scala/compare/ticket;7899?expand=1

That branch would turn the errant case into a type error.

https://scala-webapps.epfl.ch/jenkins/job/scala-checkin-manual/1016/console

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scabug commented Oct 7, 2013

@retronym said:
scala/scala#3022

@scabug scabug closed this as completed Oct 9, 2013
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scabug commented Oct 12, 2013

@retronym said:
I've moved this change behind -Xstict-inference to avoid the regression in Scala Free: scala/scala#3034.

Hopefully this will be a temporary measure.

@scabug scabug added this to the 2.11.0-M7 milestone Apr 7, 2017
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