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parameter type inference with type paramers broken #1803

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scabug opened this issue Mar 18, 2009 · 6 comments
Closed

parameter type inference with type paramers broken #1803

scabug opened this issue Mar 18, 2009 · 6 comments
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@scabug
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scabug commented Mar 18, 2009

the type infered for parameters of an overriding method do not refer to the right type parameter symbol (skolemized / deSkolemized).

lamppc26:~ luc$$ workspace/scala/build/quick/bin/scala -Xexperimental -uniqid
Welcome to Scala version (unknown) (Java HotSpot(TM) Client VM, Java 1.5.0_16).
Type in expressions to have them evaluated.
Type :help for more information.

scala> class A { def foo[A](a: A) = a }
defined class A

scala> class B extends A { override def foo[A](b) = b }
<console>:5: error: type mismatch;
 found   : ASI-10818
 required: ASI-10819
       class B extends A { override def foo[A](b) = b }
                                                    ^
@scabug
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scabug commented Mar 18, 2009

Imported From: https://issues.scala-lang.org/browse/SI-1803?orig=1
Reporter: @lrytz

@scabug
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scabug commented Feb 6, 2015

kenji yoshida said:
resolved?

$ scala -Yinfer-argument-types -uniqid
Welcome to Scala version 2.11.5 (Java HotSpot(TM) 64-Bit Server VM, Java 1.7.0_72).
Type in expressions to have them evaluated.
Type :help for more information.

scala> class A { def foo[A](a: A) = a }
defined class A

scala> class B extends A { override def foo[A](b) = b }
defined class B

@scabug scabug added this to the Backlog milestone Apr 6, 2017
@spangaer
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spangaer commented Apr 5, 2018

That one is indeed fixed but another one is broken.
When generic parameters are assigned in deriving class. Methods using those generic parameters used to support type inference when overridden (Scala 2.11), but now no longer do (Scala 2.12).

Scala 2.11

C:\Windows\System32>scala -Yinfer-argument-types
Welcome to Scala version 2.11.7 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_112).
Type in expressions to have them evaluated.
Type :help for more information.

scala> trait X[T] {  def doit(t: T): T}
defined trait X

scala> class Y extends X[String] {  override def doit(s) =    s}
defined class Y

Scala 2.12

D:\data\downloads\java\scala\scala-2.12.5\scala-2.12.5\bin>scala -Yinfer-argument-types
Welcome to Scala 2.12.5 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_112).
Type in expressions for evaluation. Or try :help.

scala> trait X[T] {  def doit(t: T): T}
defined trait X

scala> class Y extends X[String] {  override def doit(s) =    s}
<console>:12: error: type mismatch;
 found   : T
 required: String
       class Y extends X[String] {  override def doit(s) =    s}
                                                              ^

@hrhino
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hrhino commented Apr 5, 2018

I think this feature may be on the chopping block (as part of scala/scala-dev#430), so this might become a won't-fix soon.

@adriaanm
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adriaanm commented Apr 5, 2018

Yes, this will go away, sorry.

@adriaanm adriaanm closed this as completed Apr 5, 2018
@spangaer
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spangaer commented Apr 5, 2018

Faster response than expected.

Well, I got this in via -Xexperimental which I had put in in the process of enabling Java 8 lambda bytecode in 2.11. Wasn't aware of the matter, but built quite a bit of code base that relied on it :(

Ok, out it goes. Hope you get a chance to respond to my comment in the referred issue equally fast ;).

@scala scala deleted a comment from scabug Apr 5, 2018
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@adriaanm @SethTisue @spangaer @scabug @hrhino