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Enumeration and type erasure #3815

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scabug opened this issue Aug 31, 2010 · 5 comments
Open

Enumeration and type erasure #3815

scabug opened this issue Aug 31, 2010 · 5 comments
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@scabug
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@scabug scabug commented Aug 31, 2010

From the API Enumeration:

"All values in an enumeration share a common, unique type defined as the Value type member of the enumeration (Value selected on the stable identifier path of the enumeration instance)."

But there is a type erasure within Enumeration class.
That can give an unexpected type error. Example:

object X extends Enumeration { val x,y = Value }
object A extends Enumeration { val a,b = Value }

X.Value and A.Value are different types. So the functions

  def pp( z:X.Value) {}
  def pp( z:A.Value) {}

should be different too, but you get a compile error:

error: double definition:
method pp:(z: A.Value)Unit and
method pp:(z: X.Value)Unit at line 34
have same type after erasure: (z: Enumeration#Value)Unit
  def pp( z:A.Value) {}

BTW I found a curious workaround

  def pp( z:X.Value) { println("X") }
  def pp( z:A.Value)(implicit t:Int=0) { println("A") }

  pp(X.x)
  pp(A.a)

There is no compile error any more and the output shows
"X" and "A" as expected.

Frank

@scabug
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@scabug scabug commented Aug 31, 2010

Imported From: https://issues.scala-lang.org/browse/SI-3815?orig=1
Reporter: Frank Teubler (dft)
See #5211

@scabug
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@scabug scabug commented Sep 1, 2010

@paulp said:
Yikes. I say it's time to admit Enumeration is a failed experiment and go back to the drawing board.

BTW if you like that workaround here's [http://scala-programming-language.1934581.n4.nabble.com/disambiguation-of-double-definition-resulting-from-generic-type-erasure-tp2327664p2327853.html a more refined version].

@scabug
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@scabug scabug commented Sep 1, 2010

@lrytz said:
yes, enumeration needs a redesign. see also #3719, #3687

@scabug
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@scabug scabug commented Jan 4, 2011

@odersky said:
I think it's a won't fix. That's just what Enumeration and Java erasure do.

@scabug
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@scabug scabug commented Nov 4, 2011

@paulp said:
Martin came around and agrees this is a bug. Reopening.

@scabug scabug added the enum label Apr 7, 2017
@scabug scabug added this to the Backlog milestone Apr 7, 2017
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