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Macros have same type after erasure #7776

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scabug opened this issue Aug 22, 2013 · 5 comments
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Macros have same type after erasure #7776

scabug opened this issue Aug 22, 2013 · 5 comments
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@scabug
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@scabug scabug commented Aug 22, 2013

Compilation of the following fails:

class MacroErasure {
  def app(f: Any => Any, x: Any): Any = macro MacroErasure.appMacro
  def app[A](f: A => Any, x: Any): Any = macro MacroErasure.appMacroA[A]
}

object MacroErasure {
  def appMacro(c: Context)(
    f: c.Expr[Any => Any], x: c.Expr[Any]): c.Expr[Any] = {
    import c.universe._
    c.Expr(q"$f($x)")
  }
  def appMacroA[A](c: Context)(f: c.Expr[A => Any], x: c.Expr[Any])(
    implicit tt: c.WeakTypeTag[A]): c.Expr[Any] = {
    import c.universe._
    c.Expr(q"$f[${tt.tpe}]($x)")
  }
}

The error message is:

[error] /home/sast/projects/scala/scratch/src/main/scala/scratch/MacroErasure.scala:9: double definition:
[error] macro method app:[A](f: A => Any, x: Any)Any and
[error] macro method app:(f: Any => Any, x: Any)Any at line 8
[error] have same type after erasure: (f: Function1, x: Object)Object
[error]   def app[A](f: A => Any, x: Any): Any = macro MacroErasure.appMacroA[A]
[error]       ^

Can two macros really have the same type "after erasure"? Given that they are expanded at runtime, can this actually cause problems?

@scabug
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@scabug scabug commented Aug 22, 2013

Imported From: https://issues.scala-lang.org/browse/SI-7776?orig=1
Reporter: @sstucki
Affected Versions: 2.10.3-RC1, 2.11.0-M4

@scabug
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@scabug scabug commented Aug 22, 2013

@xeno-by said:
Yep, the failure is indeed spurious. How much of a blocker is this bug for you?

@scabug
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@scabug scabug commented Aug 22, 2013

@sstucki said:
Using it for some experimental stuff. Not really a blocker for now.

@scabug
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@scabug scabug commented Oct 18, 2013

@scabug
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@scabug scabug commented Nov 5, 2013

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