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implicit search should resolve ambiguities by fully resolving transitively required implicit arguments #3340

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scabug opened this issue Apr 22, 2010 · 4 comments
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implicit search should resolve ambiguities by fully resolving transitively required implicit arguments #3340

scabug opened this issue Apr 22, 2010 · 4 comments
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enhancement
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2.11.0

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@scabug
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scabug commented Apr 22, 2010

this came up in the context of Liszt:

object Test {
  class Foo(x: Meh) { def foo(a: String) = 1 }
  class Meh
  class A
  implicit object a extends A
  class B
  // implicit object b extends B
  
  implicit def mkFooA(x: Meh)(implicit w: A) : Foo = new Foo(x)
  implicit def mkFooB(x: Meh)(implicit w: B) : Foo = new Foo(x)

  (new Meh).foo("1")
}

there should be no ambiguities as mkFooB requires an implicit value of type B, which is not available
@scabug
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scabug commented Apr 22, 2010

Imported From: https://issues.scala-lang.org/browse/SI-3340?orig=1
Reporter: @adriaanm

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scabug commented Apr 22, 2010

@adriaanm said:
(In r21656) see #3340: tentative fix to resolve ambiguities by chasing transitively required implicits

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scabug commented Apr 22, 2010

@retronym said:
Cool! We've worked around this limitation Scalaz, by splitting scalaz.MA into scalaz.MA / scalaz.MACofunctor.

#2781 is of the same ilk. Are you passing type constraints, too? I mean, they basically like extra implicit params of type <:<[A, B].

@scabug scabug added this to the Backlog milestone Apr 7, 2017
@scabug scabug mentioned this issue Apr 7, 2017
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@joroKr21
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This works but implicit conversions are on the way out.

@scala scala deleted a comment from scabug Dec 30, 2019
@SethTisue SethTisue modified the milestones: Backlog, 2.11.0 Dec 30, 2019
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@adriaanm @SethTisue @joroKr21 @scabug