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Warn if implicit underscore is no-op #11618

som-snytt opened this issue Jul 8, 2019 · 1 comment


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commented Jul 8, 2019

Please warn on:

implicit val _ = 42

Normally, an extractor pattern would either fail or implicit is available.

scala> object X { def unapply(s: String) = Option(s.tail) }
defined object X

scala> val X(s) = "hello"
s: String = ello

scala> val X(_) = "hello"

scala> implicit val X(_) = "hello"

scala> implicitly[String]
       error: could not find implicit value for parameter e: String



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commented Jul 8, 2019

Oh wait, I meant to say: warn if implicit doesn't actually introduce a binding. Sorry, this isn't my day job.

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