Support pattern matching on NonEmptyVector #1265
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Current coverage is 90.47% (diff: 100%)@@ master #1265 diff @@
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| @@ -223,6 +223,8 @@ object NonEmptyVector extends NonEmptyVectorInstances { | |||
| new NonEmptyVector(buf.result) | |||
| } | |||
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| def unapply[A](nev: NonEmptyVector[A]): Some[(A, Vector[A])] = Some((nev.head, nev.tail)) | |||
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Is there a foreseeable use-case where having the static return type as Some instead of Option will cause inference (or similar) issues?
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@ceedubs There's some reason to prefer Some as the return type for extractors that can't fail—the compiler actually uses that information in some way, but I can't remember the details. I'll try to look up a reference…
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The compiler can check for exhaustiveness if it returns Some. It can't when it returns Option.
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@larsrh Got a code snippet showing that?
AFAIK Some can't check exhaustiveness any more than Option as it's not sealed (sealedness isn't transitive nor does final imply sealed, double sadly).
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scala> object MyCons1 { def unapply[A](xs: scala.collection.immutable.::[A]): Some[(A, List[A])] = Some(xs.head, xs.tail) }
defined object MyCons1
scala> object MyCons2 { def unapply[A](xs: scala.collection.immutable.::[A]): Option[(A, List[A])] = Some(xs.head, xs.tail) }
defined object MyCons2
scala> def x = List(1, 2) match { case MyCons1(_, _) => }
<console>:12: warning: match may not be exhaustive.
It would fail on the following input: Nil
def x = List(1, 2) match { case MyCons1(_, _) => }
^
x: Unit
scala> def x = List(1, 2) match { case MyCons2(_, _) => }
x: UnitThere was a problem hiding this comment.
AFAICT it's unspecced behaviour, but I think it makes a lot of sense for the pattern matcher to behave that way.
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