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POAutomatically Hash Consed Case Classes
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Id
8688486
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AcceptedAnswerId
12518123
AnswerCount
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ClosedDate
CommentCount
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CommunityOwnedDate
CreationDate
2011-12-31T13:57:00.140
FavoriteCount
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LastActivityDate
2012-09-20T21:31:03.083
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Score
10
ViewCount
676
LastEditorDisplayName
text
Body
I'm looking for a way to have classes that behave just like case classes, but that are automatically <a href="http://en.wikipedia.org/wiki/Hash_consing" rel="noreferrer">hash consed</a>. One way to achieve this for integer lists would be: <pre><code>import scala.collection.mutable.{Map=>MutableMap} sealed abstract class List class Cons(val head: Int, val tail: List) extends List case object Nil extends List object Cons { val cache : MutableMap[(Int,List),Cons] = MutableMap.empty def apply(head : Int, tail : List) = cache.getOrElse((head,tail), { val newCons = new Cons(head, tail) cache((head,tail)) = newCons newCons }) def unapply(lst : List) : Option[(Int,List)] = { if (lst != null && lst.isInstanceOf[Cons]) { val asCons = lst.asInstanceOf[Cons] Some((asCons.head, asCons.tail)) } else None } } </code></pre> And, for instance, while <pre><code>scala> (5 :: 4 :: scala.Nil) eq (5 :: 4 :: scala.Nil) resN: Boolean = false </code></pre> we get <pre><code>scala> Cons(5, Cons(4, Nil)) eq Cons(5, Cons(4, Nil)) resN: Boolean = true </code></pre> Now what I'm looking for is a generic way to achieve this (or something very similar). Ideally, I don't want to have to type much more than: <pre><code>class Cons(val head : Int, val tail : List) extends List with HashConsed2[Int,List] </code></pre> (or similar). Can someone come up with some type system voodoo to help me, or will I have to wait for the macro language to be available?
Tags
<scala><case-class>
Title
Automatically Hash Consed Case Classes
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