| [#1202] | project: compiler | priority: medium | category: bug | |
|---|---|---|---|---|
| submitter | assigned to | status | date submitted | |
| Burak | Martin | noise | 2007-07-10 12:49:19.0 | |
| subject | existentials not scoped/captured properly | |||
| code |
object foo { // example by Cardelli and Wegner
val p: (a, (a=>Int)) forSome {type a} = (3,{y:Int=>y+1})
val z:Int = p._2(p._1)
} |
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| what happened | Burak-Emirs-MacBook-Pro:~/Documents/svn/foosvn buraq$ ../scala/build/quick/bin/scalac -d /tmp -explaintypes /tmp\
/ex.scala
/tmp/ex.scala:3: error: type mismatch;
found : Any
required: Nothing
val z:Int = p._2(p._1)
^
one error found
|
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| what expected | Since it is the very same p, type a is the same. If this is beyond the "automatic opening", there should be a proper "open" operation that lets us write p._2(p._1) -- maybe use pattern matching?
This is not legal Scala syntax (existentials not allowed in type tests), but might be a good way out.
p match {
case z: (a, (a=>Int)) forSome {type a} = z._2(z._1)
}
|
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| [back to overview] | ||||
| Martin edited on 2007-07-14 13:10:14.0 |
Opening an existential type twice requires indeed a pattern match. Here is how it is done:
object foo { // example by Cardelli and Wegner
val p: (a, (a=>Int)) forSome {type a} = (3,{y:Int=>y+1})
val z: Int = p match {
case pp: (_, _) => pp._2(pp._1)
}
}
|