How can I use nested type in Scala generic function ? I'd like to implement something like this
implicit def basicDBList2List[List[A]](value : BasicDBList) = value.toList.asInstanceOf[List[A]]
Compiler gives following error:
scala: not found: type A
implicit def basicDBList2List[List[A]](value : BasicDBList) = value.toList.asInstanceOf[List[A]]
^
When you write:
implicit def basicDBList2List[List[A]](value: BasicDBList) = ...
... that doesn't mean what you think it means. You're declaring a new type parameter called List, not referring to the existing List trait in the library! You're also declaring that your newly-defined List type requires some type parameter, which you've called A, but you can't actually reference it.
What you probably meant was:
implicit def basicDBList2List[A](value: BasicDBList): List[A] = ...
... which says that, for any type A, you can convert a BasicDBList to a List[A].
This is sketchy code, though, for two reasons:
BasicDBList class actually contain? Probably not any possible A. You'll very likely get ClassCastException at runtime.BasicDBList to List[A]? That's almost always a bad idea.I think it is better have it like:
implicit def basicDBList2List[A](value : BasicDBList) = value.toList.asInstanceOf[List[A]]
