Open
Description
Currently it is possible to match a parametric case class with correct type like so:
case class Register[T](key: Key[T], value: T)
...
x match {
case r: Register[t] =>
val k: Key[t] = r.key
val v: t = r.value // matching types with the key
}What does not work is the same while extracting values (1):
case Register[t](k, v) => // says “Register[t] does not take parameters”When not including the name for the type, T is inferred to be Any (2):
case Register(k, v) => // T is Any here, even though Register is not covariantThere are two things which should be done:
- allow the extraction syntax shown in (1) above
- implicitly introduce a type with a fresh name when performing the match as in (2), leading to more precise type checking than just assuming Any instead
The second part’s current negative effect can be seen in the following (assuming generic ActorRef[-T] which only accepts messages of type T):
case class Echo[T](msg: T, replyTo: ActorRef[T])
...
x match {
case Echo(msg, replyTo) =>
replyTo ! msg // works by accident now because T=Any for both
replyTo ! 42 // works as well, but should not actually work
}