I'm trying to make Scala find the right type for a path-dependent type coming from a singleton type.
First, here is the type container for the example, and one instance:
trait Container {
type X
def get(): X
}
val container = new Container {
type X = String
def get(): X = ""
}
I can see the String in this first attempt (so I already have a working scenario):
class WithTypeParam[C <: Container](val c: C) {
def getFromContainer(): c.X = c.get()
}
val withTypeParam = new WithTypeParam[container.type](container)
// good, I see the String!
val foo: String = withTypeParam.getFromContainer()
But when there is no type parameter, this does not work anymore.
class NoTypeParam(val c: Container) {
def getFromContainer(): c.X = c.get()
}
val noTypeParam = new NoTypeParam(container)
// this does *not* compile
val bar: String = noTypeParam.getFromContainer()
Does anybody know why the type parameter is needed?
See this thread on scala-internals, in particular, Adriaan's explanation.