Attributes With Path-Dependent Types

gistfile1.scala

trait AttributeName { self => 
    type AttributeType

    def of(value : AttributeType) : Attribute = new Attribute {
        type Name = self.type
        val Value = value
    }
}

trait Attribute {
    type Name <: AttributeName
    def Value : Name#AttributeType
}

case object Health extends AttributeName {
    type AttributeType = Int
}

case object Name extends AttributeName {
    type AttributeType = String
}

class Attributes {
    val _map = scala.collection.mutable.Map[AttributeName, Attribute]()
    def get(key : AttributeName) : key.AttributeType = {
        _map(key).Value.asInstanceOf[key.AttributeType]
    }
    def add(key : AttributeName, attr : Attribute) = {
        _map(key) = attr
    }
}

val attrs = new Attributes
attrs.add(Health, Health of 3)
attrs.add(Name, Name of "Foo")

val health : Int = attrs.get(Health)
val name : String = attrs.get(Name)