DependentKeyValue.scala

class Key[V] {
  type Value = V
  def ->(value: V) = Pair(this, value)
}
trait Pair {
  val key: Key[_]
  val value: key.Value
}
trait Map {
  val pairs: Seq[Pair]
  def get[V](key: Key[V]): Option[V] =
    pairs.find(_.key eq key).map{_.value.asInstanceOf[V]}
}
object Pair {
  def apply[V](key2: Key[V], value2: V): Pair = new Pair {
    val key: Key[V] = key2
    val value = value2
  }
}

val text = new Key[String]
val count = new Key[Int]

val map: Map = new Map {
  val pairs = text -> "Hello World!" :: Nil
}

map.get(text)  // Some(Hello World!), Type: Option[String]
map.get(count) // None, Type: Option[Int]