DMap

DMap.scala

package dmap

import scala.reflect.runtime.universe._

import DMap._

class DMap private(underlying: Map[Any, Entry]) {

  def get[T](key: Any)(implicit tt: TypeTag[T]): Option[T] = {
    underlying.get(key) match {
      case Some(Entry(v, t)) if t <:< tt.tpe => Some(t.asInstanceOf[T])
      case _ => None
    }
  }


  def +[T](kv: (Any, T))(implicit tt: TypeTag[T]): DMap = new DMap(underlying + (kv._1 -> Entry(kv._2)))
}

object DMap {

  val empty = new DMap(Map())

  def apply(kvs: (Any, Entry)*): DMap = new DMap(kvs.toMap)

  class Entry private (val value: Any, val tpe:  Type)

  object Entry {
    implicit def apply[T](value: T)(implicit tt: TypeTag[T]): Entry = new Entry(value, tt.tpe)

    def unapply(entry: Entry): Option[(Any, Type)] = Some((entry.value, entry.tpe))
  }
}


object Foo extends App {


  trait F[X]

  val x = DMap("hello" -> 1, "howdy" -> new F[List[Char]] {})

  println(x.get[Int]("hello")) // Some
  println(x.get[List[Int]]("hello")) // None
  println(x.get[F[List[Char]]]("howdy")) // Some
  println(x.get[Any]("howdy")) // Some
}