scalaru

object Products {
  import scala.language.higherKinds

  case class Cat[A, B](name: A, age: B)
  case class Dog(name: String, age: Int)
  
  trait Product[P] {
    type Fst
    type Snd
    
    def fst(p: P): Fst
    def snd(p: P): Snd
  }

  object Product {
    implicit def tuple2Product[A, B] = new Product[Tuple2[A, B]] {
      type Fst = A
      type Snd = B
      override def fst(p: Tuple2[A,B]): A = p._1
      override def snd(p: Tuple2[A,B]): B = p._2
    }
    implicit def catProduct[A, B] = new Product[Cat[A, B]] {
      type Fst = A
      type Snd = B
      override def fst(p: Cat[A, B]): A = p.name
      override def snd(p: Cat[A, B]): B = p.age
    }
    implicit val dogProduct = new Product[Dog] {
      type Fst = String
      type Snd = Int
      override def fst(p: Dog): String = p.name
      override def snd(p: Dog): Int = p.age
    }
  }

  def fst[P](p: P)(implicit product: Product[P]) = product.fst(p)
  def snd[P](p: P)(implicit product: Product[P]) = product.snd(p)

  def main(args: Array[String]) {
    val d = new Dog("Waf", 5)
    
    println(fst(d))
  }

}