polydemo.scala

import shapeless._

// Given this poly:
object myPoly extends Poly1 {
  implicit val intCase: Case.Aux[Int, Double] =
    at[Int](num => num / 2.0)

  implicit val stringCase: Case.Aux[String, Int] =
    at[String](str => str.length)
}

// This compiles:
object test {
  val intResult = myPoly(123)
  val stringResult = myPoly("Hello")
  val intResult2: Double = intResult
  val stringResult2: Int = stringResult
}

// But this doesn't compile:
object test2 {
  val intResult: Double = myPoly(123)
  val stringResult: Int = myPoly("Hello")
}