Typeclass example

MyShow.scala

package bilberry.snippet

import scalaz.syntax.functor._

trait MyShow[A] {
  def show(a: A): String
}

object MyShow {
  def apply[A](implicit ev: MyShow[A]): MyShow[A] = ev // summon the implicit using syntax MyShow[X]

  def show[A](f: A => String): MyShow[A] = // smart constructor
    new MyShow[A] {
      def show(a: A): String = f(a)
    }

  implicit def syntax[A: MyShow](a: A): ShowOps[A] = ShowOps(a) // pimp any a with an instance of MyShow

  // define instances here
  implicit val stringShow: MyShow[String] = show(identity)
  implicit val intShow: MyShow[Int] = show(_.toString)
  implicit def setShow[A: MyShow]: MyShow[Set[A]] =
    show((set: Set[A]) => set.toList.map(_.myShow).mkString("(", ", ", ""))
}

case class ShowOps[A](a: A)(implicit ev: MyShow[A]){
  def myShow: String = ev.show(a)
}

case class Person(name: String, age: Int)

object Person {
  implicit val myShow: MyShow[Person] = MyShow.show(p => s"Person(name: ${p.name}, age: ${p.age})")
}