Type class DI

console.scala

import scala.language.higherKinds
import scala.language.implicitConversions
import scalaz._
import Scalaz._
import shapeless._

object console {

  case class ServiceA(name: String)
  case class ServiceB(name: String, sa: ServiceA)
  
  object Dependencies {

    trait Dependency[T] {
      def get: T
    }

    implicit def extract[T : Dependency](t: Dependency[T]): T = implicitly[Dependency[T]].get

    object Dependency {
      
      implicit val serviceA = new Dependency[ServiceA] {
         def get: ServiceA = new ServiceA("serviceA")
      }

      implicit def serviceB(implicit serviceA: Dependency[ServiceA]) = new Dependency[ServiceB] {
         def get: ServiceB = new ServiceB("serviceB", serviceA)
      }
    }
  }

  import Dependencies._


  object App {

    def printA(implicit serviceA: Dependency[ServiceA]) = {
      println(s"${serviceA.name}")
    }

    def printB(implicit serviceB: Dependency[ServiceB]) = {
      println(s"${serviceB.name}")
    }
  }

  App.printA
  App.printB
}