sullivan-

trait TopLevelComponent extends
  BlogRepoComponent with
  PostRepoComponent with
  AuthRepoComponent with
  BlogServComponent with
  PostServComponent with
  AuthServComponent

sullivan-

abstract class Application extends TopLevelComponent {
  // can access blogRepo, postRepo, authRepo, blogServ, postServ,
  // and authServ here
}

sullivan-

trait TopLevelComponentImpl extends TopLevelComponent with
  BlogRepoComponentImpl with
  PostRepoComponentImpl with
  AuthRepoComponentImpl with
  BlogServComponentImpl with
  PostServComponentImpl with
  AuthServComponentImpl

sullivan-

new Application with TopLevelComponentImpl

sullivan-

trait AuthRepo {
  def create(auth: Author): AuthId
  def retrieve(id: AuthId): Author
  def update(auth: Author): Unit
  def delete(auth: Author): Unit
}

class AuthRepoImpl extends AuthRepo {
  def create(auth: Author) = println(s"create $auth")
  def retrieve(id: AuthId) = {

sullivan-

trait AuthRepoComponent {
  val authRepo: AuthRepo
}

trait AuthRepoComponentImpl extends AuthRepoComponent {
  val authRepo: AuthRepo = new AuthRepoImpl
}

trait AuthServComponent {
  val authServ: AuthServ

sullivan-

trait TopLevelComponent {
  val blogRepo: BlogRepo
  val postRepo: PostRepo
  val authRepo: AuthRepo
  val blogServ: BlogServ
  val postServ: PostServ
  val authServ: AuthServ
}

trait TopLevelComponentImpl extends TopLevelComponent {

sullivan-

trait AuthServComponent {
  val authServ: AuthServ
}

trait AuthServComponentImpl extends AuthServComponent {
  self: AuthRepoComponent => // this is the self-type
  val authServ: AuthServ = new AuthServ(authRepo)
}

sullivan-

trait AServiceComponent {
  self: BServiceComponent =>
  val aService = new AService
  class AService {
    println(s"hi from $this constructor, b is $bService")
    def greet: Unit =
      println(s"hi from $this greet, b is $bService")
  }
}

sullivan-

trait TopComponent extends AServiceComponent with BServiceComponent

object Application extends App with TopComponent {
  aService.greet
  bService.greet
}