Scala Cake Pattern and Dependency Collisions

Question

I\'m trying to implement dependency injection in Scala with the Cake Pattern, but am running into dependency collisions. Since I could not find a detailed example with such depe

Answer 1

Seems to be the known "robot legs" problem. You need to construct two legs of a robot, however you need to supply two different feet to them.

How to use the cake pattern to have both common dependencies and separate?

Let's have L1 <- A, B1; L2 <- A, B2. And you want to have Main <- L1, L2, A.

To have separate dependencies we need two instances of smaller cakes, parameterized with common dependencies.

trait LegCommon { def a:A}
trait Bdep { def b:B }
class L(val common:LegCommon) extends Bdep { 
  import common._
  // declarations of Leg. Have both A and B.
}
trait B1module extends Bdep {
  val b = new B1
}
trait B2module extends Bdep {
  def b = new B2
}

In Main we'll have common part in cake and two legs:

trait Main extends LegCommon {
  val l1 = new L(this) with B1module
  val l2 = new L(this) with B2module
  val a = new A
}