Scala cake-pattern compile error with Precog config pattern

Question

Following from this question, I have now the following:

case class Pet(val name: String)

trait ConfigComponent {
          


        

Answer 1

What you've written should work, but doesn't, because of this bug.

There are a number of workarounds you could use. Adding type Config = PetStoreConfig with AnotherConfig to your module implementation is probably a little less unpleasant than casting.

Update: As som-snytt notes in a comment and answer, adding with PetStoreModuleImpl (crucially not with PetStoreModule, as you might expect) to the end of the self-type is a better solution.

As a footnote: as discussed in the comments on SI-7255, the Dependent Object Types calculus (which is designed to be "a new foundation for Scala's type system") will address this "fundamental problem in Scala's type system".