Trait self type bound: A with B but not A with C

scala

Solution

There is a way to do this, though I don't know if it's the only / preferred way.

sealed trait Z[T <: Z[T]]
trait A extends Z[A] { this: D => }
trait B extends Z[B] { this: D => }

scala> new D with A
res6: D with A = $anon$1@7e7584ec

scala> new D with B
res7: D with B = $anon$1@7537e98f

scala> new D with A with B
<console>:15: error: illegal inheritance;
 anonymous class $anon inherits different type instances of trait Z:
Z[B] and Z[A]
              new D with A with B
                  ^

Problem

Say I have: ``` abstract class D[T] {} trait A[T] { self => D[T] without B } trait B[T] { self => D[T] without A } ``` Bottom line, `B` cannot be mixed into D if it already extends `A`. ``` class Test extends D[String] with B[String] // ok class Test2 extends D[String] with A[String] // ok class Test3 extends D[String] with A[String] with B[whatever] // bad class Test4 extends D[String] with B[String] with A[whatever] // bad ``` How can I correctly enforce this type bound?

Original source