You can now refer to other parameters in the same parameter list, which should make the Aux pattern more or less obsolete. But the type inference doesn’t seem to work yet though…
trait Foo[In] { type Out }
trait Bar[In]
implicit def fooInt: Foo[Int]{ type Out = String } = ???
implicit def fooString: Foo[String]{ type Out = Boolean } = ???
implicit def barInt: Bar[Int] = ???
implicit def barBoolean: Bar[Boolean] = ???
def works[A, B, C](implicit f1: Foo[A] { type Out = B }, f2: Foo[B] { type Out = C }, b: Bar[C]): C = ???
// compiles, inferred a Boolean
works[A = Int]
def fails[A](implicit f1: Foo[A], f2: Foo[f1.Out], b: Bar[f2.Out]): f2.Out = ???
// doesn't compile: no implicit argument of type Foo[f1.Out] was found for parameter f2 of method fails
fails[Int]