trait Foo[T <: Foo[T, Enum], Enum <: Enumeration] { type StV = Enum#Value type Meta = MegaFoo[T, Enum] type Slog = Enumeration def getSingleton: Meta } trait MegaFoo[T <: Foo[T, Enum], Enum <: Enumeration] extends Foo[T, Enum] { def doSomething(what: T, misc: StV, dog: Meta#Event) = None abstract class Event object Event def stateEnumeration: Slog def se2: Enum } object E extends Enumeration { val A = Value val B = Value } class RFoo extends Foo[RFoo, E.type] { def getSingleton = MegaRFoo } object MegaRFoo extends RFoo with MegaFoo[RFoo, E.type] { def stateEnumeration = E def se2 = E }