dependent method types

DepFun.scala

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scala> class Outer { class Inner }
defined class Outer

scala> trait DepFun { def apply(x: Outer): x.Inner }
defined trait DepFun

scala> new DepFun { override def apply(x: Outer): x.Inner = new x.Inner }
<console>:10: error: overriding method apply in trait DepFun of type (x: Outer)x.Inner;
 method apply has incompatible type
              new DepFun { override def apply(x: Outer): x.Inner = new x.Inner }
                                        ^