Path dependent types

pdt.scala

 trait Foo {                                                                                                      
    trait Bar                                                                                                      
  }                                                                                                                
                                                                                                                   
  object FooImpl extends Foo {                                                                                     
    object ABar extends Bar                                                                                        
    object BBar extends Bar                                                                                        
  }                                                                                                                
                                                                                                                   
  val foo = new Foo {}                                                                                             
                                                                                                                   
  val a: foo.Bar = new foo.Bar {}                                                                                  
  val b: Foo#Bar = FooImpl.BBar