$DefaultInheritance

Here, we define a class hierarchy.

There is no notion of polymorphism for a.

We redefine the classes with a new default inheritance type. It is not sufficient to redefine child only, because the method fun has no notion of the changes in child.

Now, the field a is used in a polymorphic way.

The same can be achieved by an explicit specification. We delete base in oder to avoid a message during automatic regeneration of child.