"The last feature": overridable methods in interfaces

[retard]

Mon, 08 Feb 2010 11:34:10 -0800, Andrei Alexandrescu wrote:

> I know of Scala's traits. They are different from overridable methods in
> interfaces, which are not nearly interesting enough to bring fame and
> fortune to anyone.

I apologize for being so rude. If I read the proposal correctly, traits 
are its generalization:

interface Stack(T)
{
     void push(T);
     void pop();
     @property ref T top();
     @property bool empty();
     T belowTop()
     {
         auto t = top;
         pop();
         auto result = top;
         push(t);
         return result;
     }
}

vs

trait Stack[T]
{
     def push(t: T): Unit
     def pop: Unit
     def top: T // do not know how to port properties
     def empty: Boolean
     def belowTop: T
     {
         val t = top
         pop
         val result = top
         push(t)
         result
     }
}

But with these kind of features D's interfaces are getting closer and 
closer to traits. What's missing? The linearization system, type members, 
and member variables inside interfaces. OTOH Scala is lacking the 
contract system.