override(T)

[Steven Schveighoffer]

On Thu, 24 Sep 2009 09:30:46 -0400, Andrei Alexandrescu  
<SeeWebsiteForEmail at erdani.org> wrote:

> Walter and I discussed last night about contravariance and all and could  
> not find a compelling argument in favor of implementing contravariant  
> arguments right now. The feature is nontrivial to implement, potentially  
> surprising, and has a number of odd corner cases.
>
> One feature that does get requested often in C++ and Java is the ability  
> to choose which class/interface contains the method you want to  
> override. Consider:
>
> interface Lottery {  void draw();  }
> interface Figure {  void draw();  }
>
> class LotterySimulation : Lottery, Figure {
>      override void draw();
> }
>
> Right now draw() overrides both methods, but you'd want to override them  
> separately. You could do so through an intermediate interface:
>
> class Figure2 : Figure {  void draw2() { return draw(); }  }
> class LotterySimulation : Lottery, Figure2 {
>      override void draw();
>      override void draw2();
> }
>
> There are a few problems with this, among which the fact that  
> LotterySimulation now cannot inherit another class; the one class slot  
> was occupied by Figure2.
>
> So I was thinking of this:
>
> class LotterySimulation : Lottery, Figure {
>      override(Lottery) void draw();
>      override(Figure) void draw();
> }
>
> This is easy to implement, scales well, and has good real world uses.  
> What say you?

In fact, your example *still* does not work, since draw2 calls draw :)  I  
think you meant:

class Figure2 : Figure { abstract void draw2(); void draw() { return  
draw2();} }

And I think actually, this still wouldn't work because LotterySimulation  
is overriding draw from Figure2.  Maybe if you make it final in Figure2?

In the override(T) world, What does this do?

auto ls = new LotterySimulation();
ls.draw();

???

I'm not sure this works...

-Steve