how to get top N distinct elements from range?

[bearophile]

Andrea Fontana:

> Is this:
> bool[typeof(_fun((ElementType!Range).init))] mySet;
> 	
> the right way?

I don't know if that's the best way, but I think it's OK. (I 
think it should even go in the D wiki, so if it's not the best to 
do it, someone will improve it.)

Bye,
bearophile