Voldemort Types

["Luís]

Hi,

Regarding this article about Voldemort types:

     
http://www.drdobbs.com/cpp/voldemort-types-in-d/232901591?pgno=2

There's something I didn't understand. I general I understand the 
benefit of hiding the type of the "struct RandomNumberGenerator" 
so it doesn't leak out of the generator() function. But why not 
just document the generator() function as returning a Range? 
Indeed, as it is with auto it seems it might not be very friendly 
to documentation, not documenting the actual return type (a 
Range).