Retrieving the traversed range

[Manfred_Nowak]

Andrei Alexandrescu wrote:

> Of all ranges, bidirectional ranges suffer of this limitation because 
> they clearly have two underlying "ends" that are inaccessible in 
> separation from the range.

Therefore one has to access them within the range. As far as I can see the 
current implementation misses a data structure which enables a 
`constRetro' operation that reverses a bidirectional range in time O(1).

-manfred