Input ranges

[via Digitalmars-d]

Hi,

I tried to learn about input ranges and got some anonymous advice 
http://forum.dlang.org/thread/dezlxxygufocmafvleen@forum.dlang.org 
, still the topic seems to warrant broader attention.

The question is how pure input ranges (as in non-forward) should 
be build. Algorithms like take and groupBy require reference 
semantics. I did not find that communicated. Now I am looking for 
the official ruling. As in: What the D rule book says.