protocol for using InputRanges

[Rikki Cattermole]

On Sunday, 23 March 2014 at 00:50:34 UTC, Walter Bright wrote:
> It's become clear to me that we've underspecified what an 
> InputRange is. The normal way to use it is:
>
>     while (!r.empty) {
>         auto e = r.front;
>         ... do something with e ...
>         r.popFront();
>     }
>
> no argument there. But there are two issues:
>
> 1. If you know the range is not empty, is it allowed to call 
> r.front without calling r.empty first?
>
> If this is true, extra logic will need to be added to r.front 
> in many cases.
>
> 2. Can r.front be called n times in a row? I.e. is calling 
> front() destructive?
>
> If true, this means that r.front will have to cache a copy in 
> many cases.

It would be nice to have ranges full stop described. And how to 
use/make them in D. I have yet to learn them because of no 
official documentation on them.
On this topic we also need to work on common patterns and 
creating documentation on e.g. the site or wiki for it. Saw that 
we do have a bit in the wiki under tutorials. Maybe if I get some 
time I'll work on that.