Revised RFC on range design for D2

[Sergey Gromov]

Andrei Alexandrescu <SeeWebsiteForEmail at erdani.org> wrote:
> Sergey Gromov wrote:
> > Bill Baxter <wbaxter at gmail.com> wrote:
> >> On Fri, Sep 12, 2008 at 11:58 PM, Sergey Gromov <snake.scaly at gmail.com> wrote:
> >>>> So basically you changed
> >>>> done ==> empty
> >>>> head ==> tip
> >>>> retreat ==> prev
> >>>> ?
> >>> The insight was about get/put ==> next.  That's the most significant
> >>> change, others are merely renames as you rightfully point out.  Hence
> >>> the "prev" which should mean both "get at the end" and "put to the end".
> >> Ah ok.  Your switching to declaration syntax instead of usage syntax
> >> confused me. :-)
> >>
> >> That is cute.  So
> >>    r.put(e) ==> r.next = e
> >> It would also mean the copy to output idiom would become
> >>
> >> for(; ! i.done; i.next)
> >>    o.next = i.head;
> >>
> >> Would be cooler if it could be just while(!i.done) o.next = i.next;
> >> .. oh well.
> > 
> > Exactly, I wanted it to be
> > 
> > while (!i.done)
> >     o.next = i.next;
> 
> Hmm, let's see. So:
> 
> a) If i is an input range, then i.next returns by value.
> 
> b) If i is a forward range, then i.next returns by reference.
> 
> I assume that's what you had in mind?

Not quite.

You cannot mutate an input range, it must be in specs.  Therefore it's 
up to the range designer what to return.  LineEater will return a const 
reference to an internal buffer.  RNG will return int.  Array will 
return a const reference to its element.  Some could return a new class 
instance every time.

If you want to mutate though, you require a forward range and use its 
i.first which must be a reference to the first element in the range.  
Then you can safely ignore the i.next result which will most likely be a 
reference to the previous i.first contents.