Shout out to D at cppcon, when talkign about ranges.

[H. S. Teoh via Digitalmars-d]

On Sat, Oct 10, 2015 at 09:52:22AM +0300, Andrei Alexandrescu via Digitalmars-d wrote:
> On 10/10/15 12:58 AM, Eric Niebler wrote:
> >Trying to express algorithms without any clear abstraction of
> >"position within range" (independent of ranges) is hard and awkward,
> >and occasionally causes algorithms to be less efficient.
> 
> I agree that ranges are a weaker basis than iterators. But it's not
> necessarily that a notion of position is the only way out.
> 
> Ranges can be made as strong a basis by adding the O(1) primitives
> r1.before(r2) and r1.after(r2) that return the prefix/suffix following
> r2 within r1. With those I hope to be able to show easily that
> algorithms needing "iterator in the middle" can be redone.

I assume .before would be implemented in a specialization of forward
ranges, and .after in a specialization of bidirectional ranges?


> I think I need to sit down and define these primitives (albeit they
> aren't used that frequently) and use them in a few fundamental
> algorithms to just close the matter once and for all.
[...]

It would also fix the current bug in nextPermutation that claims that it
supports bidirectional ranges, when in fact it requires random access
ranges, precisely because reversing the last n elements requires the
"iterator in the middle" construct.


T

-- 
Gone Chopin. Bach in a minuet.