Re: [boost] AlRangeExandrescu?

Subject: Re: [boost] AlRangeExandrescu?
From: David Abrahams (dave_at_[hidden])
Date: 2009-07-27 07:17:07

on Sat Jul 25 2009, Andrei Alexandrescu <andrei-AT-metalanguage.com> wrote:

> Thorsten Ottosen wrote:
>> Andrei Alexandrescu skrev:
>>> Mathias Gaunard wrote:
>>
>>>>> You would pass two adjacent ranges, like D's bringToFront (a generalization of
>>>>> STL's rotate, see http://www.digitalmars.com/d/2.0/phobos/std_algorithm.html)
>>>>> takes.
>>>>
>>>> Nice idea, that could work.
>>>> But how can I generate those two adjacent ranges in the first place at reasonable
>>>> costs? Do ranges requires to provide a constant time "complement" primitive?
>>>
>>> There's no such need (a range could define it though).
>>>
>>> A design that has a bidirectional iterator walking freely up and down between two
>>> limits would be difficult to port to ranges. (If the iterator is random-access,
>>> things are trivial.) Ranges can only shrink, they never grow unless assigned from
>>> the outside. So when you move one direction it would be difficult to grow one range
>>> (shrinking the other is easy). That design would benefit from letting the iterator
>>> abstraction exposed.
>>
>> Couldn't it be done with a special range that stores three iterators?
>
> Yes, but not within the current primitive set. Sebastian's suggested interface
> extension should work.

That isn't necessarily a good idea, though.  Complicating the Range
abstraction undermines one of the best arguments in favor of the Range
abstraction.

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com