Re: [boost] [utility] prior(it, n) for n being an unsigned type

Subject: Re: [boost] [utility] prior(it, n) for n being an unsigned type
From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2014-06-23 17:21:27

On Monday 23 June 2014 12:29:27 you wrote:
> On Monday 23 June 2014 08:40:29 Adam Romanek wrote:
> > Hi!
> > 
> > This is a re-post from boost-users mailing list, as I didn't get any
> > response there.
> > 
> > I've just finished investigating an issue in my code which led it to an
> > assert/abort in certain cases. It turned out it was caused by the use of
> > boost::prior(it, n) where n was unsigned int with some non-zero value.
> > 
> > I found a question [1] on the mailing list back in 2004 which describes
> > this issue. Additionally a solution to this problem was also posted in
> > one of the replies [2].
> > 
> > My question is - why hasn't it made into the repository yet?
> 
> Probably because it got forgotten.
> 
> > The current
> > behavior of boost::prior(it, n) when n is unsigned type is far from the
> > one expected by its potential users so I think it should either be
> > properly documented (warned) or fixed immediately.
> 
> I agree this should be fixed. Although it would probably be better to follow
> the standard interface:
> 
> template <class BidirectionalIterator>
> BidirectionalIterator prev(BidirectionalIterator x,
> typename std::iterator_traits<BidirectionalIterator>::difference_type n =
> 1);
> 
> I.e. the second argument should be accepted as a signed value and not as a
> template parameter.
> 
> I'll apply the change later if noone objects.

I've created a pull request:

https://github.com/boostorg/utility/pull/15

After I read that old discussion I decided to go with a slightly more 
complicated solution than I originally intended.