Re: [boost] [iterator][range] BoostIteratorTraversalConcepts-aware boost::advance/distance

On 28/06/2017 22:14, Andrzej Krzemienski via Boost wrote:

2017-06-28 22:03 GMT+02:00 Michel Morin via Boost :

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Hi,

The Boost iterator traversal concepts have not been adopted by the C++ Standard. Because of this, some of RandomAccessTraversalIterators (Boost's concepts) are treated as InputIterators (Standard's concepts) by the stdlib.

IMHO, Boost.Iterator should provide BoostIteratorTraversalConcepts-aware `boost::advance` and `boost::distance` to avoid the inefficiencies.

Not just inefficiencies. Using `prev()` may simply cause UB. See here: https://akrzemi1.wordpress.com/2017/01/02/not-detecting-bugs/

I would like to confirm something in your post. I think the standard requires iterator_category to be one of the standard types, not something derived from them: Draft N4659 (2017/03) 27.4.2 Standard iterator tags For every iterator of type Iterator, iterator_traits<Iterator>::iterator_category shall be defined to be the most specific category tag that describes the iterator’s behavior If this is correct, in your article is_BidirectionalIterator() should be defined using is_same instead of is_base_of, and Boost.Iterator's iterator_category definitions might not compatible with the standard. Or am I missing something? Best, Ion