Re: [boost] [range] range_size<T> deprecation, updated docs etc.

From: David Abrahams (dave_at_[hidden])
Date: 2007-11-15 08:14:04

on Fri Nov 09 2007, "JOAQUIN LOPEZ MU?Z" <joaquin-AT-tid.es> wrote:

> De: David Abrahams <dave_at_[hidden]>
>> on Fri Nov 09 2007, Thorsten Ottosen <nesotto-AT-cs.aau.dk> wrote:
> [...]
>> > "template<class InputIterator>
>> > typename iterator_traits<InputIterator>::difference_type
>> > distance(InputIterator first, InputIterator last);
>> > 4 Effects: Returns the number of increments or decrements needed 
>> to get 
>> > from first to last.
>> > 5 Requires: last shall be reachable from first."
>> >
>> > How can one ever use decrements to get from first to last?
>> 
>> When InputIterator is a random access iterator, last < first does not
>> violate the precondition.
>
> I'm afraid (last<first) violates the precondition even with
> random access iterators, according to 24.1.6 and as explicitly
> acknowledged at
> http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#204 .

I don't see how to read the issue resolution so it says that.

> This is IMHO an unfortunate decision by the committee and renders
> the "or decrements" bit in the effects clause of std::distance
> void and misleading.

I do agree that the decision is unfortunate.  The wording is clearly
misleading.

-- 
Dave Abrahams
Boost Consulting
http://www.boost-consulting.com