On Wed, Oct 19, 2011 at 12:09 PM, <andrey.semashev@gmail.com> wrote:
On Wednesday, October 19, 2011 11:50:06 Jeffrey Lee Hellrung, Jr. wrote:
Making the size signed makes little sense to me and it also introduces a problem (rather theoretical, however) when iterator_range is constructed from a very large valid range, whose size exceeds numeric_limits<difference_type>::max().
How would that be possible? Doesn't that violate the conditions on difference_type that it is able to represent the (signed) distance between any two iterators within the same range?
That is only true for random access iterators. See std::distance reference (24.4.4/4):
Effects: If InputIterator meets the requirements of random access iterator, returns (last - first); otherwise, returns the number of increments needed to get from first to last.
So bidirectional iterators, for instance, may denote a valid range that exceeds difference_type capacity. This is actually a little caveat in the Standard.
A bit surprising, but I'll take your word for it. In any case, it's some irrelevant for non-random-access iterators as iterator_range::size() is only defined for random access iterators, no?
Also, assuming that size() should return an unsigned integer type (I'm not debating the merits of this), *what* unsigned integer type should that be? I don't know of any general way to go from difference_type to a "compatible" unsigned integer type. I suspect this will end up being filed away as "nice to have but ultimately unimplementable generically" given current range interfaces.
I think the following would do:
typedef typename make_unsigned< difference_type >::type size_type;
I was under the impression that most of the traits in Boost.TypeTraits of this nature are only defined for builtin types. - Jeff