On 2008-11-23, David Abrahams <dave-AT-boostpro.com> wrote:
on Sat Nov 22 2008, "Scott McMurray" <me22.ca+boost-AT-gmail.com> wrote:
It seems there's an assumption that a default-constructed iterator is either singular or past-the-end, but I saw no such requirement in either the standard or the "New iterator concepts" document.
Where was such an assumption made? I don't see it.
In both the old iterator_range implementation (which assumes that a range between default constructed iterators is empty) and the new one (which assumes that all default constructed iterators are singular). The sentence in 1.34 "This means that the iterator_range will still be usable in many contexts even though the iterators underneath are not" seems to descripe the assumption that 2 default-constructed iterators can never delimit a valid range. (This discussion does treat the previously-mentioned sentence, along with "Recall that many default constructed iterators are singular" as documentation that the begin and end iterators are default-constructed, which is backed up by the source, analogy to std::pair, and the fact that since my iterator type has a default constructor, pointless gymnastics would be required for it to not be used.) As I can find no requirement that prevents two default-constructed iterators from delimiting a valid range, I think that neither implementation properly models the range concept (under the presumption, justified above, that a default-constructed iterator_range contains default-constructed iterators).