Is this a bug in boost::range_detail::demote_iterator_traversal_tag of boost::iterator_facade?

Following code:

#include <boost/range/adaptor/transformed.hpp>
#include <boost/range/join.hpp>
struct foo {
    typedef int result_type;
    result_type operator ()(int x) { return x; }
};
int main() {
    using boost::adaptors::transformed;
    int a[] = {1, 2, 3};
    boost::join(a | transformed(foo()), a | transformed(foo()));
    return 0;
}

will get a compile error:

error C2039: 'type' : is not a member of 'boost::range_d开发者_运维问答etail::demote_iterator_traversal_tag<IteratorTraversalTag1,IteratorTraversalTag2>'
1>        with
1>        [
1>            IteratorTraversalTag1=boost::detail::iterator_category_with_traversal<std::input_iterator_tag,boost::random_access_traversal_tag>,
1>            IteratorTraversalTag2=boost::detail::iterator_category_with_traversal<std::input_iterator_tag,boost::random_access_traversal_tag>
1>        ]
...

in VS2008 with boost 1.45.

I dived into the source code of boost::range_detail::demote_iterator_traversal_tag and found it doesn't give a consideration about boost::detail::iterator_category_with_traversal which is produced by boost::detail::facade_iterator_category used by iterator_facade to deduce proper iterator category.

The transform_iterator is based on iterator_facade, so the iterator category of a | transformed(foo()) is deduced to be iterator_category_with_traversal<std::input_iterator_tag,boost::random_access_traversal_tag>, but demote_iterator_traversal_tag don't recognize it.

I don't understand why demote_iterator_traversal_tag designed like this. Or maybe its just a bug?

Thanks.

In case any future Google users end up here like I did, yes it looks like this was a bug, because it is fixed in at least version 1.54 (probably sooner, I hit the bug using 1.44 and just downloaded the current version).

IteratorTraversalTag1 and IteratorTraversalTag2 derive both from std::input_iterator_tag and boost::random_access_traversal_tag. Thus the demote_iterator_traversal_tag should have matched with BOOST_DEMOTE_TRAVERSAL_TAG( random_access_traversal_tag, random_access_traversal_tag, random_access_traversal_tag ). The ::type should have been random_access_traversal_tag. This looks really like a bug.