Hi Chris, It looks like there is a bug in the iterator concept checks. When I first created the concept checks, I was using the SGI STL web pages as a reference... and at that time I didn't know there were subtle differences between the SGI concepts and the C++ standard. Anyways, the C++ standard does not require an Input Iterator to be default constructible (the SGI docs do), so the code below should be legal. Cheers, Jeremy On Tue, 21 Oct 2003, Chris Saunders wrote: ctsa> I've tried to compile one of the examples from the filter_iterator ctsa> documentation: ctsa> ctsa> main() ctsa> { ctsa> int numbers[] = { 0, -1, 4, -3, 5, 8, -2 }; ctsa> const int N = sizeof(numbers)/sizeof(int); ctsa> ctsa> std::copy(boost::make_filter_iterator(numbers, numbers + N, ctsa> std::bind2nd(std::greater<int>(), ctsa> -2)), ctsa> boost::make_filter_iterator(numbers + N, numbers + N, ctsa> std::bind2nd(std::greater<int>(), ctsa> -2)), ctsa> std::ostream_iterator<int>(std::cout, " ")); ctsa> std::cout << std::endl; ctsa> ctsa> } ctsa> ctsa> using a version of g++ 3.3.2 that has concept-checks enabled. In this case ctsa> the compiler rejects both of the iterators returned by ctsa> make_filter_iterator in the above code because they do not fulfill the ctsa> InputIterator concept required by std::copy. This is because InputIterator ctsa> requires the DefaultConstructable concept, and the predicate: ctsa> std::bind2nd(std::greater<int>(),-2) , isn't default constructable. ctsa> ctsa> My question is this: is this type of iterator (non-default-constructable) ctsa> safe to use in general even if it fails a conceptual requirement? Of ctsa> course the above code runs as expected with a normal g++ build and I could ctsa> always wrap the predicate in another object if I really wanted to use ctsa> concept-checks... but I'm interested in whether the above code is ctsa> considered normal and safe as it stands. ---------------------------------------------------------------------- Jeremy Siek http://php.indiana.edu/~jsiek/ Ph.D. Student, Indiana Univ. B'ton email: jsiek@osl.iu.edu C++ Booster (http://www.boost.org) office phone: (812) 855-3608 ----------------------------------------------------------------------