I've tried to compile one of the examples from the filter_iterator documentation: main() { int numbers[] = { 0, -1, 4, -3, 5, 8, -2 }; const int N = sizeof(numbers)/sizeof(int); std::copy(boost::make_filter_iterator(numbers, numbers + N, std::bind2nd(std::greater<int>(), -2)), boost::make_filter_iterator(numbers + N, numbers + N, std::bind2nd(std::greater<int>(), -2)), std::ostream_iterator<int>(std::cout, " ")); std::cout << std::endl; } using a version of g++ 3.3.2 that has concept-checks enabled. In this case the compiler rejects both of the iterators returned by make_filter_iterator in the above code because they do not fulfill the InputIterator concept required by std::copy. This is because InputIterator requires the DefaultConstructable concept, and the predicate: std::bind2nd(std::greater<int>(),-2) , isn't default constructable. My question is this: is this type of iterator (non-default-constructable) safe to use in general even if it fails a conceptual requirement? Of course the above code runs as expected with a normal g++ build and I could always wrap the predicate in another object if I really wanted to use concept-checks... but I'm interested in whether the above code is considered normal and safe as it stands. Thanks for any insight. -Chris