Hi, I have got some problems with the unordered containers from the sandbox files. The problem is that iterator_base<T> can't be converted into iterator or const_iterator. I helped myself by adding "friend class const_iterator; friend class iterator;" to iterator_base and adding a constructor like "const_iterator (iterator_base_type i)" to const_iterator/iterator. I have no clue if this is could be an official solution. See sample code below to expose the problem. Bye, Martin typedef boost::unordered_set<int> MySet; { MySet myset; MySet::const_iterator citer = myset.begin(); MySet::iterator iter = myset.begin(); MySet::const_iterator citer2= ++citer; //doesn't work, but should (?) MySet::iterator iter2 = ++citer; //doesn't work, and should not work (?) MySet::iterator iter3 = ++iter; //doesn't work, but should (?) MySet::const_iterator citer3 = iter; //works, you can't do that //with std::containers (?) }