I have the code given below #include <boost/array.hpp> #include <boost/foreach.hpp> #include <vector> struct parent; struct child; typedef boost::array<child,5> childs_t; typedef std::vector<parent> parents_t; //typedef boost::array<parent,6> parents_t; //1) typedef parent* parent_pointer; //typedef parents_t::pointer parent_pointer; //2) struct child { parent_pointer par; }; struct parent { childs_t childs; }; int main() { parents_t all(6); BOOST_FOREACH(parent& p,all) { childs_t& ch = p.childs; BOOST_FOREACH(child& c,ch ) { c.par = &p; } } } I want to use the parent_pointer in a generic way as nested typedef of parents_t so that if needed I can have a different pointer type than parent* as the commented code shown in 2) .That is probably not permitted as vector of incomplete type is illegal, though it actually might work. But the same is not possible with boost::array as in 1) , as it needs complete type parent. This is because compiler tries to instantiate boost::array while accessing inner type pointer (Though actually boost::array doesn't have pointer , I can replace it by iterator, probably c++0x has pointer typedef ). On the other hand my requirement is only pointer/iterator which may not depend on complete type parent, and none of parent or child otherwise has even problem with vector, array or any other container. Is it possible (or boost has) some portable wrapper over the inner typedef of the containers which doesn't tries to instantiate the container which might depend on completeness of the type, so that I can just change the typedef of container / allocator in one location and rest will "just work". Assumption is container nested types like value_type, pointer, reference, size_type, difference_type, iterator and const counterparts doesn't depend on completeness f the parametre T. Though this question is not entirely boost related, it may not be entirely uncorrelated. Thanks abir -- Abir Basak B. Tech , IIT KGP Research Engineer & Technology Lead, Read Ink Technologies