inline typename boost::enable_if_c< boost::unordered::detail::has_max_size<Alloc>::value, SizeType >::type call_max_size(const Alloc& a) { return a.max_size(); }
size_type allocator_traits<Alloc>::max_size(Alloc& a) noexcept { return a.max_size(); //TODO: It may not be implemented! }