Hello > /home/ben/c++/packagesearch/src/packagesearchimpl.cpp:281: undefined reference to `Tagcoll::OpSet<int>::operator^=(Tagcoll::OpSet<int> const&)' After giving it some thought the reason for this not working came back to me. The implementation of the template classes must be in the header file. So Enrico should probably fix this. Greetings Ben