http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52069
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-01-31 15:47:40 UTC --- The program is ill-formed: "If a template, a member template or a member of a class template is explicitly specialized then that specialization shall be declared before the first use of that specialization that would cause an implicit instantiation to take place, in every translation unit in which such a use occurs; no diagnostic is required." When compiling main.o the compiler has no way to know that you have explicitly instantiated S<T>::id so it is implicitly instantiated. You need to declare the explicit instantiation in tmpl.h template<> struct ID S<T>::id; That will prevent the implicit instantiation of that member in main.o, and your explicit instantiation in libtmpl.so will be used.
