https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64514
--- Comment #1 from Freddie Chopin <freddie_chopin at op dot pl> --- The question at stackoverflow has an answer with much simpler test-case which also shows the problem. http://stackoverflow.com/a/27810002/157344 --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- template<typename... T> struct Functor { template <T...> struct Inner {}; }; template struct Functor<>::Inner<>; int main() { } --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- Compiled with GCC 4.9.2: --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- $ g++ -std=c++11 test.cpp test.cpp: In instantiation of ‘struct Functor<>’: test.cpp:9:26: required from here test.cpp:5:12: error: wrong number of template arguments (1, should be 0) struct Inner ^ test.cpp:5:12: error: provided for ‘template<class ... T> template<T ...<anonymous> > struct Functor<T>::Inner’ test.cpp:5:12: error: wrong number of template arguments (1, should be 0) test.cpp:5:12: error: provided for ‘template<class ... T> template<T ...<anonymous> > struct Functor<T>::Inner’ test.cpp:9:28: error: ‘Inner’ is not a class template template struct Functor<>::Inner<>; ^ test.cpp:9:28: error: ‘Inner’ in ‘struct Functor<>’ does not name a type --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- Works fine with GCC 4.8. The answer also suggests there might be another similar bug, possibly related to the first one.
