c++ - Template alias, Template specialization and Template Template parameters -

i want determine underlying template of template parameter using combination of template alias , template specializations. follwing code compiles fine on gcc 4.8, 6.2.1 not on clang 3.5, 3.8.

#include <iostream>  template <typename t> struct first {};  template <typename t> struct second {};  template <template <typename> class f, typename t> struct foo {};  template <typename t> struct foo<first, t> {   void f() { std::cout << __pretty_function__ << std::endl; } };  template <typename t> struct foo<second, t>  {   void f() { std::cout << __pretty_function__ << std::endl; } };  template <typename f, typename t> struct resolution {};  template <typename t> struct resolution<first<t>, t> {    template <typename p> using type = first<p>; };  template <typename t> struct resolution<second<t>, t> {     template <typename p> using type = second<p>; };  int main() {     foo<resolution<first<int>, int>::type, float> my_foo;     my_foo.f(); // main.cpp:34:12: error: no member named 'f' in 'foo<resolution<first<int>, int>::type, float>'      return 0; } 

which behavior standard conformant?

answer: know bug in c++ standard core language , described t.c. in comments . http://wg21.link/cwg1286