c++ - Multiple pack expansions inside class with fixed number of template arguments -

is code well-formed? declaration of function template gives error in both clang , gcc though ts empty.

// error: many template arguments class template 'pair' template<class i, class u, class... ts> void f(std::pair<i,u,ts...>);  int main() {     f(std::pair<int,int>()); } 

the function call gives error in gcc doesn't make sense. there no conversion int:

note: cannot convert 'std::pair<int, int>()' (type 'std::pair<int, int>') type 'int' 

[temp.res]/8:

if every valid specialization of variadic template requires empty template parameter pack, template ill-formed, no diagnostic required.

every valid specialization of f require ts empty pack. therefore program ill-formed ndr. both compilers correct.

as gcc's diagnostic, seems due habit of using int placeholder "something looks type doesn't make sense" error recovery purposes.