c++ - Applying a variadic function with std::apply -

is possible apply variadic function tuple std::apply?

for example, following code works fine gcc 6.2.1:

void print_t(std::string i, std::string j) {     std::cout << << " " << j << std::endl; }  int main() {         std::tuple<std::string, std::string> t{"ab", "cd"};         std::experimental::apply(print_t, t);         return 0; } 

but if try apply variadic function:

template<typename t> void vprint(t && t) {     std::cout << std::forward<t>(t) << std::endl; }  template<typename t, typename ... ts> void vprint(t && t, ts ... ts) {     std::cout << std::forward<t>(t) << " ";     vprint<ts...>(std::forward<ts>(ts)...); }  int main() {         std::tuple<std::string, std::string> t{"fd", "ab"};         std::experimental::apply(vprint, t);         return 0; } 

the compiler complains cannot deduce template arguments of vprint. ok, let's write them explicitly:

std::experimental::apply(vprint<std::string, std::string>, t); 

now compiler ends obscure errors expose standard library internals.

i wrote own implementation of std::apply in c++11 , understand why can't deduce arguments of variadic function template. but, in theory, std::apply has information needed deduction.

so application of variadic functions not yet implemented feature in gcc6? c++17-compatible compilers allow such application? if not, allow application of instantiated variadic template functions, vprint<std::string, std::string>?

with vprint<std::string, std::string>, must pass r-value references, so

std::experimental::apply(vprint<std::string, std::string>, std::move(t)); 

the better way use functor (thanks generic lambda):

std::experimental::apply([](auto&&... args) {                              vprint(std::forward<decltype(args)>(args)...);                          },                          t);