c++ - A variadic template method to accept a given number of doubles? -

template <unsigned int n> class myclass { public:     template <typename... args> void mymethod(args... args)     {        // interesting stuff     }  }; 

i want mymethod called n doubles. possible? is, have:

myclass <3> x; x.mymethod(3., 4., 5.); // works x.mymethod('q', 1., 7.); // doesn't work x.mymethod(1., 2.); // doesn't work 

how can done?

for number of arguments constraint can check if sizeof...(args) == n checking if arguments doubles need build recursive type trait checks std::is_same each of arguments.

template<typename...> struct are_same : std::true_type  {};  template<typename t> struct are_same<t> : std::true_type {};  template<typename t, typename u, typename... types> struct are_same<t, u, types...> :     std::integral_constant<bool, (std::is_same<t, u>::value && are_same<t, types...>::value)> {}; 

notice are_same first declared , specialized.

then implement constraint in method return type using std::enable_if taking advantage of sfinae.

template <unsigned int n> class myclass { public:     template <typename... args>     typename std::enable_if<(are_same<double, args...>::value && sizeof...(args) == n), void>::type     /* void */ mymethod(args... args)     {         // interesting stuff     }  };