c++ - std::is_same equivalent for unspecialised template types -

in 1 project have found possibility stay dry lot of code except small parts stay same template specialisations of template. here small working example i'm doing check templated class i'm using:

template<typename t> class a{};  template<typename t> class b{};  template<template<class> class c> void do_stuff() {     if(std::is_same<a<int>,c<int>>::value)     {     // stuff     } else if(std::is_same<b<int>,c<int>>::value)     // stuff b     } }  int main() {     do_stuff<a>(); } 

what instead using

std::is_same<a,c>::value 

to determine template type. there function me or missing pattern work better in case?

i see like

template<template<class> class c, typename t> void do_stuff();  do_stuff<a,t>(); 

but seems wrong way me.

you write is_same_template trait partially specialized when 2 template template parameters same:

template <template <typename...> class, template<typename...> class>  struct is_same_template : std::false_type{};  template <template <typename...> class t> struct is_same_template<t,t> : std::true_type{}; 

then can write is_same_template<a,c>::value.

note won't work templates have non-type template parameters, std::array.

some compilers not consider alias template equivalent template aliases, following result in std::false_type:

template <typename t, typename alloc> using myvec = std::vector<t, alloc>;  is_same_template<std::vector, myvec>; 

this considered defect in standard, shouldn't rely on behaviour until fix implemented in common compilers.

---

that said, need careful put in if branches, code needs compile regardless of template instantiated with. in c++17 you'll able use if constexpr solve problem, you'll need tag dispatch or have different specializations if branches have code valid a or b.

template <template <typename...> class> struct tag{};  template <template <typename> class t> void do_stuff() {     do_stuff(tag<t>{}); }  void do_stuff(tag<a>) {     std::cout << "a"; }  void do_stuff(tag<b>) {     std::cout << "b";    }