c++ template specialization for all subclasses

Question

I need to create a template function like this:

template
void foo(T a)
{
   if (T is a subclass of class Bar)
      do this
   else
      d         


        

Answer 1

I would use std::is_base_of along with local class as :

#include   //you must include this: C++11 solution!

template
void foo(T a)
{
   struct local
   {
        static void do_work(T & a, std::true_type const &)
        {
            //T is derived from Bar
        }
        static void do_work(T & a, std::false_type const &)
        {
            //T is not derived from Bar
        }
   };

   local::do_work(a, std::is_base_of());
}

Please note that std::is_base_of derives from std::integral_constant, so an object of former type can implicitly be converted into an object of latter type, which means std::is_base_of() will convert into std::true_type or std::false_type depending upon the value of T. Also note that std::true_type and std::false_type are nothing but just typedefs, defined as:

typedef integral_constant  true_type;
typedef integral_constant false_type;