primitive_template_expressions.cpp

#include <iostream>

namespace dtl // detail
{
  template <typename T1, typename T2 = T1>
  struct carpma_t {
    typedef T1 tipi;
  };

  template <>
  struct carpma_t<int> {
    typedef int tipi;
  };

  template <>
  struct carpma_t<double> {
    typedef double tipi;
  };

  template <>
  struct carpma_t<int, double> {
    typedef double tipi;
  };

  template <>
  struct carpma_t<double, int> {
    typedef double tipi;
  };

  template <typename T1, typename T2 = T1>
  struct toplama_t {
    typedef T1 tipi;
  };

  template <>
  struct toplama_t<int> {
    typedef int tipi;
  };

  template <>
  struct toplama_t<double> {
    typedef double tipi;
  };

  template <>
  struct toplama_t<int, double> {
    typedef double tipi;
  };

  template <>
  struct toplama_t<double, int> {
    typedef double tipi;
  };

  template <typename T1, typename T2 = T1>
  struct cikarma_t : toplama_t<T1, T2> { };

  template <typename T1, typename T2 = T1>
  struct bolme_t : carpma_t<T1, T2> { };

}  // namespace detail

template <typename T1, typename T2>
struct donus_tipi {
  typedef typename dtl::carpma_t<T1, T2>::tipi carpma;
  typedef typename dtl::toplama_t<T1, T2>::tipi toplama;
  typedef typename dtl::bolme_t<T1, T2>::tipi bolme;
  typedef typename dtl::cikarma_t<T1, T2>::tipi cikarma;
};

template <typename T>
struct tip_traits {
  static const char* tip_adi;
};
template <typename T>
const char* tip_traits<T>::tip_adi = "bilinmiyor";

template <>
const char* tip_traits<int>::tip_adi = "int";

template <>
const char* tip_traits<double>::tip_adi = "double";

template <typename type1, typename type2>
typename donus_tipi<typename donus_tipi<type1, type2>::toplama, 
                    typename donus_tipi<type1, type2>::cikarma>::carpma 
islem(type1 a, type2 b)
{
  typedef typename donus_tipi<type1, type2>::cikarma cikarma_tipi;
  typedef typename donus_tipi<type1, type2>::toplama toplama_tipi;
  typedef typename donus_tipi<toplama_tipi, cikarma_tipi>::carpma dt;
  dt sonuc = a + b * (a - b);
  std::cout 
    << "islem sonucu (" 
    << tip_traits<dt>::tip_adi << "): "
    << sonuc << "\n";
  return sonuc;
}
// compiler explorer link: https://gcc.godbolt.org/z/gJqRgH 
int main(int argc, const char* argv[])
{
  int x = islem(7, 3);
  double y = islem(7., 3);
  return 0;
}