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  1. #include <utility>
  2.  
  3. template <typename...>
  4. struct sum_impl;
  5.  
  6. /* This is the base case */
  7. template <typename T1, typename T2>
  8. struct sum_impl<T1, T2>
  9. {
  10.     typedef decltype(std::declval<const T1&>() + std::declval<const T2&>()) result_type;
  11.  
  12.     static result_type doit(const T1& v1, const T2& v2)
  13.     {
  14.         return v1 + v2;
  15.     }
  16. };
  17.  
  18. /* And here is the recursive definition for left-associativity */
  19. template <typename T1, typename T2, typename... Ts>
  20. struct sum_impl<T1, T2, Ts...>
  21. {
  22.     typedef decltype(std::declval<const T1&>() + std::declval<const T2&>()) step_type;
  23.     typedef typename sum_impl<step_type, Ts...>::result_type result_type;
  24.  
  25.     static result_type doit(const T1& v1, const T2& v2, const Ts&... rest)
  26.     {
  27.         return sum_impl<step_type, Ts...>::doit(v1 + v2, rest...);
  28.     }
  29. };
  30.  
  31. template <typename... Ts>
  32. typename sum_impl<Ts...>::result_type sum(const Ts&... args)
  33. {
  34.     return sum_impl<Ts...>::doit(args...);
  35. }
  36.  
  37. #include <iostream>
  38. int main(void)
  39. {
  40.     std::cout << sum(1, 3, 5, 7, 9, 11) << std::endl;
  41.     std::cout << sum(1, 3.4, 5, 7, 9, 11) << std::endl;
  42. }
  43.  
Success #stdin #stdout 0s 2852KB
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36
36.4
https://ideone.com/jMwgLz
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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