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  1. #include <iostream>
  2. #include <string>
  3. #include <tuple>
  4.  
  5. // helper function to print a tuple of any size
  6. template<class Tuple, std::size_t N>
  7. struct TuplePrinter {
  8.     static void print(const Tuple& t) 
  9.     {
  10.         TuplePrinter<Tuple, N-1>::print(t);
  11.         std::cout << ", " << std::get<N-1>(t);
  12.     }
  13. };
  14.  
  15. template<class Tuple>
  16. struct TuplePrinter<Tuple, 1> {
  17.     static void print(const Tuple& t) 
  18.     {
  19.         std::cout << std::get<0>(t);
  20.     }
  21. };
  22.  
  23. template<class Tuple>
  24. struct TuplePrinter<Tuple, 0> {
  25.     static void print(const Tuple& t) 
  26.     {
  27.     }
  28. };
  29.  
  30. template<class... Args>
  31. void print(const std::tuple<Args...>& t) 
  32. {
  33.     std::cout << "(";
  34.     TuplePrinter<decltype(t), sizeof...(Args)>::print(t);
  35.     std::cout << ")\n";
  36. }
  37.  
  38. struct Row
  39. {
  40.    template <int N, typename ... Args> struct Helper;
  41.  
  42.    template <typename Arg1> struct Helper<1, Arg1>
  43.    {
  44.       static std::tuple<Arg1> getResult(Row& r)
  45.       {
  46.          return std::make_tuple(r.getResult<Arg1>(0));
  47.       }
  48.    };
  49.  
  50.    template <int N, typename Arg1, typename ... Args>
  51.       struct Helper<N, Arg1, Args...>
  52.       {
  53.          static std::tuple <Arg1, Args ...> getResult(Row& r)
  54.          {
  55.             return std::tuple_cat(std::make_tuple(r.getResult<Arg1>(N-1)),
  56.                                   Helper<N-1, Args...>::getResult(r));
  57.          }
  58.       };
  59.  
  60.    template <typename Arg> Arg getResult(int index)
  61.    {
  62.       // This is where the value needs to be extracted from the row.
  63.       // It is a dummy implementation for testing purposes.
  64.       return Arg{};
  65.    }
  66.  
  67.    template <typename ... Args>
  68.       std::tuple <Args ...> getResult()
  69.       {
  70.          return Helper<sizeof...(Args), Args...>::getResult(*this);
  71.       }
  72. };
  73.  
  74. int main()
  75. {
  76.    Row r;
  77.    auto res1 = r.getResult<std::string>();
  78.    auto res2 = r.getResult<int>();
  79.    auto res3 = r.getResult<int, double, int>();
  80.    auto res4 = r.getResult<int, int, double, double>();
  81.    auto res5 = r.getResult<std::string, std::string, int, int, double, double>();
  82.  
  83.    print(res1);
  84.    print(res2);
  85.    print(res3);
  86.    print(res4);
  87.    print(res5);
  88.  
  89.    return 0;
  90. }
  91.  
Success #stdin #stdout 0s 3300KB
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https://ideone.com/6IpJ8q
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
secret

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