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  1. // needed for is_same
  2. #include <type_traits>
  3. #include <tuple>
  4. #include <iostream>
  5.  
  6. using namespace std;
  7.  
  8. // this should be an inner and private metafunction of exists_type
  9. // I put here for clarity
  10. template<typename T, typename Tuple, const int index>
  11. struct exists_type_index
  12. {
  13.     static const bool value =
  14.         is_same < T, typename tuple_element<index, Tuple>::type >::value ||
  15.                   exists_type_index<T, Tuple, index-1>::value;
  16. };
  17.  
  18. // stop the recursion when reach the first element
  19. template<typename T, typename Tuple>
  20. struct exists_type_index<T, Tuple, 0>
  21. {
  22.     static const bool value = is_same < T, typename tuple_element<0, Tuple>::type >::value;
  23. };
  24.  
  25. // exists_type metafunction (clients call this)
  26. template<typename T, typename Tuple>
  27. struct exists_type
  28. {
  29.     static const bool value = exists_type_index<T, Tuple, tuple_size<Tuple>::value-1>::value;
  30. };
  31.  
  32. ////////////////////////// Executor
  33.  
  34. template<bool b>
  35. struct Executor
  36. {
  37.  template<typename T>
  38.  static void execute(T&&)
  39.  {
  40.     cout << "General case" << endl;
  41.  }
  42. };
  43.  
  44. template<>
  45. struct Executor <true>
  46. {
  47.  template<typename T>
  48.  static void execute(T&&)
  49.  {
  50.     cout << "Specific case" << endl;
  51.  }
  52. };
  53.  
  54. // clients call this
  55. template<typename Tuple>
  56. struct MultiTypeDispatcher
  57. {
  58.  template<typename T>
  59.  void function( T&& t )
  60.  {
  61.       Executor<exists_type<T, Tuple>::value>::execute(forward<T>(t));
  62.  }
  63. };
  64.  
  65.  
  66. int main()
  67. {
  68.     MultiTypeDispatcher< tuple<int, float, string> > dispatcher;
  69.  
  70.     dispatcher.function(string("hello!")); // Specific case!
  71.     dispatcher.function(1.0f); // Specific case!
  72.     dispatcher.function(1.0); // General case!
  73.  
  74.     return 0;
  75. }
Success #stdin #stdout 0s 3016KB
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https://ideone.com/JEXMAX
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
secret

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