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  1. #include <type_traits>
  2. #include <iostream>
  3.  
  4. template <typename... Ts>
  5. struct TypeList;
  6.  
  7. template <>
  8. struct TypeList<>
  9. {
  10.     static const int size = 0;
  11.     static std::integral_constant<int, -1> indexOf(...);
  12. };
  13.  
  14. template <typename Head, typename... Tail>
  15. struct TypeList<Head, Tail...> : TypeList<Tail...>
  16. {
  17.     static const int size = sizeof...(Tail) + 1;
  18.     static std::integral_constant<int, sizeof...(Tail)> indexOf(Head&&);
  19.     using TypeList<Tail...>::indexOf;
  20. };
  21.  
  22. template <typename TypeList, typename T>
  23. using IndexOf = std::integral_constant<int,
  24.     TypeList::size - decltype(TypeList::indexOf(std::declval<T>()))::value - 1>;
  25.  
  26. struct Type00 { };
  27. struct Type01 { };
  28. struct Type02 { };
  29. struct Type03 { };
  30. struct TypeXX { };
  31. struct TypeYY { };
  32.  
  33. using MyTypeList = TypeList<
  34.     Type00,
  35.     Type01,
  36.     Type02,
  37.     Type03,
  38.     TypeXX,
  39.     TypeYY
  40. >;
  41.  
  42. int main()
  43. {
  44.     std::cout << IndexOf<MyTypeList, Type00>::value
  45.               << IndexOf<MyTypeList, Type01>::value
  46.               << IndexOf<MyTypeList, Type02>::value
  47.               << IndexOf<MyTypeList, Type03>::value
  48.               << IndexOf<MyTypeList, TypeXX>::value
  49.               << IndexOf<MyTypeList, TypeYY>::value;
  50. }
Success #stdin #stdout 0s 3296KB
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https://ideone.com/FdkSIj
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
secret

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