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  1. #include <iostream>
  2. #include <type_traits>
  3. #include <map>
  4.  
  5. template <typename E>
  6. struct enum_traits
  7. {
  8.     static const char* const name;
  9.     static const std::map<E, std::string> mapping;
  10. };
  11.  
  12. template <typename E>
  13. struct ECategory_impl : std::error_category
  14. {
  15.     static_assert(std::is_enum<E>::value, "!");
  16.  
  17.     const char* name() const noexcept override
  18.     {
  19.       return enum_traits<E>::name;
  20.     }
  21.  
  22.     std::string message(int c) const override
  23.     {
  24.         const auto& Map = enum_traits<E>::mapping;
  25.         E code = static_cast<E>(c);
  26.         auto itr = Map.find(code);
  27.         if (itr != Map.end())
  28.         {
  29.             return itr->second;
  30.         }
  31.         else
  32.         {
  33.             return "(unrecognized error)";
  34.         }
  35.     }
  36. };
  37.  
  38. template <typename E>
  39. std::error_code make_error_code(E e)
  40. {
  41.     static_assert(std::is_enum<E>::value, "!");
  42.     static const ECategory_impl<E> categ{};
  43.     return {static_cast<int>(e), categ};
  44. }
  45.  
  46. #define MAKE_ERROR_CODE_CATEGORY(E) \
  47.      template <> const char* const enum_traits<E>::name = #E; \
  48. namespace std \
  49. { \
  50.     template <> \
  51.     struct is_error_code_enum<E> : true_type {}; \
  52. } \
  53. using E##_category = ECategory_impl<E>;
  54.  
  55. enum class E {A, B};
  56. template <> const std::map<E, std::string> enum_traits<E>::mapping
  57. {
  58.     {E::A, "A"},
  59.     {E::B, "E::B"}
  60. };
  61.  
  62. MAKE_ERROR_CODE_CATEGORY(E)
  63.  
  64. int main()
  65. {
  66.     auto ec = make_error_code(E::A);
  67.     static_cast<void>(ec);
  68. }
  69.  
Success #stdin #stdout 0s 4472KB
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stdout 
Standard output is empty
https://ideone.com/4CQWeF
language:
C++14 (gcc 8.3)
created:
5 years ago
visibility:
public

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