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  1. #include <iostream>
  2. #include <stdexcept>
  3. #include <type_traits>
  4. //Concept looted from https://stackoverflow.com/a/16000226
  5. // definitely take the time to read the answer to grok what's going on.
  6. template <typename T, typename = int>
  7. struct HasFirst : std::false_type { };
  8.  
  9. template <typename T>
  10. struct HasFirst <T, decltype((void) T::First, 0)> : std::true_type { };
  11.  
  12. template <typename T, typename = int>
  13. struct HasLast : std::false_type { };
  14.  
  15. template <typename T>
  16. struct HasLast <T, decltype((void) T::Last, 0)> : std::true_type { };
  17.  
  18. template <class TYPE>
  19. TYPE do_conversion(int value)
  20. {
  21.     static_assert(HasFirst<TYPE>::value, "Need First");
  22.     static_assert(HasLast<TYPE>::value, "Need Last");
  23.     if (value >= static_cast<int>(TYPE::First) &&
  24.         value < static_cast<int>(TYPE::Last))
  25.     {
  26.         return static_cast<TYPE>(value);
  27.     }
  28.     throw std::out_of_range("Inv value");
  29. }
  30.  
  31. enum class Weekday
  32. {
  33.     Monday,
  34.     Tuesday,
  35.     Wednesday,
  36.     Thursday,
  37.     Friday,
  38.     Saturday,
  39.     Sunday,
  40.     Last,
  41.     First = Monday
  42. };
  43.  
  44. void demo(int value)
  45. {
  46.     try
  47.     {
  48.         std::cout << "Day " << value << " is ";
  49.         switch (do_conversion<Weekday>(value))
  50.         {
  51.             case Weekday::Monday:
  52.                 std::cout << "Monday\n";
  53.                 break;
  54.             case Weekday::Tuesday:
  55.                 std::cout << "Tuesday\n";
  56.                 break;
  57.             case Weekday::Wednesday:
  58.                 std::cout << "Wednesday\n";
  59.                 break;
  60.             case Weekday::Thursday:
  61.                 std::cout << "Thursday\n";
  62.                 break;
  63.             case Weekday::Friday:
  64.                 std::cout << "Friday\n";
  65.                 break;
  66.             case Weekday::Saturday:
  67.                 std::cout << "Saturday\n";
  68.                 break;
  69.             case Weekday::Sunday:
  70.                 std::cout << "Sunday\n";
  71.                 break;
  72.             default:
  73.                 std::cout << "Huh. How did we get here?\n";
  74.                 break;
  75.         }
  76.     }
  77.     catch (const std::out_of_range& ) {
  78.         std::cout << "Invalid\n";
  79.     }
  80. }
  81.  
  82. int main()
  83. {
  84.     for (int i = -1; i < 10; i++)
  85.     {
  86.         demo(i);
  87.     }
  88. }
  89.  
Success #stdin #stdout 0s 4436KB
comments (?)
stdin
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Standard input is empty
stdout
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Day -1 is Invalid
Day 0 is Monday
Day 1 is Tuesday
Day 2 is Wednesday
Day 3 is Thursday
Day 4 is Friday
Day 5 is Saturday
Day 6 is Sunday
Day 7 is Invalid
Day 8 is Invalid
Day 9 is Invalid
https://ideone.com/KkAMBG
language:
C++ (gcc 8.3)
created:
4 years ago
visibility:
public

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