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  1. #include <cstdint>
  2. #include <iostream>
  3.  
  4. template <typename U>
  5. class has_special
  6. {
  7. private:
  8.     template<typename T, typename = typename T::special>
  9.     static std::uint8_t check(int);
  10.     template<typename T> static std::uint16_t check(...);
  11. public:
  12.     static
  13.     constexpr bool value = sizeof(check<U>(0)) == sizeof(std::uint8_t);
  14. };
  15.  
  16. struct NormalType { };
  17. struct SpecialType { typedef int special; };
  18.  
  19. static_assert(has_special<SpecialType>::value, "");
  20. static_assert(!has_special<NormalType>::value, "");
  21.  
  22. template <typename T, bool = has_special<T>::value>
  23. struct DetectSpecial {
  24.     void detected() { std::cout << "Not special...\n"; }
  25. };
  26.  
  27. template <typename T>
  28. struct DetectSpecial<T, true> {
  29.     void detected() { std::cout << "Special!\n"; }
  30. };
  31.  
  32. int main()
  33. {
  34.     DetectSpecial<NormalType>().detected();
  35.     DetectSpecial<SpecialType>().detected();
  36.  
  37.     return 0;
  38. }
  39.  
  40.  
Success #stdin #stdout 0s 3296KB
comments (?)
stdin
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Standard input is empty
stdout
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Not special...
Special!
https://ideone.com/XISlZ6
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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