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  1. #include <iostream>
  2.     #include <type_traits>
  3.  
  4.     // Traits class
  5.     template <typename T, typename = void>
  6.     struct VectorTraits;
  7.  
  8.     template <typename T>
  9.     struct VectorTraits<T, std::enable_if_t<(T::dimension > 0)>>
  10.     {
  11.       typedef T                       VectorType;
  12.       typedef typename T::ValueType   ValueType;
  13.       static const std::uint16_t      dimension = T::dimension;
  14.     };
  15.  
  16.  
  17.     // Fake vector class. Defines the required typedef.
  18.     struct Vec
  19.     {
  20.       typedef float   ValueType;
  21.       static const std::uint16_t dimension = 2;
  22.     };
  23.  
  24.     // Fake vector class. Defines the required typedef.
  25.     struct VecFake
  26.     {
  27.     };
  28.  
  29.     template <>
  30.     struct VectorTraits<VecFake>
  31.     {
  32.       typedef VecFake                       VectorType;
  33.       typedef float   ValueType;
  34.       static const std::uint16_t      dimension = 12;
  35.     };
  36.  
  37.     // Streaming operator attempt for classes defining VectorTraits.
  38.     template <class T, typename = std::enable_if_t<(sizeof(VectorTraits<T>) > 0)>>
  39.     std::ostream& operator << (std::ostream& stream, const T& )
  40.     {
  41.         return stream << "Traits. Dimension = " << VectorTraits<T>::dimension << "\n";
  42.     }
  43.  
  44.     int main()
  45.     {
  46.         std::cout << "Test\n";
  47.         std::cout << Vec();
  48.         std::cout << VecFake();
  49.     }
Success #stdin #stdout 0s 3456KB
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Standard input is empty
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Test
Traits. Dimension = 2
Traits. Dimension = 12
https://ideone.com/NbHKHS
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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