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  1. #include <iostream>
  2. #include <type_traits>
  3. #include <cstddef>
  4.  
  5. template <typename T> struct vector_fields_1 { union { T values[1]; struct { T x;          }; }; };
  6. template <typename T> struct vector_fields_2 { union { T values[2]; struct { T x, y;       }; }; };
  7. template <typename T> struct vector_fields_3 { union { T values[3]; struct { T x, y, z;    }; }; };
  8. template <typename T> struct vector_fields_4 { union { T values[4]; struct { T x, y, z, w; }; }; };
  9. template <typename T, std::size_t N> struct vector_fields_n { T values[N]; };
  10.  
  11. template <class T, std::size_t N>
  12. struct vector : public
  13. 	std::conditional<
  14. 		N == 1
  15. 			&& offsetof(vector_fields_1<T>, x) == offsetof(vector_fields_1<T>, values[0])
  16. 		,
  17. 		vector_fields_1<T>,
  18. 		typename std::conditional<
  19. 			N == 2
  20. 				&& offsetof(vector_fields_2<T>, x) == offsetof(vector_fields_2<T>, values[0])
  21. 				&& offsetof(vector_fields_2<T>, y) == offsetof(vector_fields_2<T>, values[1])
  22. 			,
  23. 			vector_fields_2<T>,
  24. 			typename std::conditional<
  25. 				N == 3
  26. 					&& offsetof(vector_fields_3<T>, x) == offsetof(vector_fields_3<T>, values[0])
  27. 					&& offsetof(vector_fields_3<T>, y) == offsetof(vector_fields_3<T>, values[1])
  28. 					&& offsetof(vector_fields_3<T>, z) == offsetof(vector_fields_3<T>, values[2])
  29. 				,
  30. 				vector_fields_3<T>,
  31. 				typename std::conditional<
  32. 					N == 4
  33. 						&& offsetof(vector_fields_4<T>, x) == offsetof(vector_fields_4<T>, values[0])
  34. 						&& offsetof(vector_fields_4<T>, y) == offsetof(vector_fields_4<T>, values[1])
  35. 						&& offsetof(vector_fields_4<T>, z) == offsetof(vector_fields_4<T>, values[2])
  36. 						&& offsetof(vector_fields_4<T>, w) == offsetof(vector_fields_4<T>, values[3])
  37. 					,
  38. 					vector_fields_4<T>,
  39. 					vector_fields_n<T, N>
  40. 				>::type
  41. 			>::type
  42. 		>::type
  43. 	>::type
  44. {
  45. 	T& operator[](std::size_t pos) { return this->values[pos]; }
  46. 	const T& operator[](std::size_t pos) const { return this->values[pos]; }
  47. };
  48.  
  49. int main(int, char**) {
  50. 	vector<int, 3> obj;
  51. 	obj[0] = 1;
  52. 	obj.y  = 2;
  53. 	obj[2] = 3;
  54. 	std::cout << "(" << obj.x << ", " << obj[1] << ", " << obj.z << ")" << std::endl;
  55. 	return 0;
  56. }
  57.  
Success #stdin #stdout 0s 3468KB
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https://ideone.com/ZB3SPM
language:
C++14 (gcc 8.3)
created:
7 years ago
visibility:
public

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