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  1. #include <tuple>
  2. #include <vector>
  3. #include <array>
  4. #include <cstdint>
  5. #include <iostream>
  6.  
  7. namespace cpp98
  8. {
  9. 	namespace detail
  10. 	{
  11. 		template <typename T>
  12. 		T declval();
  13. 	}
  14.  
  15. 	template <typename T>
  16. 	struct is_copy_assignable
  17. 	{
  18. 	private:
  19.  
  20. 		typedef char One;
  21. 		typedef struct { char a[2]; } Two;
  22.  
  23. 		template <int N = sizeof(detail::declval<T&>() = detail::declval<T const&>())>
  24. 		static One try_assign(int);
  25.  
  26. 		static Two try_assign(...);
  27.  
  28. 	public:
  29.  
  30. 		typedef typename std::conditional<sizeof(try_assign(0)) == sizeof(One),
  31. 			std::true_type, std::false_type>::type type;
  32. 	};
  33. }
  34.  
  35. namespace cpp11
  36. {
  37. 	template <typename T>
  38. 	struct is_copy_assignable
  39. 	{
  40. 	private:
  41. 		template <typename U, typename = decltype(std::declval<T&>() = std::declval<T const&>())>
  42. 		static std::true_type try_assign(U&&);
  43.  
  44. 		static std::false_type try_assign(...);
  45.  
  46. 	public:
  47. 		using type = decltype(try_assign(std::declval<T>()));
  48. 	};
  49. }
  50.  
  51. namespace cpp1y
  52. {
  53. 	template <typename ... Args>
  54. 	struct voider 
  55. 	{
  56. 		typedef void type;
  57. 	};
  58.  
  59. 	template <typename ... Args>
  60. 	using void_t = typename voider<Args...>::type;
  61.  
  62. 	template <typename T, typename = void>
  63. 	struct has_type_member : std::false_type
  64. 	{};
  65.  
  66. 	template <typename T>
  67. 	struct has_type_member<T, void_t<typename T::type>> : std::true_type
  68. 	{};
  69.  
  70. 	template <typename T, typename = void>
  71. 	struct is_copy_assignable : std::false_type
  72. 	{};
  73.  
  74. 	template <typename T>
  75. 	struct is_copy_assignable<T, void_t<decltype(std::declval<T&>() = std::declval<T const&>())>> : std::true_type
  76. 	{};
  77. }
  78.  
  79. class Foo
  80. {
  81. public:
  82. 	Foo() {}
  83. public:
  84. 	Foo(Foo const& rhs) = delete;
  85. 	Foo& operator= (Foo const& rhs) = delete;
  86. };
  87.  
  88. int main()
  89. {	
  90. 	bool result;
  91. 	result = cpp98::is_copy_assignable<Foo>::type::value;
  92. 	std::cout << result << std::endl;
  93. 	result = cpp11::is_copy_assignable<Foo>::type::value;
  94. 	std::cout << result << std::endl;
  95. 	result = cpp1y::is_copy_assignable<Foo>::type::value;
  96. 	std::cout << result << std::endl;
  97.  
  98. 	return 0;
  99. }
Success #stdin #stdout 0s 3140KB
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https://ideone.com/ZUCvhY
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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