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  1. #include <iostream>
  2. #include <tuple>
  3. #include <cassert>
  4.  
  5. struct foo 
  6. {
  7. 	foo() = delete;
  8.  
  9. 	foo(int i, int k)
  10. 	: i(i), k(k){}
  11.  
  12. 	void operator()()
  13. 	{ std::cout << i << " " << k << std::endl;}
  14.  
  15. 	int i;
  16. 	int k;
  17. };
  18.  
  19. struct bar
  20. {
  21. 	bar() = delete;
  22.  
  23. 	bar(int x)
  24. 	: x(x){}
  25.  
  26. 	void operator()()
  27. 	{ std::cout << x << std::endl;}
  28.  
  29. 	int x;
  30. };
  31.  
  32.  
  33. template <size_t I>
  34. struct visit_impl
  35. {
  36.     template <typename T, typename F>
  37.     static void visit(T& tup, size_t idx, F fun)
  38.     {
  39.         if (idx == I - 1) fun(std::get<I - 1>(tup));
  40.         else visit_impl<I - 1>::visit(tup, idx, fun);
  41.     }
  42. };
  43.  
  44. template <>
  45. struct visit_impl<0>
  46. {
  47.     template <typename T, typename F>
  48.     static void visit(T& tup, size_t idx, F fun) { assert(false); }
  49. };
  50.  
  51. /// visit at runtime the tuple item at idx and run F
  52. template <typename F, typename... Ts>
  53. void visit_at(std::tuple<Ts...> const& tup, size_t idx, F fun)
  54. {
  55.     visit_impl<sizeof...(Ts)>::visit(tup, idx, fun);
  56. }
  57.  
  58. /// visit at runtime the tuple item at idx and run F
  59. template <typename F, typename... Ts>
  60. void visit_at(std::tuple<Ts...>& tup, size_t idx, F fun)
  61. {
  62.     visit_impl<sizeof...(Ts)>::visit(tup, idx, fun);
  63. }
  64.  
  65. /// make an object
  66. template <typename T, typename... Args>
  67. T make_class(Args ...args)
  68. {
  69. 	return T(args...);
  70. }
  71.  
  72. template <typename... Args>
  73. void make_classes(Args... args)
  74. {
  75. 	auto t = std::tuple<Args...>(args...);
  76. 	unsigned int size = std::tuple_size<decltype(t)>::value;
  77. 	auto execute = [](auto & obj){ obj.operator()(); };
  78.  
  79. 	for (int i = 0; i < size; i++) {
  80. 		visit_at(t, i, execute);
  81. 	}
  82. }
  83.  
  84. int main() 
  85. {
  86. 	make_classes(
  87. 				 foo(2, 6),
  88. 				 bar(3),
  89. 				 foo(10,11),
  90. 				 bar(9)
  91. 			   );
  92. }
  93.  
Success #stdin #stdout 0s 3468KB
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Standard input is empty
stdout
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2 6
3
10 11
9
https://ideone.com/Fq242E
language:
C++14 (gcc 8.3)
created:
7 years ago
visibility:
public

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