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  1. #include <iostream>
  2. #include <tuple>
  3. #include <type_traits>
  4. using namespace std;
  5.  
  6.  
  7. template<typename Derived>
  8. class BaseData {
  9. public:
  10.     template<typename Visitor>
  11.     void accept(Visitor &v){
  12.          static_cast<Derived*>(this)->accept(v);
  13.     }
  14. };
  15.  
  16. class DerivedBaseData1: BaseData<DerivedBaseData1> {
  17. public:
  18.     template<typename Visitor>
  19.     void accept(Visitor &v){
  20.     	std::cout << "DerivedBaseData1: accepting visitor " << v << std::endl;
  21.     }    
  22. };
  23. class DerivedBaseData2: BaseData<DerivedBaseData2> {
  24. public:
  25.     template<typename Visitor>
  26.     void accept(Visitor &v){
  27.     	std::cout << "DerivedBaseData2: accepting visitor " << v << std::endl;
  28.     }    
  29. };
  30.  
  31. namespace impl {
  32.  
  33. 	template <size_t N> 
  34. 	struct num2type {};
  35.  
  36. 	template <size_t Idx, typename T, typename Visitor>
  37. 	void accept_impl(Visitor &v, T &&collection, num2type<Idx>) {
  38. 		// run accept on current object
  39. 		auto &object = std::get<Idx>(collection);
  40. 		object.accept(v);
  41. 		// move iteration forward
  42. 		accept_impl(v, std::forward<T>(collection), num2type<Idx - 1>{});
  43. 	}
  44.  
  45. 	template <typename T, typename Visitor>
  46. 	void accept_impl(Visitor &v, T &&collection, num2type<0>) {
  47. 		// run accept on current object
  48. 		auto &object = std::get<0>(collection);
  49. 		object.accept(v);
  50. 	}
  51. }
  52.  
  53. template<typename ...Ts, typename Visitor>
  54. void accept(Visitor &v, std::tuple<Ts...> &&collection) {
  55. 	using T = decltype(collection);
  56. 	impl::accept_impl(v, std::forward<T>(collection), impl::num2type<std::tuple_size<std::decay_t<T>>::value - 1>{});
  57. }
  58.  
  59.  
  60. int main() {
  61. 	using visitor_type = int;
  62. 	visitor_type visitor = 42;
  63.  
  64. 	DerivedBaseData1 a1, a3;
  65. 	DerivedBaseData2 a2;
  66. 	accept(visitor, std::tie(a1, a2, a3));
  67.  
  68. 	return 0;
  69. }
Success #stdin #stdout 0s 3460KB
comments (?)
stdin 
Standard input is empty
stdout 
DerivedBaseData1: accepting visitor 42
DerivedBaseData2: accepting visitor 42
DerivedBaseData1: accepting visitor 42
https://ideone.com/onOBAc
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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