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  1. #include <iostream>
  2. #include <tuple>
  3. #include <cassert>
  4.  
  5. template<std::size_t ...Indices>
  6. struct index_tuple{
  7. };
  8. template<typename Left,typename Right>
  9. struct concat_index_tuple;
  10. template<std::size_t ...Lefts,std::size_t ...Rights>
  11. struct concat_index_tuple<index_tuple<Lefts...>,index_tuple<Rights...>>{
  12. 	using type = index_tuple<Lefts...,Rights...>;
  13. };
  14. template<std::size_t Beg,std::size_t End>
  15. struct make_index_tuple{
  16. 	using type = typename concat_index_tuple<
  17. 					index_tuple<Beg>,
  18. 					typename make_index_tuple<Beg + 1,End>::type
  19. 	>::type;
  20. };
  21. template<std::size_t End>
  22. struct make_index_tuple<End,End>{
  23. 	using type = index_tuple<End>;
  24. };
  25. template<typename Tuple>
  26. struct tuple_index;
  27. template<typename ...Ts>
  28. struct tuple_index<std::tuple<Ts...>>{
  29. 	using type = typename make_index_tuple<0,sizeof...(Ts) - 1>::type;
  30. };
  31.  
  32. struct outputter{
  33. 	std::ostream &os;
  34. 	outputter(std::ostream &s) : os(s){
  35. 	}
  36.  
  37. 	template<typename T>
  38. 	void operator ()(T const& v){
  39. 		os << v << std::endl;
  40. 	}
  41. };
  42. struct add_x{
  43. 	int i;
  44. 	add_x(int v) : i(v){
  45. 	}
  46.  
  47. 	template<typename T>
  48. 	void operator ()(T &v){
  49. 		v += i;
  50. 	}
  51. };
  52.  
  53. template<typename F,typename T>
  54. void work_impl(F func,std::size_t s,T &&x){
  55. 	assert(s == 0);
  56. 	func(std::forward<T>(x));
  57. }
  58. template<typename F,typename T,typename ...Us>
  59. void work_impl(F func,std::size_t s,T &&x,Us &&...xs){
  60. 	if(s){
  61. 		work_impl(func,s - 1,std::forward<Us>(xs)...);
  62. 	}
  63. 	else{
  64. 		func(std::forward<T>(x));
  65. 	}
  66. }
  67. template<typename F,typename Tuple,std::size_t ...Indices>
  68. void work_unpack(F func,std::size_t s,Tuple &&t,index_tuple<Indices...>){
  69. 	work_impl(func,s,std::get<Indices>(std::forward<Tuple>(t))...);
  70. }
  71. template<typename F,typename Tuple>
  72. void work(F func,std::size_t s,Tuple &&t){
  73. 	work_unpack(func,s,std::forward<Tuple>(t),typename tuple_index<typename std::remove_reference<Tuple>::type>::type{});
  74. }
  75.  
  76. int main() {
  77. 	int i;
  78. 	std::cout << "Enter index" << std::endl;
  79. 	std::cin >> i;
  80.  
  81. 	auto t = std::make_tuple(1,2.0,3ull,4.f);
  82. 	work(outputter{std::cout},i,t);
  83. 	work(add_x{2},i,t);
  84. 	work(outputter{std::cout},i,t);
  85. 	work(outputter{std::cout},i,std::make_tuple("a",42,3.14f,&i));
  86. 	return 0;
  87. }
Success #stdin #stdout 0s 3304KB
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Enter index
3
5
3.14
https://ideone.com/nOv2E1
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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