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  1. #include <tuple>
  2. #include <iostream>
  3.  
  4. namespace details
  5. {
  6.     template<typename Int, typename, Int Begin, bool Increasing>
  7.     struct integer_range_impl;
  8.  
  9.     template<typename Int, Int... N, Int Begin>
  10.     struct integer_range_impl<Int, std::integer_sequence<Int, N...>, Begin, true> {
  11.         using type = std::integer_sequence<Int, N+Begin...>;
  12.     };
  13.  
  14.     template<typename Int, Int... N, Int Begin>
  15.     struct integer_range_impl<Int, std::integer_sequence<Int, N...>, Begin, false> {
  16.         using type = std::integer_sequence<Int, Begin-N...>;
  17.     };
  18. }
  19.  
  20. template<typename Int, Int Begin, Int End>
  21. using integer_range = typename details::integer_range_impl<
  22.     Int,
  23.     std::make_integer_sequence<Int, (Begin<End) ? End-Begin : Begin-End>,
  24.     Begin,
  25.     (Begin<End) >::type;
  26.  
  27. template<std::size_t Begin, std::size_t End>
  28. using index_range = integer_range<std::size_t, Begin, End>;
  29.  
  30. template<size_t SN, size_t DN, class TSrc, class TDest, class Func>
  31. void tuple_call_assign(TSrc&& source, TDest& target, Func f)
  32. {
  33.     std::get<DN>(target) = f(std::get<SN>(std::forward<TSrc>(source)));	
  34. }
  35.  
  36. template<size_t From, size_t To, class TSrc, class TDest, class Func, size_t...Is, size_t...DIs>
  37. void tuple_transform(TSrc&& source, TDest& target, Func f,
  38.                      std::index_sequence<Is...>, std::index_sequence<DIs...>)
  39. {
  40.     using expander = int[];
  41.     (void)expander { 0, (tuple_call_assign<Is,DIs>(std::forward<TSrc>(source),target,f), 0)... };
  42. }
  43.  
  44. template<size_t From, size_t To, size_t FromDest, class TSrc, class TDest, class Func>
  45. void tuple_transform(TSrc&& source, TDest& target, Func f)
  46. {
  47. 	static_assert(To > From, "Range must be increasing");
  48. 	static_assert(To <= std::tuple_size<std::decay_t<TSrc>>::value+1, 
  49. 	     "Range must be valid for source tuple");
  50. 	constexpr size_t RangeSize = To-From;
  51. 	static_assert(FromDest+RangeSize <= std::tuple_size<std::decay_t<TDest>>::value, 
  52. 	     "Range must be valid for target tuple");
  53.  
  54.     tuple_transform<From,To>(std::forward<TSrc>(source), target, f,
  55.                     index_range<From,To>(), index_range<FromDest, FromDest+RangeSize>());
  56. }
  57.  
  58.  
  59. int main()
  60. {
  61. 	std::tuple<int,int,int> a = std::make_tuple(1,2,3);
  62. 	std::tuple<int,int,int> b;
  63. 	tuple_transform<0,2,1>(a,b,[](int a){return a*2;});
  64. 	std::cout << std::get<0>(b);
  65. 	std::cout << std::get<1>(b);
  66. 	std::cout << std::get<2>(b);
  67. }
Success #stdin #stdout 0s 3096KB
comments (?)
stdin 
Standard input is empty
stdout 
024
https://ideone.com/BuT1Xi
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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