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  1.  
  2.  
  3. #include <iostream>
  4. #include <vector>
  5. #include <tuple>
  6. #include <functional>
  7.  
  8. template<typename C>
  9. struct indexed_container
  10. {
  11.     struct indexed_iterator
  12. 	{
  13. 		typedef typename C::value_type value_type;
  14. 		typedef std::tuple<size_t, std::reference_wrapper<value_type>> tuple_type;
  15.  
  16. 		typename C::iterator _it;
  17. 		size_t _index;
  18.  
  19. 		indexed_iterator(typename C::iterator it) : _it(it), _index(0) {}
  20.  
  21. 		indexed_iterator& operator++()
  22. 		{
  23. 			++_it;
  24. 			++_index;
  25. 			return *this;
  26. 		}
  27. 		bool operator == (indexed_iterator const & other)
  28. 		{
  29. 			return _it == other._it;
  30. 		}
  31. 		bool operator != (indexed_iterator const & other)
  32. 		{
  33. 			return _it != other._it;
  34. 		}
  35. 		tuple_type operator*()
  36. 		{
  37. 			return std::make_tuple(_index, std::ref(*_it));
  38. 		}
  39. 	};
  40.  
  41. 	indexed_container(C & c) : _c(c) {}
  42.  
  43. 	indexed_iterator begin()
  44. 	{
  45. 		return indexed_iterator(_c.begin());
  46. 	}
  47. 	indexed_iterator end()
  48. 	{
  49. 		return indexed_iterator(_c.end());
  50. 	}
  51. private:
  52. 	C & _c;
  53. };
  54.  
  55. template<typename C>
  56. auto make_indexable(C & c) -> indexed_container<C>
  57. {
  58. 	return indexed_container<C>(c); 
  59. }
  60.  
  61. int main()
  62. {
  63. 	std::vector<int> v{1,2,3};
  64. 	for(auto item : make_indexable(v))
  65. 	{
  66. 		std::cout << std::get<0>(item) << " => " << std::get<1>(item) << std::endl;
  67.  
  68. 		std::get<1>(item) *= 10; //modify value
  69. 	}
  70. 	std::cout << "\nModified\n";
  71. 	for(auto item : make_indexable(v))
  72. 	{
  73. 		std::cout << std::get<0>(item) << " => " << std::get<1>(item) << std::endl;
  74. 	}
  75. }
  76.  
Success #stdin #stdout 0s 2984KB
comments (?)
stdin
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Standard input is empty
stdout
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0 => 1
1 => 2
2 => 3

Modified
0 => 10
1 => 20
2 => 30
https://ideone.com/K7MLD7
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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