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  1.     #include <iostream>
  2.     #include <iterator>
  3.     #include <limits>
  4.     #include <vector>
  5.  
  6.  
  7.     template <typename T>
  8.     struct iterator_extractor { typedef typename T::iterator type; };
  9.  
  10.     template <typename T>
  11.     struct iterator_extractor<T const> { typedef typename T::const_iterator type; };
  12.  
  13.  
  14.     template <typename T>
  15.     class Indexer {
  16.     public:
  17.         class iterator {
  18.             typedef typename iterator_extractor<T>::type inner_iterator;
  19.  
  20.             typedef typename std::iterator_traits<inner_iterator>::reference inner_reference;
  21.         public:
  22.             typedef std::pair<size_t, inner_reference> reference;
  23.  
  24.             iterator(inner_iterator it): _pos(0), _it(it) {}
  25.  
  26.             reference operator*() const { return reference(_pos, *_it); }
  27.  
  28.             iterator& operator++() { ++_pos; ++_it; return *this; }
  29.             iterator operator++(int) { iterator tmp(*this); ++*this; return tmp; }
  30.  
  31.             bool operator==(iterator const& it) const { return _it == it._it; }
  32.             bool operator!=(iterator const& it) const { return !(*this == it); }
  33.  
  34.         private:
  35.             size_t _pos;
  36.             inner_iterator _it;
  37.         };
  38.  
  39.         Indexer(T& t): _container(t) {}
  40.  
  41.         iterator begin() const { return iterator(_container.begin()); }
  42.         iterator end() const { return iterator(_container.end()); }
  43.  
  44.     private:
  45.         T& _container;
  46.     }; // class Indexer
  47.  
  48.     template <typename T>
  49.     Indexer<T> index(T& t) { return Indexer<T>(t); }
  50.  
  51.     int main() {
  52.         std::vector<int> v{1, 2, 3, 4, 5, 6, 7, 8, 9};
  53.  
  54.         auto in = index(v);
  55.  
  56.         for (auto it = in.begin(), end = in.end(); it != end; ++it) {
  57.             auto p = *it;
  58.             std::cout << p.first << ": " << p.second << "\n";
  59.         }
  60.     }
Success #stdin #stdout 0s 3016KB
comments (?)
stdin
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Standard input is empty
stdout
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0: 1
1: 2
2: 3
3: 4
4: 5
5: 6
6: 7
7: 8
8: 9
https://ideone.com/rAcaZ
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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