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  1. #include <iterator>
  2.  
  3. // This comes from the outer image class.
  4. typedef float color_type;
  5.  
  6. template<bool IS_CONST = false>
  7. struct Iterator : public std::iterator<std::random_access_iterator_tag, color_type>
  8. {
  9.     // This is myself...
  10.     typedef Iterator<IS_CONST> iterator;
  11.     // ... and my variants.
  12.     typedef Iterator<true> const_iterator;
  13.     typedef std::reverse_iterator<iterator> reverse_iterator;
  14.     typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
  15.  
  16.     // Make base class typedefs available.
  17.     typedef typename iterator::value_type value_type;
  18.     typedef typename iterator::difference_type difference_type;
  19.  
  20.     // My own typedefs to deal with immutability.
  21.     typedef value_type const & const_reference;
  22.     typedef typename std::conditional<IS_CONST, const_reference, typename iterator::reference>::type reference;
  23.  
  24.     Iterator()
  25.         : _position(nullptr),
  26.         _step()
  27.     {
  28.     }
  29.  
  30.     Iterator(value_type * const position, difference_type const step)
  31.         : _position(position),
  32.         _step(step)
  33.     {
  34.     }
  35.  
  36.     iterator const operator-(difference_type n) const
  37.     {
  38.         return iterator(*this) -= n;
  39.     }
  40.  
  41.     difference_type operator-(iterator const rhs) const
  42.     {
  43.         assert(_step == rhs._step);
  44.         return (_position - rhs._position) / _step;
  45.     }
  46.  
  47. protected:
  48.     value_type * _position;
  49.     difference_type _step;
  50. };
  51.  
  52. int main()
  53. {
  54.     float a = 3.141f;
  55.     // Instanciate all variants.
  56.     Iterator<false> empty;
  57.     Iterator<true> const_empty;
  58.     Iterator<false> some(&a, 5);
  59.     Iterator<true> const_some(&a, 5);
  60.     return 0;
  61. }
Success #stdin #stdout 0s 2892KB
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https://ideone.com/RflAiS
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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