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  1. #include <iterator>
  2. #include <iostream>
  3.  
  4. // This comes from the outer image class. 
  5. typedef float color_type;
  6.  
  7. template<bool IS_CONST = false>
  8. struct Iterator : public std::iterator<std::random_access_iterator_tag, color_type>
  9. {
  10.     // This is myself...
  11.     typedef Iterator<IS_CONST> iterator;
  12.     // ... and my variants.
  13.     typedef Iterator<true> const_iterator;
  14.     typedef std::reverse_iterator<iterator> reverse_iterator;
  15.     typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
  16.  
  17.     // My own typedefs to deal with immutability.
  18.     typedef value_type const & const_reference;
  19.     typedef typename std::conditional<IS_CONST, const_reference, typename iterator::reference>::type reference;
  20.  
  21.     Iterator()
  22.         : _position(nullptr),
  23.         _step()
  24.     {
  25.     }
  26.  
  27.     Iterator(value_type * const position, difference_type const step)
  28.        : _position(position),
  29.          _step(step)
  30.     {
  31.     }
  32.  
  33.     iterator const operator-(difference_type n) const
  34.     {
  35.         return iterator(*this) -= n;
  36.     }
  37.  
  38.     difference_type operator-(iterator const rhs) const
  39.     {
  40.         assert(_step == rhs._step);
  41.         return (_position - rhs._position) / _step;
  42.     }
  43.  
  44. protected:
  45.     value_type * _position;
  46.     difference_type _step;
  47. };
  48.  
  49. int main()
  50. {
  51.     float a = 3.141f;
  52.     // Instanciate all variants.
  53.     Iterator<false> empty;
  54.     Iterator<true> const_empty;
  55.     Iterator<false> some(&a, 5);
  56.     Iterator<true> const_some(&a, 5);
  57.  
  58.     Iterator<>::difference_type diff_type = Iterator<>::difference_type();
  59.     Iterator<>::value_type val_type = Iterator<>::value_type();
  60.  
  61.     std::cout << diff_type << " " << val_type << std::endl;
  62.  
  63.     return 0;
  64. }
Success #stdin #stdout 0s 2896KB
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https://ideone.com/mEX18H
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
secret

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