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  1. #include <array>
  2. #include <cstddef>
  3. #include <memory>
  4. #include <tuple>
  5.  
  6. namespace detail {
  7.   template<std::size_t, typename>
  8.   class slide_iterator;
  9. }
  10. template<std::size_t N, typename I>
  11. detail::slide_iterator<N, I> slide_begin(const I&);
  12. template<std::size_t N, typename I>
  13. detail::slide_iterator<N, I> slide_end(const I&);
  14.  
  15. namespace detail {
  16.  
  17. template<std::size_t N, typename T, typename... Args>
  18. struct repeat {
  19.   typedef typename repeat<N - 1, T, T, Args...>::type type;
  20.   template<typename I>
  21.   type operator()(const I& it, Args&... args) const {
  22.     auto jt = it;
  23.     return repeat<N - 1, T, T, Args...>()(++jt, args..., *it);
  24.   }
  25. };
  26. template<typename T, typename... Args>
  27. struct repeat<0, T, Args...> {
  28.   typedef std::tuple<Args&...> type;
  29.   template<typename I>
  30.   type operator()(const I&, Args&... args) const {
  31.     return type(args...);
  32.   }
  33. };
  34.  
  35. template<std::size_t N, typename I /* forward iterator */>
  36. class slide_iterator {
  37. public:
  38.  
  39.   typedef slide_iterator iterator;
  40.   typedef decltype(*I{}) reference;
  41.   typedef typename repeat<N, reference>::type window_tuple;
  42.  
  43.   slide_iterator() = default;
  44.   ~slide_iterator() = default;
  45.   slide_iterator(const iterator& it) = default;
  46.   iterator& operator=(const iterator& it) = default;
  47.  
  48.   window_tuple operator*() const {
  49.     return repeat<N, reference>()(first_);
  50.   }
  51.  
  52.   iterator& operator++() { // prefix
  53.     ++first_;
  54.     ++last_;
  55.     return *this;
  56.   }
  57.  
  58.   iterator operator++(int) { // postfix
  59.     auto tmp{*this};
  60.     operator++();
  61.     return tmp;
  62.   }
  63.  
  64.   friend void swap(iterator& lhs, iterator& rhs) {
  65.     swap(lhs.first_, rhs.first_);
  66.     swap(lhs.last_, rhs.last_);
  67.     swap(lhs.dirty_, rhs.dirty_);
  68.     swap(lhs.window_, rhs.window_);
  69.   }
  70.  
  71.   friend bool operator==(const iterator& lhs, const iterator& rhs) {
  72.     return lhs.last_ == rhs.last_;
  73.   }
  74.  
  75.   friend bool operator!=(const iterator& lhs, const iterator& rhs) {
  76.     return !operator==(lhs, rhs);
  77.   }
  78.  
  79.   friend iterator slide_begin<N, I>(const I& it);
  80.   friend iterator slide_end<N, I>(const I& it);
  81.  
  82. private:
  83.  
  84.   I first_;
  85.   I last_; // for equality only
  86.  
  87. };
  88.  
  89. template<typename T, std::size_t N>
  90. struct slide_helper {
  91.   T& t;
  92.   auto begin() -> decltype(slide_begin<N>(t.begin())) {
  93.     return slide_begin<N>(t.begin());
  94.   }
  95.   auto end() -> decltype(slide_end<N>(t.end())) {
  96.     return slide_end<N>(t.end());
  97.   }
  98. };
  99.  
  100. } // ::detail
  101.  
  102. // note it is undefined to call slide_begin<N>() on an iterator which cannot
  103. // be incremented at least N - 1 times
  104. template<std::size_t N, typename I>
  105. detail::slide_iterator<N, I> slide_begin(const I& it) {
  106.   detail::slide_iterator<N, I> r;
  107.   r.first_ = r.last_ = it;
  108.   std::advance(r.last_, N - 1);
  109.   return r;
  110. }
  111.  
  112. template<std::size_t N, typename I>
  113. detail::slide_iterator<N, I> slide_end(const I& it) {
  114.   detail::slide_iterator<N, I> r;
  115.   r.last_ = it;
  116.   return r;
  117. }
  118.  
  119. template<std::size_t N, typename T>
  120. detail::slide_helper<T, N> slide(T& t) {
  121.   return {t};
  122. }
  123.  
  124. // example usage
  125. #include <iostream>
  126. #include <vector>
  127.  
  128. int main() {
  129.   std::vector<int> v{1, 2, 3, 4};
  130.   for (const auto& t : slide<2>(v)) {
  131.     std::get<1>(t) *= std::get<0>(t);
  132.   }
  133.   for (const auto& i : v) {
  134.     std::cerr << i << std::endl;
  135.   }
  136. }
Success #stdin #stdout #stderr 0s 3472KB
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https://ideone.com/aHE4Zu
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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