25 Ranges library [ranges]

25.7 Range adaptors [range.adaptors]

25.7.30 Slide view [range.slide]

25.7.30.1 Overview [range.slide.overview]

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slide_view takes a view and a number N and produces a view whose element is a view over the through elements of the original view.
If the original view has fewer than N elements, the resulting view is empty.
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The name views​::​slide denotes a range adaptor object ([range.adaptor.object]).
Given subexpressions E and N, the expression views​::​slide(E, N) is expression-equivalent to slide_view(E, N).
[Example 1: vector v = {1, 2, 3, 4}; for (auto i : v | views::slide(2)) { cout << '[' << i[0] << ", " << i[1] << "] "; // prints [1, 2] [2, 3] [3, 4] } — end example]

25.7.30.2 Class template slide_view [range.slide.view]

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namespace std::ranges { template<class V> concept slide-caches-nothing = random_access_range<V> && sized_range<V>; // exposition only template<class V> concept slide-caches-last = // exposition only !slide-caches-nothing<V> && bidirectional_range<V> && common_range<V>; template<class V> concept slide-caches-first = // exposition only !slide-caches-nothing<V> && !slide-caches-last<V>; template<forward_range V> requires view<V> class slide_view : public view_interface<slide_view<V>> { V base_; // exposition only range_difference_t<V> n_; // exposition only // [range.slide.iterator], class template slide_view​::​iterator template<bool> class iterator; // exposition only // [range.slide.sentinel], class slide_view​::​sentinel class sentinel; // exposition only public: constexpr explicit slide_view(V base, range_difference_t<V> n); constexpr V base() const & requires copy_constructible<V> { return base_; } constexpr V base() && { return std::move(base_); } constexpr auto begin() requires (!(simple-view<V> && slide-caches-nothing<const V>)); constexpr auto begin() const requires slide-caches-nothing<const V>; constexpr auto end() requires (!(simple-view<V> && slide-caches-nothing<const V>)); constexpr auto end() const requires slide-caches-nothing<const V>; constexpr auto size() requires sized_range<V>; constexpr auto size() const requires sized_range<const V>; }; template<class R> slide_view(R&&, range_difference_t<R>) -> slide_view<views::all_t<R>>; }
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constexpr explicit slide_view(V base, range_difference_t<V> n);
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Preconditions: n > 0 is true.
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Effects: Initializes base_ with std​::​move(base) and n_ with n.
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constexpr auto begin() requires (!(simple-view<V> && slide-caches-nothing<const V>));
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Returns:
  • (3.1)
    If V models slide-caches-first, iterator<false>(ranges::begin(base_), ranges::next(ranges::begin(base_), n_ - 1, ranges::end(base_)), n_)
  • (3.2)
    Otherwise, iterator<false>(ranges​::​begin(base_), n_).
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Remarks: In order to provide the amortized constant-time complexity required by the range concept, this function caches the result within the slide_view for use on subsequent calls when V models slide-caches-first.
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constexpr auto begin() const requires slide-caches-nothing<const V>;
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Returns: iterator<true>(ranges​::​begin(base_), n_).
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constexpr auto end() requires (!(simple-view<V> && slide-caches-nothing<const V>));
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Returns:
  • (6.1)
    If V models slide-caches-nothing, iterator<false>(ranges::begin(base_) + range_difference_t<V>(size()), n_)
  • (6.2)
    Otherwise, if V models slide-caches-last, iterator<false>(ranges::prev(ranges::end(base_), n_ - 1, ranges::begin(base_)), n_)
  • (6.3)
    Otherwise, if V models common_range, iterator<false>(ranges::end(base_), ranges::end(base_), n_)
  • (6.4)
    Otherwise, sentinel(ranges​::​end(base_)).
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Remarks: In order to provide the amortized constant-time complexity required by the range concept, this function caches the result within the slide_view for use on subsequent calls when V models slide-caches-last.
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constexpr auto end() const requires slide-caches-nothing<const V>;
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Returns: begin() + range_difference_t<const V>(size()).
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constexpr auto size() requires sized_range<V>; constexpr auto size() const requires sized_range<const V>;
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Effects: Equivalent to: auto sz = ranges::distance(base_) - n_ + 1; if (sz < 0) sz = 0; return to-unsigned-like(sz);

25.7.30.3 Class template slide_view​::​iterator [range.slide.iterator]

namespace std::ranges { template<forward_range V> requires view<V> template<bool Const> class slide_view<V>::iterator { using Base = maybe-const<Const, V>; // exposition only iterator_t<Base> current_ = iterator_t<Base>(); // exposition only iterator_t<Base> last_ele_ = iterator_t<Base>(); // exposition only, // present only if Base models slide-caches-first range_difference_t<Base> n_ = 0; // exposition only constexpr iterator(iterator_t<Base> current, range_difference_t<Base> n) // exposition only requires (!slide-caches-first<Base>); constexpr iterator(iterator_t<Base> current, iterator_t<Base> last_ele, // exposition only range_difference_t<Base> n) requires slide-caches-first<Base>; public: using iterator_category = input_iterator_tag; using iterator_concept = see below; using value_type = decltype(views::counted(current_, n_)); using difference_type = range_difference_t<Base>; iterator() = default; constexpr iterator(iterator<!Const> i) requires Const && convertible_to<iterator_t<V>, iterator_t<Base>>; constexpr auto operator*() const; constexpr iterator& operator++(); constexpr iterator operator++(int); constexpr iterator& operator--() requires bidirectional_range<Base>; constexpr iterator operator--(int) requires bidirectional_range<Base>; constexpr iterator& operator+=(difference_type x) requires random_access_range<Base>; constexpr iterator& operator-=(difference_type x) requires random_access_range<Base>; constexpr auto operator[](difference_type n) const requires random_access_range<Base>; friend constexpr bool operator==(const iterator& x, const iterator& y); friend constexpr bool operator<(const iterator& x, const iterator& y) requires random_access_range<Base>; friend constexpr bool operator>(const iterator& x, const iterator& y) requires random_access_range<Base>; friend constexpr bool operator<=(const iterator& x, const iterator& y) requires random_access_range<Base>; friend constexpr bool operator>=(const iterator& x, const iterator& y) requires random_access_range<Base>; friend constexpr auto operator<=>(const iterator& x, const iterator& y) requires random_access_range<Base> && three_way_comparable<iterator_t<Base>>; friend constexpr iterator operator+(const iterator& i, difference_type n) requires random_access_range<Base>; friend constexpr iterator operator+(difference_type n, const iterator& i) requires random_access_range<Base>; friend constexpr iterator operator-(const iterator& i, difference_type n) requires random_access_range<Base>; friend constexpr difference_type operator-(const iterator& x, const iterator& y) requires sized_sentinel_for<iterator_t<Base>, iterator_t<Base>>; }; }
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iterator​::​iterator_concept is defined as follows:
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If the invocation of any non-const member function of iterator exits via an exception, the iterator acquires a singular value.
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constexpr iterator(iterator_t<Base> current, range_difference_t<Base> n) requires (!slide-caches-first<Base>);
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Effects: Initializes current_ with current and n_ with n.
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constexpr iterator(iterator_t<Base> current, iterator_t<Base> last_ele, range_difference_t<Base> n) requires slide-caches-first<Base>;
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Effects: Initializes current_ with current, last_ele_ with last_ele, and n_ with n.
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constexpr iterator(iterator<!Const> i) requires Const && convertible_to<iterator_t<V>, iterator_t<Base>>;
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Effects: Initializes current_ with std​::​move(i.current_) and n_ with i.n_.
[Note 1: 
iterator<true> can only be formed when Base models slide-caches-nothing, in which case last_ele_ is not present.
— end note]
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constexpr auto operator*() const;
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Returns: views​::​counted(current_, n_).
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constexpr iterator& operator++();
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Preconditions: current_ and last_ele_ (if present) are incrementable.
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Postconditions: current_ and last_ele_ (if present) are each equal to ranges​::​next(i), where i is the value of that data member before the call.
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Returns: *this.
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constexpr iterator operator++(int);
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Effects: Equivalent to: auto tmp = *this; ++*this; return tmp;
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constexpr iterator& operator--() requires bidirectional_range<Base>;
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Preconditions: current_ and last_ele_ (if present) are decrementable.
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Postconditions: current_ and last_ele_ (if present) are each equal to ranges​::​prev(i), where i is the value of that data member before the call.
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Returns: *this.
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constexpr iterator operator--(int) requires bidirectional_range<Base>;
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Effects: Equivalent to: auto tmp = *this; --*this; return tmp;
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constexpr iterator& operator+=(difference_type x) requires random_access_range<Base>;
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Preconditions: current_ + x and last_ele_ + x (if last_ele_ is present) have well-defined behavior.
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Postconditions: current_ and last_ele_ (if present) are each equal to i + x, where i is the value of that data member before the call.
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Returns: *this.
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constexpr iterator& operator-=(difference_type x) requires random_access_range<Base>;
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Preconditions: current_ - x and last_ele_ - x (if last_ele_ is present) have well-defined behavior.
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Postconditions: current_ and last_ele_ (if present) are each equal to i - x, where i is the value of that data member before the call.
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Returns: *this.
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constexpr auto operator[](difference_type n) const requires random_access_range<Base>;
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Effects: Equivalent to: return views​::​counted(current_ + n, n_);
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friend constexpr bool operator==(const iterator& x, const iterator& y);
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Returns: If last_ele_ is present, x.last_ele_ == y.last_ele_; otherwise, x.current_ == y.current_.
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friend constexpr bool operator<(const iterator& x, const iterator& y) requires random_access_range<Base>;
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Returns: x.current_ < y.current_.
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friend constexpr bool operator>(const iterator& x, const iterator& y) requires random_access_range<Base>;
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Effects: Equivalent to: return y < x;
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friend constexpr bool operator<=(const iterator& x, const iterator& y) requires random_access_range<Base>;
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Effects: Equivalent to: return !(y < x);
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friend constexpr bool operator>=(const iterator& x, const iterator& y) requires random_access_range<Base>;
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Effects: Equivalent to: return !(x < y);
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friend constexpr auto operator<=>(const iterator& x, const iterator& y) requires random_access_range<Base> && three_way_comparable<iterator_t<Base>>;
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Returns: x.current_ <=> y.current_.
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friend constexpr iterator operator+(const iterator& i, difference_type n) requires random_access_range<Base>; friend constexpr iterator operator+(difference_type n, const iterator& i) requires random_access_range<Base>;
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Effects: Equivalent to: auto r = i; r += n; return r;
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friend constexpr iterator operator-(const iterator& i, difference_type n) requires random_access_range<Base>;
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Effects: Equivalent to: auto r = i; r -= n; return r;
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friend constexpr difference_type operator-(const iterator& x, const iterator& y) requires sized_sentinel_for<iterator_t<Base>, iterator_t<Base>>;
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Returns: If last_ele_ is present, x.last_ele_ - y.last_ele_; otherwise, x.current_ - y.current_.

25.7.30.4 Class slide_view​::​sentinel [range.slide.sentinel]

namespace std::ranges { template<forward_range V> requires view<V> class slide_view<V>::sentinel { sentinel_t<V> end_ = sentinel_t<V>(); // exposition only constexpr explicit sentinel(sentinel_t<V> end); // exposition only public: sentinel() = default; friend constexpr bool operator==(const iterator<false>& x, const sentinel& y); friend constexpr range_difference_t<V> operator-(const iterator<false>& x, const sentinel& y) requires sized_sentinel_for<sentinel_t<V>, iterator_t<V>>; friend constexpr range_difference_t<V> operator-(const sentinel& y, const iterator<false>& x) requires sized_sentinel_for<sentinel_t<V>, iterator_t<V>>; }; }
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[Note 1: 
sentinel is used only when slide-caches-first<V> is true.
— end note]
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constexpr explicit sentinel(sentinel_t<V> end);
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Effects: Initializes end_ with end.
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friend constexpr bool operator==(const iterator<false>& x, const sentinel& y);
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Returns: x.last_ele_ == y.end_.
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friend constexpr range_difference_t<V> operator-(const iterator<false>& x, const sentinel& y) requires sized_sentinel_for<sentinel_t<V>, iterator_t<V>>;
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Returns: x.last_ele_ - y.end_.
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friend constexpr range_difference_t<V> operator-(const sentinel& y, const iterator<false>& x) requires sized_sentinel_for<sentinel_t<V>, iterator_t<V>>;
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Returns: y.end_ - x.last_ele_.