cppdraft_translate/cppdraft/range/stride.md

[range.stride]

25 Ranges library [ranges]

25.7 Range adaptors [range.adaptors]

25.7.32 Stride view [range.stride]

25.7.32.1 Overview [range.stride.overview]

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stride_view presents a view of an underlying sequence, advancing over n elements at a time, as opposed to the usual single-step succession.

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The name views​::​stride denotes a range adaptor object ([range.adaptor.object]).

Given subexpressions E and N, the expression views​::​stride(E, N) is expression-equivalent to stride_view(E, N).

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[Example 1: auto input = views::iota(0, 12) | views::stride(3); ranges::copy(input, ostream_iterator(cout, " ")); // prints 0 3 6 9 ranges::copy(input | views::reverse, ostream_iterator(cout, " ")); // prints 9 6 3 0 — end example]

25.7.32.2 Class template stride_view [range.stride.view]

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namespace std::ranges {template<input_range V>requires viewclass stride_view : public view_interface<stride_view> { V base_; // exposition only range_difference_t stride_; // exposition only// [range.stride.iterator], class template stride_view​::​iteratortemplate class iterator; // exposition onlypublic:constexpr explicit stride_view(V base, range_difference_t stride); constexpr V base() const & requires copy_constructible { return base_; }constexpr V base() && { return std::move(base_); }constexpr range_difference_t stride() const noexcept; constexpr auto begin() requires () {return iterator(this, ranges::begin(base_)); }constexpr auto begin() const requires range {return iterator(this, ranges::begin(base_)); }constexpr auto end() requires () {if constexpr (common_range && sized_range && forward_range) {auto missing = (stride_ - ranges::distance(base_) % stride_) % stride_; return iterator(this, ranges::end(base_), missing); } else if constexpr (common_range && ) {return iterator(this, ranges::end(base_)); } else {return default_sentinel; }}constexpr auto end() const requires range {if constexpr (common_range && sized_range && forward_range) {auto missing = (stride_ - ranges::distance(base_) % stride_) % stride_; return iterator(this, ranges::end(base_), missing); } else if constexpr (common_range && ) {return iterator(this, ranges::end(base_)); } else {return default_sentinel; }}constexpr auto size() requires sized_range; constexpr auto size() const requires sized_range; constexpr auto reserve_hint() requires approximately_sized_range; constexpr auto reserve_hint() const requires approximately_sized_range; }; template stride_view(R&&, range_difference_t) -> stride_view<views::all_t>;}

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constexpr stride_view(V base, range_difference_t<V> stride);

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Preconditions: stride > 0 is true.

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Effects: Initializes base_ with std​::​move(base) andstride_ with stride.

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constexpr range_difference_t<V> stride() const noexcept;

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Returns: stride_.

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constexpr auto size() requires [sized_range](range.sized#concept:sized_range "25.4.4 Sized ranges [range.sized]")<V>; constexpr auto size() const requires [sized_range](range.sized#concept:sized_range "25.4.4 Sized ranges [range.sized]")<const V>;

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Effects: Equivalent to:return to-unsigned-like(div-ceil(ranges::distance(base_), stride_));

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constexpr auto reserve_hint() requires [approximately_sized_range](range.approximately.sized#concept:approximately_sized_range "25.4.3 Approximately sized ranges [range.approximately.sized]")<V>; constexpr auto reserve_hint() const requires [approximately_sized_range](range.approximately.sized#concept:approximately_sized_range "25.4.3 Approximately sized ranges [range.approximately.sized]")<const V>;

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Effects: Equivalent to:auto s = static_cast<range_difference_t<decltype((base_))>>(ranges::reserve_hint(base_));return to-unsigned-like(div-ceil(s, stride_));

25.7.32.3 Class template stride_view​::​iterator [range.stride.iterator]

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namespace std::ranges {template<input_range V>requires viewtemplateclass stride_view::iterator {using Parent = maybe-const<Const, stride_view>; // exposition onlyusing Base = maybe-const<Const, V>; // exposition only iterator_t<Base> current_ = iterator_t<Base>(); // exposition only sentinel_t<Base> end_ = sentinel_t<Base>(); // exposition only range_difference_t<Base> stride_ = 0; // exposition only range_difference_t<Base> missing_ = 0; // exposition onlyconstexpr iterator(Parent* parent, iterator_t<Base> current, // exposition only range_difference_t<Base> missing = 0); public:using difference_type = range_difference_t<Base>; using value_type = range_value_t<Base>; using iterator_concept = see below; using iterator_category = see below; // not always presentiterator() requires default_initializable<iterator_t<Base>> = default; constexpr iterator(iterator other)requires Const && convertible_to<iterator_t, iterator_t<Base>>&& convertible_to<sentinel_t, sentinel_t<Base>>; constexpr iterator_t<Base> base() &&; constexpr const iterator_t<Base>& base() const & noexcept; constexpr decltype(auto) operator*() const { return **current_*; }constexpr iterator& operator++(); constexpr void operator++(int); constexpr iterator operator++(int) requires forward_range<Base>; constexpr iterator& operator--() requires bidirectional_range<Base>; constexpr iterator operator--(int) requires bidirectional_range<Base>; constexpr iterator& operator+=(difference_type n) requires random_access_range<Base>; constexpr iterator& operator-=(difference_type n) requires random_access_range<Base>; constexpr decltype(auto) operator[](difference_type n) constrequires random_access_range<Base>{ return *(*this + n); }friend constexpr bool operator==(const iterator& x, default_sentinel_t); friend constexpr bool operator==(const iterator& x, const iterator& y)requires equality_comparable<iterator_t<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 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& x, difference_type n)requires random_access_range<Base>; friend constexpr iterator operator+(difference_type n, const iterator& x)requires random_access_range<Base>; friend constexpr iterator operator-(const iterator& x, 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>>; friend constexpr difference_type operator-(default_sentinel_t y, const iterator& x)requires sized_sentinel_for<sentinel_t<Base>, iterator_t<Base>>; friend constexpr difference_type operator-(const iterator& x, default_sentinel_t y)requires sized_sentinel_for<sentinel_t<Base>, iterator_t<Base>>; friend constexpr range_rvalue_reference_t<Base> iter_move(const iterator& i)noexcept(noexcept(ranges::iter_move(i.current_))); friend constexpr void iter_swap(const iterator& x, const iterator& y)noexcept(noexcept(ranges::iter_swap(x.current_, y.current_)))requires indirectly_swappable<iterator_t<Base>>; };}

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iterator​::​iterator_concept is defined as follows:

• (1.1)

  If Base models random_access_range, then iterator_concept denotes random_access_iterator_tag.

• (1.2)

  Otherwise, if Base models bidirectional_range, then iterator_concept denotes bidirectional_iterator_tag.

• (1.3)

  Otherwise, if Base models forward_range, then iterator_concept denotes forward_iterator_tag.

• (1.4)

  Otherwise, iterator_concept denotes input_iterator_tag.

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The member typedef-name iterator_category is defined if and only if Base models forward_range.

In that case,iterator​::​iterator_category is defined as follows:

• (2.1)

  Let C denote the type iterator_traits<iterator_t<Base>>​::​iterator_category.

• (2.2)

  If C modelsderived_from<random_access_iterator_tag>, then iterator_category denotes random_access_iterator_tag.

• (2.3)

  Otherwise, iterator_category denotes C.

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constexpr iterator(Parent* parent, iterator_t<Base> current, range_difference_t<Base> missing = 0);

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Effects: Initializes current_ with std​::​move(current),end_ with ranges​::​end(parent->base_),stride_ with parent->stride_, andmissing_ with missing.

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constexpr iterator(iterator<!Const> i) requires Const && [convertible_to](concept.convertible#concept:convertible_to "18.4.4 Concept convertible_­to [concept.convertible]")<iterator_t<V>, iterator_t<Base>> && [convertible_to](concept.convertible#concept:convertible_to "18.4.4 Concept convertible_­to [concept.convertible]")<sentinel_t<V>, sentinel_t<Base>>;

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Effects: Initializes current_ with std​::​move(i.current_),end_ with std​::​move(i.end_),stride_ with i.stride_, andmissing_ with i.missing_.

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constexpr iterator_t<Base> base() &&;

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Returns: std​::​move(current_).

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constexpr const iterator_t<Base>& base() const & noexcept;

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Returns: current_.

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constexpr iterator& operator++();

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Preconditions: current_ != end_ is true.

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Effects: Equivalent to:missing_ = ranges::advance(current_, stride_, end_);return *this;

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constexpr void operator++(int);

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Effects: Equivalent to ++*this;

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constexpr iterator operator++(int) requires [forward_range](range.refinements#concept:forward_range "25.4.6 Other range refinements [range.refinements]")<Base>;

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Effects: Equivalent to:auto tmp = *this;++*this;return tmp;

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constexpr iterator& operator--() requires [bidirectional_range](range.refinements#concept:bidirectional_range "25.4.6 Other range refinements [range.refinements]")<Base>;

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Effects: Equivalent to:ranges::advance(current_, missing_ - stride_);missing_ = 0;return *this;

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constexpr iterator operator--(int) requires [bidirectional_range](range.refinements#concept:bidirectional_range "25.4.6 Other range refinements [range.refinements]")<Base>;

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Effects: Equivalent to:auto tmp = *this;--*this;return tmp;

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constexpr iterator& operator+=(difference_type n) requires [random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<Base>;

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Preconditions: If n is positive,ranges​::​distance(current_, end_) > stride_ * (n - 1) is true.

[Note 1:

If n is negative, the Effects paragraph implies a precondition.

— end note]

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Effects: Equivalent to:if (n > 0) { ranges::advance(current_, stride_ * (n - 1)); missing_ = ranges::advance(current_, stride_, end_);} else if (n < 0) { ranges::advance(current_, stride_ * n + missing_); missing_ = 0;}return *this;

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constexpr iterator& operator-=(difference_type x) requires [random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<Base>;

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Effects: Equivalent to: return *this += -x;

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friend constexpr bool operator==(const iterator& x, default_sentinel_t);

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Returns: x.current_ == x.end_.

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friend constexpr bool operator==(const iterator& x, const iterator& y) requires [equality_comparable](concept.equalitycomparable#concept:equality_comparable "18.5.4 Concept equality_­comparable [concept.equalitycomparable]")<iterator_t<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](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<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](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<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](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<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](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<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](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<Base> && [three_way_comparable](cmp.concept#concept:three_way_comparable "17.12.4 Concept three_­way_­comparable [cmp.concept]")<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](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<Base>; friend constexpr iterator operator+(difference_type n, const iterator& i) requires [random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<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](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<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.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<iterator_t<Base>, iterator_t<Base>>;

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Returns: Let N be (x.current_ - y.current_).

• (25.1)

  If Base models forward_range,(N + x.missing_ - y.missing_) / x.stride_.

• (25.2)

  Otherwise, if N is negative, -div-ceil(-N, x.stride_).

• (25.3)

  Otherwise, div-ceil(N, x.stride_).

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friend constexpr difference_type operator-(default_sentinel_t y, const iterator& x) requires [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<sentinel_t<Base>, iterator_t<Base>>;

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Returns: div-ceil(x.end_ - x.current_, x.stride_).

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friend constexpr difference_type operator-(const iterator& x, default_sentinel_t y) requires [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<sentinel_t<Base>, iterator_t<Base>>;

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Effects: Equivalent to: return -(y - x);

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friend constexpr range_rvalue_reference_t<Base> iter_move(const iterator& i) noexcept(noexcept(ranges::iter_move(i.current_)));

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Effects: Equivalent to: return ranges​::​iter_move(i.current_);

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friend constexpr void iter_swap(const iterator& x, const iterator& y) noexcept(noexcept(ranges::iter_swap(x.current_, y.current_))) requires [indirectly_swappable](alg.req.ind.swap#concept:indirectly_swappable "24.3.7.4 Concept indirectly_­swappable [alg.req.ind.swap]")<iterator_t<Base>>;

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Effects: Equivalent to:ranges​::​iter_swap(x.current_, y.current_);