25 Ranges library [ranges]

25.7 Range adaptors [range.adaptors]

25.7.31 Chunk by view [range.chunk.by]

25.7.31.1 Overview [range.chunk.by.overview]

chunk_by_view takes a view and a predicate, and splits the view into subranges between each pair of adjacent elements for which the predicate returns false.

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

Given subexpressions E and F, the expression views::chunk_by(E, F) is expression-equivalent to chunk_by_view(E, F).

[Example 1: vector v = {1, 2, 2, 3, 0, 4, 5, 2}; for (auto r : v | views::chunk_by(ranges::less_equal{})) { cout << '['; auto sep = ""; for (auto i : r) { cout << sep << i; sep = ", "; } cout << "] "; } // The above prints [1, 2, 2, 3] [0, 4, 5] [2] — end example]

25.7.31.2 Class template chunk_by_view [range.chunk.by.view]

namespace std::ranges { template<forward_range V, indirect_binary_predicate<iterator_t<V>, iterator_t<V>> Pred> requires view<V> && is_object_v<Pred> class chunk_by_view : public view_interface<chunk_by_view<V, Pred>> { V base_ = V(); // exposition only movable-box<Pred> pred_; // exposition only // [range.chunk.by.iter], class chunk_by_view::iterator class iterator; // exposition only public: chunk_by_view() requires default_initializable<V> && default_initializable<Pred> = default; constexpr explicit chunk_by_view(V base, Pred pred); constexpr V base() const & requires copy_constructible<V> { return base_; } constexpr V base() && { return std::move(base_); } constexpr const Pred& pred() const; constexpr iterator begin(); constexpr auto end(); constexpr iterator_t<V> find-next(iterator_t<V>); // exposition only constexpr iterator_t<V> find-prev(iterator_t<V>) // exposition only requires bidirectional_range<V>; }; template<class R, class Pred> chunk_by_view(R&&, Pred) -> chunk_by_view<views::all_t<R>, Pred>; }

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constexpr explicit chunk_by_view(V base, Pred pred);

Effects: Initializes base_ with std::move(base) and pred_ with std::move(pred).

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constexpr const Pred& pred() const;

Effects: Equivalent to: return *pred_;

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constexpr iterator begin();

Preconditions: pred_.has_value() is true.

Returns: iterator(*this, ranges::begin(base_), find-next(ranges::begin(base_))).

Remarks: In order to provide the amortized constant-time complexity required by the range concept, this function caches the result within the chunk_by_view for use on subsequent calls.

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constexpr auto end();

Effects: Equivalent to: if constexpr (common_range<V>) { return iterator(*this, ranges::end(base_), ranges::end(base_)); } else { return default_sentinel; }

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constexpr iterator_t<V> find-next(iterator_t<V> current);

Preconditions: pred_.has_value() is true.

Returns: ranges::next(ranges::adjacent_find(current, ranges::end(base_), not_fn(ref(*pred_))), 1, ranges::end(base_))

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constexpr iterator_t<V> find-prev(iterator_t<V> current) requires bidirectional_range<V>;

Preconditions:

(9.1)
current is not equal to ranges::begin(base_).
(9.2)
pred_.has_value() is true.

Returns: An iterator i in the range [ranges::begin(base_), current) such that:

(10.1)
ranges::adjacent_find(i, current, not_fn(ref(*pred_))) is equal to current; and
(10.2)
if i is not equal to ranges::begin(base_), then bool(invoke(*pred_, *ranges::prev(i), *i)) is false.

25.7.31.3 Class chunk_by_view::iterator [range.chunk.by.iter]

namespace std::ranges { template<forward_range V, indirect_binary_predicate<iterator_t<V>, iterator_t<V>> Pred> requires view<V> && is_object_v<Pred> class chunk_by_view<V, Pred>::iterator { chunk_by_view* parent_ = nullptr; // exposition only iterator_t<V> current_ = iterator_t<V>(); // exposition only iterator_t<V> next_ = iterator_t<V>(); // exposition only constexpr iterator(chunk_by_view& parent, iterator_t<V> current, // exposition only iterator_t<V> next); public: using value_type = subrange<iterator_t<V>>; using difference_type = range_difference_t<V>; using iterator_category = input_iterator_tag; using iterator_concept = see below; iterator() = default; constexpr value_type operator*() const; constexpr iterator& operator++(); constexpr iterator operator++(int); constexpr iterator& operator--() requires bidirectional_range<V>; constexpr iterator operator--(int) requires bidirectional_range<V>; friend constexpr bool operator==(const iterator& x, const iterator& y); friend constexpr bool operator==(const iterator& x, default_sentinel_t); }; }

iterator::iterator_concept is defined as follows:

(1.1)
If V models bidirectional_range, then iterator_concept denotes bidirectional_iterator_tag.
(1.2)
Otherwise, iterator_concept denotes forward_iterator_tag.

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constexpr iterator(chunk_by_view& parent, iterator_t<V> current, iterator_t<V> next);

Effects: Initializes parent_ with addressof(parent), current_ with current, and next_ with next.

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constexpr value_type operator*() const;

Preconditions: current_ is not equal to next_.

Returns: subrange(current_, next_).

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constexpr iterator& operator++();

Preconditions: current_ is not equal to next_.

Effects: Equivalent to: current_ = next_; next_ = parent_->find-next(current_); return *this;

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constexpr iterator operator++(int);

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

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constexpr iterator& operator--() requires bidirectional_range<V>;

Effects: Equivalent to: next_ = current_; current_ = parent_->find-prev(next_); return *this;

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constexpr iterator operator--(int) requires bidirectional_range<V>;

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

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

Returns: x.current_ == y.current_.

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

Returns: x.current_ == x.next_.

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