26 Ranges library [ranges]

26.7 Range adaptors [range.adaptors]

26.7.15 Join with view [range.join.with]

26.7.15.1 Overview [range.join.with.overview]

join_with_view takes a view and a delimiter, and flattens the view, inserting every element of the delimiter in between elements of the view.

The delimiter can be a single element or a view of elements.

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

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

[Example 1: vector<string> vs = {"the", "quick", "brown", "fox"}; for (char c : vs | views::join_with('-')) { cout << c; } // The above prints the-quick-brown-fox — end example]

26.7.15.2 Class template join_with_view [range.join.with.view]

namespace std::ranges { template<class R, class P> concept compatible-joinable-ranges = // exposition only common_with<range_value_t<R>, range_value_t<P>> && common_reference_with<range_reference_t<R>, range_reference_t<P>> && common_reference_with<range_rvalue_reference_t<R>, range_rvalue_reference_t<P>>; template<class R> concept bidirectional-common = bidirectional_range<R> && common_range<R>; // exposition only template<input_range V, forward_range Pattern> requires view<V> && input_range<range_reference_t<V>> && view<Pattern> && compatible-joinable-ranges<range_reference_t<V>, Pattern> class join_with_view : public view_interface<join_with_view<V, Pattern>> { using InnerRng = range_reference_t<V>; // exposition only V base_ = V(); // exposition only non-propagating-cache<iterator_t<V>> outer_it_; // exposition only, present only // when !forward_range<V> non-propagating-cache<remove_cv_t<InnerRng>> inner_; // exposition only, present only // if is_reference_v<InnerRng> is false Pattern pattern_ = Pattern(); // exposition only // [range.join.with.iterator], class template join_with_view::iterator template<bool Const> struct iterator; // exposition only // [range.join.with.sentinel], class template join_with_view::sentinel template<bool Const> struct sentinel; // exposition only public: join_with_view() requires default_initializable<V> && default_initializable<Pattern> = default; constexpr explicit join_with_view(V base, Pattern pattern); template<input_range R> requires constructible_from<V, views::all_t<R>> && constructible_from<Pattern, single_view<range_value_t<InnerRng>>> constexpr explicit join_with_view(R&& r, range_value_t<InnerRng> e); constexpr V base() const & requires copy_constructible<V> { return base_; } constexpr V base() && { return std::move(base_); } constexpr auto begin() { if constexpr (forward_range<V>) { constexpr bool use_const = simple-view<V> && is_reference_v<InnerRng> && simple-view<Pattern>; return iterator<use_const>{*this, ranges::begin(base_)}; } else { outer_it_ = ranges::begin(base_); return iterator<false>{*this}; } } constexpr auto begin() const requires forward_range<const V> && forward_range<const Pattern> && is_reference_v<range_reference_t<const V>> && input_range<range_reference_t<const V>> { return iterator<true>{*this, ranges::begin(base_)}; } constexpr auto end() { if constexpr (forward_range<V> && is_reference_v<InnerRng> && forward_range<InnerRng> && common_range<V> && common_range<InnerRng>) return iterator<simple-view<V> && simple-view<Pattern>>{*this, ranges::end(base_)}; else return sentinel<simple-view<V> && simple-view<Pattern>>{*this}; } constexpr auto end() const requires forward_range<const V> && forward_range<const Pattern> && is_reference_v<range_reference_t<const V>> && input_range<range_reference_t<const V>> { using InnerConstRng = range_reference_t<const V>; if constexpr (forward_range<InnerConstRng> && common_range<const V> && common_range<InnerConstRng>) return iterator<true>{*this, ranges::end(base_)}; else return sentinel<true>{*this}; } }; template<class R, class P> join_with_view(R&&, P&&) -> join_with_view<views::all_t<R>, views::all_t<P>>; template<input_range R> join_with_view(R&&, range_value_t<range_reference_t<R>>) -> join_with_view<views::all_t<R>, single_view<range_value_t<range_reference_t<R>>>>; }

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constexpr explicit join_with_view(V base, Pattern pattern);

Effects: Initializes base_ with std::move(base) and pattern_ with std::move(pattern).

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template<input_range R>
  requires constructible_from<V, views::all_t<R>> &&
           constructible_from<Pattern, single_view<range_value_t<InnerRng>>>
constexpr explicit join_with_view(R&& r, range_value_t<InnerRng> e);

Effects: Initializes base_ with views::all(std::forward<R>(r)) and pattern_ with views::single(std::move(e)).

26.7.15.3 Class template join_with_view::iterator [range.join.with.iterator]

namespace std::ranges { template<input_range V, forward_range Pattern> requires view<V> && input_range<range_reference_t<V>> && view<Pattern> && compatible-joinable-ranges<range_reference_t<V>, Pattern> template<bool Const> class join_with_view<V, Pattern>::iterator { using Parent = maybe-const<Const, join_with_view>; // exposition only using Base = maybe-const<Const, V>; // exposition only using InnerBase = range_reference_t<Base>; // exposition only using PatternBase = maybe-const<Const, Pattern>; // exposition only using OuterIter = iterator_t<Base>; // exposition only using InnerIter = iterator_t<InnerBase>; // exposition only using PatternIter = iterator_t<PatternBase>; // exposition only static constexpr bool ref-is-glvalue = is_reference_v<InnerBase>; // exposition only Parent* parent_ = nullptr; // exposition only OuterIter outer_it_ = OuterIter(); // exposition only, present only // if Base models forward_range variant<PatternIter, InnerIter> inner_it_; // exposition only constexpr iterator(Parent& parent, OuterIter outer) requires forward_range<Base>; // exposition only constexpr explicit iterator(Parent& parent) requires (!forward_range<Base>); // exposition only constexpr OuterIter& outer(); // exposition only constexpr const OuterIter& outer() const; // exposition only constexpr auto& update-inner(); // exposition only constexpr auto& get-inner(); // exposition only constexpr void satisfy(); // exposition only public: using iterator_concept = see below; using iterator_category = see below; // not always present using value_type = see below; using difference_type = see below; iterator() = default; constexpr iterator(iterator<!Const> i) requires Const && convertible_to<iterator_t<V>, OuterIter> && convertible_to<iterator_t<InnerRng>, InnerIter> && convertible_to<iterator_t<Pattern>, PatternIter>; constexpr decltype(auto) operator*() const; constexpr iterator& operator++(); constexpr void operator++(int); constexpr iterator operator++(int) requires ref-is-glvalue && forward_iterator<OuterIter> && forward_iterator<InnerIter>; constexpr iterator& operator--() requires ref-is-glvalue && bidirectional_range<Base> && bidirectional-common<InnerBase> && bidirectional-common<PatternBase>; constexpr iterator operator--(int) requires ref-is-glvalue && bidirectional_range<Base> && bidirectional-common<InnerBase> && bidirectional-common<PatternBase>; friend constexpr bool operator==(const iterator& x, const iterator& y) requires ref-is-glvalue && forward_range<Base> && equality_comparable<InnerIter>; friend constexpr decltype(auto) iter_move(const iterator& x) { using rvalue_reference = common_reference_t< iter_rvalue_reference_t<InnerIter>, iter_rvalue_reference_t<PatternIter>>; return visit<rvalue_reference>(ranges::iter_move, x.inner_it_); } friend constexpr void iter_swap(const iterator& x, const iterator& y) requires indirectly_swappable<InnerIter, PatternIter> { visit(ranges::iter_swap, x.inner_it_, y.inner_it_); } }; }

iterator::iterator_concept is defined as follows:

(1.1)
If ref-is-glvalue is true, Base models bidirectional_range, and InnerBase and PatternBase each model bidirectional-common, then iterator_concept denotes bidirectional_iterator_tag.
(1.2)
Otherwise, if ref-is-glvalue is true and Base and InnerBase each model forward_range, then iterator_concept denotes forward_iterator_tag.
(1.3)
Otherwise, iterator_concept denotes input_iterator_tag.

The member typedef-name iterator_category is defined if and only if ref-is-glvalue is true, and Base and InnerBase each model forward_range .

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

(2.1)
Let OUTERC denote iterator_traits<OuterIter>::iterator_category, let INNERC denote iterator_traits<InnerIter>::iterator_category, and let PATTERNC denote iterator_-
traits<PatternIter>::iterator_category.
(2.2)
If is_reference_v<common_reference_t<iter_reference_t<InnerIter>, iter_reference_t<PatternIter>>> is false, iterator_category denotes input_iterator_tag.
(2.3)
Otherwise, if OUTERC, INNERC, and PATTERNC each model derived_from<bidirectional_iterator_category> and InnerBase and PatternBase each model common_range, iterator_category denotes bidirectional_iterator_tag.
(2.4)
Otherwise, if OUTERC, INNERC, and PATTERNC each model derived_from<forward_iterator_tag>, iterator_category denotes forward_iterator_tag.
(2.5)
Otherwise, iterator_category denotes input_iterator_tag.

iterator::value_type denotes the type: common_type_t<iter_value_t<InnerIter>, iter_value_t<PatternIter>>

iterator::difference_type denotes the type: common_type_t< iter_difference_t<OuterIter>, iter_difference_t<InnerIter>, iter_difference_t<PatternIter>>

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constexpr OuterIter& outer();
constexpr const OuterIter& outer() const;

Returns: outer_it_ if Base models forward_range; otherwise, *parent_->outer_it_.

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constexpr auto& update-inner();

Effects: Equivalent to: if constexpr (ref-is-glvalue) return as-lvalue(*outer()); else return parent_->inner_.emplace-deref(outer());

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constexpr auto& get-inner();

Effects: Equivalent to: if constexpr (ref-is-glvalue) return as-lvalue(*outer()); else return *parent_->inner_;

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constexpr void satisfy();

Effects: Equivalent to: while (true) { if (inner_it_.index() == 0) { if (std::get<0>(inner_it_) != ranges::end(parent_->pattern_)) break; inner_it_.emplace<1>(ranges::begin(update-inner())); } else { if (std::get<1>(inner_it_) != ranges::end(get-inner())) break; if (++outer() == ranges::end(parent_->base_)) { if constexpr (ref-is-glvalue) inner_it_.emplace<0>(); break; } inner_it_.emplace<0>(ranges::begin(parent_->pattern_)); } }

[Note 1:

join_with_view iterators use the satisfy function to skip over empty inner ranges.

— end note]

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constexpr iterator(Parent& parent, OuterIter outer)
  requires forward_range<Base>;
constexpr explicit iterator(Parent& parent)
  requires (!forward_range<Base>);

Effects: Initializes parent_ with addressof(parent).

For the first overload, also initializes outer_it_ with std::move(outer).

Then, equivalent to: if (outer() != ranges::end(parent_->base_)) { inner_it_.emplace<1>(ranges::begin(update-inner())); satisfy(); }

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constexpr iterator(iterator<!Const> i)
    requires Const && convertible_to<iterator_t<V>, OuterIter> &&
             convertible_to<iterator_t<InnerRng>, InnerIter> &&
             convertible_to<iterator_t<Pattern>, PatternIter>;

Effects: Initializes outer_it_ with std::move(i.outer_it_) and parent_ with i.parent_.

Then, equivalent to: if (i.inner_it_.index() == 0) inner_it_.emplace<0>(std::get<0>(std::move(i.inner_it_))); else inner_it_.emplace<1>(std::get<1>(std::move(i.inner_it_)));

[Note 2:

Const can only be true when Base models forward_range .

— end note]

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constexpr decltype(auto) operator*() const;

Effects: Equivalent to: using reference = common_reference_t<iter_reference_t<InnerIter>, iter_reference_t<PatternIter>>; return visit([](auto& it) -> reference { return *it; }, inner_it_);

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constexpr iterator& operator++();

Effects: Equivalent to: visit([](auto& it){ ++it; }, inner_it_); satisfy(); return *this;

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constexpr void operator++(int);

Effects: Equivalent to ++*this.

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constexpr iterator operator++(int)
  requires ref-is-glvalue && forward_iterator<OuterIter> && forward_iterator<InnerIter>;

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

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constexpr iterator& operator--()
  requires ref-is-glvalue && bidirectional_range<Base> &&
           bidirectional-common<InnerBase> && bidirectional-common<PatternBase>;

Effects: Equivalent to: if (outer_it_ == ranges::end(parent_->base_)) { auto&& inner = *--outer_it_; inner_it_.emplace<1>(ranges::end(inner)); } while (true) { if (inner_it_.index() == 0) { auto& it = std::get<0>(inner_it_); if (it == ranges::begin(parent_->pattern_)) { auto&& inner = *--outer_it_; inner_it_.emplace<1>(ranges::end(inner)); } else { break; } } else { auto& it = std::get<1>(inner_it_); auto&& inner = *outer_it_; if (it == ranges::begin(inner)) { inner_it_.emplace<0>(ranges::end(parent_->pattern_)); } else { break; } } } visit([](auto& it){ --it; }, inner_it_); return *this;

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constexpr iterator operator--(int)
  requires ref-is-glvalue && bidirectional_range<Base> &&
           bidirectional-common<InnerBase> && bidirectional-common<PatternBase>;

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

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friend constexpr bool operator==(const iterator& x, const iterator& y)
  requires ref-is-glvalue && forward_range<Base> &&
           equality_comparable<InnerIter>;

Effects: Equivalent to: return x.outer_it_ == y.outer_it_ && x.inner_it_ == y.inner_it_;

26.7.15.4 Class template join_with_view::sentinel [range.join.with.sentinel]

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constexpr explicit sentinel(Parent& parent);

Effects: Initializes end_ with ranges::end(parent.base_).

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constexpr sentinel(sentinel<!Const> s)
  requires Const && convertible_to<sentinel_t<V>, sentinel_t<Base>>;

Effects: Initializes end_ with std::move(s.end_).

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template<bool OtherConst>
  requires sentinel_for<sentinel_t<Base>, iterator_t<maybe-const<OtherConst, V>>>
friend constexpr bool operator==(const iterator<OtherConst>& x, const sentinel& y);

Effects: Equivalent to: return x.outer() == y.end_;