25 Ranges library [ranges]

25.7 Range adaptors [range.adaptors]

25.7.24 Enumerate view [range.enumerate]

25.7.24.1 Overview [range.enumerate.overview]

enumerate_view is a view whose elements represent both the position and value from a sequence of elements.

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

Given a subexpression E, the expression views::enumerate(E) is expression-equivalent to enumerate_view<views::all_t<decltype((E))>>(E).

[Example 1: vector<int> vec{ 1, 2, 3 }; for (auto [index, value] : views::enumerate(vec)) cout << index << ":" << value << ' '; // prints 0:1 1:2 2:3 — end example]

25.7.24.2 Class template enumerate_view [range.enumerate.view]

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namespace std::ranges { template<view V> requires range-with-movable-references<V> class enumerate_view : public view_interface<enumerate_view<V>> { V base_ = V(); // exposition only // [range.enumerate.iterator], class template enumerate_view::iterator template<bool Const> class iterator; // exposition only // [range.enumerate.sentinel], class template enumerate_view::sentinel template<bool Const> class sentinel; // exposition only public: constexpr enumerate_view() requires default_initializable<V> = default; constexpr explicit enumerate_view(V base); constexpr auto begin() requires (!simple-view<V>) { return iterator<false>(ranges::begin(base_), 0); } constexpr auto begin() const requires range-with-movable-references<const V> { return iterator<true>(ranges::begin(base_), 0); } constexpr auto end() requires (!simple-view<V>) { if constexpr (forward_range<V> && common_range<V> && sized_range<V>) return iterator<false>(ranges::end(base_), ranges::distance(base_)); else return sentinel<false>(ranges::end(base_)); } constexpr auto end() const requires range-with-movable-references<const V> { if constexpr (forward_range<const V> && common_range<const V> && sized_range<const V>) return iterator<true>(ranges::end(base_), ranges::distance(base_)); else return sentinel<true>(ranges::end(base_)); } constexpr auto size() requires sized_range<V> { return ranges::size(base_); } constexpr auto size() const requires sized_range<const V> { return ranges::size(base_); } constexpr V base() const & requires copy_constructible<V> { return base_; } constexpr V base() && { return std::move(base_); } }; template<class R> enumerate_view(R&&) -> enumerate_view<views::all_t<R>>; }

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constexpr explicit enumerate_view(V base);

Effects: Initializes base_ with std::move(base).

25.7.24.3 Class template enumerate_view::iterator [range.enumerate.iterator]

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namespace std::ranges { template<view V> requires range-with-movable-references<V> template<bool Const> class enumerate_view<V>::iterator { using Base = maybe-const<Const, V>; // exposition only public: using iterator_category = input_iterator_tag; using iterator_concept = see below; using difference_type = range_difference_t<Base>; using value_type = tuple<difference_type, range_value_t<Base>>; private: using reference-type = // exposition only tuple<difference_type, range_reference_t<Base>>; iterator_t<Base> current_ = iterator_t<Base>(); // exposition only difference_type pos_ = 0; // exposition only constexpr explicit iterator(iterator_t<Base> current, difference_type pos); // exposition only public: iterator() requires default_initializable<iterator_t<Base>> = default; constexpr iterator(iterator<!Const> i) requires Const && convertible_to<iterator_t<V>, iterator_t<Base>>; constexpr const iterator_t<Base>& base() const & noexcept; constexpr iterator_t<Base> base() &&; constexpr difference_type index() const noexcept; constexpr auto operator*() const { return reference-type(pos_, *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 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> { return reference-type(pos_ + n, current_[n]); } friend constexpr bool operator==(const iterator& x, const iterator& y) noexcept; friend constexpr strong_ordering operator<=>(const iterator& x, const iterator& y) noexcept; friend constexpr iterator operator+(const iterator& x, difference_type y) requires random_access_range<Base>; friend constexpr iterator operator+(difference_type x, const iterator& y) requires random_access_range<Base>; friend constexpr iterator operator-(const iterator& x, difference_type y) requires random_access_range<Base>; friend constexpr difference_type operator-(const iterator& x, const iterator& y) noexcept; friend constexpr auto iter_move(const iterator& i) noexcept(noexcept(ranges::iter_move(i.current_)) && is_nothrow_move_constructible_v<range_rvalue_reference_t<Base>>) { return tuple<difference_type, range_rvalue_reference_t<Base>>(i.pos_, ranges::iter_move(i.current_)); } }; }

The member typedef-name 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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constexpr explicit iterator(iterator_t<Base> current, difference_type pos);

Effects: Initializes current_ with std::move(current) and pos_ with pos.

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constexpr iterator(iterator<!Const> i)
  requires Const && convertible_to<iterator_t<V>, iterator_t<Base>>;

Effects: Initializes current_ with std::move(i.current_) and pos_ with i.pos_.

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

Effects: Equivalent to: return current_;

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constexpr iterator_t<Base> base() &&;

Effects: Equivalent to: return std::move(current_);

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constexpr difference_type index() const noexcept;

Effects: Equivalent to: return pos_;

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constexpr iterator& operator++();

Effects: Equivalent to: ++current_; ++pos_; return *this;

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constexpr void operator++(int);

Effects: Equivalent to ++*this.

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constexpr iterator operator++(int) requires forward_range<Base>;

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

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

Effects: Equivalent to: --current_; --pos_; return *this;

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

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

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constexpr iterator& operator+=(difference_type n)
  requires random_access_range<Base>;

Effects: Equivalent to: current_ += n; pos_ += n; return *this;

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constexpr iterator& operator-=(difference_type n)
  requires random_access_range<Base>;

Effects: Equivalent to: current_ -= n; pos_ -= n; return *this;

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

Effects: Equivalent to: return x.pos_ == y.pos_;

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friend constexpr strong_ordering operator<=>(const iterator& x, const iterator& y) noexcept;

Effects: Equivalent to: return x.pos_ <=> y.pos_;

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friend constexpr iterator operator+(const iterator& x, difference_type y)
  requires random_access_range<Base>;

Effects: Equivalent to: auto temp = x; temp += y; return temp;

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friend constexpr iterator operator+(difference_type x, const iterator& y)
  requires random_access_range<Base>;

Effects: Equivalent to: return y + x;

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friend constexpr iterator operator-(const iterator& x, difference_type y)
  requires random_access_range<Base>;

Effects: Equivalent to: auto temp = x; temp -= y; return temp;

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friend constexpr difference_type operator-(const iterator& x, const iterator& y) noexcept;

Effects: Equivalent to: return x.pos_ - y.pos_;

25.7.24.4 Class template enumerate_view::sentinel [range.enumerate.sentinel]

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namespace std::ranges { template<view V> requires range-with-movable-references<V> template<bool Const> class enumerate_view<V>::sentinel { using Base = maybe-const<Const, V>; // exposition only sentinel_t<Base> end_ = sentinel_t<Base>(); // exposition only constexpr explicit sentinel(sentinel_t<Base> end); // exposition only public: sentinel() = default; constexpr sentinel(sentinel<!Const> other) requires Const && convertible_to<sentinel_t<V>, sentinel_t<Base>>; constexpr sentinel_t<Base> base() const; 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); template<bool OtherConst> requires sized_sentinel_for<sentinel_t<Base>, iterator_t<maybe-const<OtherConst, V>>> friend constexpr range_difference_t<maybe-const<OtherConst, V>> operator-(const iterator<OtherConst>& x, const sentinel& y); template<bool OtherConst> requires sized_sentinel_for<sentinel_t<Base>, iterator_t<maybe-const<OtherConst, V>>> friend constexpr range_difference_t<maybe-const<OtherConst, V>> operator-(const sentinel& x, const iterator<OtherConst>& y); }; }

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constexpr explicit sentinel(sentinel_t<Base> end);

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

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

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

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constexpr sentinel_t<Base> base() const;

Effects: Equivalent to: return 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.current_ == y.end_;

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

Effects: Equivalent to: return x.current_ - y.end_;

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

Effects: Equivalent to: return x.end_ - y.current_;