25 Ranges library [ranges]

25.7 Range adaptors [range.adaptors]

25.7.23 Elements view [range.elements]

25.7.23.3 Class template elements_view​::​iterator [range.elements.iterator]

namespace std::ranges { template<input_range V, size_t N> requires view<V> && has-tuple-element<range_value_t<V>, N> && has-tuple-element<remove_reference_t<range_reference_t<V>>, N> && returnable-element<range_reference_t<V>, N> template<bool Const> class elements_view<V, N>::iterator { using Base = maybe-const<Const, V>; // exposition only iterator_t<Base> current_ = iterator_t<Base>(); // exposition only static constexpr decltype(auto) get-element(const iterator_t<Base>& i); // exposition only public: using iterator_concept = see below; using iterator_category = see below; // not always present using value_type = remove_cvref_t<tuple_element_t<N, range_value_t<Base>>>; using difference_type = range_difference_t<Base>; iterator() requires default_initializable<iterator_t<Base>> = default; constexpr explicit iterator(iterator_t<Base> current); 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 decltype(auto) operator*() const { return get-element(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 decltype(auto) operator[](difference_type n) const requires random_access_range<Base> { return get-element(current_ + n); } 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 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) requires sized_sentinel_for<iterator_t<Base>, iterator_t<Base>>; }; }
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The member typedef-name iterator_concept is defined as follows:
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The member typedef-name iterator_category is defined if and only if Base models forward_range.
In that case, iterator_category is defined as follows: Let C denote the type iterator_traits<iterator_t<Base>>​::​iterator_category.
  • (2.1)
    If std​::​get<N>(*current_) is an rvalue, iterator_category denotes input_iterator_tag.
  • (2.2)
    Otherwise, if C models derived_from<random_access_iterator_tag>, iterator_category denotes random_access_iterator_tag.
  • (2.3)
    Otherwise, iterator_category denotes C.
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static constexpr decltype(auto) get-element(const iterator_t<Base>& i);
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Effects: Equivalent to: if constexpr (is_reference_v<range_reference_t<Base>>) { return std::get<N>(*i); } else { using E = remove_cv_t<tuple_element_t<N, range_reference_t<Base>>>; return static_cast<E>(std::get<N>(*i)); }
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constexpr explicit iterator(iterator_t<Base> current);
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Effects: Initializes current_ with std​::​move(current).
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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_).
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constexpr const iterator_t<Base>& base() const & noexcept;
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Effects: Equivalent to: return current_;
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constexpr iterator_t<Base> base() &&;
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Effects: Equivalent to: return std​::​move(current_);
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constexpr iterator& operator++();
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Effects: Equivalent to: ++current_; return *this;
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constexpr void operator++(int);
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Effects: Equivalent to: ++current_.
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constexpr iterator operator++(int) requires forward_range<Base>;
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Effects: Equivalent to: auto temp = *this; ++current_; return temp;
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constexpr iterator& operator--() requires bidirectional_range<Base>;
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Effects: Equivalent to: --current_; return *this;
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constexpr iterator operator--(int) requires bidirectional_range<Base>;
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Effects: Equivalent to: auto temp = *this; --current_; return temp;
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constexpr iterator& operator+=(difference_type n) requires random_access_range<Base>;
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Effects: Equivalent to: current_ += n; return *this;
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constexpr iterator& operator-=(difference_type n) requires random_access_range<Base>;
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Effects: Equivalent to: current_ -= n; return *this;
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friend constexpr bool operator==(const iterator& x, const iterator& y) requires equality_comparable<Base>;
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Effects: Equivalent to: return 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 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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Effects: Equivalent to: return x.current_ <=> y.current_;
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friend constexpr iterator operator+(const iterator& x, difference_type y) requires random_access_range<Base>;
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Effects: Equivalent to: return iterator{x} += y;
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friend constexpr iterator operator+(difference_type 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 iterator operator-(const iterator& x, difference_type y) requires random_access_range<Base>;
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Effects: Equivalent to: return iterator{x} -= y;
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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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Effects: Equivalent to: return x.current_ - y.current_;