24 Ranges library [ranges]

24.7 Range adaptors [range.adaptors]

24.7.15 Elements view [range.elements]

24.7.15.3 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>
  template<bool Const>
  class elements_view<V, N>::iterator {                 // exposition only
    using Base = conditional_t<Const, const V, V>;      // exposition only

    iterator_t<Base> current_ = iterator_t<Base>();
  public:
    using iterator_category = typename iterator_traits<iterator_t<Base>>::iterator_category;
    using value_type = remove_cvref_t<tuple_element_t<N, range_value_t<Base>>>;
    using difference_type = range_difference_t<Base>;

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

    constexpr iterator_t<Base> base() const&
      requires copyable<iterator_t<Base>>;
    constexpr iterator_t<Base> base() &&;

    constexpr decltype(auto) operator*() const
    { return get<N>(*current_); }

    constexpr iterator& operator++();
    constexpr void operator++(int) requires (!forward_range<Base>);
    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<N>(*(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 random_access_range<Base>;
  };
}
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constexpr explicit iterator(iterator_t<Base> current);
1
#
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>>;
2
#
Effects: Initializes current_­ with std​::​move(i.current_­).
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constexpr iterator_t<Base> base() const& requires copyable<iterator_t<Base>>;
3
#
Effects: Equivalent to: return current_­;
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constexpr iterator_t<Base> base() &&;
4
#
Effects: Equivalent to: return std​::​move(current_­);
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constexpr iterator& operator++();
5
#
Effects: Equivalent to: 
++current_;
return *this;
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constexpr void operator++(int) requires (!forward_­range<Base>);
6
#
Effects: Equivalent to: ++current_­.
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constexpr iterator operator++(int) requires forward_­range<Base>;
7
#
Effects: Equivalent to: 
auto temp = *this;
++current_;
return temp;
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constexpr iterator& operator--() requires bidirectional_­range<Base>;
8
#
Effects: Equivalent to: 
--current_;
return *this;
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constexpr iterator operator--(int) requires bidirectional_­range<Base>;
9
#
Effects: Equivalent to: 
auto temp = *this;
--current_;
return temp;
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constexpr iterator& operator+=(difference_type n); requires random_­access_­range<Base>;
10
#
Effects: Equivalent to: 
current_ += n;
return *this;
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constexpr iterator& operator-=(difference_type n) requires random_­access_­range<Base>;
11
#
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>;
12
#
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>;
13
#
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>;
14
#
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>;
15
#
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>;
16
#
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>>;
17
#
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>;
18
#
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>;
19
#
Effects: Equivalent to: return y + x;
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constexpr iterator operator-(const iterator& x, difference_type y) requires random_­access_­range<Base>;
20
#
Effects: Equivalent to: return iterator{x} -= y;
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constexpr difference_type operator-(const iterator& x, const iterator& y) requires random_­access_­range<Base>;
21
#
Effects: Equivalent to: return x.current_­ - y.current_­;