tmp/tmp2jxhxka0/{from.md → to.md}
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| 1 |
+
#### Class template `counted_iterator` <a id="counted.iterator">[[counted.iterator]]</a>
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Class template `counted_iterator` is an iterator adaptor with the same
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behavior as the underlying iterator except that it keeps track of the
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distance to the end of its range. It can be used together with
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`default_sentinel` in calls to generic algorithms to operate on a range
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of N elements starting at a given position without needing to know the
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end position a priori.
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[*Example 1*:
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``` cpp
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list<string> s;
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// populate the list s with at least 10 strings
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vector<string> v;
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// copies 10 strings into v:
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ranges::copy(counted_iterator(s.begin(), 10), default_sentinel, back_inserter(v));
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```
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— *end example*]
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Two values `i1` and `i2` of types `counted_iterator<I1>` and
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`counted_iterator<I2>` refer to elements of the same sequence if and
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only if `next(i1.base(), i1.count())` and `next(i2.base(), i2.count())`
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refer to the same (possibly past-the-end) element.
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``` cpp
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namespace std {
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template<input_or_output_iterator I>
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class counted_iterator {
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public:
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using iterator_type = I;
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constexpr counted_iterator() = default;
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constexpr counted_iterator(I x, iter_difference_t<I> n);
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template<class I2>
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requires convertible_to<const I2&, I>
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constexpr counted_iterator(const counted_iterator<I2>& x);
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template<class I2>
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requires assignable_from<I&, const I2&>
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constexpr counted_iterator& operator=(const counted_iterator<I2>& x);
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constexpr I base() const & requires copy_constructible<I>;
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constexpr I base() &&;
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constexpr iter_difference_t<I> count() const noexcept;
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constexpr decltype(auto) operator*();
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constexpr decltype(auto) operator*() const
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requires dereferenceable<const I>;
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constexpr counted_iterator& operator++();
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decltype(auto) operator++(int);
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constexpr counted_iterator operator++(int)
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requires forward_iterator<I>;
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constexpr counted_iterator& operator--()
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requires bidirectional_iterator<I>;
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constexpr counted_iterator operator--(int)
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requires bidirectional_iterator<I>;
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constexpr counted_iterator operator+(iter_difference_t<I> n) const
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requires random_access_iterator<I>;
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friend constexpr counted_iterator operator+(
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iter_difference_t<I> n, const counted_iterator& x)
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requires random_access_iterator<I>;
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constexpr counted_iterator& operator+=(iter_difference_t<I> n)
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requires random_access_iterator<I>;
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constexpr counted_iterator operator-(iter_difference_t<I> n) const
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requires random_access_iterator<I>;
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template<common_with<I> I2>
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friend constexpr iter_difference_t<I2> operator-(
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const counted_iterator& x, const counted_iterator<I2>& y);
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friend constexpr iter_difference_t<I> operator-(
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const counted_iterator& x, default_sentinel_t);
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friend constexpr iter_difference_t<I> operator-(
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default_sentinel_t, const counted_iterator& y);
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constexpr counted_iterator& operator-=(iter_difference_t<I> n)
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requires random_access_iterator<I>;
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constexpr decltype(auto) operator[](iter_difference_t<I> n) const
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requires random_access_iterator<I>;
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template<common_with<I> I2>
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friend constexpr bool operator==(
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const counted_iterator& x, const counted_iterator<I2>& y);
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friend constexpr bool operator==(
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const counted_iterator& x, default_sentinel_t);
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template<common_with<I> I2>
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friend constexpr strong_ordering operator<=>(
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const counted_iterator& x, const counted_iterator<I2>& y);
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friend constexpr iter_rvalue_reference_t<I> iter_move(const counted_iterator& i)
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noexcept(noexcept(ranges::iter_move(i.current)))
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requires input_iterator<I>;
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template<indirectly_swappable<I> I2>
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friend constexpr void iter_swap(const counted_iterator& x, const counted_iterator<I2>& y)
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noexcept(noexcept(ranges::iter_swap(x.current, y.current)));
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private:
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I current = I(); // exposition only
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iter_difference_t<I> length = 0; // exposition only
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};
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template<class I>
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struct incrementable_traits<counted_iterator<I>> {
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using difference_type = iter_difference_t<I>;
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};
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template<input_iterator I>
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struct iterator_traits<counted_iterator<I>> : iterator_traits<I> {
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using pointer = void;
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};
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}
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```
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