cppdraft_translate/cppdraft/range/common.md

[range.common]

25 Ranges library [ranges]

25.7 Range adaptors [range.adaptors]

25.7.20 Common view [range.common]

25.7.20.1 Overview [range.common.overview]

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common_view takes a view which has different types for its iterator and sentinel and turns it into a view of the same elements with an iterator and sentinel of the same type.

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[Note 1:

common_view is useful for calling legacy algorithms that expect a range's iterator and sentinel types to be the same.

— end note]

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

Given a subexpression E, the expression views​::​common(E) is expression-equivalent to:

• (3.1)

  views​::​all(E), if decltype((E)) models common_range and views​::​all(E) is a well-formed expression.

• (3.2)

  Otherwise, common_view{E}.

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[Example 1: // Legacy algorithm:template size_t count(ForwardIterator first, ForwardIterator last);

template<forward_range R>void my_algo(R&& r) {auto&& common = views::common(r); auto cnt = count(common.begin(), common.end()); // ...} — end example]

25.7.20.2 Class template common_view [range.common.view]

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namespace std::ranges {template<view V>requires ( && copyable<iterator_t>)class common_view : public view_interface<common_view> {private: V base_ = V(); // exposition onlypublic: common_view() requires default_initializable = default; constexpr explicit common_view(V r); constexpr V base() const & requires copy_constructible { return base_; }constexpr V base() && { return std::move(base_); }constexpr auto begin() requires () {if constexpr (random_access_range && sized_range)return ranges::begin(base_); elsereturn common_iterator<iterator_t, sentinel_t>(ranges::begin(base_)); }constexpr auto begin() const requires range {if constexpr (random_access_range && sized_range)return ranges::begin(base_); elsereturn common_iterator<iterator_t, sentinel_t>(ranges::begin(base_)); }constexpr auto end() requires () {if constexpr (random_access_range && sized_range)return ranges::begin(base_) + ranges::distance(base_); elsereturn common_iterator<iterator_t, sentinel_t>(ranges::end(base_)); }constexpr auto end() const requires range {if constexpr (random_access_range && sized_range)return ranges::begin(base_) + ranges::distance(base_); elsereturn common_iterator<iterator_t, sentinel_t>(ranges::end(base_)); }constexpr auto size() requires sized_range {return ranges::size(base_); }constexpr auto size() const requires sized_range {return ranges::size(base_); }constexpr auto reserve_hint() requires approximately_sized_range {return ranges::reserve_hint(base_); }constexpr auto reserve_hint() const requires approximately_sized_range {return ranges::reserve_hint(base_); }}; template common_view(R&&) -> common_view<views::all_t>;}

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constexpr explicit common_view(V base);

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