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| <html> | ||
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| <meta charset="utf-8"> | ||
| <title>Issue 4012: common_view::begin/end are missing the simple-view check</title> | ||
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| <p><em>This page is a snapshot from the LWG issues list, see the <a href="lwg-active.html">Library Active Issues List</a> for more information and the meaning of <a href="lwg-active.html#New">New</a> status.</em></p> | ||
| <h3><a name="4012" href="lwg-active.html#4012">4012</a>. <tt>common_view::begin/end</tt> are missing the <tt><i>simple-view</i></tt> check</h3> | ||
| <p><b>Section:</b> 26.7.19.2 <a href="https://wg21.link/range.common.view">[range.common.view]</a> <b>Status:</b> <a href="lwg-active.html#New">New</a> | ||
| <b>Submitter:</b> Hewill Kang <b>Opened:</b> 2023-11-11 <b>Last modified:</b> 2023-11-18</p> | ||
| <p><b>Priority: </b>Not Prioritized | ||
| </p> | ||
| <p><b>View all other</b> <a href="lwg-index.html#range.common.view">issues</a> in [range.common.view].</p> | ||
| <p><b>View all issues with</b> <a href="lwg-status.html#New">New</a> status.</p> | ||
| <p><b>Discussion:</b></p> | ||
| <p> | ||
| <tt>common_view::begin/end</tt> have exactly the same implementation as their corresponding <tt>const</tt> versions, | ||
| which implies that when the underlying <tt>V</tt> satisfies <tt><i>simple-view</i></tt>, it is sufficient to | ||
| just provide <tt>const</tt>-qualified members. | ||
| </p> | ||
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| <p id="res-4012"><b>Proposed resolution:</b></p> | ||
| <p> | ||
| This wording is relative to <a href="https://wg21.link/N4964">N4964</a>. | ||
| </p> | ||
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| <ol> | ||
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| <li><p>Modify 26.7.19.2 <a href="https://wg21.link/range.common.view">[range.common.view]</a> as indicated:</p> | ||
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| <blockquote><pre> | ||
| namespace std::ranges { | ||
| template<view V> | ||
| requires (!common_range<V> && copyable<iterator_t<V>>) | ||
| class common_view : public view_interface<common_view<V>> { | ||
| private: | ||
| V <i>base_</i> = V(); // <i>exposition only</i> | ||
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| public: | ||
| […] | ||
| constexpr auto begin() <ins>requires (!<i>simple-view</i><V>)</ins> { | ||
| if constexpr (random_access_range<V> && sized_range<V>) | ||
| return ranges::begin(<i>base_</i>); | ||
| else | ||
| return common_iterator<iterator_t<V>, sentinel_t<V>>(ranges::begin(<i>base_</i>)); | ||
| } | ||
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| constexpr auto begin() const requires range<const V> { | ||
| if constexpr (random_access_range<const V> && sized_range<const V>) | ||
| return ranges::begin(<i>base_</i>); | ||
| else | ||
| return common_iterator<iterator_t<const V>, sentinel_t<const V>>(ranges::begin(<i>base_</i>)); | ||
| } | ||
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| constexpr auto end() <ins>requires (!<i>simple-view</i><V>)</ins> { | ||
| if constexpr (random_access_range<V> && sized_range<V>) | ||
| return ranges::begin(<i>base_</i>) + ranges::distance(<i>base_</i>); | ||
| else | ||
| return common_iterator<iterator_t<V>, sentinel_t<V>>(ranges::end(<i>base_</i>)); | ||
| } | ||
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| constexpr auto end() const requires range<const V> { | ||
| if constexpr (random_access_range<const V> && sized_range<const V>) | ||
| return ranges::begin(<i>base_</i>) + ranges::distance(<i>base_</i>); | ||
| else | ||
| return common_iterator<iterator_t<const V>, sentinel_t<const V>>(ranges::end(<i>base_</i>)); | ||
| } | ||
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| […] | ||
| }; | ||
| […] | ||
| } | ||
| </pre></blockquote> | ||
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| </html> |
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