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| <title>Issue 4013: lazy_split_view::outer-iterator::value_type should not provide default constructor</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="4013" href="lwg-active.html#4013">4013</a>. <tt>lazy_split_view::<i>outer-iterator</i>::value_type</tt> should not provide default constructor</h3> | ||
| <p><b>Section:</b> 26.7.16.4 <a href="https://wg21.link/range.lazy.split.outer.value">[range.lazy.split.outer.value]</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.lazy.split.outer.value">issues</a> in [range.lazy.split.outer.value].</p> | ||
| <p><b>View all issues with</b> <a href="lwg-status.html#New">New</a> status.</p> | ||
| <p><b>Discussion:</b></p> | ||
| <p> | ||
| After <a href="https://wg21.link/P2325">P2325</a>, there is no reason for <tt>lazy_split_view::<i>outer-iterator</i>::value_type</tt> | ||
| to provide a default constructor, which only leads to <a href="https://godbolt.org/z/rM4WdMz79">unexpected behavior</a>: | ||
| </p> | ||
| <blockquote><pre> | ||
| #include <ranges> | ||
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| constexpr int arr[] = {42}; | ||
| constexpr auto split = arr | std::views::lazy_split(0); | ||
| static_assert(!std::ranges::range_value_t<decltype(split)>{}); // <span style="color:red;font-weight:bolder">UB, dereferencing a null pointer</span> | ||
| </pre></blockquote> | ||
| <p> | ||
| Also, the other constructor should be private because it makes no sense for the user to construct it arbitrarily, | ||
| which is not the intention. | ||
| </p> | ||
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| <p id="res-4013"><b>Proposed resolution:</b></p> | ||
| <p> | ||
| This wording is relative to <a href="https://wg21.link/N4964">N4964</a>. | ||
| </p> | ||
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| <li><p>Modify 26.7.16.4 <a href="https://wg21.link/range.lazy.split.outer.value">[range.lazy.split.outer.value]</a>, class <tt>split_view::<i>outer-iterator</i>::value_type</tt> synopsis, | ||
| as indicated:</p> | ||
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| <blockquote><pre> | ||
| namespace std::ranges { | ||
| template<input_range V, forward_range Pattern> | ||
| requires view<V> && view<Pattern> && | ||
| indirectly_comparable<iterator_t<V>, iterator_t<Pattern>, ranges::equal_to> && | ||
| (forward_range<V> || <i>tiny-range</i><Pattern>) | ||
| template<bool Const> | ||
| struct lazy_split_view<V, Pattern>::<i>outer-iterator</i><Const>::value_type | ||
| : view_interface<value_type> { | ||
| private: | ||
| <i>outer-iterator i_</i> = <i>outer-iterator</i>(); <i>// exposition only</i> | ||
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| <ins>constexpr explicit value_type(<i>outer-iterator</i> i); <i>// exposition only</i></ins> | ||
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| public: | ||
| <del>value_type() = default;</del> | ||
| <del>constexpr explicit value_type(<i>outer-iterator</i> i);</del> | ||
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| constexpr <i>inner-iterator</i><Const> begin() const; | ||
| constexpr default_sentinel_t end() const noexcept; | ||
| }; | ||
| } | ||
| </pre></blockquote> | ||
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