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| <!DOCTYPE html> | ||
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| <title>Issue 4053: Unary call to std::views::repeat does not decay the argument</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 id="4053"><a href="lwg-active.html#4053">4053</a>. Unary call to <code>std::views::repeat</code> does not decay the argument</h3> | ||
| <p><b>Section:</b> 26.6.5.2 <a href="https://wg21.link/range.repeat.view">[range.repeat.view]</a> <b>Status:</b> <a href="lwg-active.html#New">New</a> | ||
| <b>Submitter:</b> Jiang An <b>Opened:</b> 2024-02-05 <b>Last modified:</b> 2024-02-10</p> | ||
| <p><b>Priority: </b>Not Prioritized | ||
| </p> | ||
| <p><b>View other</b> <a href="lwg-index-open.html#range.repeat.view">active issues</a> in [range.repeat.view].</p> | ||
| <p><b>View all other</b> <a href="lwg-index.html#range.repeat.view">issues</a> in [range.repeat.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> | ||
| Currently, a binary call to <code>std::views::repeat</code> decay the arguments due to the deduction guide, | ||
| but a unary call doesn't, which is inconsistent. | ||
| <p/> | ||
| For example: | ||
| </p> | ||
| <blockquote><pre> | ||
| #include <concepts> | ||
| #include <ranges> | ||
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| using RPV = std::ranges::repeat_view<const char*>; | ||
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| static_assert(std::same_as<decltype(std::views::repeat("foo", std::unreachable_sentinel)), RPV>); // OK | ||
| static_assert(std::same_as<decltype(std::views::repeat(+"foo", std::unreachable_sentinel)), RPV>); // OK | ||
| static_assert(std::same_as<decltype(std::views::repeat("foo")), RPV>); // <span style="color:red;font-weight:bolder">ill-formed</span> | ||
| static_assert(std::same_as<decltype(std::views::repeat(+"foo")), RPV>); // OK | ||
| </pre></blockquote> | ||
| <p> | ||
| Presumably we should extend the deduction guide of <code>std::ranges::repeat_view</code> to cover the unary cases. | ||
| </p> | ||
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| <p id="res-4053"><b>Proposed resolution:</b></p> | ||
| <p> | ||
| This wording is relative to <a href="https://wg21.link/N4971" title=" Working Draft, Programming Languages — C++">N4971</a>. | ||
| </p> | ||
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| <ol> | ||
| <li><p>Modify 26.6.5.2 <a href="https://wg21.link/range.repeat.view">[range.repeat.view]</a>, class template <code>repeat_view</code> synopsis, as indicated:</p> | ||
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| <blockquote class="note"> | ||
| <p> | ||
| [<i>Drafting note:</i> The proposed wording has been suggested by Casey Carter, see | ||
| <a href="https://github.com/microsoft/STL/issues/3576">microsoft/STL#3576</a>] | ||
| </p> | ||
| </blockquote> | ||
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| <blockquote> | ||
| <pre> | ||
| namespace std::ranges { | ||
| […] | ||
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| template<class T, class Bound <ins>= unreachable_sentinel_t</ins>> | ||
| repeat_view(T, Bound <ins>= Bound()</ins>) -> repeat_view<T, Bound>; | ||
| } | ||
| </pre> | ||
| </blockquote> | ||
| </li> | ||
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