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<title>Issue 3333: ranges::cbegin/ranges::cend, (and maybe ranges::crbegin/ranges::crend) are under-specified to allow rvalue-arrays</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#NAD">NAD</a> status.</em></p>
<h3 id="3333"><a href="lwg-closed.html#3333">3333</a>. <code>ranges::cbegin/ranges::cend</code>, (and maybe <code>ranges::crbegin/ranges::crend</code>) are under-specified to allow rvalue-arrays</h3>
<p><b>Section:</b> 25.3.4 <a href="https://wg21.link/range.access.cbegin">[range.access.cbegin]</a>, 25.3.5 <a href="https://wg21.link/range.access.cend">[range.access.cend]</a> <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a>
 <b>Submitter:</b> Christopher Di Bella <b>Opened:</b> 2019-11-06 <b>Last modified:</b> 2020-02-13</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p>
<p><b>Discussion:</b></p>
<p>
The following should be ill-formed, but is not, likely due to decay-to-pointer or reference collapsing.
</p>
<blockquote><pre>
double x[321];
ranges::cbegin(std::move(x)); <i>// should be ill-formed</i>
ranges::cend(std::move(x));   <i>// should be ill-formed</i>
</pre></blockquote>
<p>
This might be a problem for <code>ranges::crbegin</code> and <code>ranges::crend</code>, but I haven't implemented 
any of <code>rbegin</code>, <code>rend</code>, <code>crbegin</code>, and <code>crend</code> to confirm as much.
</p>
<p><i>[2020-02 Status to NAD on Thursday morning in Prague.]</i></p>



<p id="res-3333"><b>Proposed resolution:</b></p>
<p>This wording is relative to <a href="https://wg21.link/n4835">N4835</a>.</p>

<ol>
<li><p>Change 25.3.4 <a href="https://wg21.link/range.access.cbegin">[range.access.cbegin]</a> as indicated:</p>

<blockquote>
<p>
-1- The name <code>ranges::cbegin</code> denotes a customization point object (16.3.3.3.5 <a href="https://wg21.link/customization.point.object">[customization.point.object]</a>). 
<ins>If t</ins><del>T</del>he expression <code>ranges::<del>c</del>begin(E)</code> for some subexpression 
<code>E</code> of type <code>T</code> <ins>is well-formed, then the expression <code>ranges::cbegin(E)</code></ins> 
is expression-equivalent to:
<ol style="list-style-type: none">
  <li><p>(1.1) &mdash; <code>ranges::begin(static_cast&lt;const T&amp;&gt;(E))</code> if <code>E</code> is an lvalue.</p></li>
  <li><p>(1.2) &mdash; Otherwise, <code>ranges::begin(static_cast&lt;const T&amp;&amp;&gt;(E))</code>.</p></li>
</ol>
</p>
</blockquote>
</li>

<li><p>Change 25.3.5 <a href="https://wg21.link/range.access.cend">[range.access.cend]</a> as indicated:</p>

<blockquote>
<p>
-1- The name <code>ranges::cend</code> denotes a customization point object (16.3.3.3.5 <a href="https://wg21.link/customization.point.object">[customization.point.object]</a>). 
<ins>If t</ins><del>T</del>he expression <code>ranges::<del>c</del>end(E)</code> for some subexpression 
<code>E</code> of type <code>T</code> <ins>is well-formed, then the expression <code>ranges::cend(E)</code></ins> 
is expression-equivalent to:
<ol style="list-style-type: none">
  <li><p>(1.1) &mdash; <code>ranges::end(static_cast&lt;const T&amp;&gt;(E))</code> if <code>E</code> is an lvalue.</p></li>
  <li><p>(1.2) &mdash; Otherwise, <code>ranges::end(static_cast&lt;const T&amp;&amp;&gt;(E))</code>.</p></li>
</ol>
</p>
</blockquote>
</li>
</ol>




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