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<title>Issue 2979: aligned_union should require complete object types</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#C++20">C++20</a> status.</em></p>
<h3 id="2979"><a href="lwg-defects.html#2979">2979</a>. <code>aligned_union</code> should require complete object types</h3>
<p><b>Section:</b> 21.3.9.7 <a href="https://wg21.link/meta.trans.other">[meta.trans.other]</a> <b>Status:</b> <a href="lwg-active.html#C++20">C++20</a>
 <b>Submitter:</b> Tim Song <b>Opened:</b> 2017-06-14 <b>Last modified:</b> 2021-02-25</p>
<p><b>Priority: </b>0
</p>
<p><b>View all other</b> <a href="lwg-index.html#meta.trans.other">issues</a> in [meta.trans.other].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++20">C++20</a> status.</p>
<p><b>Discussion:</b></p>
<p>
<code>aligned_union</code>'s description doesn't, but should, require the types provided to be complete object types.
</p>

<p><i>[2017-07 Toronto Monday issue prioritization]</i></p>

<p>Priority 0; move to Ready</p>


<p id="res-2979"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/n4659">N4659</a>.
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<ol>
<li><p> In 21.3.9.7 <a href="https://wg21.link/meta.trans.other">[meta.trans.other]</a>, edit Table 50 "Other transformations" as indicated:</p>
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<caption>Table 50 &mdash; Other transformations</caption>
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<th>Template</th>
<th>Comments</th>
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<code>[&hellip;]</code>
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<code>template &lt;size_t Len, class... Types&gt;<br />
struct aligned_union;</code>
</td>
<td>
The member typedef <code>type</code> shall be a POD type suitable for use as uninitialized storage for any object whose type is listed in <code>Types</code>; its size shall be at least <code>Len</code>. The static member <code>alignment_value</code> shall be an integral constant of type <code>size_t</code> whose value is the strictest alignment of all types listed in <code>Types</code>. <br />
<i>Requires:</i> At least one type is provided. <ins>Each type in the parameter pack <code>Types</code> shall be a complete object type.</ins>
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<code>[&hellip;]</code>
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