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<title>Issue 1020: Restore aligned_union</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="1020"><a href="lwg-closed.html#1020">1020</a>. Restore <code>aligned_union</code></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#NAD">NAD</a>
 <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-11 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</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#NAD">NAD</a> status.</p>
<p><b>Discussion:</b></p>

<p><b>Addresses UK 204 [CD1]</b></p>

<p>
It is not possible to create a variant union based on a parameter pack
expansion, e.g. to implement a classic discriminated union template. 
</p>

<p><b>Original proposed resolutuion:</b></p>

<p>
Restore <code>aligned_union</code> template that was removed by LWG issue <a href="lwg-defects.html#856" title="Removal of aligned_union (Status: CD1)">856</a><sup><a href="https://cplusplus.github.io/LWG/issue856" title="Latest snapshot">(i)</a></sup>. 
</p>

<p><i>[
Summit:
]</i></p>


<blockquote><p>
Agree. The need for <code>aligned_union</code> is compelling enough to reinstate.
</p></blockquote>

<p><i>[
Post Summit, Alisdair adds:
]</i></p>


<blockquote><p>
Paper
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2843.html">N2843</a>
proposes an extension to the <code>[[align]]</code> attribute
that further diminishes the need for this template.  Recommend NAD.
</p></blockquote>

<p><i>[
2009-10 Santa Cruz:
]</i></p>


<blockquote><p>
Mark NAD as suggested.
</p></blockquote>



<p id="res-1020"><b>Proposed resolution:</b></p>





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