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<title>Issue 2823: std::array initialization is still not permissive enough</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#Open">Open</a> status.</em></p>
<h3 id="2823"><a href="lwg-active.html#2823">2823</a>. <code>std::array</code> initialization is still not permissive enough</h3>
<p><b>Section:</b> 23.3.3.1 <a href="https://wg21.link/array.overview">[array.overview]</a> <b>Status:</b> <a href="lwg-active.html#Open">Open</a>
 <b>Submitter:</b> Robert Haberlach <b>Opened:</b> 2016-11-16 <b>Last modified:</b> 2018-03-19</p>
<p><b>Priority: </b>3
</p>
<p><b>View other</b> <a href="lwg-index-open.html#array.overview">active issues</a> in [array.overview].</p>
<p><b>View all other</b> <a href="lwg-index.html#array.overview">issues</a> in [array.overview].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#Open">Open</a> status.</p>
<p><b>Discussion:</b></p>
<p>
LWG <a href="lwg-defects.html#2590" title="Aggregate initialization for std::array (Status: C++17)">2590</a><sup><a href="https://cplusplus.github.io/LWG/issue2590" title="Latest snapshot">(i)</a></sup>'s resolution is incomplete:
</p>
<blockquote><pre>
std::array&lt;int, 1&gt; arr{{0}};
</pre></blockquote>
<p>
should be fine, but isn't guaranteed, since <code>{0}</code> has no type. We should rather go for implicit conversion:
</p>
<blockquote><p>
An array is an aggregate (9.5.2 <a href="https://wg21.link/dcl.init.aggr">[dcl.init.aggr]</a>) that can be list-initialized with up to <code>N</code> elements 
<del>whose types are convertible to <code>T</code></del><ins>that can be implicitly converted to <code>T</code></ins>.
</p></blockquote>

<p><i>[2016-11-26, Tim Song comments]</i></p>

<p> 
This is not possible as written, because due to the brace elision rules for aggregate initialization,
<code>std::array&lt;int, 2&gt; arr{{0}, {1}};</code> will never work: the <code>{0}</code> 
is taken as initializing the inner array, and the <code>{1}</code> causes an error.
</p>

<p><i>[2017-01-27 Telecon]</i></p>

<p>Priority 2; consensus is that the P/R is not quite right.</p>

<p><i>[2018-3-14 Wednesday evening issues processing; priority to 3; move to Open]</i></p>

<p>Jens: There's nothing you can do about the double braces in std::array. That's a core thing.</p>
<p>STL to write paper to resolve this.</p>



<p id="res-2823"><b>Proposed resolution:</b></p>
<p>
This wording is relative to N4606.
</p>
<ol>
<li><p>Change 23.3.3.1 <a href="https://wg21.link/array.overview">[array.overview]</a> p2 as indicated:</p>

<blockquote>
<p>
-2- An <code>array</code> is an aggregate (9.5.2 <a href="https://wg21.link/dcl.init.aggr">[dcl.init.aggr]</a>) that can be list-initialized with up to <code>N</code> 
elements <del>whose types are convertible</del><ins>that can be implicitly converted</ins> to <code>T</code>.
</p>
</blockquote>
</li>
</ol>





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