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<title>Issue 2805: void and reference type alternatives in variant, variant&lt;&gt; and 
index()</title>
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index()">
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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#Resolved">Resolved</a> status.</em></p>
<h3 id="2805"><a href="lwg-defects.html#2805">2805</a>. <code>void</code> and reference type alternatives in <code>variant</code>, <code>variant&lt;&gt;</code> and 
<code>index()</code></h3>
<p><b>Section:</b> 22.6 <a href="https://wg21.link/variant">[variant]</a>, 22.6.3 <a href="https://wg21.link/variant.variant">[variant.variant]</a>, 22.6.3.2 <a href="https://wg21.link/variant.ctor">[variant.ctor]</a> <b>Status:</b> <a href="lwg-active.html#Resolved">Resolved</a>
 <b>Submitter:</b> Switzerland <b>Opened:</b> 2016-11-10 <b>Last modified:</b> 2020-09-06</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all issues with</b> <a href="lwg-status.html#Resolved">Resolved</a> status.</p>
<p><b>Discussion:</b></p>
<p>
<b>Addresses CH 3, CH 4, CH 5, CH 6, CH 8</b>
</p>
<ol>
<li><p><code>variant</code> allows reference types as   
alternatives; <code>optional</code> explicitly forbids  
to  be  instantiated for reference types.  
This is inconsistent.</p></li>
<li><p><code>variant&lt;int, void&gt;</code> should be as   
usable as <code>variant&lt;int&gt;</code>.</p></li>
<li><p><code>variant&lt;&gt;</code> should not have an     
<code>index()</code> function.</p></li>
<li><p>Clarify the intended behavior of     
<code>variant</code> for alternative  types  that  are  
references.</p></li>
<li><p>Clarify <code>variant</code> construction.</p></li>
</ol>
<p>
Proposed change:
<p/>
<ol>
<li><p>Consider allowing reference types for both or none.</p></li>
<li><p>&mdash;</p></li>
<li><p>Consider  specifying a specialization for <code>variant&lt;&gt;</code>
like:</p>
<blockquote><pre>
template&lt;&gt; 
class variant&lt;&gt; 
{ 
public: 
  variant() = delete; 
  variant(const variant&amp;) = delete; 
  variant&amp; operator=(variant const&amp;) = delete;
};
</pre></blockquote>
</li>
<li><p>Add a respective note.</p></li>
<li><p>Add a note that <code>variant&lt;&gt;</code> cannot be constructed.</p></li>
</ol>
</p>

<p><i>[Issues Telecon 16-Dec-2016]</i></p>

<p>Resolved by the adoption of <a href="https://wg21.link/P0510R0">P0501R0</a>.</p>


<p id="res-2805"><b>Proposed resolution:</b></p>





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