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<title>Issue 2031: std::future&lt;&gt;::share() only applies to rvalues</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++11">C++11</a> status.</em></p>
<h3 id="2031"><a href="lwg-defects.html#2031">2031</a>. <code>std::future&lt;&gt;::share()</code> only applies to rvalues</h3>
<p><b>Section:</b> 32.10.7 <a href="https://wg21.link/futures.unique.future">[futures.unique.future]</a> <b>Status:</b> <a href="lwg-active.html#C++11">C++11</a>
 <b>Submitter:</b> Anthony Williams <b>Opened:</b> 2011-02-17 <b>Last modified:</b> 2021-06-06</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#futures.unique.future">issues</a> in [futures.unique.future].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++11">C++11</a> status.</p>
<p><b>Discussion:</b></p>
<p>
As specified, <code>future&lt;&gt;::share()</code> has the signature
</p>

<blockquote><pre>
shared_future&lt;R&gt; share() &amp;&amp;;
</pre></blockquote>

<p>
This means that it can only be applied to rvalues. One of the key benefits of <code>share()</code> is
that it can be used with the new <code>auto</code> facility:
</p>

<blockquote><pre>
std::promise&lt;<em>some_long_winded_type_name</em>&gt; some_promise;
auto f = some_promise.get_future(); // std::future
auto sf = std::move(f).share();
</pre></blockquote>

<p>
<code>share()</code> is sufficiently explicit that the move should not be required. We should be able to write:
</p>

<blockquote><pre>
auto sf = f.share();
</pre></blockquote>

<p><i>[2011-02-22 Reflector discussion]</i></p>

<p>
Moved to Tentatively Ready after 5 votes.
</p>


<p id="res-2031"><b>Proposed resolution:</b></p>
<p>Alter the declaration of <code>share()</code> to remove the "&amp;&amp;" rvalue qualifier in
 [futures.unique_future] p. 3, and  [futures.unique_future] p. 11:</p>

<blockquote><pre>
shared_future&lt;R&gt; share() <del>&amp;&amp;</del>;
</pre></blockquote>






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