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<title>Issue 1161: Unnecessary unique_future limitations</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#Resolved">Resolved</a> status.</em></p>
<h3 id="1161"><a href="lwg-defects.html#1161">1161</a>. Unnecessary <code>unique_future</code> limitations</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#Resolved">Resolved</a>
 <b>Submitter:</b> LWG <b>Opened:</b> 2009-06-28 <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#Resolved">Resolved</a> status.</p>
<p><b>Discussion:</b></p>

<p><b>Addresses UK 336</b></p>

<p><b>Description</b></p>

        <p>It is possible
        to transfer ownership of the asynchronous result from one
        unique_future instance to another via the move-constructor.
        However, it is not possible to transfer it back, and nor is
        it possible to create a default-constructed unique_future
        instance to use as a later move target. This unduly limits
        the use of <code>unique_future</code> in code. Also, the lack of a
        move-assignment operator restricts the use of <code>unique_future</code>
        in containers such as <code>std::vector</code> - <code>vector::insert</code> requires
        move-assignable for example.</p>
<p><b>Suggestion</b></p>
        <p>Add a default constructor with the
        semantics that it creates a <code>unique_future</code> with no
        associated asynchronous result. Add a move-assignment
        operator which transfers ownership.</p>
<p><b>Notes</b></p>
<p>Create an issue. Detlef will look into it.</p>

<p><i>[
2009-07 Frankfurt
]</i></p>


<blockquote><p>
Pending a paper from Anthony Williams &#47; Detlef Vollmann.
</p></blockquote>

<p><i>[
2009-10-14 Pending paper:
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2967.html">N2967</a>.
]</i></p>


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


<blockquote><p>
<del>NAD Editorial</del><ins>Resolved</ins>.  Addressed by
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2997.htm">N2997</a>.
</p></blockquote>



<p id="res-1161"><b>Proposed resolution:</b></p>





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