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<title>Issue 3060: XXX_scan algorithms are specified to work with move-only T, but are 
specified to make N copies of T into the destination range</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#New">New</a> status.</em></p>
<h3 id="3060"><a href="lwg-active.html#3060">3060</a>. <code>XXX_scan</code> algorithms are specified to work with move-only <code>T</code>, but are 
specified to make <code><i>N</i></code> copies of <code>T</code> into the destination range</h3>
<p><b>Section:</b> 26.10.8 <a href="https://wg21.link/exclusive.scan">[exclusive.scan]</a>, 26.10.9 <a href="https://wg21.link/inclusive.scan">[inclusive.scan]</a>, 26.10.10 <a href="https://wg21.link/transform.exclusive.scan">[transform.exclusive.scan]</a>, 26.10.11 <a href="https://wg21.link/transform.inclusive.scan">[transform.inclusive.scan]</a> <b>Status:</b> <a href="lwg-active.html#New">New</a>
 <b>Submitter:</b> Billy O'Neal III <b>Opened:</b> 2018-02-06 <b>Last modified:</b> 2019-01-20</p>
<p><b>Priority: </b>2
</p>
<p><b>View all other</b> <a href="lwg-index.html#exclusive.scan">issues</a> in [exclusive.scan].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#New">New</a> status.</p>
<p><b>Discussion:</b></p>
<p>
All of the scan algorithms ([exclusive.scan], [inclusive.scan], [transform.exclusive.scan], [transform.inclusive.scan]) have language like "If <code>init</code> is provided, <code>T</code> shall be 
<code>MoveConstructible</code> (Table 23); otherwise, <code>ForwardIterator1</code>'s value type shall be
<code>MoveConstructible</code>.". However, the algorithms operational semantics require that that type 
be written "by copy" to the destination range, making support for move only types impossible.
<p/>
We probably need to examine real implementations of these things and see what requirements are actually 
necessary, as in general <code><i>GENERALIZED_SUM</i></code> and <code><i>GENERALIZED_NONCOMMUTATIVE_SUM</i></code> 
need to specify the type used to store intermediate calculations.
</p>

<p><i>[2019-01-20 Reflector prioritization]</i></p>

<p>Set Priority to 2</p>


<p id="res-3060"><b>Proposed resolution:</b></p>





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