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<title>Issue 3747: ranges::uninitialized_copy_n, ranges::uninitialized_move_n, and 
ranges::destroy_n should use std::move</title>
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ranges::destroy_n should use std::move">
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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++23">C++23</a> status.</em></p>
<h3 id="3747"><a href="lwg-defects.html#3747">3747</a>. <code>ranges::uninitialized_copy_n</code>, <code>ranges::uninitialized_move_n</code>, and 
<code>ranges::destroy_n</code> should use <code>std::move</code></h3>
<p><b>Section:</b> 26.11.5 <a href="https://wg21.link/uninitialized.copy">[uninitialized.copy]</a>, 26.11.6 <a href="https://wg21.link/uninitialized.move">[uninitialized.move]</a>, 26.11.9 <a href="https://wg21.link/specialized.destroy">[specialized.destroy]</a> <b>Status:</b> <a href="lwg-active.html#C++23">C++23</a>
 <b>Submitter:</b> Hewill Kang <b>Opened:</b> 2022-07-28 <b>Last modified:</b> 2023-11-22</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#uninitialized.copy">issues</a> in [uninitialized.copy].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++23">C++23</a> status.</p>
<p><b>Discussion:</b></p>
<p>
Currently, <code>ranges::uninitialized_copy_n</code> has the following equivalent <i>Effects</i>:
</p>
<blockquote><pre>
auto t = uninitialized_copy(counted_iterator(ifirst, n),
                            default_sentinel, ofirst, olast);
return {std::move(t.in).base(), t.out};
</pre></blockquote>
<p>
Given that <code>ifirst</code> is just an <code>input_iterator</code> which is not guaranteed to be <code>copyable</code>, 
we should move it into <code>counted_iterator</code>. The same goes for <code>ranges::uninitialized_move_n</code> 
and <code>ranges::destroy_n</code>.
</p>

<p><i>[2022-08-23; Reflector poll]</i></p>

<p>
Set status to Tentatively Ready after eight votes in favour during reflector poll.
</p>

<p><i>[2022-11-12 Approved at November 2022 meeting in Kona. Status changed: Voting &rarr; WP.]</i></p>



<p id="res-3747"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/N4910" title=" Working Draft, Standard for Programming Language C++">N4910</a>.
</p>

<ol>
<li><p>Modify 26.11.5 <a href="https://wg21.link/uninitialized.copy">[uninitialized.copy]</a> as indicated:</p>

<blockquote>
<pre>
namespace ranges {
  template&lt;input_iterator I, <i>nothrow-forward-iterator</i> O, <i>nothrow-sentinel-for</i>&lt;O&gt; S&gt;
    requires constructible_from&lt;iter_value_t&lt;O&gt;, iter_reference_t&lt;I&gt;&gt;
    uninitialized_copy_n_result&lt;I, O&gt;
      uninitialized_copy_n(I ifirst, iter_difference_t&lt;I&gt; n, O ofirst, S olast);
}
</pre>
<blockquote>
<p>
-9- <i>Preconditions</i>: [<code>ofirst, olast</code>) does not overlap with <code>ifirst +</code> [<code>0, n</code>) .
</p>
<p>
-10- <i>Effects</i>: Equivalent to:
</p>
<blockquote><pre>
auto t = uninitialized_copy(counted_iterator(<ins>std::move(</ins>ifirst<ins>)</ins>, n),
                            default_sentinel, ofirst, olast);
return {std::move(t.in).base(), t.out};
</pre></blockquote>
</blockquote>
</blockquote>
</li>

<li><p>Modify 26.11.6 <a href="https://wg21.link/uninitialized.move">[uninitialized.move]</a> as indicated:</p>

<blockquote>
<pre>
namespace ranges {
  template&lt;input_iterator I, <i>nothrow-forward-iterator</i> O, <i>nothrow-sentinel-for</i>&lt;O&gt; S&gt;
    requires constructible_from&lt;iter_value_t&lt;O&gt;, iter_rvalue_reference_t&lt;I&gt;&gt;
    uninitialized_move_n_result&lt;I, O&gt;
      uninitialized_move_n(I ifirst, iter_difference_t&lt;I&gt; n, O ofirst, S olast);
}
</pre>
<blockquote>
<p>
-8- <i>Preconditions</i>: [<code>ofirst, olast</code>) does not overlap with <code>ifirst +</code> [<code>0, n</code>) .
</p>
<p>
-9- <i>Effects</i>: Equivalent to:
</p>
<blockquote><pre>
auto t = uninitialized_move(counted_iterator(<ins>std::move(</ins>ifirst<ins>)</ins>, n),
                            default_sentinel, ofirst, olast);
return {std::move(t.in).base(), t.out};
</pre></blockquote>
</blockquote>
</blockquote>
</li>

<li><p>Modify 26.11.9 <a href="https://wg21.link/specialized.destroy">[specialized.destroy]</a> as indicated:</p>

<blockquote>
<pre>
namespace ranges {
  template&lt;<i>nothrow-input-iterator</i> I&gt;
    requires destructible&lt;iter_value_t&lt;I&gt;&gt;
    constexpr I destroy_n(I first, iter_difference_t&lt;I&gt; n) noexcept;
}
</pre>
<blockquote>
<p>
-5- <i>Effects</i>: Equivalent to:
</p>
<blockquote><pre>
return destroy(counted_iterator(<ins>std::move(</ins>first<ins>)</ins>, n), default_sentinel).base();
</pre></blockquote>
</blockquote>
</blockquote>
</li>
</ol>





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