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<title>Issue 3738: Missing preconditions for take_view constructor</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++23">C++23</a> status.</em></p>
<h3 id="3738"><a href="lwg-defects.html#3738">3738</a>. Missing preconditions for <code>take_view</code> constructor</h3>
<p><b>Section:</b> 25.7.10.2 <a href="https://wg21.link/range.take.view">[range.take.view]</a> <b>Status:</b> <a href="lwg-active.html#C++23">C++23</a>
 <b>Submitter:</b> Hewill Kang <b>Opened:</b> 2022-07-15 <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#range.take.view">issues</a> in [range.take.view].</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>
When <code>V</code> does not model <code>sized_range</code>, <code>take_view::begin</code> returns 
<code>counted_iterator(ranges::begin(<i>base_</i>), <i>count_</i>)</code>. Since the 
<code>counted_iterator</code> constructor (24.5.7.2 <a href="https://wg21.link/counted.iter.const">[counted.iter.const]</a>) already has 
a precondition that <code>n &gt;= 0</code>, we should add this to <code>take_view</code> as well,
which is consistent with <code>drop_view</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-3738"><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 25.7.10.2 <a href="https://wg21.link/range.take.view">[range.take.view]</a> as indicated:</p>

<blockquote>
<pre>
constexpr take_view(V base, range_difference_t&lt;V&gt; count);
</pre>
<blockquote>
<p>
<ins>-?- <i>Preconditions</i>: <code>count &gt;= 0</code> is <code>true</code>.</ins>
</p>
<p>
-1- <i>Effects</i>: Initializes <code><i>base_</i></code> with <code>std::move(base)</code> and 
<code><i>count_</i></code> with <code>count</code>.
</p>
</blockquote>
</blockquote>
</li>
</ol>





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