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<title>Issue 4076: concat_view should be freestanding</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#WP">WP</a> status.</em></p>
<h3 id="4076"><a href="lwg-defects.html#4076">4076</a>. <code>concat_view</code> should be freestanding</h3>
<p><b>Section:</b> 17.3.2 <a href="https://wg21.link/version.syn">[version.syn]</a> <b>Status:</b> <a href="lwg-active.html#WP">WP</a>
 <b>Submitter:</b> Hewill Kang <b>Opened:</b> 2024-04-21 <b>Last modified:</b> 2024-07-08</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View other</b> <a href="lwg-index-open.html#version.syn">active issues</a> in [version.syn].</p>
<p><b>View all other</b> <a href="lwg-index.html#version.syn">issues</a> in [version.syn].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#WP">WP</a> status.</p>
<p><b>Discussion:</b></p>
<p>
<code>concat_view</code> can be freestanding, but this never seems to come up in the discussion, 
which seems to be an oversight.
</p>

<p><i>[2024-04-21; Daniel comments]</i></p>

<p>
The specification of some member functions of <code>concat_view</code> seem to depend on freestanding-deleted
<code>get</code> overloads for <code>variant</code>, but so does <code>join_with_view</code>, which is marked as freestanding,
so it does not seem to be a good reason to accept <code>join_with_view</code> but not <code>concat_view</code> as freestanding.
</p>

<p><i>[2024-05-08; Reflector poll]</i></p>

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

<p><i>[St. Louis 2024-06-29; Status changed: Voting &rarr; WP.]</i></p>



<p id="res-4076"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/N4981" title=" Working Draft, Programming Languages — C++">N4981</a>.
</p>

<ol>
<li><p>Modify 17.3.2 <a href="https://wg21.link/version.syn">[version.syn]</a> as indicated:</p>

<blockquote>
<pre>
#define __cpp_lib_ranges_concat 202403L // <ins><i>freestanding</i>,</ins> <i>also in</i> &lt;ranges&gt;
</pre>
</blockquote>
</li>

<li><p>Modify 25.2 <a href="https://wg21.link/ranges.syn">[ranges.syn]</a> as indicated:</p>

<blockquote>
<pre>
#include &lt;compare&gt;              // <i>see 17.12.1 <a href="https://wg21.link/compare.syn">[compare.syn]</a></i>
#include &lt;initializer_list&gt;     // <i>see 17.11.2 <a href="https://wg21.link/initializer.list.syn">[initializer.list.syn]</a></i>
#include &lt;iterator&gt;             // <i>see 24.2 <a href="https://wg21.link/iterator.synopsis">[iterator.synopsis]</a></i>

namespace std::ranges {
  [&hellip;]
  // <i>25.7.18 <a href="https://wg21.link/range.concat">[range.concat]</a>, concat view</i>
  template&lt;input_range... Views&gt;
    requires <i>see below</i>
  class concat_view;                                                                <ins>// <i>freestanding</i></ins>
  
  namespace views { inline constexpr <i>unspecified</i> concat = <i>unspecified</i>; }            <ins>// <i>freestanding</i></ins>
  [&hellip;]
}
</pre>
</blockquote>
</li>

</ol>





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