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<title>Issue 4189: cache_latest_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="4189"><a href="lwg-defects.html#4189">4189</a>. <code class='backtick'>cache_latest_view</code> should be freestanding</h3>
<p><b>Section:</b> 17.3.2 <a href="https://wg21.link/version.syn">[version.syn]</a>, 25.2 <a href="https://wg21.link/ranges.syn">[ranges.syn]</a> <b>Status:</b> <a href="lwg-active.html#WP">WP</a>
 <b>Submitter:</b> Hewill Kang <b>Opened:</b> 2024-12-23 <b>Last modified:</b> 2025-02-16</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 class='backtick'>cache_latest_view</code> can be freestanding, but this never comes up in the discussion, which seems to be an oversight.
</p>

<p><strong>Previous resolution [SUPERSEDED]:</strong></p>
<blockquote class="note">

<p>
This wording is relative to <a href="https://wg21.link/N5001" title=" Working Draft, Programming Languages — C++">N5001</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_cache_latest 202411L // <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>25.7.34 <a href="https://wg21.link/range.cache.latest">[range.cache.latest]</a>, cache latest view</i>
  template&lt;input_range V&gt;
    requires view&lt;V&gt;
  class cache_latest_view;                                                                <ins>// <i>freestanding</i></ins>
  
  namespace views { inline constexpr <i>unspecified</i> cache_latest = <i>unspecified</i>; }            <ins>// <i>freestanding</i></ins>
  [&hellip;]
}
</pre></blockquote>
</li>
</ol>
</blockquote>

<p><i>[2025-01-04; Tim Song suggests alternative wording]</i></p>

<p>
While we are here, we can use the new convention from <a href="https://wg21.link/P2407" title=" Freestanding Library: Partial Classes">P2407</a> to dramatically simplify 
<code>&lt;ranges&gt;</code>. Most future additions to this header should have no problem being freestanding, 
so that is the right default.
</p>

<p><i>[2025-02-07; Reflector poll]</i></p>

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

<p><i>[Hagenberg 2025-02-16; Status changed: Voting &rarr; WP.]</i></p>



<p id="res-4189"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/N5001" title=" Working Draft, Programming Languages — C++">N5001</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_cache_latest 202411L // <ins><i>freestanding</i>,</ins> <i>also in</i> &lt;ranges&gt;
</pre></blockquote>

</li>

<li><p>Delete all "// <i>freestanding</i>" comments in 25.2 <a href="https://wg21.link/ranges.syn">[ranges.syn]</a>, header <code>&lt;ranges&gt;</code> 
synopsis, and then modify as indicated:</p>

<blockquote><pre>
<ins>// <i>mostly freestanding</i></ins>
#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>

[&hellip;]
namespace std::ranges {
  // <i>25.5.6 <a href="https://wg21.link/range.elementsof">[range.elementsof]</a>, class template elements_of</i>
  template&lt;range R, class Allocator = allocator&lt;byte&gt;&gt;
    struct elements_of;  <ins>// <i>hosted</i></ins>
  [&hellip;]

  // <i>25.6.6 <a href="https://wg21.link/range.istream">[range.istream]</a>, istream view</i>
  template&lt;movable Val, class CharT, class Traits = char_traits&lt;CharT&gt;&gt;
    requires <i>see below</i>
  class basic_istream_view;  <ins>// <i>hosted</i></ins>
  template&lt;class Val&gt;
    using istream_view = basic_istream_view&lt;Val, char&gt;;   <ins>// <i>hosted</i></ins>
  template&lt;class Val&gt;
    using wistream_view = basic_istream_view&lt;Val, wchar_t&gt;;   <ins>// <i>hosted</i></ins>

  namespace views {
    template&lt;class T&gt; constexpr <i>unspecified</i> istream = <i>unspecified</i>; <ins>// <i>hosted</i></ins>
  }
  [&hellip;]
}
[&hellip;]
</pre></blockquote>
</li>
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