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<title>Issue 3710: The end of chunk_view for input ranges can be const</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="3710"><a href="lwg-defects.html#3710">3710</a>. The <code>end</code> of <code>chunk_view</code> for input ranges can be <code>const</code></h3>
<p><b>Section:</b> 25.7.29.2 <a href="https://wg21.link/range.chunk.view.input">[range.chunk.view.input]</a> <b>Status:</b> <a href="lwg-active.html#C++23">C++23</a>
 <b>Submitter:</b> Hewill Kang <b>Opened:</b> 2022-06-09 <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.chunk.view.input">issues</a> in [range.chunk.view.input].</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>
The input range version of <code>chunk_view</code>'s <code>end</code> is a very simple function that only returns 
<code>default_sentinel</code>, and simple <code>end</code>s like this also appear in other range adaptors, such 
as <code>basic_istream_view</code>, <code>lazy_split_view::<i>outer-iterator</i>::value_type</code>, and 
<code>chunk_view::<i>outer-iterator</i>::value_type</code>. 
<p/>
However, unlike <code>chunk_view</code>, their <code>end</code>s all are <code>const</code>-qualified, 
which allows us to freely get <code>default_sentinel</code> through the <code>end</code> of these <code>const</code> 
objects even though they may not themselves be <code>range</code>s.
<p/>
I think we should add <code>const</code> to this <code>chunk_view</code>'s <code>end</code> as 
I don't see any harm in doing this, and in some cases, it may have a certain value. Also, this makes it 
consistent with <code>basic_istream_view</code> and the upcoming <code>std::generator</code>, which, like it, only 
has a non-<code>const begin</code>.
</p>

<p><i>[2022-06-21; Reflector poll]</i></p>

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

<p><i>[2022-07-15; LWG telecon: move to Ready]</i></p>


<p><i>[2022-07-25 Approved at July 2022 virtual plenary. Status changed: Ready &rarr; WP.]</i></p>



<p id="res-3710"><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 25.7.29.2 <a href="https://wg21.link/range.chunk.view.input">[range.chunk.view.input]</a> as indicated:</p>

<blockquote>
<blockquote>
<pre>
namespace std::ranges {
  [&hellip;]
 
  template&lt;view V&gt;
    requires input_range&lt;V&gt;
  class chunk_view : public view_interface&lt;chunk_view&lt;V&gt;&gt; {
    V <i>base_</i> = V();                                        <i>// exposition only</i>
    [&hellip;]
  public:
    [&hellip;]

    constexpr <i>outer-iterator</i> begin();
    constexpr default_sentinel_t end() <ins>const</ins> noexcept;

    constexpr auto size() requires sized_range&lt;V&gt;;
    constexpr auto size() const requires sized_range&lt;const V&gt;;
  };
  [&hellip;]
}
</pre>
</blockquote>
[&hellip;]
<pre>
constexpr default_sentinel_t end() <ins>const</ins> noexcept;
</pre>
<blockquote>
<p>
-4- <i>Returns</i>: <code>default_sentinel</code>.
</p>
</blockquote>
</blockquote>
</li>

</ol>





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