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<title>Issue 3915: Redundant paragraph about expression variations</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="3915"><a href="lwg-defects.html#3915">3915</a>. Redundant paragraph about expression variations</h3>
<p><b>Section:</b> 25.4.2 <a href="https://wg21.link/range.range">[range.range]</a> <b>Status:</b> <a href="lwg-active.html#WP">WP</a>
 <b>Submitter:</b> Johel Ernesto Guerrero Pe&ntilde;a <b>Opened:</b> 2023-04-01 <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.range">issues</a> in [range.range].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#WP">WP</a> status.</p>
<p><b>Discussion:</b></p>
<p>
Originally editorial issue <a href="https://github.com/cplusplus/draft/issues/4431">Editorial issue #4431</a>.
<p/>
Expression variations kick in for "an expression that is non-modifying for some constant lvalue operand", but 
<code>std::ranges::range</code>'s is an non-constant lvalue, so 25.4.2 <a href="https://wg21.link/range.range">[range.range]</a> p2 is redundant.
<p/>
I suppose that the change that clarified the template parameters' <i>cv</i>-qualification for purposes of 
equality-preservation and requiring additional variations happened concurrently with the change of 
<code>std::ranges::range</code>'s operand from a forwarding reference to a non-constant lvalue reference.
</p>

<p><i>[2023-05-24; Reflector poll]</i></p>

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

<p><i>[2023-06-17 Approved at June 2023 meeting in Varna. Status changed: Voting &rarr; WP.]</i></p>



<p id="res-3915"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/N4944" title=" Working Draft, Standard for Programming Language C++">N4944</a>.
</p>

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

<blockquote>
<p>
-1- The <code>range</code> concept defines the requirements of a type that allows iteration over its elements by providing an
iterator and sentinel that denote the elements of the range.
</p>
<pre>
template&lt;class T&gt;
  concept range =
    requires(T&amp; t) {
      ranges::begin(t); // <i>sometimes equality-preserving (see below)</i>
      ranges::end(t);
    };
</pre>
<blockquote>
<del>-2- The required expressions <code>ranges::begin(t)</code> and <code>ranges::end(t)</code> of the <code>range</code> 
concept do not require implicit expression variations (18.2 <a href="https://wg21.link/concepts.equality">[concepts.equality]</a>).</del>
<p/>
-3- [&hellip;]
</blockquote>
</blockquote>

</li>
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