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<title>Issue 3555: {transform,elements}_view::iterator::iterator_concept
should consider const-qualification of the underlying range</title>
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should consider const-qualification of the underlying range">
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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="3555"><a href="lwg-defects.html#3555">3555</a>. <code>{transform,elements}_view::<i>iterator</i>::iterator_concept</code>
should consider const-qualification of the underlying range</h3>
<p><b>Section:</b> 25.7.9.3 <a href="https://wg21.link/range.transform.iterator">[range.transform.iterator]</a>, 25.7.23.3 <a href="https://wg21.link/range.elements.iterator">[range.elements.iterator]</a> <b>Status:</b> <a href="lwg-active.html#C++23">C++23</a>
 <b>Submitter:</b> Tim Song <b>Opened:</b> 2021-05-23 <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.transform.iterator">issues</a> in [range.transform.iterator].</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>
<code>transform_view::<i>iterator&lt;true&gt;</i>::iterator_concept</code> and
<code>elements_view::<i>iterator&lt;true&gt;</i>::iterator_concept</code> (i.e.,
the const versions) are currently specified as looking at the properties of <code>V</code>
(i.e., the underlying view without const), while the actual iterator operations
are all correctly specified as using <code><i>Base</i></code> (which includes
the const). <code>iterator_concept</code> should do so too.
<p/>
The proposed resolution has been implemented and tested on top of libstdc++.
</p>

<p><i>[2021-05-26; Reflector poll]</i></p>

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

<p><i>[2021-06-07 Approved at June 2021 virtual plenary. Status changed: Voting &rarr; WP.]</i></p>



<p id="res-3555"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/N4885" title=" Working Draft, Standard for Programming Language C++">N4885</a>.
</p>
<ol>
<li>
<p>Modify 25.7.9.3 <a href="https://wg21.link/range.transform.iterator">[range.transform.iterator]</a> as indicated:</p>
<blockquote>
<p>-1- <code>iterator::iterator_concept</code> is defined as follows: </p>
<ol style="list-style-type: none">
<li><p>(1.1) &mdash; If <code><del>V</del><ins><i>Base</i></ins></code> models <code>random_access_range</code>, then
<code>iterator_concept</code> denotes <code>random_access_iterator_tag</code>.</p></li>
<li><p>(1.2) &mdash; Otherwise, if <code><del>V</del><ins><i>Base</i></ins></code> models <code>bidirectional_range</code>,
then <code>iterator_concept</code> denotes <code>bidirectional_iterator_tag</code>.</p></li>
<li><p>(1.3) &mdash; Otherwise, if <code><del>V</del><ins><i>Base</i></ins></code> models <code>forward_range</code>,
then <code>iterator_concept</code> denotes <code>forward_iterator_tag</code>.</p></li>
<li><p>(1.4) &mdash; Otherwise, <code>iterator_concept</code> denotes <code>input_iterator_tag</code>.</p></li>
</ol>
</blockquote>
</li>
<li>
<p>Modify 25.7.23.3 <a href="https://wg21.link/range.elements.iterator">[range.elements.iterator]</a> as indicated:</p>
<blockquote>
<p>-1- The member <i>typedef-name</i> <code>iterator_concept</code> is defined as follows: </p>
<ol style="list-style-type: none">
<li><p>(1.1) &mdash; If <code><del>V</del><ins><i>Base</i></ins></code> models <code>random_access_range</code>, then
<code>iterator_concept</code> denotes <code>random_access_iterator_tag</code>.</p></li>
<li><p>(1.2) &mdash; Otherwise, if <code><del>V</del><ins><i>Base</i></ins></code> models <code>bidirectional_range</code>,
then <code>iterator_concept</code> denotes <code>bidirectional_iterator_tag</code>.</p></li>
<li><p>(1.3) &mdash; Otherwise, if <code><del>V</del><ins><i>Base</i></ins></code> models <code>forward_range</code>,
then <code>iterator_concept</code> denotes <code>forward_iterator_tag</code>.</p></li>
<li><p>(1.4) &mdash; Otherwise, <code>iterator_concept</code> denotes <code>input_iterator_tag</code>.</p></li>
</ol>
</blockquote>
</li>
</ol>




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