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<title>Issue 3966: The value_type and reference members of std::flat_(multi)map::(const_)iterator are unclear</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#New">New</a> status.</em></p>
<h3 id="3966"><a href="lwg-active.html#3966">3966</a>. The <code>value_type</code> and <code>reference</code> members of <code>std::flat_(multi)map::(const_)iterator</code> are unclear</h3>
<p><b>Section:</b> 23.6.8.1 <a href="https://wg21.link/flat.map.overview">[flat.map.overview]</a>, 23.6.9.1 <a href="https://wg21.link/flat.multimap.overview">[flat.multimap.overview]</a> <b>Status:</b> <a href="lwg-active.html#New">New</a>
 <b>Submitter:</b> Jiang An <b>Opened:</b> 2023-08-04 <b>Last modified:</b> 2023-10-30</p>
<p><b>Priority: </b>3
</p>
<p><b>View all other</b> <a href="lwg-index.html#flat.map.overview">issues</a> in [flat.map.overview].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#New">New</a> status.</p>
<p><b>Discussion:</b></p>
<p>
23.6.8.1 <a href="https://wg21.link/flat.map.overview">[flat.map.overview]</a> and 23.6.9.1 <a href="https://wg21.link/flat.multimap.overview">[flat.multimap.overview]</a> currently only require that the iterator types 
meet <i>Cpp17InputIterator</i> requirements and model the <code>std::random_access_iterator</code> concept.
<p/>
The intent seems to be that
</p>
<ul>
<li><p>the <code>operator*()</code> returns proxy references of type <code>std::pair&lt;const K&amp;, V&amp;&gt;</code> or 
<code>std::pair&lt;const K&amp;, const V&amp;&gt;</code> (same as the <code>reference</code> or <code>const_reference</code> 
types of the container adaptors), and</p></li>
<li><p>the <code>value_type</code> of these iterators is <code>std::pair&lt;K, V&gt;</code> (same as the <code>value_type</code> 
of the container adaptors).</p></li>
</ul>
<p>
However, such intent doesn't seem to be clear.
<p/>
Moreover, given such possibly intended iterator types don't meet <i>Cpp17ForwardIterator</i> requirements, 
we may need to mention the exceptions in 23.2.2.2 <a href="https://wg21.link/container.reqmts">[container.reqmts]</a> or 23.2.7.1 <a href="https://wg21.link/associative.reqmts.general">[associative.reqmts.general]</a>.
</p>

<p><i>[2023-10-30; Reflector poll]</i></p>

<p>
Set priority to 3 after reflector poll.
</p>



<p id="res-3966"><b>Proposed resolution:</b></p>





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