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<title>Issue 3986: basic_const_iterator doesn't work with optional</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="3986"><a href="lwg-active.html#3986">3986</a>. <code>basic_const_iterator</code> doesn't work with <code>optional</code></h3>
<p><b>Section:</b> 24.5.3 <a href="https://wg21.link/const.iterators">[const.iterators]</a> <b>Status:</b> <a href="lwg-active.html#New">New</a>
 <b>Submitter:</b> Hewill Kang <b>Opened:</b> 2023-08-26 <b>Last modified:</b> 2023-10-30</p>
<p><b>Priority: </b>3
</p>
<p><b>View other</b> <a href="lwg-index-open.html#const.iterators">active issues</a> in [const.iterators].</p>
<p><b>View all other</b> <a href="lwg-index.html#const.iterators">issues</a> in [const.iterators].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#New">New</a> status.</p>
<p><b>Discussion:</b></p>
<p>
The heterogeneous comparison operators of <code>basic_const_iterator</code> only constrain type <code>I</code> to be 
comparable with the underlying iterator type, which allows non-iterator types such as <code>optional</code>, and 
the heterogeneous comparison operators of the latter would make the situation worse 
(<a href="https://godbolt.org/z/76evPfGnh">demo</a>):
</p>
<blockquote><pre>
#include &lt;iterator&gt;
#include &lt;optional&gt;
  
int main() {
  std::basic_const_iterator&lt;const int*&gt; it;
  std::optional opt{it};
  auto c = opt &lt; it; // <span style="color:red;font-weight:bolder">infinite meta-recursion</span>
  auto d = it - opt; // <span style="color:red;font-weight:bolder">infinite meta-recursion</span>
}
</pre></blockquote>

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

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



<p id="res-3986"><b>Proposed resolution:</b></p>





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