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<title>Issue 3558: elements_view::sentinel's first operator- has wrong return type</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#NAD_Editorial">NAD Editorial</a> status.</em></p>
<h3 id="3558"><a href="lwg-closed.html#3558">3558</a>. <code>elements_view::<i>sentinel</i></code>'s first <code>operator-</code> has wrong return type</h3>
<p><b>Section:</b> 25.7.23.4 <a href="https://wg21.link/range.elements.sentinel">[range.elements.sentinel]</a> <b>Status:</b> <a href="lwg-active.html#NAD_Editorial">NAD Editorial</a>
 <b>Submitter:</b> Hewill Kang <b>Opened:</b> 2021-05-28 <b>Last modified:</b> 2021-06-07</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p>
<p><b>Discussion:</b></p>
<p>
Because the iterator type of the first <code>operator-</code> is <code>const <i>iterator</i>&lt;OtherConst&gt;&amp;</code>, its 
return type should be <code>range_difference_t&lt;<i>maybe-const</i>&lt;OtherConst, V&gt;&gt;</code>.
</p>
<p><i>[2021-06-07 Fixed by editorial issue
<a href="https://github.com/cplusplus/draft/pull/4603">#4603</a>.
Status changed: New &rarr; NAD Editorial.]</i></p>



<p id="res-3558"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/n4885">N4885</a>.
</p>

<ol>
<li><p>Modify 25.7.23.4 <a href="https://wg21.link/range.elements.sentinel">[range.elements.sentinel]</a> as indicated:</p>

<blockquote>
<blockquote>
<pre>
    [&hellip;]
    template&lt;bool OtherConst&gt;
      requires sized_sentinel_for&lt;sentinel_t&lt;<i>Base</i>&gt;, iterator_t&lt;<i>maybe-const</i>&lt;OtherConst, V&gt;&gt;&gt;
    friend constexpr range_difference_t&lt;<del><i>Base</i></del><ins><i>maybe-const</i>&lt;OtherConst, V&gt;</ins>&gt;
      operator-(const <i>iterator</i>&lt;OtherConst&gt;&amp; x, const <i>sentinel</i>&amp; y);
    
    template&lt;bool OtherConst&gt;
      requires sized_sentinel_for&lt;sentinel_t&lt;<i>Base</i>&gt;, iterator_t&lt;<i>maybe-const</i>&lt;OtherConst, V&gt;&gt;&gt;
    friend constexpr range_difference_t&lt;<i>maybe-const</i>&lt;OtherConst, V&gt;&gt;
      operator-(const <i>sentinel</i>&amp; x, const <i>iterator</i>&lt;OtherConst&gt;&amp; y);
  };
}
</pre>
</blockquote>
[&hellip;]
<pre>
template&lt;bool OtherConst&gt;
  requires sized_sentinel_for&lt;sentinel_t&lt;<i>Base</i>&gt;, iterator_t&lt;<i>maybe-const</i>&lt;OtherConst, V&gt;&gt;&gt;
friend constexpr range_difference_t&lt;<del><i>Base</i></del><ins><i>maybe-const</i>&lt;OtherConst, V&gt;</ins>&gt;
  operator-(const <i>iterator</i>&lt;OtherConst&gt;&amp; x, const <i>sentinel</i>&amp; y);
</pre>
<blockquote>
<p>
-5- <i>Effects:</i> Equivalent to: <code>return x.<i>current_</i> - y.<i>end_</i>;</code>
</p>
</blockquote>
</blockquote>
</li>
</ol>




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