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<title>Issue 3254: Strike stop_token's operator!=</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#C++20">C++20</a> status.</em></p>
<h3 id="3254"><a href="lwg-defects.html#3254">3254</a>. Strike <code>stop_token</code>'s <code>operator!=</code></h3>
<p><b>Section:</b> 32.3.4 <a href="https://wg21.link/stoptoken">[stoptoken]</a> <b>Status:</b> <a href="lwg-active.html#C++20">C++20</a>
 <b>Submitter:</b> Casey Carter <b>Opened:</b> 2019-08-06 <b>Last modified:</b> 2021-02-25</p>
<p><b>Priority: </b>0
</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++20">C++20</a> status.</p>
<p><b>Discussion:</b></p>
<p>
In the shiny new world of the future, we need not declare overloads of <code>operator!=</code> that 
<code>return !(x == y);</code> the rewrite rule in 12.2.2.3 <a href="https://wg21.link/over.match.oper">[over.match.oper]</a> para 3.4.3 
achieves the same effect. Consequently, we should not declare such unnecessary 
<code>operator!=</code> overloads. The synopsis of class <code>stop_token</code> in 32.3.4 <a href="https://wg21.link/stoptoken">[stoptoken]</a> 
declares exactly such an <code>operator!=</code> friend which should be struck.
</p>
<p><i>[01-2020 Moved to Tentatively Ready after 5 positive votes on the reflector.]</i></p>



<p id="res-3254"><b>Proposed resolution:</b></p>
<p>This wording is relative to <a href="https://wg21.link/n4830">N4830</a>.</p>

<ol>
<li><p>Modify 32.3.4 <a href="https://wg21.link/stoptoken">[stoptoken]</a>, class <code>stop_token</code> synopsis, as indicated:</p>

<blockquote>
<pre>
namespace std {
  class stop_token {
  public:  
    [&hellip;]
    [[nodiscard]] friend bool operator==(const stop_token&amp; lhs, const stop_token&amp; rhs) noexcept;
    <del>[[nodiscard]] friend bool operator!=(const stop_token&amp; lhs, const stop_token&amp; rhs) noexcept;</del>
    friend void swap(stop_token&amp; lhs, stop_token&amp; rhs) noexcept;
  };
}
</pre>
</blockquote>

</li>

<li><p>Modify  [stoptoken.cmp] and  [stoptoken.special] as indicated:</p>

<blockquote>
<p>
<b>32.3.3.3 <ins>Non-member functions</ins><del>Comparisons</del> [stoptoken.<ins>nonmembers</ins><del>cmp</del>]</b>
</p>
<pre>
[[nodiscard]] bool operator==(const stop_token&amp; lhs, const stop_token&amp; rhs) noexcept;
</pre>
<blockquote>
<p>
-1- <i>Returns:</i> <code>true</code> if <code>lhs</code> and <code>rhs</code> have ownership of the same stop 
state or if both <code>lhs</code> and <code>rhs</code> do not have ownership of a stop state; otherwise <code>false</code>.
</p>
</blockquote>
<pre>
<del>[[nodiscard]] bool operator!=(const stop_token&amp; lhs, const stop_token&amp; rhs) noexcept;</del>
</pre>
<blockquote>
<p>
<del>-2- <i>Returns:</i> <code>!(lhs==rhs)</code>.</del>
</p>
</blockquote>
<p>
<del><b>32.3.3.4 Specialized algorithms [stoptoken.special]</b></del>
</p>
<pre>
friend void swap(stop_token&amp; x, stop_token&amp; y) noexcept;
</pre>
<blockquote>
<p>
-1- <i>Effects:</i> Equivalent to: <code>x.swap(y)</code>.
</p>
</blockquote>
</blockquote>

</li>
</ol>





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