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<title>Issue 769: std::function should use nullptr_t instead of "unspecified-null-pointer-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#CD1">CD1</a> status.</em></p>
<h3 id="769"><a href="lwg-defects.html#769">769</a>. std::function should use nullptr_t instead of "unspecified-null-pointer-type"</h3>
<p><b>Section:</b> 22.10.17.3 <a href="https://wg21.link/func.wrap.func">[func.wrap.func]</a> <b>Status:</b> <a href="lwg-active.html#CD1">CD1</a>
 <b>Submitter:</b> Daniel Kr&uuml;gler <b>Opened:</b> 2008-01-10 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#func.wrap.func">issues</a> in [func.wrap.func].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#CD1">CD1</a> status.</p>
<p><b>Discussion:</b></p>
<p>
N2461 already replaced in 22.10.17.3 <a href="https://wg21.link/func.wrap.func">[func.wrap.func]</a> it's originally proposed
(implicit) conversion operator to "unspecified-bool-type" by the new
explicit bool conversion, but the inverse conversion should also
use the new <code>std::nullptr_t</code> type instead of "unspecified-null-pointer-
type".
</p>


<p id="res-769"><b>Proposed resolution:</b></p>

<p>
In 22.10 <a href="https://wg21.link/function.objects">[function.objects]</a>, header <code>&lt;functional&gt;</code> synopsis replace:
</p>

<blockquote><pre>
template&lt;class R, class... ArgTypes&gt;
  bool operator==(const function&lt;R(ArgTypes...)&gt;&amp;, <del>unspecified-null-pointer-type</del> <ins>nullptr_t</ins>);
template&lt;class R, class... ArgTypes&gt;
  bool operator==(<del>unspecified-null-pointer-type</del> <ins>nullptr_t</ins> , const function&lt;R(ArgTypes...)&gt;&amp;);
template&lt;class R, class... ArgTypes&gt;
  bool operator!=(const function&lt;R(ArgTypes...)&gt;&amp;, <del>unspecified-null-pointer-type</del> <ins>nullptr_t</ins>);
template&lt;class R, class... ArgTypes&gt;
  bool operator!=(<del>unspecified-null-pointer-type</del> <ins>nullptr_t</ins> , const function&lt;R(ArgTypes...)&gt;&amp;);
</pre></blockquote>

<p>
In the class function synopsis of 22.10.17.3 <a href="https://wg21.link/func.wrap.func">[func.wrap.func]</a> replace
</p>

<blockquote><pre>
function(<del>unspecified-null-pointer-type</del> <ins>nullptr_t</ins>);
...
function&amp; operator=(<del>unspecified-null-pointer-type</del> <ins>nullptr_t</ins>);
</pre></blockquote>

<p>
In 22.10.17.3 <a href="https://wg21.link/func.wrap.func">[func.wrap.func]</a>, "Null pointer comparisons" replace:
</p>

<blockquote><pre>
template &lt;class R, class... ArgTypes&gt;
  bool operator==(const function&lt;R(ArgTypes...)&gt;&amp;, <del>unspecified-null-pointer-type</del> <ins>nullptr_t</ins>);
template &lt;class R, class... ArgTypes&gt;
  bool operator==(<del>unspecified-null-pointer-type</del> <ins>nullptr_t</ins> , const function&lt;R(ArgTypes...)&gt;&amp;);
template &lt;class R, class... ArgTypes&gt;
  bool operator!=(const function&lt;R(ArgTypes...)&gt;&amp;, <del>unspecified-null-pointer-type</del> <ins>nullptr_t</ins>);
template &lt;class R, class... ArgTypes&gt;
  bool operator!=(<del>unspecified-null-pointer-type</del> <ins>nullptr_t</ins> , const function&lt;R(ArgTypes...)&gt;&amp;);
</pre></blockquote>

<p>
In 22.10.17.3.2 <a href="https://wg21.link/func.wrap.func.con">[func.wrap.func.con]</a>, replace
</p>

<blockquote><pre>
function(<del>unspecified-null-pointer-type</del> <ins>nullptr_t</ins>);
...
function&amp; operator=(<del>unspecified-null-pointer-type</del> <ins>nullptr_t</ins>);
</pre></blockquote>

<p>
In 22.10.17.3.7 <a href="https://wg21.link/func.wrap.func.nullptr">[func.wrap.func.nullptr]</a>, replace
</p>

<blockquote><pre>
template &lt;class R, class... ArgTypes&gt;
  bool operator==(const function&lt;R(ArgTypes...)&gt;&amp; f, <del>unspecified-null-pointer-type</del> <ins>nullptr_t</ins>);
template &lt;class R, class... ArgTypes&gt;
  bool operator==(<del>unspecified-null-pointer-type</del> <ins>nullptr_t</ins> , const function&lt;R(ArgTypes...)&gt;&amp; f);
</pre></blockquote>

<p>
and replace
</p>

<blockquote><pre>
template &lt;class R, class... ArgTypes&gt;
  bool operator!=(const function&lt;R(ArgTypes...)&gt;&amp; f, <del>unspecified-null-pointer-type</del> <ins>nullptr_t</ins>);
template &lt;class R, class... ArgTypes&gt;
  bool operator!=(<del>unspecified-null-pointer-type</del> <ins>nullptr_t</ins> , const function&lt;R(ArgTypes...)&gt;&amp; f);
</pre></blockquote>






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