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<title>Issue 1279: forbid [u|bi]nary_function specialization</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++11">C++11</a> status.</em></p>
<h3 id="1279"><a href="lwg-defects.html#1279">1279</a>. forbid <code>[u|bi]nary_function</code> specialization</h3>
<p><b>Section:</b> 99 [depr.base] <b>Status:</b> <a href="lwg-active.html#C++11">C++11</a>
 <b>Submitter:</b> Alberto Ganesh Barbati <b>Opened:</b> 2009-11-30 <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#depr.base">issues</a> in [depr.base].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++11">C++11</a> status.</p>
<p><b>Discussion:</b></p>
<p>
A program should not be allowed to add specialization of class templates
<code>unary_function</code> and <code>binary_function</code>, in force of 16.4.5.2.1 <a href="https://wg21.link/namespace.std">[namespace.std]</a>/1.
If a program were allowed to specialize these templates, the library could no
longer rely on them to provide the intended typedefs or there might be other
undesired interactions.
</p>

<p><i>[
2010-03-27 Daniel adds:
]</i></p>


<blockquote><p>
Accepting issue <a href="lwg-defects.html#1290" title="Don't require [u|bi]nary_function inheritance (Status: Resolved)">1290</a><sup><a href="https://cplusplus.github.io/LWG/issue1290" title="Latest snapshot">(i)</a></sup> would resolve this issue as NAD editorial.
</p></blockquote>

<p><i>[
2010-10-24 Daniel adds:
]</i></p>


<blockquote><p>
Accepting <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3145.html">n3145</a> would resolve this issue as NAD editorial.
</p></blockquote>

<p><i>[
2010 Batavia:
]</i></p>


<blockquote><p>
Pete: Is this issue actually addressed by N3198, or did deprecating unary/binary_function?
<p/>
We determined that this issue is NOT resolved and that it must be resolved or else 
N3198 could break code that does specialize unary&#47;binary function.
<p/>
Matt: don't move to NAD
<p/>
Howard: I suggest we go further and move 1279 to ready for Madrid.
<p/>
Group: Agrees move 1279 to ready for Madrid 
</p></blockquote>

<p>
Previous proposed resolution:
</p>

<blockquote><p>
1 The following <del>classes</del> <ins>class templates</ins> are provided to
simplify the typedefs of the argument and result types<del>:</del><ins>. A
program shall not declare specializations of these templates.</ins>
</p></blockquote>

<p><i>[2011-03-06 Daniel comments]</i></p>


<blockquote><p>
This meeting outcome was not properly reflected in the proposed resolution. I
also adapted the suggested wording to the N3242 numbering and content state.
During this course of action it turned out that the first suggested wording
change has already been applied.
</p></blockquote>



<p id="res-1279"><b>Proposed resolution:</b></p>
<p>
Change paragraph 99 [depr.base]/1 as follows:
</p>

<blockquote><p>
1 The class templates <code>unary_function</code> and <code>binary_function</code> are deprecated. 
<ins>A program shall not declare specializations of these templates.</ins>
</p></blockquote>





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