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<title>Issue 1295: Contradictory call wrapper requirements</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="1295"><a href="lwg-defects.html#1295">1295</a>. Contradictory call wrapper requirements</h3>
<p><b>Section:</b> 22.10.4 <a href="https://wg21.link/func.require">[func.require]</a> <b>Status:</b> <a href="lwg-active.html#C++11">C++11</a>
 <b>Submitter:</b> Daniel Kr&uuml;gler <b>Opened:</b> 2009-12-22 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View other</b> <a href="lwg-index-open.html#func.require">active issues</a> in [func.require].</p>
<p><b>View all other</b> <a href="lwg-index.html#func.require">issues</a> in [func.require].</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>
22.10.4 <a href="https://wg21.link/func.require">[func.require]</a>/3 b 1 says
</p>

<blockquote>
<p>
3 If a call wrapper (22.10.3 <a href="https://wg21.link/func.def">[func.def]</a>) has a <i>weak result type</i> the
type of its member type <code>result_type</code> is based on the type <code>T</code> of
the wrapper's target object (22.10.3 <a href="https://wg21.link/func.def">[func.def]</a>):
</p>

<ul>
<li>
if <code>T</code> is a function, reference to function, or pointer to function type,
<code>result_type</code> shall be a synonym for the return type of <code>T</code>;
</li>
<li>
[..]
</li>
</ul>
</blockquote>

<p>
The first two enumerated types (function and reference to function)
can never be valid types for <code>T</code>, because
</p>

<p>
22.10.3 <a href="https://wg21.link/func.def">[func.def]</a>/7
</p>

<blockquote><p>
7 A <i>target object</i> is the callable object held by a call wrapper.
</p></blockquote>

<p>
and 22.10.3 <a href="https://wg21.link/func.def">[func.def]</a>/3
</p>

<blockquote><p>
3 A <i>callable type</i> is a pointer to function, a pointer to member function,
a pointer to member data, or a class type whose objects can appear immediately
to the left of a function call operator.
</p></blockquote>

<p>
exclude functions and references to function as "target objects".
</p>

<p><i>[
Post-Rapperswil:
]</i></p>


<blockquote><p>
Moved to Tentatively Ready after 5 positive votes on c++std-lib.
</p></blockquote>

<p><i>[
Adopted at 2010-11 Batavia
]</i></p>




<p id="res-1295"><b>Proposed resolution:</b></p>
<p>
Change 22.10.4 <a href="https://wg21.link/func.require">[func.require]</a>/3 b 1 as indicated:
</p>

<blockquote>
<p>
3 If a call wrapper (22.10.3 <a href="https://wg21.link/func.def">[func.def]</a>) has a <i>weak result type</i> the
type of its member type <code>result_type</code> is based on the type <code>T</code> of
the wrapper's target object (22.10.3 <a href="https://wg21.link/func.def">[func.def]</a>):
</p>

<ul>
<li>
if <code>T</code> is a <del>function, reference to function, or</del> pointer to
function type, <code>result_type</code> shall be a synonym for the return type of
<code>T</code>;
</li>
<li>
[..]
</li>
</ul>
</blockquote>






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