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<title>Issue 2526: [fund.ts.v2] Incorrect precondition for experimental::function::swap</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#TS">TS</a> status.</em></p>
<h3 id="2526"><a href="lwg-defects.html#2526">2526</a>. [fund.ts.v2] Incorrect precondition for <code>experimental::function::swap</code></h3>
<p><b>Section:</b> 4.2.2 <a href="https://cplusplus.github.io/fundamentals-ts/v2.html#func.wrap.func.mod">[fund.ts.v2::func.wrap.func.mod]</a> <b>Status:</b> <a href="lwg-active.html#TS">TS</a>
 <b>Submitter:</b> Tim Song <b>Opened:</b> 2015-08-04 <b>Last modified:</b> 2017-07-30</p>
<p><b>Priority: </b>0
</p>
<p><b>View all issues with</b> <a href="lwg-status.html#TS">TS</a> status.</p>
<p><b>Discussion:</b></p>
<p><b>Addresses: fund.ts.v2</b></p>
<p>
4.2.2 <a href="https://cplusplus.github.io/fundamentals-ts/v2.html#func.wrap.func.mod">[fund.ts.v2::func.wrap.func.mod]</a> says that the precondition of <code>swap</code> is
</p>
<blockquote><pre>
this-&gt;get_memory_resource() == other-&gt;get_memory_resource()
</pre></blockquote>
<p>
That compares two pointers and so requires the memory resource used by <code>*this</code> and <code>other</code> to be 
the exact same object. That doesn't seem correct (for one, it would essentially outlaw swapping all <code>function</code>s 
constructed with "plain" allocators, since they would each have their own <code>resource_adaptor</code> object 
and so the pointers will not compare equal). Presumably the intent is to compare the <code>memory_resource</code>s for equality.
</p>
<p>
Also, <code>other</code> is a reference, not a pointer.
</p>

<p><i>[2015-09-11, Telecon]</i></p>

<p>
Move to Tentatively Ready
</p>

<p><i>[2015-10-26]</i></p>

<p>
Daniel adjusts wording to lib. fund. v2.
</p>


<p id="res-2526"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4529.html">N4529</a>.
</p>

<ol>
<li><p>Edit 4.2.2 <a href="https://cplusplus.github.io/fundamentals-ts/v2.html#func.wrap.func.mod">[fund.ts.v2::func.wrap.func.mod]</a> as indicated:</p>
<blockquote>
<pre>
void swap(function&amp; other);
</pre>
<blockquote>
<p>
-2- <i>Requires</i>: <code><ins>*</ins>this-&gt;get_memory_resource() == <ins>*</ins>other<del>-&gt;</del><ins>.</ins>get_memory_resource()</code>. 
<p/>
-3- <i>Effects</i>: Interchanges the targets of <code>*this</code> and <code>other</code>.
<p/>
-4- <i>Remarks</i>: The allocators of <code>*this</code> and <code>other</code> are not interchanged. 
</p>
</blockquote>
</blockquote>
</li>
</ol>





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