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<title>Issue 3649: [fund.ts.v3] Reinstate and bump __cpp_lib_experimental_memory_resource feature test macro</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="3649"><a href="lwg-defects.html#3649">3649</a>. [fund.ts.v3] Reinstate and bump <code>__cpp_lib_experimental_memory_resource</code> feature test macro</h3>
<p><b>Section:</b> 4.2 <a href="https://cplusplus.github.io/fundamentals-ts/v3.html#general.feature.test">[fund.ts.v3::general.feature.test]</a> <b>Status:</b> <a href="lwg-active.html#TS">TS</a>
 <b>Submitter:</b> Thomas K&ouml;ppe <b>Opened:</b> 2021-12-03 <b>Last modified:</b> 2022-07-11</p>
<p><b>Priority: </b>Not Prioritized
</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.v3</b></p>
<p>
The rebase on C++17 in <a href="https://wg21.link/P0996" title=" Rebase Library Fundamentals TS on C++17">P0996</a> had the effect of deleting the feature test macro 
<code>__cpp_lib_experimental_memory_resource</code>: the macro was ostensibly tied to the 
<code>memory_resource</code> facility that had become part of C++17, but we overlooked that there 
was a residual piece that has not been adopted in the IS, namely the <code>resource_adaptor</code> 
class template.
<p/>
It is still useful to be able to detect the presence of <code>resource_adaptor</code>, so we should 
reinstate the feature test macro and bump its value.
</p>

<p><i>[2022-01-30; Reflector poll]</i></p>

<p>
Set status to Tentatively Ready after six votes in favour during reflector poll.
</p>

<p><i>[2022-07-11 Approved at February 2022 virtual plenary. Status changed: Tentatively Ready &rarr; TS.]</i></p>



<p id="res-3649"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/N4853" title=" Working Draft, C++ Extensions for Library Fundamentals, Version 3">N4853</a>.
</p>

<ol>

<li><p>Modify 4.2 <a href="https://cplusplus.github.io/fundamentals-ts/v3.html#general.feature.test">[fund.ts.v3::general.feature.test]</a>, Table 2, as indicated:</p>

<blockquote>
<table border="1">
<caption>Table 2 &mdash; Significant features in this technical specification</caption>
<tr style="text-align:center">
<th>Doc. No.</th>
<th>Title</th>
<th>Primary<br/>Section</th>
<th>Macro Name Suffix</th>
<th>Value</th>
<th>Header</th>
</tr>
<tr>
<td colspan="6" align="center">
<code>&hellip;</code>
</td>
</tr>

<tr>
<td>N3916</td>
<td>Type-erased allocator for std::function</td>
<td>4.2</td>
<td><code>function_erased_allocator</code></td>
<td><code>201406</code></td>
<td><code>&lt;experimental/functional&gt;</code></td>
</tr>

<tr>
<td><ins>N3916</ins></td>
<td><ins>Polymorphic Memory Resources</ins></td>
<td><ins>8.3 <a href="https://cplusplus.github.io/fundamentals-ts/v3.html#memory.resource.syn">[fund.ts.v3::memory.resource.syn]</a></ins></td>
<td><ins><code>memory_resources</code></ins></td>
<td><ins><i>[new value]</i></ins></td>
<td><ins><code>&lt;experimental/memory_resource&gt;</code></ins></td>
</tr>

<tr>
<td>N4282</td>
<td>The World's Dumbest Smart Pointer</td>
<td>8.12</td>
<td><code>observer_ptr</code></td>
<td><code>201411</code></td>
<td><code>&lt;experimental/memory&gt;</code></td>
</tr>

<tr>
<td colspan="6" align="center">
<code>&hellip;</code>
</td>
</tr>
</table>
</blockquote>
</li>

</ol>





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