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<title>Issue 3307: std::allocator&lt;void&gt;().allocate(n)</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++20">C++20</a> status.</em></p>
<h3 id="3307"><a href="lwg-defects.html#3307">3307</a>. <code>std::allocator&lt;void&gt;().allocate(n)</code></h3>
<p><b>Section:</b> 20.2.10 <a href="https://wg21.link/default.allocator">[default.allocator]</a> <b>Status:</b> <a href="lwg-active.html#C++20">C++20</a>
 <b>Submitter:</b> Jonathan Wakely <b>Opened:</b> 2019-10-25 <b>Last modified:</b> 2021-02-25</p>
<p><b>Priority: </b>0
</p>
<p><b>View other</b> <a href="lwg-index-open.html#default.allocator">active issues</a> in [default.allocator].</p>
<p><b>View all other</b> <a href="lwg-index.html#default.allocator">issues</a> in [default.allocator].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++20">C++20</a> status.</p>
<p><b>Discussion:</b></p>
<p>
In C++20 the <code>std::allocator&lt;void&gt;</code> explicit specialization is gone, which means it uses the 
primary template, which has allocate and deallocate members.
<p/>
Although it's implied by the use of <code>sizeof(T)</code>, <code>std::allocator&lt;T&gt;::allocate</code> 
doesn't have an explicit precondition that the value type is complete.
</p>

<p><i>[2019-11 Status to 'Ready' in Monday issue prioritization in Belfast]</i></p>



<p id="res-3307"><b>Proposed resolution:</b></p>
<p>This wording is relative to <a href="https://wg21.link/n4835">N4835</a>.</p>

<ol>
<li><p>Modify 20.2.10.2 <a href="https://wg21.link/allocator.members">[allocator.members]</a> as indicated:</p>

<blockquote>
<pre>
[[nodiscard]] constexpr T* allocate(size_t n);
</pre>
<p>
<ins>-?- <i>Mandates:</i> <code>T</code> is not an incomplete type (6.9 <a href="https://wg21.link/basic.types">[basic.types]</a>).</ins>
<p/>
-2- <i>Returns:</i> A pointer to the initial element of an array of storage of size 
<code>n * sizeof(T)</code>, aligned appropriately for objects of type <code>T</code>.
<p/>
[&hellip;]
</p>
</blockquote>
</li>
</ol>





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