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<title>Issue 4356: connect() should use get_allocator(get_env(rcvr)) to allocate the coroutine-state for a 
connect-awaitable coroutine</title>
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connect-awaitable coroutine">
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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#New">New</a> status.</em></p>
<h3 id="4356"><a href="lwg-active.html#4356">4356</a>. <code class='backtick'>connect()</code> should use <code class='backtick'>get_allocator(get_env(rcvr))</code> to allocate the coroutine-state for a 
<code><i>connect-awaitable</i></code> coroutine</h3>
<p><b>Section:</b> 33.9.10 <a href="https://wg21.link/exec.connect">[exec.connect]</a> <b>Status:</b> <a href="lwg-active.html#New">New</a>
 <b>Submitter:</b> Lewis Baker <b>Opened:</b> 2025-08-27 <b>Last modified:</b> 2025-09-14</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View other</b> <a href="lwg-index-open.html#exec.connect">active issues</a> in [exec.connect].</p>
<p><b>View all other</b> <a href="lwg-index.html#exec.connect">issues</a> in [exec.connect].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#New">New</a> status.</p>
<p><b>Discussion:</b></p>
<p>
The wording for <code class='backtick'>connect()</code> (33.9.10 <a href="https://wg21.link/exec.connect">[exec.connect]</a>) handles passing awaitable types as the sender argument 
by calling the <code><i>connect-awaitable</i></code>() coroutine and having it execute a <code class='backtick'>co_await</code> expression.
<p/>
The <code><i>connect-awaitable</i></code>() coroutine will typically need to dynamically allocate storage for 
the coroutine state and, as specified, this currently just always uses the global default allocator.
This is because the <code><i>connect-awaitable-promise</i></code> type does not define any member operator 
<code class='backtick'>new/delete</code> overloads.
<p/>
It seems desirable for this facility to use the allocator obtained from the receiver, by calling 
<code class='backtick'>get_allocator(get_env(rcvr))</code>, in order to allocate storage for the coroutine-state instead of always 
using global operator <code class='backtick'>new</code>. This would give the user at least some level of control over how this 
allocation is performed.
</p>


<p id="res-4356"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/N5014">N5014</a>.
</p>

<ol>

<li><p>Modify 33.9.10 <a href="https://wg21.link/exec.connect">[exec.connect]</a> as indicated:</p>

<blockquote class="note">
<p>
[<i>Drafting note: </i> This should cover the design intent, although we may want to spell this out 
more explicitly in terms of the exact semantics in a similar way to 25.8.5 <a href="https://wg21.link/coro.generator.promise">[coro.generator.promise]</a> p17, 
which lists overloads of operator <code class='backtick'>new()</code> and describes the rebound allocator type which allocates storage 
in chunks of size <code class='backtick'>__STDCPP_DEFAULT_NEW_ALIGNMENT__</code>.]
</p>
</blockquote>

<blockquote>
<p>
-5- Let <code class='backtick'>V</code> name the type <code><i>await-result-type</i>&lt;DS, <i>connect-awaitable-promise</i>&gt;</code>, 
let <code class='backtick'>Sigs</code> name the type
</p>
<blockquote><pre>
[&hellip;]
</pre></blockquote>
<p>
and let <code><i>connect-awaitable</i></code> be an exposition-only coroutine defined as follows:
</p>
<blockquote><pre>
namespace std::execution {
  [&hellip;]
}  
</pre></blockquote>
<p>
<ins>Any dynamically allocated storage required for the coroutine state allocated by an invocation 
of the form <code><i>connect-awaitable</i>(sndr, rcvr)</code> is allocated using the allocator obtained 
from <code class='backtick'>get_allocator(get_env(rcvr))</code>.</ins>
<p/>
-6- [&hellip;]
</p>
</blockquote>

</li>

</ol>





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