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<title>Issue 4360: awaitable-sender concept should qualify use of awaitable-receiver type</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#New">New</a> status.</em></p>
<h3 id="4360"><a href="lwg-active.html#4360">4360</a>. <code><i>awaitable-sender</i></code> concept should qualify use of <code><i>awaitable-receiver</i></code> type</h3>
<p><b>Section:</b> 33.13.1 <a href="https://wg21.link/exec.as.awaitable">[exec.as.awaitable]</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.as.awaitable">active issues</a> in [exec.as.awaitable].</p>
<p><b>View all other</b> <a href="lwg-index.html#exec.as.awaitable">issues</a> in [exec.as.awaitable].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#New">New</a> status.</p>
<p><b>Discussion:</b></p>
<p>
In 33.13.1 <a href="https://wg21.link/exec.as.awaitable">[exec.as.awaitable]</a> p1 there is an exposition-only helper concept 
<code><i>awaitable-sender</i></code> defined as follows:
</p>
<blockquote><pre>
namespace std::execution {
  template&lt;class Sndr, class Promise&gt;
    concept <i>awaitable-sender</i> =
      <i>single-sender</i>&lt;Sndr, env_of_t&lt;Promise&gt;&gt; &amp;&amp;
      sender_to&lt;Sndr, <i>awaitable-receiver</i>&gt; &amp;&amp; // <i>see below</i>
      requires (Promise&amp; p) {
        { p.unhandled_stopped() } -> convertible_to&lt;coroutine_handle&lt;&gt;&gt;;
      };
}
</pre></blockquote>
<p>
The mention of the type <code><i>awaitable-receiver</i></code> here does not refer to any exposition-only type 
defined at namespace-scope. It seems to, instead, be referring to the nested member-type 
<code><i>sender-awaitable</i>&lt;Sndr, Promise&gt;::<i>awaitable-receiver</i></code> and so should be 
qualified as such.
</p>


<p id="res-4360"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/N5014">N5014</a>.
</p>

<ol>

<li><p>Modify 33.13.1 <a href="https://wg21.link/exec.as.awaitable">[exec.as.awaitable]</a> as indicated:</p>

<blockquote>
<p>
-1- <code class='backtick'>as_awaitable</code> transforms an object into one that is awaitable within a particular coroutine. 
Subclause 33.13 <a href="https://wg21.link/exec.coro.util">[exec.coro.util]</a> makes use of the following exposition-only entities:
</p>
<blockquote><pre>
namespace std::execution {
  template&lt;class Sndr, class Promise&gt;
    concept <i>awaitable-sender</i> =
      <i>single-sender</i>&lt;Sndr, env_of_t&lt;Promise&gt;&gt; &amp;&amp;
      sender_to&lt;Sndr, <ins>typename <i>sender-awaitable</i>&lt;Sndr, Promise&gt;::</ins><i>awaitable-receiver</i>&gt; &amp;&amp; // <i>see below</i>
      requires (Promise&amp; p) {
        { p.unhandled_stopped() } -> convertible_to&lt;coroutine_handle&lt;&gt;&gt;;
      };
  [&hellip;]
}
</pre></blockquote>
</blockquote>

</li>

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