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<title>Issue 4357: connect-awaitable should use is_void_v to check for result-type of 
co_await expression instead of same_as&lt;void&gt;</title>
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co_await expression instead of same_as&lt;void&gt;">
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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="4357"><a href="lwg-active.html#4357">4357</a>. <code><i>connect-awaitable</i></code> should use <code class='backtick'>is_void_v</code> to check for result-type of 
<code class='backtick'>co_await</code> expression instead of <code>same_as&lt;void&gt;</code></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 in 33.9.10 <a href="https://wg21.link/exec.connect">[exec.connect]</a> p5 defines the <code><i>connect-awaitable</i>()</code> function as follows:
</p>
<blockquote><pre>
<i>operation-state-task</i> <i>connect-awaitable</i>(DS sndr, DR rcvr) requires receiver_of&lt;DR, Sigs&gt; {
  exception_ptr ep;
  try {
    if constexpr (same_as&lt;V, void&gt;) {
      co_await std::move(sndr);
      co_await <i>suspend-complete</i>(set_value, std::move(rcvr));
    } else {
      co_await <i>suspend-complete</i>(set_value, std::move(rcvr), co_await std::move(sndr));
    }
  } catch(...) {
    ep = current_exception();
  }
  co_await <i>suspend-complete</i>(set_error, std::move(rcvr), std::move(ep));
}
</pre></blockquote>
<p>
The use of <code>same_as&lt;V, void&gt;</code> in the if-constexpr condition does not cover the case where the 
result of the <code class='backtick'>co_await</code> expression has type <i>cv</i> <code class='backtick'>void</code>. It should use <code>is_void_v&lt;V&gt;</code> 
instead to allow it to match all <code class='backtick'>void</code> types, not just unqualified <code class='backtick'>void</code>.
</p>



<p id="res-4357"><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>
<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>
completion_signatures&lt;
  <i>SET-VALUE-SIG</i>(V), // <i>see 33.9.3 <a href="https://wg21.link/exec.snd.concepts">[exec.snd.concepts]</a></i>
  set_error_t(exception_ptr),
  set_stopped_t()&gt;
</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;]
  <i>operation-state-task</i> <i>connect-awaitable</i>(DS sndr, DR rcvr) requires receiver_of&lt;DR, Sigs&gt; {
    exception_ptr ep;
    try {
      if constexpr (<del>same_as&lt;V, void&gt;</del><ins>is_void_v&lt;V&gt;</ins>) {
        co_await std::move(sndr);
        co_await <i>suspend-complete</i>(set_value, std::move(rcvr));
      } else {
        co_await <i>suspend-complete</i>(set_value, std::move(rcvr), co_await std::move(sndr));
      }
    } catch(...) {
      ep = current_exception();
    }
    co_await <i>suspend-complete</i>(set_error, std::move(rcvr), std::move(ep));
  }
}  
</pre></blockquote>
</blockquote>

</li>

</ol>





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