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<title>Issue 4359: as_awaitable(expr, p) does not define semantics of call if p is not an lvalue</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="4359"><a href="lwg-active.html#4359">4359</a>. <code class='backtick'>as_awaitable(expr, p)</code> does not define semantics of call if <code class='backtick'>p</code> is not an lvalue</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> 2025-09-17</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>
The wording in 33.13.1 <a href="https://wg21.link/exec.as.awaitable">[exec.as.awaitable]</a> p7 defines the semantics of a call to <code class='backtick'>as_awaitable(expr, p)</code> 
where <code class='backtick'>p</code> is an lvalue. However, it does not specify what the behaviour is if <code class='backtick'>p</code> is not an lvalue.
<p/>
We should probably say that <code class='backtick'>as_awaitable(expr, p)</code> is ill-formed if <code class='backtick'>p</code> is not an lvalue.
</p>



<p id="res-4359"><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>
-7- <code class='backtick'>as_awaitable</code> is a customization point object. For subexpressions <code class='backtick'>expr</code> and <code class='backtick'>p</code> where <del><code class='backtick'>p</code> 
is an lvalue,</del> <code class='backtick'>Expr</code> names the type <code class='backtick'>decltype((expr))</code> and <code class='backtick'>Promise</code> names the type 
<code>decay_t&lt;decltype((p))&gt;</code>, <ins>if <code class='backtick'>p</code> is not an lvalue, <code class='backtick'>as_awaitable(expr, p)</code> is 
ill-formed, otherwise</ins> <code class='backtick'>as_awaitable(expr, p)</code> is expression-equivalent to, 
except that the evaluations of <code class='backtick'>expr</code> and <code class='backtick'>p</code> are indeterminately sequenced:
</p>
</blockquote>

</li>

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