New issue from Ian Petersen: "Missing noexcept operator in [exec.when.all]"

Author: Dani-Hub

xml/issue4227.xml

@@ -0,0 +1,72 @@
+<?xml version='1.0' encoding='utf-8' standalone='no'?>
+<!DOCTYPE issue SYSTEM "lwg-issue.dtd">
+
+<issue num="4227" status="New">
+<title>Missing `noexcept` operator in [exec.when.all]</title>
+<section>
+<sref ref="[exec.when.all]"/>
+</section>
+<submitter>Ian Petersen</submitter>
+<date>17 Mar 2025</date>
+<priority>99</priority>
+
+<discussion>
+<p>
+In <sref ref="[exec.when.all]"/> p7, the <tt><i>impls-for</i>&lt;when_all_t&gt;::<i>get-state</i></tt> 
+member is defined to be equivalent to the following lambda:
+</p>
+<blockquote><pre>
+[]&lt;class Sndr, class Rcvr&gt;(Sndr&amp;&amp; sndr, Rcvr&amp; rcvr) noexcept(<i>e</i>) -> decltype(<i>e</i>) {
+  return <i>e</i>;
+}
+</pre></blockquote>
+<p>
+and <tt><i>e</i></tt> is later defined to be:
+</p>
+<blockquote><pre>
+std::forward&lt;Sndr&gt;(sndr).apply(<i>make-state</i>&lt;Rcvr&gt;())
+</pre></blockquote>
+<p>
+Together, the two definitions imply that the `noexcept` clause on the provided lambda is:
+</p>
+<blockquote><pre>
+noexcept(std::forward&lt;Sndr&gt;(sndr).apply(<i>make-state</i>&lt;Rcvr&gt;()))
+</pre></blockquote>
+<p>
+which is invalid.
+<p/>
+Presumably, the lambda should be defined like so (with an extra `noexcept` operator in the `noexcept` clause):
+</p>
+<blockquote><pre>
+[]&lt;class Sndr, class Rcvr&gt;(Sndr&amp;&amp; sndr, Rcvr&amp; rcvr) noexcept(<ins>noexcept(</ins><i>e</i><ins>)</ins>) -&gt; decltype(<i>e</i>) {
+  return <i>e</i>;
+}
+</pre></blockquote>
+</discussion>
+
+<resolution>
+<p>
+This wording is relative to <paper num="N5008"/>.
+</p>
+
+<ol>
+
+<li><p>Modify <sref ref="[exec.when.all]"/> as indicated:</p>
+
+<blockquote>
+<p>
+-7- The member <tt><i>impls-for</i>&lt;when_all_t&gt;::<i>get-state</i></tt> is initialized with a callable object 
+equivalent to the following lambda expression:
+</p>
+<blockquote><pre>
+[]&lt;class Sndr, class Rcvr&gt;(Sndr&amp;&amp; sndr, Rcvr&amp; rcvr) noexcept(<ins>noexcept(</ins><i>e</i><ins>)</ins>) -&gt; decltype(<i>e</i>) {
+  return <i>e</i>;
+}
+</pre></blockquote>
+</blockquote>
+</li>
+
+</ol>
+</resolution>
+
+</issue>