New issue from Jiang An: "Move assignment operator of std::expected<cv void, E> should not be conditionally deleted"

Author: Dani-Hub

xml/issue4025.xml

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+<?xml version='1.0' encoding='utf-8' standalone='no'?>
+<!DOCTYPE issue SYSTEM "lwg-issue.dtd">
+
+<issue num="4025" status="New">
+<title>Move assignment operator of <tt>std::expected&lt;<i>cv</i> void, E&gt;</tt> should not be conditionally deleted</title>
+<section><sref ref="[expected.void.assign]"/></section>
+<submitter>Jiang An</submitter>
+<date>16 Dec 2023</date>
+<priority>99</priority>
+
+<discussion>
+<p>
+It seems intended that copy functions of <tt>std::optional</tt>, <tt>std::variant</tt>, and <tt>std::expected</tt> 
+are conditionally deleted, while move functions are constrained. However, the move assignment operator of 
+<tt>std::expected&lt;<i>cv</i> void, E&gt;</tt> is currently conditionally deleted, which is inconsistent.
+</p>
+</discussion>
+
+<resolution>
+<p>
+This wording is relative to <paper num="N4971"/>.
+</p>
+
+<ol>
+
+<li><p>Modify <sref ref="[expected.void.assign]"/> as indicated:</p>
+
+<blockquote>
+<pre>
+constexpr expected&amp; operator=(expected&amp;&amp; rhs) noexcept(<i>see below</i>);
+</pre>
+<blockquote>
+<p>
+<ins>-?- <i>Constraints</i>: <tt>is_move_constructible_v&lt;E&gt;</tt> is <tt>true</tt> and 
+<tt>is_move_assignable_v&lt;E&gt;</tt> is <tt>true</tt>.</ins>
+<p/>
+[&hellip;]
+<p/>
+-6- <i>Remarks</i>: The exception specification is equivalent to <tt>is_nothrow_move_constructible_v&lt;E&gt; &amp;&amp;
+is_nothrow_move_assignable_v&lt;E&gt;</tt>.
+<p/>
+<del>-7- This operator is defined as deleted unless <tt>is_move_constructible_v&lt;E&gt;</tt> is <tt>true</tt> 
+and <tt>is_move_assignable_v&lt;E&gt;</tt> is <tt>true</tt>.</del>
+</p>
+</blockquote>
+</blockquote>
+</li>
+
+</ol>
+
+
+</resolution>
+
+</issue>