New P/R for 4460

Author: jwakely

xml/issue4460.xml

@@ -23,9 +23,55 @@ Note how in R0 neither one of the `emplaced_type_t`/`emplaced_index_t`
 (as they were then called) + `initializer_list` constructors have a
 throws clause. In R1 only one of them gained it."
 </blockquote>
+<superseded>
+<p>
+This wording is relative to <paper num="N5014"/>.
+</p>
+
+<ol>
+<li><p>Modify <sref ref="[variant.ctor]"/>, as indicated:</p>
+
+<blockquote>
+<pre>
+template&lt;size_t I, class U, class... Args&gt;
+  constexpr explicit variant(in_place_index_t&lt;I&gt;, initializer_list&lt;U&gt; il, Args&amp;&amp;... args);
+</pre>
+<blockquote>
+<p>-35- <i>Constraints</i>:
+<ol style="list-style-type: none">
+<li>(35.1) &mdash; `I` is less than `sizeof...(Types)` and</li>
+<li>(35.2) &mdash;
+<code>is_constructible_v&lt;T<sub>I</sub>, initializer_list&lt;U&gt;&amp;, Args...&gt;</code>
+is `true`.
+</li>
+</ol>
+</p>
+<p>-36- <i>Effects</i>:
+Direct-non-list-initializes the contained value of type
+<tt>T<sub>I</sub></tt> with <code>il, std::forward&lt;Args&gt;(args)...</code>.
+</p>
+<p>-37- <i>Postconditions</i>: `index()` is `I`.</p>
+<p><ins>-?- <i>Throws</i>:
+Any exception thrown by calling the selected constructor of
+<tt>T<sub>I</sub></tt>.
+</ins>
+</p>
+<p>-38- <i>Remarks</i>:
+If <tt>T<sub>I</sub></tt>’s selected constructor is a constexpr constructor,
+this constructor is a constexpr constructor.
+</p>
+</blockquote>
+</blockquote>
+</li>
+</ol>
+</superseded>
+
+<note>2025-11-11; Jonathan provides improved wording</note>
+
 </discussion>
 
 <resolution>
+
 <p>
 This wording is relative to <paper num="N5014"/>.
 </p>
@@ -34,6 +80,176 @@ This wording is relative to <paper num="N5014"/>.
 <li><p>Modify <sref ref="[variant.ctor]"/>, as indicated:</p>
 
 <blockquote>
+<pre>
+constexpr variant() noexcept(<i>see below</i>);
+</pre>
+<blockquote>
+<p>-2- <i>Constraints</i>:
+<code>is_default_constructible_v&lt;T<sub>0</sub>&gt;</code> is `true`.
+</p>
+<p>-3- <i>Effects</i>:
+Constructs a `variant` holding a value-initialized value of type <tt>T<sub>0</sub></tt>.
+</p>
+<p>-4- <i>Postconditions</i>:
+`valueless_by_exception()` is `false` and `index()` is `0`.
+</p>
+<p>-5- <i>Throws</i>:
+Any exception thrown by the value-initialization of <tt>T<sub>0</sub></tt>.
+</p>
+<p>-6- <i>Remarks</i>: [&hellip;]
+</p>
+</blockquote>
+
+<pre>
+constexpr variant(const variant&amp;);
+</pre>
+<blockquote>
+<p>-7- <i>Effects</i>:
+If `w` holds a value, initializes the `variant` to hold the same alternative
+as `w` and direct-initializes the contained value with
+<code><i>GET</i>&lt;j&gt;(w)</code>, where `j` is `w.index()`.
+Otherwise, initializes the `variant` to not hold a value.
+</p>
+<p>-8- <i>Throws</i>:
+Any exception thrown by
+<del>direct-initializating any <tt>T<sub>i</sub></tt> for all <i>i</i></del>
+<ins>the initialization of the contained value</ins>.
+</p>
+<p>-9- <i>Remarks</i>: [&hellip;]
+</p>
+</blockquote>
+
+<pre>
+constexpr variant(variant&amp;&amp;) noexcept(<i>see below</i>);
+</pre>
+<blockquote>
+<p>-10- <i>Constraints</i>:
+<code>is_move_constructible_v&lt;T<sub>i</sub>&gt;</code> is `true`
+for all <i>i</i>.
+</p>
+<p>-11- <i>Effects</i>:
+If `w` holds a value, initializes the `variant` to hold the same alternative
+as `w` and direct-initializes the contained value with
+<code><i>GET</i>&lt;j&gt;(std::move(w))</code>, where `j` is `w.index()`.
+Otherwise, initializes the `variant` to not hold a value.
+</p>
+<p>-12- <i>Throws</i>:
+Any exception thrown by
+<del>move-constructing any <tt>T<sub>i</sub></tt> for all <i>i</i></del>
+<ins>the initialization of the contained value</ins>.
+</p>
+<p>-13- <i>Remarks</i>: [&hellip;]
+</p>
+</blockquote>
+
+<pre>
+template&lt;class T&gt; constexpr variant(T&amp;&amp;) noexcept(<i>see below</i>);
+</pre>
+<blockquote>
+<p>-14-
+Let <tt>T<sub>j</sub></tt> be a type that is determined as follows:
+build an imaginary function <tt><i>FUN</i>(T<sub>i</sub>)</tt>
+for each alternative type <tt>T<sub>i</sub></tt>
+for which <tt>T<sub>i</sub> x[] = {std::forward&lt;T&gt;(t)};</tt>
+is well-formed for some invented variable `x`.
+The overload <tt><i>FUN</i>(T<sub>j</sub>)</tt> selected by overload resolution
+for the expression <tt><i>FUN</i>(std::forward&lt;T&gt;(t))</tt> defines
+the alternative <tt>T<sub>j</sub></tt> which is the type
+of the contained value after construction.
+</p>
+<p>-15- <i>Constraints</i>: [&hellip;]
+</p>
+<p>-16- <i>Effects</i>:
+Initializes `*this` to hold the alternative type <tt>T<sub>j</sub></tt>
+and direct-non-list-initializes the contained value with
+<code>std::forward&lt;T&gt;(t)</code>.
+</p>
+<p>-17- <i>Postconditions</i>: [&hellip;]
+</p>
+<p>-18- <i>Throws</i>:
+Any exception thrown by the initialization of the
+<del>selected alternative <tt>T<sub>j</sub></tt></del>
+<ins>contained value</ins>.
+</p>
+<p>-19- <i>Remarks</i>: [&hellip;]
+</p>
+</blockquote>
+
+<pre>
+template&lt;class T, class... Args&gt; constexpr variant(in_place_type_t&lt;T&gt;, Args&amp;&amp;... args);
+</pre>
+<blockquote>
+<p>-20- <i>Constraints</i>: [&hellip;]
+</p>
+<p>-21- <i>Effects</i>:
+Direct-non-list-initializes the contained value of type `T`
+with
+<code>std::forward&lt;Args&gt;(args)...</code>.
+</p>
+<p>-22- <i>Postconditions</i>: [&hellip;]
+</p>
+<p>-23- <i>Throws</i>:
+Any exception thrown by
+<del>the selected constructor of `T`</del>
+<ins>the initialization of the contained value</ins>.
+</p>
+<p>-24- <i>Remarks</i>: [&hellip;]
+</p>
+</blockquote>
+
+<pre>
+template&lt;class T, class U, class... Args&gt;
+  constexpr variant(in_place_type_t&lt;T&gt;, initializer_list&lt;U&gt; li, Args&amp;&amp;... args);
+</pre>
+<blockquote>
+<p>-25- <i>Constraints</i>: [&hellip;]
+</p>
+<p>-26- <i>Effects</i>:
+Direct-non-list-initializes the contained value of type `T`
+with
+<code>il, std::forward&lt;Args&gt;(args)...</code>.
+</p>
+<p>-27- <i>Postconditions</i>: [&hellip;]
+</p>
+<p>-28- <i>Throws</i>:
+Any exception thrown by
+<del>the selected constructor of `T`</del>
+<ins>the initialization of the contained value</ins>.
+</p>
+<p>-29- <i>Remarks</i>: [&hellip;]
+</p>
+</blockquote>
+
+<pre>
+template&lt;size_t I, class... Args&gt;
+  constexpr explicit variant(in_place_index_t&lt;I&gt;, Args&amp;&amp;... args);
+</pre>
+<blockquote>
+<p>-30- <i>Constraints</i>:
+<ol style="list-style-type: none">
+<li>(30.1) &mdash; `I` is less than `sizeof...(Types)` and</li>
+<li>(30.2) &mdash;
+<code>is_constructible_v&lt;T<sub>I</sub>, Args...&gt;</code>
+is `true`.
+</li>
+</ol>
+</p>
+<p>-31- <i>Effects</i>:
+Direct-non-list-initializes the contained value of type
+<tt>T<sub>I</sub></tt> with <code>std::forward&lt;Args&gt;(args)...</code>.
+</p>
+<p>-32- <i>Postconditions</i>: `index()` is `I`.</p>
+<p>-33- <i>Throws</i>:
+Any exception thrown by
+<del>the selected constructor of <tt>T<sub>i</sub></tt></del>
+<ins>the initialization of the contained value</ins>.
+</p>
+<p>-34- <i>Remarks</i>:
+If <tt>T<sub>I</sub></tt>’s selected constructor is a constexpr constructor,
+this constructor is a constexpr constructor.
+</p>
+</blockquote>
+
 <pre>
 template&lt;size_t I, class U, class... Args&gt;
   constexpr explicit variant(in_place_index_t&lt;I&gt;, initializer_list&lt;U&gt; il, Args&amp;&amp;... args);
@@ -54,8 +270,7 @@ Direct-non-list-initializes the contained value of type
 </p>
 <p>-37- <i>Postconditions</i>: `index()` is `I`.</p>
 <p><ins>-?- <i>Throws</i>:
-Any exception thrown by calling the selected constructor of
-<tt>T<sub>I</sub></tt>.
+Any exception thrown by the initialization of the contained value.
 </ins>
 </p>
 <p>-38- <i>Remarks</i>:
@@ -66,6 +281,7 @@ this constructor is a constexpr constructor.
 </blockquote>
 </li>
 </ol>
+
 </resolution>
 
 </issue>