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New issue to address US 161-258: ranges::rotate do not handle sized-but-not-sized-sentinel ranges correctly #508

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jwakely merged 4 commits into from
Nov 4, 2025
Merged

New issue to address US 161-258: ranges::rotate do not handle sized-but-not-sized-sentinel ranges correctly #508

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4cd438d
New issue to address US 161-258: ranges::rotate do not handle sized-b…
tomaszkam Nov 3, 2025
f122fa9
Updates P/R for 4316, following reflector discussion
tomaszkam Nov 3, 2025
aaa76fc
Updates P/R for 4251, covering polymorphic
tomaszkam Nov 3, 2025
e8c8f82
Fix working paper number in 4251
jwakely Nov 4, 2025
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157 changes: 153 additions & 4 deletions xml/issue4251.xml
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Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,10 @@

<issue num="4251" status="New">
<title>Move assignment for `indirect` unnecessarily requires copy construction</title>
<section><sref ref="[indirect.asgn]"/></section>
<section>
<sref ref="[indirect.assign]"/>
<sref ref="[polymorphic.assign]"/>
</section>
<submitter>Jonathan Wakely</submitter>
<date>01 May 2025</date>
<priority>1</priority>
Expand Down Expand Up @@ -46,15 +49,14 @@ Set priority to 1 after reflector poll.
Similar change needed for `std::polymorphic`.
</p>

</discussion>

<resolution>
<superseded>
<p>
This wording is relative to <paper num="N5008"/>.
</p>
<ol>

<li><p>Modify <sref ref="[indirect.asgn]"/> as indicated:</p>
<li><p>Modify <sref ref="[indirect.assign]"/> as indicated:</p>
<blockquote>
<pre><code>
constexpr indirect&amp; operator=(indirect&amp;&amp; other)
Expand Down Expand Up @@ -122,6 +124,153 @@ the allocator in `*this` is replaced with a copy of the allocator in `other`.
</blockquote>
</blockquote>
</li>
</ol>
</superseded>

<note>2025-11-03; Tomasz provides wording.</note>
</discussion>

<resolution>
<p>
This wording is relative to <paper num="N5008"/>.
</p>
<ol>

<li><p>Modify <sref ref="[indirect.assign]"/> as indicated:</p>
<blockquote>
<pre><code>
constexpr indirect&amp; operator=(indirect&amp;&amp; other)
noexcept(allocator_traits&lt;Allocator&gt;::propagate_on_container_move_assignment::value ||
allocator_traits&lt;Allocator&gt;::is_always_equal::value);
</code></pre>
<blockquote>
<p>
-5- <i>Mandates</i>:
<ins>
If
<code>allocator_traits&lt;Allocator&gt;::propagate_on_container_move_assignment::value</code>
is `false`
and
<code>allocator_traits&lt;Allocator&gt;::is_always_equal::value</code>
is `false`,
</ins>
<code>is_<del>copy</del><ins>move</ins>_constructible_t&lt;T&gt;</code> is `true`.
</p>
<p>
-6- <i>Effects</i>:
If `addressof(other) == this` is `true`, there are no effects.
Otherwise:
<ol style="list-style-type:none">
<li>(6.1) &mdash;
The allocator needs updating if
<code>allocator_traits&lt;Allocator&gt;::propagate_on_container_move_assignment::value</code>
is `true`.
</li>
<li>(6.2) &mdash;
If `other` is valueless, `*this` becomes valueless<del> and the owned object
in `*this`, if any, is destroyed using
<code>allocator_traits&lt;Allocator&gt;::destroy</code>
and then the storage is deallocated</del>.
</li>
<li>(6.3) &mdash;
Otherwise,
<ins>if the allocator needs updating or</ins>
if <code><i>alloc</i> == other.<i>alloc</i></code> is `true`,
<del>
swaps the owned objects in `*this` and `other`;
the owned object in `other`, if any, is then destroyed using
<code>allocator_traits&lt;Allocator&gt;::destroy</code>
and then the storage is deallocated
</del>
<ins>`*this` takes ownership of the owned object of `other`</ins>.
</li>
<li>(6.4) &mdash;
Otherwise, constructs a new owned object with the owned object of `other`
as the argument as an rvalue, using <del>either</del> the allocator in `*this`
<del>or the allocator in `other` if the allocator needs updating</del>.
</li>
<li>(6.5) &mdash;
The previously owned object in `*this`, if any, is destroyed using
<code>allocator_traits&lt;Allocator&gt;::destroy</code>
and then the storage is deallocated.
</li>
<li>(6.6) &mdash;
If the allocator needs updating,
the allocator in `*this` is replaced with a copy of the allocator in `other`.
</li>
</ol>
</p>
<p>-7- <i>Postcondition</i>: `other` is valueless.</p>
</blockquote>
</blockquote>
</li>

<li><p>Modify <sref ref="[polymorphic.assign]"/> as indicated:</p>
<blockquote>
<pre><code>
constexpr polymorphic&amp; operator=(polymorphic&amp;&amp; other)
noexcept(allocator_traits&lt;Allocator&gt;::propagate_on_container_move_assignment::value ||
allocator_traits&lt;Allocator&gt;::is_always_equal::value);
</code></pre>
<blockquote>
<p>
-5- <i>Mandates</i>:
If
<ins>
<code>allocator_traits&lt;Allocator&gt;::propagate_on_container_move_assignment::value</code>
is `false`
and
</ins>
<code>allocator_traits&lt;Allocator&gt;::is_always_equal::value</code>
is `false`,
`T` is complete type.
</p>
<p>
-6- <i>Effects</i>:
If `addressof(other) == this` is `true`, there are no effects.
Otherwise:
<ol style="list-style-type:none">
<li>(6.1) &mdash;
The allocator needs updating if
<code>allocator_traits&lt;Allocator&gt;::propagate_on_container_move_assignment::value</code>
is `true`.
</li>
<li><ins>(6.?) &mdash; If `other` is valueless, `*this` becomes valueless.</ins></li>
<li>(6.2) &mdash;
<ins>Otherwise, if the allocator needs updating or</ins><del>If</del>
<code><i>alloc</i> == other.<i>alloc</i></code> is `true`,
<del>
swaps the owned objects in `*this` and `other`;
the owned object in `other`, if any, is then destroyed using
<code>allocator_traits&lt;Allocator&gt;::destroy</code>
and then the storage is deallocated
</del>
<ins>`*this` takes ownership of the owned object of `other`</ins>.
</li>
<li>(6.3) &mdash;
<del>Otherwise, if `alloc != other.alloc` is `true`; if `other` is not valueless,
a new owned object is constructed in `*this` using <tt>allocator_traits::construct</tt>
with the owned object from</del>
<ins>Otherwise, constructs a new owned object with the owned object of</ins>
`other` as the argument as an rvalue, using <del>either</del> the allocator in `*this`
<del>or the allocator in `other` if the allocator needs updating</del>.
</li>
<li>(6.4) &mdash;
The previously owned object in `*this`, if any, is destroyed using
<code>allocator_traits&lt;Allocator&gt;::destroy</code>
and then the storage is deallocated.
</li>
<li>(6.5) &mdash;
If the allocator needs updating,
the allocator in `*this` is replaced with a copy of the allocator in `other`.
</li>
</ol>
</p>
[&hellip;]
</blockquote>
</blockquote>
</li>

</ol>
</resolution>

Expand Down
87 changes: 84 additions & 3 deletions xml/issue4316.xml
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Original file line number Diff line number Diff line change
Expand Up @@ -43,9 +43,7 @@ Set priority to 1 after reflector poll.
</p>

<note>2025-10-27; Tomasz provides wording.</note>
</discussion>

<resolution>
<superseded>

<p>
This wording is relative to <paper num="N5014"/>.
Expand Down Expand Up @@ -126,6 +124,89 @@ context, the program is ill-formed. &mdash; <i>end note</i>]
</li>
</ol>

</superseded>

<note>2025-10-27; Reflector comments.</note>
<p>
We lost definition of `Z`. Use <tt><i>TARG-SPLICE</i>([:Args:])...</tt>.
</p>

<note>2025-11-03; Tomasz provides wording.</note>
</discussion>

<resolution>

<p>
This wording is relative to <paper num="N5014"/>.
</p>

<ol>

<li><p>Modify <sref ref="[meta.reflection.substitute]"/> as indicated:</p>

<blockquote>
<blockquote>
<p>
<ins>-1- For value `x` of type `info`, and prvalue constant expression `X` that computes the
reflection held by `x`, let <tt><i>TARG-SPLICE</i>(x)</tt> be:</ins>
<ul>
<li><ins>-1.1- <tt>template [: X :]</tt> if `is_template(x)` is `true`, otherwise</ins></li>
<li><ins>-1.2- <tt>typename [: X :]</tt> if `is_type(x)` is `true`, otherwise</ins></li>
<li><ins>-1.3- <tt>([: X :])</tt></ins></li>
</ul>
</p>
</blockquote>

<pre>
template&lt;reflection_range R = initializer_list&lt;info&gt;&gt;
consteval bool can_substitute(info templ, R&amp;&amp; arguments);
</pre>
<blockquote>
<p>
-1- Let `Z` be the template represented by `templ` and let `Args...` be a
sequence of prvalue constant expressions that compute the reflections held by
the elements of `arguments`, in order.
</p>
<p>
-2- <i>Returns</i>: `true` if <tt>Z&lt;<ins><i>TARG-SPLICE</i>(</ins>[:Args:]<ins>)</ins>...&gt;</tt> is a valid <i>template-id</i>
(<sref ref="[temp.names]"/>) that does not name a function whose type contains an undeduced placeholder type.
Otherwise, `false`.
</p>
<p>
-3- <i>Throws</i>: `meta::exception` unless `templ` represents a template, and every reflection
in `arguments` represents a construct usable as a template argument (<sref ref="[temp.arg]"/>).
</p>
<p>
-4- [<i>Note</i>: If forming <tt>Z&lt;<ins><i>TARG-SPLICE</i>(</ins>[:Args:]<ins>)</ins>...&gt;</tt>
leads to a failure outside of the immediate context, the program is ill-formed. &mdash; <i>end note</i>]
</p>
</blockquote>

<pre>
template&lt;reflection_range R = initializer_list&lt;info&gt;&gt;
consteval info substitute(info templ, R&amp;&amp; arguments);
</pre>
<blockquote>
<p>
-5- Let `Z` be the template represented by `templ` and let `Args...` be a
sequence of prvalue constant expressions that compute the reflections held by
the elements of `arguments`, in order.
</p>
<p>
-6- <i>Returns</i>: <tt>Z&lt;<ins><i>TARG-SPLICE</i>(</ins>[:Args:]<ins>)</ins>...&gt;</tt>.</p>
<p>
-7- <i>Throws</i>: `meta::exception` unless `can_substitute(templ, arguments)` is `true`.
</p>
<p>
-8- [<i>Note</i>: If forming <tt>Z&lt;<ins><i>TARG-SPLICE</i>(</ins>[:Args:]<ins>)</ins>...&gt;</tt>
leads to a failure outside of the immediate context, the program is ill-formed. &mdash; <i>end note</i>]
</p>
</blockquote>

</blockquote>
</li>
</ol>

</resolution>

</issue>
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