Skip to content

Commit ff9b09d

Browse files
author
github-actions
committed
Automatic update from GitHub Actions workflow
1 parent af663c9 commit ff9b09d

23 files changed

+457
-44
lines changed

‎issue4168.html‎

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -67,6 +67,8 @@ <h3 id="4168"><a href="lwg-active.html#4168">4168</a>. <code class='backtick'>st
6767
<b>Submitter:</b> Jan Schultke <b>Opened:</b> 2024-10-23 <b>Last modified:</b> 2024-10-31</p>
6868
<p><b>Priority: </b>Not Prioritized
6969
</p>
70+
<p><b>View other</b> <a href="lwg-index-open.html#obj.lifetime">active issues</a> in [obj.lifetime].</p>
71+
<p><b>View all other</b> <a href="lwg-index.html#obj.lifetime">issues</a> in [obj.lifetime].</p>
7072
<p><b>View all issues with</b> <a href="lwg-status.html#New">New</a> status.</p>
7173
<p><b>Discussion:</b></p>
7274
<p>

‎issue4282.html‎

Lines changed: 149 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,149 @@
1+
<!DOCTYPE html>
2+
<html lang="en">
3+
<head>
4+
<meta charset="utf-8">
5+
<title>Issue 4282: Imprecise Throws: clause in std::relocate</title>
6+
<meta property="og:title" content="Issue 4282: Imprecise Throws: clause in std::relocate">
7+
<meta property="og:description" content="C++ library issue. Status: New">
8+
<meta property="og:url" content="https://cplusplus.github.io/LWG/issue4282.html">
9+
<meta property="og:type" content="website">
10+
<meta property="og:image" content="http://cplusplus.github.io/LWG/images/cpp_logo.png">
11+
<meta property="og:image:alt" content="C++ logo">
12+
<style>
13+
p {text-align:justify}
14+
li {text-align:justify}
15+
pre code.backtick::before { content: "`" }
16+
pre code.backtick::after { content: "`" }
17+
blockquote.note
18+
{
19+
background-color:#E0E0E0;
20+
padding-left: 15px;
21+
padding-right: 15px;
22+
padding-top: 1px;
23+
padding-bottom: 1px;
24+
}
25+
ins {background-color:#A0FFA0}
26+
del {background-color:#FFA0A0}
27+
table.issues-index { border: 1px solid; border-collapse: collapse; }
28+
table.issues-index th { text-align: center; padding: 4px; border: 1px solid; }
29+
table.issues-index td { padding: 4px; border: 1px solid; }
30+
table.issues-index td:nth-child(1) { text-align: right; }
31+
table.issues-index td:nth-child(2) { text-align: left; }
32+
table.issues-index td:nth-child(3) { text-align: left; }
33+
table.issues-index td:nth-child(4) { text-align: left; }
34+
table.issues-index td:nth-child(5) { text-align: center; }
35+
table.issues-index td:nth-child(6) { text-align: center; }
36+
table.issues-index td:nth-child(7) { text-align: left; }
37+
table.issues-index td:nth-child(5) span.no-pr { color: red; }
38+
@media (prefers-color-scheme: dark) {
39+
html {
40+
color: #ddd;
41+
background-color: black;
42+
}
43+
ins {
44+
background-color: #225522
45+
}
46+
del {
47+
background-color: #662222
48+
}
49+
a {
50+
color: #6af
51+
}
52+
a:visited {
53+
color: #6af
54+
}
55+
blockquote.note
56+
{
57+
background-color: rgba(255, 255, 255, .10)
58+
}
59+
}
60+
</style>
61+
</head>
62+
<body>
63+
<hr>
64+
<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>
65+
<h3 id="4282"><a href="lwg-active.html#4282">4282</a>. Imprecise <i>Throws</i>: clause in <code class='backtick'>std::relocate</code></h3>
66+
<p><b>Section:</b> 20.2.6 <a href="https://wg21.link/obj.lifetime">[obj.lifetime]</a> <b>Status:</b> <a href="lwg-active.html#New">New</a>
67+
<b>Submitter:</b> Giuseppe D'Angelo <b>Opened:</b> 2025-06-23 <b>Last modified:</b> 2025-06-28</p>
68+
<p><b>Priority: </b>Not Prioritized
69+
</p>
70+
<p><b>View other</b> <a href="lwg-index-open.html#obj.lifetime">active issues</a> in [obj.lifetime].</p>
71+
<p><b>View all other</b> <a href="lwg-index.html#obj.lifetime">issues</a> in [obj.lifetime].</p>
72+
<p><b>View all issues with</b> <a href="lwg-status.html#New">New</a> status.</p>
73+
<p><b>Discussion:</b></p>
74+
<p>
75+
The current specification of <code class='backtick'>std::relocate</code> in 20.2.6 <a href="https://wg21.link/obj.lifetime">[obj.lifetime]</a> says
76+
</p>
77+
<blockquote style="border-left: 3px solid #ccc;padding-left: 15px;">
78+
<p>
79+
<i>Throws</i>: Nothing.
80+
</p>
81+
</blockquote>
82+
<p>
83+
This is imprecise. A trivially relocatable type may feature a throwing
84+
move constructor (or a throwing destructor); for instance, a linked-list
85+
implementation with an externally allocated sentinel node may have a
86+
throwing move constructor, but still be trivially relocatable. Such a
87+
type is nothrow relocatable (as per <code class='backtick'>is_nothrow_relocatable_v</code>, cf.
88+
21.3.5.4 <a href="https://wg21.link/meta.unary.prop">[meta.unary.prop]</a>) and therefore one can call <code class='backtick'>std::relocate</code>
89+
on objects of that type.
90+
<p/>
91+
During constant evaluation, a call to <code class='backtick'>std::relocate</code> is specified to
92+
relocate objects via move construction and destruction.
93+
(<code class='backtick'>std::trivially_relocate</code> is unavailable during constant evaluation.)
94+
<p/>
95+
Since <a href="https://wg21.link/P3068" title=" Allowing exception throwing in constant-evaluation">P3068</a> we are allowed to throw during constant evaluation,
96+
and therefore it's unclear whether <code class='backtick'>std::relocate</code> should propagate such an
97+
exception to the caller or should instead make the evaluation not a
98+
constant expression (and therefore make the program ill-formed, since by
99+
construction we end up in this possibility during constant evaluation).
100+
<p/>
101+
Given the rationale brought forward for <code class='backtick'>std::relocate</code> in <a href="https://wg21.link/P2786" title=" Trivial Relocatability For C++26">P2786</a>
102+
is to be always a nofail operation, I'm proposing a resolution that goes in
103+
that direction.
104+
</p>
105+
106+
107+
<p id="res-4282"><b>Proposed resolution:</b></p>
108+
<p>
109+
This wording is relative to <a href="https://wg21.link/N5008">N5008</a>.
110+
</p>
111+
112+
<ol>
113+
<li><p>Modify 20.2.6 <a href="https://wg21.link/obj.lifetime">[obj.lifetime]</a> as indicated:</p>
114+
115+
<blockquote>
116+
<pre>
117+
template&lt;class T&gt;
118+
constexpr T* relocate(T* first, T* last, T* result);
119+
</pre>
120+
<blockquote>
121+
<p>
122+
-16 <i>Mandates</i>: [&hellip;]
123+
<p/>
124+
-17- <i>Preconditions</i>: [&hellip;]
125+
<p/>
126+
-18- <i>Effects</i>: [&hellip;]
127+
<p/>
128+
-19- <i>Returns</i>: <code class='backtick'>result + (last - first)</code>.
129+
<p/>
130+
-20- <i>Throws:</i>: Nothing.
131+
<p/>
132+
<ins>-?- <i>Remarks</i>: If <code class='backtick'>relocate</code> is called during constant evaluation, and an
133+
exception is thrown by a constructor or destructor of <code class='backtick'>T</code>, the call to <code class='backtick'>relocate</code>
134+
is not a core constant expression (7.7 <a href="https://wg21.link/expr.const">[expr.const]</a>).</ins>
135+
<p/>
136+
[<i>Note 3</i>: Overlapping ranges are supported. &mdash; <i>end note</i>]
137+
</p>
138+
</blockquote>
139+
</blockquote>
140+
</li>
141+
142+
</ol>
143+
144+
145+
146+
147+
148+
</body>
149+
</html>

0 commit comments

Comments
 (0)