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p3171r0.html
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p3171r0.html
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<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml" lang xml:lang>
<head>
<meta charset="utf-8" />
<meta name="generator" content="mpark/wg21" />
<meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes" />
<meta name="dcterms.date" content="2024-03-02" />
<title>Adding functionality to placeholder types</title>
<style>
code{white-space: pre-wrap;}
span.smallcaps{font-variant: small-caps;}
span.underline{text-decoration: underline;}
div.column{display: inline-block; vertical-align: top; width: 50%;}
div.hanging-indent{margin-left: 1.5em; text-indent: -1.5em;}
ul.task-list{list-style: none;}
pre > code.sourceCode { white-space: pre; position: relative; }
pre > code.sourceCode > span { display: inline-block; line-height: 1.25; }
pre > code.sourceCode > span:empty { height: 1.2em; }
code.sourceCode > span { color: inherit; text-decoration: inherit; }
div.sourceCode { margin: 1em 0; }
pre.sourceCode { margin: 0; }
@media screen {
div.sourceCode { overflow: auto; }
}
@media print {
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pre > code.sourceCode > span { text-indent: -5em; padding-left: 5em; }
}
pre.numberSource code
{ counter-reset: source-line 0; }
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{ position: relative; left: -4em; counter-increment: source-line; }
pre.numberSource code > span > a:first-child::before
{ content: counter(source-line);
position: relative; left: -1em; text-align: right; vertical-align: baseline;
border: none; display: inline-block;
-webkit-touch-callout: none; -webkit-user-select: none;
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color: #aaaaaa;
}
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div.sourceCode
{ background-color: #f6f8fa; }
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}
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code span.fl { color: #9f6807; } /* Float */
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code span.in { color: #008000; } /* Information */
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code span.pp { color: #6f4e37; } /* Preprocessor */
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code span.ss { color: #9f6807; } /* SpecialString */
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code span.vs { color: #9f6807; } /* VerbatimString */
code span.wa { color: #008000; font-weight: bold; } /* Warning */
code.diff {color: #898887}
code.diff span.va {color: #006e28}
code.diff span.st {color: #bf0303}
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margin-bottom: -0.2em;
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margin-bottom: 0.6em;
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font-family: sans-serif;
font-weight: normal;
font-size: 83%;
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li ul > li ul > li span.marginalizedparent { left: -11em; }
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margin-right: auto;
margin-top: 1.2em;
margin-bottom: 1.2em;
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span.synopsis {
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.footnote {
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margin-bottom: 0.6em;
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div.minipage {
display: inline-block;
margin-right: 3em;
}
div.numberedTable {
text-align: center;
margin: 2em;
}
div.figure {
text-align: center;
margin: 2em;
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table {
border: 1px solid black;
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margin-right: auto;
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td, th {
padding-left: 1em;
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}
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td.center {
text-align: center;
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td.justify {
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td.border {
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tr.rowsep, td.cline {
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tr.even, tr.odd {
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border-top-style: double;
}
tr.header {
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border-bottom-style: double;
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th {
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span.centry {
font-weight: bold;
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div.table {
display: block;
margin-left: auto;
margin-right: auto;
text-align: center;
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display: block;
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margin-bottom: 1em;
margin-top: 1em;
}
ol.enumeratea { list-style-type: none; background: inherit; }
ol.enumerate { list-style-type: none; background: inherit; }
code.sourceCode > span { display: inline; }
</style>
<style type="text/css">a {
color : #4183C4;
text-decoration: underline;
}
a.marginalized {
text-decoration: none;
}
a.self-link {
text-decoration: none;
}
h1#toctitle {
border-bottom: 1px solid #cccccc;
}
#TOC li {
margin-top: 1px;
margin-bottom: 1px;
}
#TOC ul>li:before { display: none; }
h3.subtitle { margin-top: -15px; }
h1:target { background-color: transparent; }
h2:target { background-color: transparent; }
h3:target { background-color: transparent; }
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h5:target { background-color: transparent; }
h6:target { background-color: transparent; }
code span.co { font-family: monospace; }
table tr {
background-color: white;
}
table tr:nth-child(2n) {
background-color: #f6f8fa;
}
#title-block-header > table tr:nth-child(2n) {
background-color: white;
}
td > div.sourceCode {
background-color: inherit;
}
table {
border-collapse: collapse;
}
table td, table th {
border: 1px solid #cccccc;
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table th {
border-bottom: 1px solid black;
text-align: center;
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table tr:last-child td {
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table tr td:first-child,
table tr th:first-child {
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table tr td:last-child,
table tr th:last-child {
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table tbody tr:first-child td {
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@media all {
body {
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}
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body {
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}
#refs code{padding-left: 0px; text-indent: 0px;}
:root {
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<h1 class="title" style="text-align:center">Adding functionality to placeholder types</h1>
<table style="border:none;float:right">
<tr>
<td>Document #:</td>
<td>P3171R0</td>
</tr>
<tr>
<td>Date:</td>
<td>2024-03-02</td>
</tr>
<tr>
<td style="vertical-align:top">Project:</td>
<td>Programming Language C++</td>
</tr>
<tr>
<td style="vertical-align:top">Audience:</td>
<td>
LEWG<br>
</td>
</tr>
<tr>
<td style="vertical-align:top">Reply-to:</td>
<td>
Peter Dimov<br><<a href="mailto:pdimov@gmail.com" class="email">pdimov@gmail.com</a>><br>
Barry Revzin<br><<a href="mailto:barry.revzin@gmail.com" class="email">barry.revzin@gmail.com</a>><br>
</td>
</tr>
</table>
</header>
<div style="clear:both">
<div id="TOC" role="doc-toc">
<h1 id="toctitle">Contents</h1>
<ul>
<li><a href="#introduction"><span class="toc-section-number">1</span> Introduction<span></span></a></li>
<li><a href="#proposal"><span class="toc-section-number">2</span> Proposal<span></span></a>
<ul>
<li><a href="#implementation-experience"><span class="toc-section-number">2.1</span> Implementation Experience<span></span></a></li>
<li><a href="#wording"><span class="toc-section-number">2.2</span> Wording<span></span></a></li>
</ul></li>
<li><a href="#bibliography"><span class="toc-section-number">3</span> References<span></span></a></li>
</ul>
</div>
<h1 data-number="1" style="border-bottom:1px solid #cccccc" id="introduction"><span class="header-section-number">1</span> Introduction<a href="#introduction" class="self-link"></a></h1>
<p>As noted in <span class="citation" data-cites="P2760R0">[<a href="#ref-P2760R0" role="doc-biblioref">P2760R0</a>]</span>, there are a lot of function objects for operators in the standard library, but several operators are missing. This paper proposes to add the functionality for all the missing operators, but to also do it in a different way than simply by adding function objects.</p>
<p><span class="citation" data-cites="Boost.Lambda2">[<a href="#ref-Boost.Lambda2" role="doc-biblioref">Boost.Lambda2</a>]</span> is a Boost library (writen by Peter) which makes it possible to write very terse, simple operations, by building upon the <code class="sourceCode cpp">std<span class="op">::</span>bind</code> machinery. When Barry was implementing <code class="sourceCode cpp">std<span class="op">::</span>views<span class="op">::</span>zip</code> <span class="citation" data-cites="P2321R2">[<a href="#ref-P2321R2" role="doc-biblioref">P2321R2</a>]</span>, a range adaptor whose implementation requires forwarding various operators across a <code class="sourceCode cpp">tuple</code>, Boost.Lambda2 provided a very nice way to implement those operations. Here is a comparison between a hand-written lambda solution, function objects, and the placeholder solution that Lambda2 offers:</p>
<table>
<tr>
<th>
Handwritten Lambdas
</th>
<th>
Named Function Objects
</th>
<th>
Boost.Lambda2
</th>
</tr>
<tr>
<td>
<div class="sourceCode" id="cb1"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb1-1"><a href="#cb1-1"></a><span class="kw">auto</span> <span class="kw">operator</span><span class="op">*()</span> <span class="kw">const</span> <span class="op">{</span></span>
<span id="cb1-2"><a href="#cb1-2"></a> <span class="cf">return</span> tuple_transform<span class="op">(</span><em>current_</em>,</span>
<span id="cb1-3"><a href="#cb1-3"></a> <span class="op">[](</span><span class="kw">auto</span><span class="op">&</span> it<span class="op">)</span> <span class="op">-></span> <span class="kw">decltype</span><span class="op">(</span><span class="kw">auto</span><span class="op">)</span> <span class="op">{</span></span>
<span id="cb1-4"><a href="#cb1-4"></a> <span class="cf">return</span> <span class="op">*</span>it;</span>
<span id="cb1-5"><a href="#cb1-5"></a> <span class="op">})</span>;</span>
<span id="cb1-6"><a href="#cb1-6"></a><span class="op">}</span></span></code></pre></div>
</td>
<td>
<div class="sourceCode" id="cb2"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb2-1"><a href="#cb2-1"></a><span class="kw">auto</span> <span class="kw">operator</span><span class="op">*()</span> <span class="kw">const</span> <span class="op">{</span></span>
<span id="cb2-2"><a href="#cb2-2"></a> <span class="cf">return</span> tuple_transform<span class="op">(</span><em>current_</em>,</span>
<span id="cb2-3"><a href="#cb2-3"></a> dereference<span class="op">{})</span>;</span>
<span id="cb2-4"><a href="#cb2-4"></a><span class="op">}</span></span></code></pre></div>
</td>
<td>
<div class="sourceCode" id="cb3"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb3-1"><a href="#cb3-1"></a><span class="kw">auto</span> <span class="kw">operator</span><span class="op">*()</span> <span class="kw">const</span> <span class="op">{</span></span>
<span id="cb3-2"><a href="#cb3-2"></a> <span class="cf">return</span> tuple_transform<span class="op">(</span><em>current_</em>, <span class="op">*</span>_1<span class="op">)</span>;</span>
<span id="cb3-3"><a href="#cb3-3"></a><span class="op">}</span></span></code></pre></div>
</td>
</tr>
<tr>
<td>
<div class="sourceCode" id="cb4"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb4-1"><a href="#cb4-1"></a><span class="kw">auto</span> <span class="kw">operator</span><span class="op">++()</span> <span class="op">-></span> iterator<span class="op">&</span> <span class="op">{</span></span>
<span id="cb4-2"><a href="#cb4-2"></a> tuple_for_each<span class="op">(</span><em>current_</em>,</span>
<span id="cb4-3"><a href="#cb4-3"></a> <span class="op">[](</span><span class="kw">auto</span><span class="op">&</span> it<span class="op">)</span> <span class="op">{</span> <span class="op">++</span>it; <span class="op">})</span>;</span>
<span id="cb4-4"><a href="#cb4-4"></a> <span class="cf">return</span> <span class="op">*</span><span class="kw">this</span>;</span>
<span id="cb4-5"><a href="#cb4-5"></a><span class="op">}</span></span></code></pre></div>
</td>
<td>
<div class="sourceCode" id="cb5"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb5-1"><a href="#cb5-1"></a><span class="kw">auto</span> <span class="kw">operator</span><span class="op">++()</span> <span class="op">-></span> iterator<span class="op">&</span> <span class="op">{</span></span>
<span id="cb5-2"><a href="#cb5-2"></a> tuple_for_each<span class="op">(</span><em>current_</em>,</span>
<span id="cb5-3"><a href="#cb5-3"></a> prefix_increment<span class="op">{})</span>;</span>
<span id="cb5-4"><a href="#cb5-4"></a> <span class="cf">return</span> <span class="op">*</span><span class="kw">this</span>;</span>
<span id="cb5-5"><a href="#cb5-5"></a><span class="op">}</span></span></code></pre></div>
</td>
<td>
<div class="sourceCode" id="cb6"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb6-1"><a href="#cb6-1"></a><span class="kw">auto</span> <span class="kw">operator</span><span class="op">++()</span> <span class="op">-></span> iterator<span class="op">&</span> <span class="op">{</span></span>
<span id="cb6-2"><a href="#cb6-2"></a> tuple_for_each<span class="op">(</span><em>current_</em>, <span class="op">++</span>_1<span class="op">)</span>;</span>
<span id="cb6-3"><a href="#cb6-3"></a> <span class="cf">return</span> <span class="op">*</span><span class="kw">this</span>;</span>
<span id="cb6-4"><a href="#cb6-4"></a><span class="op">}</span></span></code></pre></div>
</td>
</tr>
</table>
<p>It’s not just that the Lambda2 alternatives are overwhelmingly terser (it’s very hard to beat 3 characters for the dereference operation, especially compared to the handwritten lambda that must use <code class="sourceCode cpp"><span class="op">-></span> <span class="kw">decltype</span><span class="op">(</span><span class="kw">auto</span><span class="op">)</span></code> and is thus 46 characters long), they more directly express exactly the work being done.</p>
<p>Lambda2 also offers a more expressive way of doing common predicates, even in the case where the named function object already exists. Let’s take an example where you want to write a predicate for if the argument is negative (an example Barry previously wrote about on his blog <a href="https://brevzin.github.io/c++/2020/06/18/lambda-lambda-lambda/">here</a>), there are several ways to do it:</p>
<blockquote>
<div class="sourceCode" id="cb7"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb7-1"><a href="#cb7-1"></a><span class="co">// hand-written lambda (28 characters)</span></span>
<span id="cb7-2"><a href="#cb7-2"></a><span class="op">[](</span><span class="kw">auto</span> e<span class="op">)</span> <span class="op">{</span> <span class="cf">return</span> e <span class="op"><</span> <span class="dv">0</span>; <span class="op">}</span></span>
<span id="cb7-3"><a href="#cb7-3"></a></span>
<span id="cb7-4"><a href="#cb7-4"></a><span class="co">// attempting to use std::less{} (19 characters, but... uh...)</span></span>
<span id="cb7-5"><a href="#cb7-5"></a>bind<span class="op">(</span>less<span class="op">{}</span>, _1, <span class="dv">0</span><span class="op">)</span></span>
<span id="cb7-6"><a href="#cb7-6"></a></span>
<span id="cb7-7"><a href="#cb7-7"></a><span class="co">// Boost.Lambda2 (6 characters)</span></span>
<span id="cb7-8"><a href="#cb7-8"></a>_1 <span class="op"><</span> <span class="dv">0</span></span></code></pre></div>
</blockquote>
<p>It also allows for an approach to address the question of projections. Let’s say that rather than finding a negative number, we want to find a <code class="sourceCode cpp">Point</code> whose <code class="sourceCode cpp">x</code> coordinate is negative:</p>
<blockquote>
<div class="sourceCode" id="cb8"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb8-1"><a href="#cb8-1"></a><span class="co">// hand-written lambda (30 characters)</span></span>
<span id="cb8-2"><a href="#cb8-2"></a>find_if<span class="op">(</span>points, <span class="op">[](</span>Point p<span class="op">){</span> <span class="cf">return</span> p<span class="op">.</span>x <span class="op"><</span> <span class="dv">0</span>; <span class="op">})</span></span>
<span id="cb8-3"><a href="#cb8-3"></a></span>
<span id="cb8-4"><a href="#cb8-4"></a><span class="co">// Boost.Lambda 2 (18 characters)</span></span>
<span id="cb8-5"><a href="#cb8-5"></a>find_if<span class="op">(</span>points, _1<span class="op">->*&</span>Point<span class="op">::</span>x <span class="op"><</span> <span class="dv">0</span><span class="op">)</span></span></code></pre></div>
</blockquote>
<p>Or if the <code class="sourceCode cpp">x</code> coordinate is 0:</p>
<blockquote>
<div class="sourceCode" id="cb9"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb9-1"><a href="#cb9-1"></a><span class="co">// hand-written lambda (31 characters)</span></span>
<span id="cb9-2"><a href="#cb9-2"></a>find_if<span class="op">(</span>points, <span class="op">[](</span>Point p<span class="op">){</span> <span class="cf">return</span> p<span class="op">.</span>x <span class="op">==</span> <span class="dv">0</span>; <span class="op">})</span></span>
<span id="cb9-3"><a href="#cb9-3"></a></span>
<span id="cb9-4"><a href="#cb9-4"></a><span class="co">// using projection (!2 characters, but cryptic)</span></span>
<span id="cb9-5"><a href="#cb9-5"></a>find<span class="op">(</span>points, <span class="dv">0</span>, <span class="op">&</span>Point<span class="op">::</span>x<span class="op">)</span>;</span>
<span id="cb9-6"><a href="#cb9-6"></a></span>
<span id="cb9-7"><a href="#cb9-7"></a><span class="co">// Boost.Lambda 2 (19 characters)</span></span>
<span id="cb9-8"><a href="#cb9-8"></a>find_if<span class="op">(</span>points, _1<span class="op">->*&</span>Point<span class="op">::</span>x <span class="op">==</span> <span class="dv">0</span><span class="op">)</span></span></code></pre></div>
</blockquote>
<p>Note that this latter usage could be improved significantly with something like <span class="citation" data-cites="P0060R0">[<a href="#ref-P0060R0" role="doc-biblioref">P0060R0</a>]</span>, which would actually allow for writing the predicate <code class="sourceCode cpp">_1<span class="op">.</span>x <span class="op">==</span> <span class="dv">0</span></code>. Which is difficult to beat.</p>
<p>You can see more examples in the <span class="citation" data-cites="Boost.Lambda2">[<a href="#ref-Boost.Lambda2" role="doc-biblioref">Boost.Lambda2</a>]</span> docs.</p>
<h1 data-number="2" style="border-bottom:1px solid #cccccc" id="proposal"><span class="header-section-number">2</span> Proposal<a href="#proposal" class="self-link"></a></h1>
<p>We propose to solve the issue of missing operator function objects in the standard library, as well as less-than-ergonomic lambda syntax for common predicates, by standardizing Boost.Lambda2. That is not a large proposal. The standard library already provides placeholders, <code class="sourceCode cpp">std<span class="op">::</span><span class="kw">namespace</span><span class="op">::</span>_1</code> and friends. The standard library also already provides <code class="sourceCode cpp">std<span class="op">::</span>bind</code>, which is already implemented in a way that supports composition of bind expressions. All we need to do is add operators.</p>
<p>We additionally add the missing operator function objects. Now, most of the missing operator function objects and placeholder operators are easy enough to add, except one: taking the address. <code class="sourceCode cpp"><span class="op">&</span>_1</code> is a bit squeamish, although this actually seems like justified place to overload this operator. But as far as function objects go, the obvious name for it would be <code class="sourceCode cpp">std<span class="op">::</span>addressof</code>. But this one already exists as an overloaded function template.</p>
<p>This leaves us with two options:</p>
<ol type="1">
<li>Respecify <code class="sourceCode cpp">std<span class="op">::</span>addressof</code> as a customziation point object with the same behavior. This would be inconsistent with the other function objects (in all the other cases, we specify a type - <code class="sourceCode cpp">std<span class="op">::</span>compare_three_way</code> is a type, the proposed <code class="sourceCode cpp">std<span class="op">::</span>subscript</code> is a type, etc., whereas this would be the only object) and would break attempts to use <code class="sourceCode cpp">addressof</code> unqualified outside of <code class="sourceCode cpp"><span class="kw">namespace</span> std</code>.</li>
<li>Come up with a new name for the object, such that <code class="sourceCode cpp">std<span class="op">::</span>addressof<span class="op">(</span>x<span class="op">)</span></code> and maybe <code class="sourceCode cpp">std<span class="op">::</span>address_of<span class="op">{}(</span>x<span class="op">)</span></code> are equivalent.</li>
</ol>
<p>We propose the former.</p>
<h2 data-number="2.1" id="implementation-experience"><span class="header-section-number">2.1</span> Implementation Experience<a href="#implementation-experience" class="self-link"></a></h2>
<p>Has been shipping in Boost since 1.77 (August 2021).</p>
<h2 data-number="2.2" id="wording"><span class="header-section-number">2.2</span> Wording<a href="#wording" class="self-link"></a></h2>
<p>Change <span>20.2.2 <a href="https://wg21.link/memory.syn">[memory.syn]</a></span>:</p>
<blockquote>
<div>
<div class="sourceCode" id="cb10"><pre class="sourceCode diff"><code class="sourceCode diff"><span id="cb10-1"><a href="#cb10-1"></a>namespace std {</span>
<span id="cb10-2"><a href="#cb10-2"></a> // ...</span>
<span id="cb10-3"><a href="#cb10-3"></a> // [specialized.addressof], addressof</span>
<span id="cb10-4"><a href="#cb10-4"></a><span class="st">- template<class T></span></span>
<span id="cb10-5"><a href="#cb10-5"></a><span class="st">- constexpr T* addressof(T& r) noexcept; // freestanding</span></span>
<span id="cb10-6"><a href="#cb10-6"></a><span class="st">- template<class T></span></span>
<span id="cb10-7"><a href="#cb10-7"></a><span class="st">- const T* addressof(const T&&) = delete; // freestanding</span></span>
<span id="cb10-8"><a href="#cb10-8"></a><span class="va">+ inline constexpr <em>unspecified</em> addressof; // freestanding</span></span>
<span id="cb10-9"><a href="#cb10-9"></a> // ...</span>
<span id="cb10-10"><a href="#cb10-10"></a>}</span></code></pre></div>
</div>
</blockquote>
<p>Change <span>20.2.11 <a href="https://wg21.link/specialized.addressof">[specialized.addressof]</a></span>:</p>
<blockquote>
<div class="addu">
<div class="sourceCode" id="cb11"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb11-1"><a href="#cb11-1"></a>struct <em>addressof_t</em> { // exposition-only</span>
<span id="cb11-2"><a href="#cb11-2"></a> template<class T></span>
<span id="cb11-3"><a href="#cb11-3"></a> constexpr T* operator()(T& r) const noexcept;</span>
<span id="cb11-4"><a href="#cb11-4"></a> template<class T></span>
<span id="cb11-5"><a href="#cb11-5"></a> constexpr T* operator()(const T&&) const = delete;</span>
<span id="cb11-6"><a href="#cb11-6"></a>};</span>
<span id="cb11-7"><a href="#cb11-7"></a></span>
<span id="cb11-8"><a href="#cb11-8"></a>inline constexpr <em>addressof_t</em> addressof{};</span></code></pre></div>
<div class="sourceCode" id="cb12"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb12-1"><a href="#cb12-1"></a>template<clsas T></span>
<span id="cb12-2"><a href="#cb12-2"></a> constexpr T* <em>addressof_t</em>::operator()(T& r) const noexcept;</span></code></pre></div>
</div>
<div class="rm" style="color: #bf0303">
<div class="sourceCode" id="cb13"><pre class="sourceCode default default"><code class="sourceCode default"><span id="cb13-1"><a href="#cb13-1"></a>template<class T> constexpr T* addressof(T& r) noexcept;</span></code></pre></div>
</div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_1" id="pnum_1">1</a></span> <em>Returns</em>: The actual address of the object or function referenced by <code class="sourceCode cpp">r</code>, even in the presence of an overloaded <code class="sourceCode cpp"><span class="kw">operator</span><span class="op">&</span></code>.</p>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_2" id="pnum_2">2</a></span> <em>Remarks</em>: An expression <code class="sourceCode cpp">addressof<span class="op">(</span>E<span class="op">)</span></code> is a constant subexpression ([defns.const.subexpr]) if <code class="sourceCode cpp">E</code> is an lvalue constant subexpression.</p>
</blockquote>
<p>Extend <span>22.10.2 <a href="https://wg21.link/functional.syn">[functional.syn]</a></span> to add the additional function objects:</p>
<blockquote>
<div>
<div class="sourceCode" id="cb14"><pre class="sourceCode diff"><code class="sourceCode diff"><span id="cb14-1"><a href="#cb14-1"></a>namespace std {</span>
<span id="cb14-2"><a href="#cb14-2"></a></span>
<span id="cb14-3"><a href="#cb14-3"></a> // ...</span>
<span id="cb14-4"><a href="#cb14-4"></a></span>
<span id="cb14-5"><a href="#cb14-5"></a> // [bitwise.operations], bitwise operations</span>
<span id="cb14-6"><a href="#cb14-6"></a> template<class T = void> struct bit_and; // freestanding</span>
<span id="cb14-7"><a href="#cb14-7"></a> template<class T = void> struct bit_or; // freestanding</span>
<span id="cb14-8"><a href="#cb14-8"></a> template<class T = void> struct bit_xor; // freestanding</span>
<span id="cb14-9"><a href="#cb14-9"></a> template<class T = void> struct bit_not; // freestanding</span>
<span id="cb14-10"><a href="#cb14-10"></a> template<> struct bit_and<void>; // freestanding</span>
<span id="cb14-11"><a href="#cb14-11"></a> template<> struct bit_or<void>; // freestanding</span>
<span id="cb14-12"><a href="#cb14-12"></a> template<> struct bit_xor<void>; // freestanding</span>
<span id="cb14-13"><a href="#cb14-13"></a> template<> struct bit_not<void>; // freestanding</span>
<span id="cb14-14"><a href="#cb14-14"></a></span>
<span id="cb14-15"><a href="#cb14-15"></a><span class="va">+ // [additional.operations], additional transparent operations</span></span>
<span id="cb14-16"><a href="#cb14-16"></a><span class="va">+ struct subscript; // freestanding</span></span>
<span id="cb14-17"><a href="#cb14-17"></a><span class="va">+ struct left_shift; // freestanding</span></span>
<span id="cb14-18"><a href="#cb14-18"></a><span class="va">+ struct right_shift; // freestanding</span></span>
<span id="cb14-19"><a href="#cb14-19"></a><span class="va">+ struct unary_plus; // freestanding</span></span>
<span id="cb14-20"><a href="#cb14-20"></a><span class="va">+ struct dereference; // freestanding</span></span>
<span id="cb14-21"><a href="#cb14-21"></a><span class="va">+ struct increment; // freestanding</span></span>
<span id="cb14-22"><a href="#cb14-22"></a><span class="va">+ struct decrement; // freestanding</span></span>
<span id="cb14-23"><a href="#cb14-23"></a><span class="va">+ struct postfix_increment; // freestanding</span></span>
<span id="cb14-24"><a href="#cb14-24"></a><span class="va">+ struct postfix_decrement; // freestanding</span></span>
<span id="cb14-25"><a href="#cb14-25"></a><span class="va">+</span></span>
<span id="cb14-26"><a href="#cb14-26"></a><span class="va">+ // [compound.operations], compound assignment operations</span></span>
<span id="cb14-27"><a href="#cb14-27"></a><span class="va">+ struct plus_equal; // freestanding</span></span>
<span id="cb14-28"><a href="#cb14-28"></a><span class="va">+ struct minus_equal; // freestanding</span></span>
<span id="cb14-29"><a href="#cb14-29"></a><span class="va">+ struct multiplies_equal; // freestanding</span></span>
<span id="cb14-30"><a href="#cb14-30"></a><span class="va">+ struct divides_equal; // freestanding</span></span>
<span id="cb14-31"><a href="#cb14-31"></a><span class="va">+ struct modulus_equal; // freestanding</span></span>
<span id="cb14-32"><a href="#cb14-32"></a><span class="va">+ struct bit_and_equal; // freestanding</span></span>
<span id="cb14-33"><a href="#cb14-33"></a><span class="va">+ struct bit_or_equal; // freestanding</span></span>
<span id="cb14-34"><a href="#cb14-34"></a><span class="va">+ struct bit_xor_equal; // freestanding</span></span>
<span id="cb14-35"><a href="#cb14-35"></a><span class="va">+ struct left_shift_equal; // freestanding</span></span>
<span id="cb14-36"><a href="#cb14-36"></a><span class="va">+ struct right_shift_equal; // freestanding</span></span>
<span id="cb14-37"><a href="#cb14-37"></a></span>
<span id="cb14-38"><a href="#cb14-38"></a> // ...</span>
<span id="cb14-39"><a href="#cb14-39"></a></span>
<span id="cb14-40"><a href="#cb14-40"></a>}</span></code></pre></div>
</div>
</blockquote>
<p>Extend <span>22.10.2 <a href="https://wg21.link/functional.syn">[functional.syn]</a></span> to add operators:</p>
<blockquote>
<div>
<div class="sourceCode" id="cb15"><pre class="sourceCode diff"><code class="sourceCode diff"><span id="cb15-1"><a href="#cb15-1"></a>namespace std {</span>
<span id="cb15-2"><a href="#cb15-2"></a> // ...</span>
<span id="cb15-3"><a href="#cb15-3"></a> namespace placeholders {</span>
<span id="cb15-4"><a href="#cb15-4"></a> // M is the implementation-defined number of placeholders</span>
<span id="cb15-5"><a href="#cb15-5"></a> <em>see below</em> _1; // freestanding</span>
<span id="cb15-6"><a href="#cb15-6"></a> <em>see below</em> _2; // freestanding</span>
<span id="cb15-7"><a href="#cb15-7"></a> .</span>
<span id="cb15-8"><a href="#cb15-8"></a> .</span>
<span id="cb15-9"><a href="#cb15-9"></a> .</span>
<span id="cb15-10"><a href="#cb15-10"></a> <em>see below</em> _M; // freestanding</span>
<span id="cb15-11"><a href="#cb15-11"></a></span>
<span id="cb15-12"><a href="#cb15-12"></a><span class="va">+ template<class A, class B> constexpr auto operator+(A&&, B&&);</span></span>
<span id="cb15-13"><a href="#cb15-13"></a><span class="va">+ template<class A, class B> constexpr auto operator-(A&&, B&&);</span></span>
<span id="cb15-14"><a href="#cb15-14"></a><span class="va">+ template<class A, class B> constexpr auto operator*(A&&, B&&);</span></span>
<span id="cb15-15"><a href="#cb15-15"></a><span class="va">+ template<class A, class B> constexpr auto operator/(A&&, B&&);</span></span>
<span id="cb15-16"><a href="#cb15-16"></a><span class="va">+ template<class A, class B> constexpr auto operator%(A&&, B&&);</span></span>
<span id="cb15-17"><a href="#cb15-17"></a><span class="va">+ template<class A> constexpr auto operator-(A&&);</span></span>
<span id="cb15-18"><a href="#cb15-18"></a><span class="va">+</span></span>
<span id="cb15-19"><a href="#cb15-19"></a><span class="va">+ template<class A, class B> constexpr auto operator==(A&&, B&&);</span></span>
<span id="cb15-20"><a href="#cb15-20"></a><span class="va">+ template<class A, class B> constexpr auto operator!=(A&&, B&&);</span></span>
<span id="cb15-21"><a href="#cb15-21"></a><span class="va">+ template<class A, class B> constexpr auto operator<(A&&, B&&);</span></span>
<span id="cb15-22"><a href="#cb15-22"></a><span class="va">+ template<class A, class B> constexpr auto operator>(A&&, B&&);</span></span>
<span id="cb15-23"><a href="#cb15-23"></a><span class="va">+ template<class A, class B> constexpr auto operator<=(A&&, B&&);</span></span>
<span id="cb15-24"><a href="#cb15-24"></a><span class="va">+ template<class A, class B> constexpr auto operator>=(A&&, B&&);</span></span>
<span id="cb15-25"><a href="#cb15-25"></a><span class="va">+ template<class A, class B> constexpr auto operator<=>(A&&, B&&);</span></span>
<span id="cb15-26"><a href="#cb15-26"></a><span class="va">+</span></span>
<span id="cb15-27"><a href="#cb15-27"></a><span class="va">+ template<class A, class B> constexpr auto operator&&(A&&, B&&);</span></span>
<span id="cb15-28"><a href="#cb15-28"></a><span class="va">+ template<class A, class B> constexpr auto operator||(A&&, B&&);</span></span>
<span id="cb15-29"><a href="#cb15-29"></a><span class="va">+ template<class A> constexpr auto operator!(A&&);</span></span>
<span id="cb15-30"><a href="#cb15-30"></a><span class="va">+</span></span>
<span id="cb15-31"><a href="#cb15-31"></a><span class="va">+ template<class A, class B> constexpr auto operator&(A&&, B&&);</span></span>
<span id="cb15-32"><a href="#cb15-32"></a><span class="va">+ template<class A, class B> constexpr auto operator|(A&&, B&&);</span></span>
<span id="cb15-33"><a href="#cb15-33"></a><span class="va">+ template<class A, class B> constexpr auto operator^(A&&, B&&);</span></span>
<span id="cb15-34"><a href="#cb15-34"></a><span class="va">+ template<class A> constexpr auto operator~(A&&);</span></span>
<span id="cb15-35"><a href="#cb15-35"></a><span class="va">+</span></span>
<span id="cb15-36"><a href="#cb15-36"></a><span class="va">+ template<class A, class B> constexpr auto operator<<(A&&, B&&);</span></span>
<span id="cb15-37"><a href="#cb15-37"></a><span class="va">+ template<class A, class B> constexpr auto operator<<(A&, B&&);</span></span>
<span id="cb15-38"><a href="#cb15-38"></a><span class="va">+</span></span>
<span id="cb15-39"><a href="#cb15-39"></a><span class="va">+ template<class A, class B> constexpr auto operator>>(A&&, B&&);</span></span>
<span id="cb15-40"><a href="#cb15-40"></a><span class="va">+ template<class A, class B> constexpr auto operator>>(A&, B&&);</span></span>
<span id="cb15-41"><a href="#cb15-41"></a><span class="va">+</span></span>
<span id="cb15-42"><a href="#cb15-42"></a><span class="va">+ template<class A> constexpr auto operator+(A&&);</span></span>
<span id="cb15-43"><a href="#cb15-43"></a><span class="va">+ template<class A> constexpr auto operator*(A&&);</span></span>
<span id="cb15-44"><a href="#cb15-44"></a><span class="va">+ template<class A> constexpr auto operator++(A&&);</span></span>
<span id="cb15-45"><a href="#cb15-45"></a><span class="va">+ template<class A> constexpr auto operator--(A&&);</span></span>
<span id="cb15-46"><a href="#cb15-46"></a><span class="va">+ template<class A> constexpr auto operator++(A&&, int);</span></span>
<span id="cb15-47"><a href="#cb15-47"></a><span class="va">+ template<class A> constexpr auto operator--(A&&, int);</span></span>
<span id="cb15-48"><a href="#cb15-48"></a><span class="va">+</span></span>
<span id="cb15-49"><a href="#cb15-49"></a><span class="va">+ template<class A, class B> constexpr auto operator+=(A&&, B&&);</span></span>
<span id="cb15-50"><a href="#cb15-50"></a><span class="va">+ template<class A, class B> constexpr auto operator-=(A&&, B&&);</span></span>
<span id="cb15-51"><a href="#cb15-51"></a><span class="va">+ template<class A, class B> constexpr auto operator*=(A&&, B&&);</span></span>
<span id="cb15-52"><a href="#cb15-52"></a><span class="va">+ template<class A, class B> constexpr auto operator/=(A&&, B&&);</span></span>
<span id="cb15-53"><a href="#cb15-53"></a><span class="va">+ template<class A, class B> constexpr auto operator%=(A&&, B&&);</span></span>
<span id="cb15-54"><a href="#cb15-54"></a><span class="va">+ template<class A, class B> constexpr auto operator&=(A&&, B&&);</span></span>
<span id="cb15-55"><a href="#cb15-55"></a><span class="va">+ template<class A, class B> constexpr auto operator|=(A&&, B&&);</span></span>
<span id="cb15-56"><a href="#cb15-56"></a><span class="va">+ template<class A, class B> constexpr auto operator^=(A&&, B&&);</span></span>
<span id="cb15-57"><a href="#cb15-57"></a><span class="va">+ template<class A, class B> constexpr auto operator<<=(A&&, B&&);</span></span>
<span id="cb15-58"><a href="#cb15-58"></a><span class="va">+ template<class A, class B> constexpr auto operator>>=(A&&, B&&);</span></span>
<span id="cb15-59"><a href="#cb15-59"></a><span class="va">+</span></span>
<span id="cb15-60"><a href="#cb15-60"></a><span class="va">+ template<class A, class B> constexpr auto operator->*(A&&, B&&);</span></span>
<span id="cb15-61"><a href="#cb15-61"></a> }</span>
<span id="cb15-62"><a href="#cb15-62"></a> // ...</span>
<span id="cb15-63"><a href="#cb15-63"></a>}</span></code></pre></div>
</div>
</blockquote>
<p>Add two new sections after <span>22.10.11 <a href="https://wg21.link/bitwise.operations">[bitwise.operations]</a></span>:</p>
<blockquote>
<div class="addu">
<h3 id="additional-operations-additional.operations">Additional operations [additional.operations]<a href="#additional-operations-additional.operations" class="self-link"></a></h3>
<h4 id="class-subscript-additional.operations.subscript">Class <code class="sourceCode cpp">subscript</code> [additional.operations.subscript]<a href="#class-subscript-additional.operations.subscript" class="self-link"></a></h4>
<div class="sourceCode" id="cb16"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb16-1"><a href="#cb16-1"></a>struct subscript {</span>
<span id="cb16-2"><a href="#cb16-2"></a> template<class T, class U> constexpr auto operator()(T&& t, U&& u) const</span>
<span id="cb16-3"><a href="#cb16-3"></a> -> decltype(std::forward<T>(t)[std::forward<U>(u)]);</span>
<span id="cb16-4"><a href="#cb16-4"></a></span>
<span id="cb16-5"><a href="#cb16-5"></a> using is_transparent = <em>unspecified</em>;</span>
<span id="cb16-6"><a href="#cb16-6"></a>};</span></code></pre></div>
<div class="sourceCode" id="cb17"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb17-1"><a href="#cb17-1"></a>template<class T, class U> constexpr auto operator()(T&& t, U&& u) const</span>
<span id="cb17-2"><a href="#cb17-2"></a> -> decltype(std::forward<T>(t)[std::forward<U>(u)]);</span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_3" id="pnum_3">1</a></span> <em>Returns</em>: <code class="sourceCode cpp">std<span class="op">::</span>forward<span class="op"><</span>T<span class="op">>(</span>t<span class="op">)[</span>std<span class="op">::</span>forward<span class="op"><</span>U<span class="op">>(</span>u<span class="op">)]</span></code>.</p>
<h4 id="class-left_shift-additional.operations.left_shift">Class <code class="sourceCode cpp">left_shift</code> [additional.operations.left_shift]<a href="#class-left_shift-additional.operations.left_shift" class="self-link"></a></h4>
<div class="sourceCode" id="cb18"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb18-1"><a href="#cb18-1"></a>struct left_shift {</span>
<span id="cb18-2"><a href="#cb18-2"></a> template<class T, class U> constexpr auto operator()(T&& t, U&& u) const</span>
<span id="cb18-3"><a href="#cb18-3"></a> -> decltype(std::forward<T>(t) << std::forward<U>(u));</span>
<span id="cb18-4"><a href="#cb18-4"></a></span>
<span id="cb18-5"><a href="#cb18-5"></a> using is_transparent = <em>unspecified</em>;</span>
<span id="cb18-6"><a href="#cb18-6"></a>};</span></code></pre></div>
<div class="sourceCode" id="cb19"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb19-1"><a href="#cb19-1"></a>template<class T, class U> constexpr auto operator()(T&& t, U&& u) const</span>
<span id="cb19-2"><a href="#cb19-2"></a> -> decltype(std::forward<T>(t) << std::forward<U>(u));</span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_4" id="pnum_4">1</a></span> <em>Returns</em>: <code class="sourceCode cpp">std<span class="op">::</span>forward<span class="op"><</span>T<span class="op">>(</span>t<span class="op">)</span> <span class="op"><<</span> std<span class="op">::</span>forward<span class="op"><</span>U<span class="op">>(</span>u<span class="op">)</span></code>.</p>
<h4 id="class-right_shift-additional.operations.right_shift">Class <code class="sourceCode cpp">right_shift</code> [additional.operations.right_shift]<a href="#class-right_shift-additional.operations.right_shift" class="self-link"></a></h4>
<div class="sourceCode" id="cb20"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb20-1"><a href="#cb20-1"></a>struct right_shift {</span>
<span id="cb20-2"><a href="#cb20-2"></a> template<class T, class U> constexpr auto operator()(T&& t, U&& u) const</span>
<span id="cb20-3"><a href="#cb20-3"></a> -> decltype(std::forward<T>(t) >> std::forward<U>(u));</span>
<span id="cb20-4"><a href="#cb20-4"></a></span>
<span id="cb20-5"><a href="#cb20-5"></a> using is_transparent = <em>unspecified</em>;</span>
<span id="cb20-6"><a href="#cb20-6"></a>};</span></code></pre></div>
<div class="sourceCode" id="cb21"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb21-1"><a href="#cb21-1"></a>template<class T, class U> constexpr auto operator()(T&& t, U&& u) const</span>
<span id="cb21-2"><a href="#cb21-2"></a> -> decltype(std::forward<T>(t) >> std::forward<U>(u));</span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_5" id="pnum_5">1</a></span> <em>Returns</em>: <code class="sourceCode cpp">std<span class="op">::</span>forward<span class="op"><</span>T<span class="op">>(</span>t<span class="op">)</span> <span class="op">>></span> std<span class="op">::</span>forward<span class="op"><</span>U<span class="op">>(</span>u<span class="op">)</span></code>.</p>
<h4 id="class-unary_plus-additional.operations.unary_plus">Class <code class="sourceCode cpp">unary_plus</code> [additional.operations.unary_plus]<a href="#class-unary_plus-additional.operations.unary_plus" class="self-link"></a></h4>
<div class="sourceCode" id="cb22"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb22-1"><a href="#cb22-1"></a>struct unary_plus {</span>
<span id="cb22-2"><a href="#cb22-2"></a> template<class T> constexpr auto operator()(T&& t) const</span>
<span id="cb22-3"><a href="#cb22-3"></a> -> decltype(+std::forward<T>(t));</span>
<span id="cb22-4"><a href="#cb22-4"></a></span>
<span id="cb22-5"><a href="#cb22-5"></a> using is_transparent = <em>unspecified</em>;</span>
<span id="cb22-6"><a href="#cb22-6"></a>};</span></code></pre></div>
<div class="sourceCode" id="cb23"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb23-1"><a href="#cb23-1"></a>template<class T> constexpr auto operator()(T&& t) const</span>
<span id="cb23-2"><a href="#cb23-2"></a> -> decltype(+std::forward<T>(t));</span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_6" id="pnum_6">1</a></span> <em>Returns</em>: <code class="sourceCode cpp"><span class="op">+</span>std<span class="op">::</span>forward<span class="op"><</span>T<span class="op">>(</span>t<span class="op">)</span></code>.</p>
<h4 id="class-dereference-additional.operations.dereference">Class <code class="sourceCode cpp">dereference</code> [additional.operations.dereference]<a href="#class-dereference-additional.operations.dereference" class="self-link"></a></h4>
<div class="sourceCode" id="cb24"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb24-1"><a href="#cb24-1"></a>struct dereference {</span>
<span id="cb24-2"><a href="#cb24-2"></a> template<class T> constexpr auto operator()(T&& t) const</span>
<span id="cb24-3"><a href="#cb24-3"></a> -> decltype(*std::forward<T>(t));</span>
<span id="cb24-4"><a href="#cb24-4"></a></span>
<span id="cb24-5"><a href="#cb24-5"></a> using is_transparent = <em>unspecified</em>;</span>
<span id="cb24-6"><a href="#cb24-6"></a>};</span></code></pre></div>
<div class="sourceCode" id="cb25"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb25-1"><a href="#cb25-1"></a>template<class T> constexpr auto operator()(T&& t) const</span>
<span id="cb25-2"><a href="#cb25-2"></a> -> decltype(*std::forward<T>(t));</span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_7" id="pnum_7">1</a></span> <em>Returns</em>: <code class="sourceCode cpp"><span class="op">*</span>std<span class="op">::</span>forward<span class="op"><</span>T<span class="op">>(</span>t<span class="op">)</span></code>.</p>
<h4 id="class-increment-additional.operations.increment">Class <code class="sourceCode cpp">increment</code> [additional.operations.increment]<a href="#class-increment-additional.operations.increment" class="self-link"></a></h4>
<div class="sourceCode" id="cb26"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb26-1"><a href="#cb26-1"></a>struct increment {</span>
<span id="cb26-2"><a href="#cb26-2"></a> template<class T> constexpr auto operator()(T&& t) const</span>
<span id="cb26-3"><a href="#cb26-3"></a> -> decltype(++std::forward<T>(t));</span>
<span id="cb26-4"><a href="#cb26-4"></a></span>
<span id="cb26-5"><a href="#cb26-5"></a> using is_transparent = <em>unspecified</em>;</span>
<span id="cb26-6"><a href="#cb26-6"></a>};</span></code></pre></div>
<div class="sourceCode" id="cb27"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb27-1"><a href="#cb27-1"></a>template<class T> constexpr auto operator()(T&& t) const</span>
<span id="cb27-2"><a href="#cb27-2"></a> -> decltype(++std::forward<T>(t));</span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_8" id="pnum_8">1</a></span> <em>Returns</em>: <code class="sourceCode cpp"><span class="op">++</span>std<span class="op">::</span>forward<span class="op"><</span>T<span class="op">>(</span>t<span class="op">)</span></code>.</p>
<h4 id="class-decrement-additional.operations.decrement">Class <code class="sourceCode cpp">decrement</code> [additional.operations.decrement]<a href="#class-decrement-additional.operations.decrement" class="self-link"></a></h4>
<div class="sourceCode" id="cb28"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb28-1"><a href="#cb28-1"></a>struct decrement {</span>
<span id="cb28-2"><a href="#cb28-2"></a> template<class T> constexpr auto operator()(T&& t) const</span>
<span id="cb28-3"><a href="#cb28-3"></a> -> decltype(--std::forward<T>(t));</span>
<span id="cb28-4"><a href="#cb28-4"></a></span>
<span id="cb28-5"><a href="#cb28-5"></a> using is_transparent = <em>unspecified</em>;</span>
<span id="cb28-6"><a href="#cb28-6"></a>};</span></code></pre></div>
<div class="sourceCode" id="cb29"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb29-1"><a href="#cb29-1"></a>template<class T> constexpr auto operator()(T&& t) const</span>
<span id="cb29-2"><a href="#cb29-2"></a> -> decltype(--std::forward<T>(t));</span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_9" id="pnum_9">1</a></span> <em>Returns</em>: <code class="sourceCode cpp"><span class="op">--</span>std<span class="op">::</span>forward<span class="op"><</span>T<span class="op">>(</span>t<span class="op">)</span></code>.</p>
<h4 id="class-postfix_increment-additional.operations.postfix_increment">Class <code class="sourceCode cpp">postfix_increment</code> [additional.operations.postfix_increment]<a href="#class-postfix_increment-additional.operations.postfix_increment" class="self-link"></a></h4>
<div class="sourceCode" id="cb30"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb30-1"><a href="#cb30-1"></a>struct postfix_increment {</span>
<span id="cb30-2"><a href="#cb30-2"></a> template<class T> constexpr auto operator()(T&& t) const</span>
<span id="cb30-3"><a href="#cb30-3"></a> -> decltype(std::forward<T>(t)++);</span>
<span id="cb30-4"><a href="#cb30-4"></a></span>
<span id="cb30-5"><a href="#cb30-5"></a> using is_transparent = <em>unspecified</em>;</span>
<span id="cb30-6"><a href="#cb30-6"></a>};</span></code></pre></div>
<div class="sourceCode" id="cb31"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb31-1"><a href="#cb31-1"></a>template<class T> constexpr auto operator()(T&& t) const</span>
<span id="cb31-2"><a href="#cb31-2"></a> -> decltype(std::forward<T>(t)++);</span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_10" id="pnum_10">1</a></span> <em>Returns</em>: <code class="sourceCode cpp">std<span class="op">::</span>forward<span class="op"><</span>T<span class="op">>(</span>t<span class="op">)++</span></code>.</p>
<h4 id="class-postfix_decrement-additional.operations.postfix_decrement">Class <code class="sourceCode cpp">postfix_decrement</code> [additional.operations.postfix_decrement]<a href="#class-postfix_decrement-additional.operations.postfix_decrement" class="self-link"></a></h4>
<div class="sourceCode" id="cb32"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb32-1"><a href="#cb32-1"></a>struct postfix_decrement {</span>
<span id="cb32-2"><a href="#cb32-2"></a> template<class T> constexpr auto operator()(T&& t) const</span>
<span id="cb32-3"><a href="#cb32-3"></a> -> decltype(std::forward<T>(t)--);</span>
<span id="cb32-4"><a href="#cb32-4"></a></span>
<span id="cb32-5"><a href="#cb32-5"></a> using is_transparent = <em>unspecified</em>;</span>
<span id="cb32-6"><a href="#cb32-6"></a>};</span></code></pre></div>
<div class="sourceCode" id="cb33"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb33-1"><a href="#cb33-1"></a>template<class T> constexpr auto operator()(T&& t) const</span>
<span id="cb33-2"><a href="#cb33-2"></a> -> decltype(std::forward<T>(t)--);</span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_11" id="pnum_11">1</a></span> <em>Returns</em>: <code class="sourceCode cpp">std<span class="op">::</span>forward<span class="op"><</span>T<span class="op">>(</span>t<span class="op">)--</span></code>.</p>
<h3 id="compound-assignment-operations-compound.operations">Compound assignment operations [compound.operations]<a href="#compound-assignment-operations-compound.operations" class="self-link"></a></h3>
<h4 id="class-plus_equal-compound.operations.plus_equal">Class <code class="sourceCode cpp">plus_equal</code> [compound.operations.plus_equal]<a href="#class-plus_equal-compound.operations.plus_equal" class="self-link"></a></h4>
<div class="sourceCode" id="cb34"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb34-1"><a href="#cb34-1"></a>struct plus_equal {</span>
<span id="cb34-2"><a href="#cb34-2"></a> template<class T, class U> constexpr auto operator()(T&& t, U&& u) const</span>
<span id="cb34-3"><a href="#cb34-3"></a> -> decltype(std::forward<T>(t) += std::forward<U>(u));</span>
<span id="cb34-4"><a href="#cb34-4"></a></span>
<span id="cb34-5"><a href="#cb34-5"></a> using is_transparent = <em>unspecified</em>;</span>
<span id="cb34-6"><a href="#cb34-6"></a>};</span></code></pre></div>
<div class="sourceCode" id="cb35"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb35-1"><a href="#cb35-1"></a>template<class T, class U> constexpr auto operator()(T&& t, U&& u) const</span>
<span id="cb35-2"><a href="#cb35-2"></a> -> decltype(std::forward<T>(t) += std::forward<U>(u));</span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_12" id="pnum_12">1</a></span> <em>Returns</em>: <code class="sourceCode cpp">std<span class="op">::</span>forward<span class="op"><</span>T<span class="op">>(</span>t<span class="op">)</span> <span class="op">+=</span> std<span class="op">::</span>forward<span class="op"><</span>U<span class="op">>(</span>u<span class="op">)</span></code>.</p>
<h4 id="class-minus_equal-compound.operations.minus_equal">Class <code class="sourceCode cpp">minus_equal</code> [compound.operations.minus_equal]<a href="#class-minus_equal-compound.operations.minus_equal" class="self-link"></a></h4>
<div class="sourceCode" id="cb36"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb36-1"><a href="#cb36-1"></a>struct minus_equal {</span>
<span id="cb36-2"><a href="#cb36-2"></a> template<class T, class U> constexpr auto operator()(T&& t, U&& u) const</span>
<span id="cb36-3"><a href="#cb36-3"></a> -> decltype(std::forward<T>(t) -= std::forward<U>(u));</span>
<span id="cb36-4"><a href="#cb36-4"></a></span>
<span id="cb36-5"><a href="#cb36-5"></a> using is_transparent = <em>unspecified</em>;</span>
<span id="cb36-6"><a href="#cb36-6"></a>};</span></code></pre></div>
<div class="sourceCode" id="cb37"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb37-1"><a href="#cb37-1"></a>template<class T, class U> constexpr auto operator()(T&& t, U&& u) const</span>
<span id="cb37-2"><a href="#cb37-2"></a> -> decltype(std::forward<T>(t) -= std::forward<U>(u));</span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_13" id="pnum_13">1</a></span> <em>Returns</em>: <code class="sourceCode cpp">std<span class="op">::</span>forward<span class="op"><</span>T<span class="op">>(</span>t<span class="op">)</span> <span class="op">-=</span> std<span class="op">::</span>forward<span class="op"><</span>U<span class="op">>(</span>u<span class="op">)</span></code>.</p>
<h4 id="class-multiplies_equal-compound.operations.multiplies_equal">Class <code class="sourceCode cpp">multiplies_equal</code> [compound.operations.multiplies_equal]<a href="#class-multiplies_equal-compound.operations.multiplies_equal" class="self-link"></a></h4>
<div class="sourceCode" id="cb38"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb38-1"><a href="#cb38-1"></a>struct multiplies_equal {</span>
<span id="cb38-2"><a href="#cb38-2"></a> template<class T, class U> constexpr auto operator()(T&& t, U&& u) const</span>
<span id="cb38-3"><a href="#cb38-3"></a> -> decltype(std::forward<T>(t) *= std::forward<U>(u));</span>
<span id="cb38-4"><a href="#cb38-4"></a></span>
<span id="cb38-5"><a href="#cb38-5"></a> using is_transparent = <em>unspecified</em>;</span>
<span id="cb38-6"><a href="#cb38-6"></a>};</span></code></pre></div>
<div class="sourceCode" id="cb39"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb39-1"><a href="#cb39-1"></a>template<class T, class U> constexpr auto operator()(T&& t, U&& u) const</span>
<span id="cb39-2"><a href="#cb39-2"></a> -> decltype(std::forward<T>(t) *= std::forward<U>(u));</span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_14" id="pnum_14">1</a></span> <em>Returns</em>: <code class="sourceCode cpp">std<span class="op">::</span>forward<span class="op"><</span>T<span class="op">>(</span>t<span class="op">)</span> <span class="op">*=</span> std<span class="op">::</span>forward<span class="op"><</span>U<span class="op">>(</span>u<span class="op">)</span></code>.</p>
<h4 id="class-divides_equal-compound.operations.divides_equal">Class <code class="sourceCode cpp">divides_equal</code> [compound.operations.divides_equal]<a href="#class-divides_equal-compound.operations.divides_equal" class="self-link"></a></h4>
<div class="sourceCode" id="cb40"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb40-1"><a href="#cb40-1"></a>struct divides_equal {</span>
<span id="cb40-2"><a href="#cb40-2"></a> template<class T, class U> constexpr auto operator()(T&& t, U&& u) const</span>
<span id="cb40-3"><a href="#cb40-3"></a> -> decltype(std::forward<T>(t) /= std::forward<U>(u));</span>
<span id="cb40-4"><a href="#cb40-4"></a></span>
<span id="cb40-5"><a href="#cb40-5"></a> using is_transparent = <em>unspecified</em>;</span>
<span id="cb40-6"><a href="#cb40-6"></a>};</span></code></pre></div>
<div class="sourceCode" id="cb41"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb41-1"><a href="#cb41-1"></a>template<class T, class U> constexpr auto operator()(T&& t, U&& u) const</span>
<span id="cb41-2"><a href="#cb41-2"></a> -> decltype(std::forward<T>(t) /= std::forward<U>(u));</span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_15" id="pnum_15">1</a></span> <em>Returns</em>: <code class="sourceCode cpp">std<span class="op">::</span>forward<span class="op"><</span>T<span class="op">>(</span>t<span class="op">)</span> <span class="op">/=</span> std<span class="op">::</span>forward<span class="op"><</span>U<span class="op">>(</span>u<span class="op">)</span></code>.</p>
<h4 id="class-modulus_equal-compound.operations.modulus_equal">Class <code class="sourceCode cpp">modulus_equal</code> [compound.operations.modulus_equal]<a href="#class-modulus_equal-compound.operations.modulus_equal" class="self-link"></a></h4>
<div class="sourceCode" id="cb42"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb42-1"><a href="#cb42-1"></a>struct modulus_equal {</span>
<span id="cb42-2"><a href="#cb42-2"></a> template<class T, class U> constexpr auto operator()(T&& t, U&& u) const</span>
<span id="cb42-3"><a href="#cb42-3"></a> -> decltype(std::forward<T>(t) %= std::forward<U>(u));</span>
<span id="cb42-4"><a href="#cb42-4"></a></span>
<span id="cb42-5"><a href="#cb42-5"></a> using is_transparent = <em>unspecified</em>;</span>
<span id="cb42-6"><a href="#cb42-6"></a>};</span></code></pre></div>
<div class="sourceCode" id="cb43"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb43-1"><a href="#cb43-1"></a>template<class T, class U> constexpr auto operator()(T&& t, U&& u) const</span>
<span id="cb43-2"><a href="#cb43-2"></a> -> decltype(std::forward<T>(t) %= std::forward<U>(u));</span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_16" id="pnum_16">1</a></span> <em>Returns</em>: <code class="sourceCode cpp">std<span class="op">::</span>forward<span class="op"><</span>T<span class="op">>(</span>t<span class="op">)</span> <span class="op">%=</span> std<span class="op">::</span>forward<span class="op"><</span>U<span class="op">>(</span>u<span class="op">)</span></code>.</p>
<h4 id="class-bit_and_equal-compound.operations.bit_and_equal">Class <code class="sourceCode cpp">bit_and_equal</code> [compound.operations.bit_and_equal]<a href="#class-bit_and_equal-compound.operations.bit_and_equal" class="self-link"></a></h4>
<div class="sourceCode" id="cb44"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb44-1"><a href="#cb44-1"></a>struct bit_and_equal {</span>
<span id="cb44-2"><a href="#cb44-2"></a> template<class T, class U> constexpr auto operator()(T&& t, U&& u) const</span>
<span id="cb44-3"><a href="#cb44-3"></a> -> decltype(std::forward<T>(t) &= std::forward<U>(u));</span>
<span id="cb44-4"><a href="#cb44-4"></a></span>
<span id="cb44-5"><a href="#cb44-5"></a> using is_transparent = <em>unspecified</em>;</span>
<span id="cb44-6"><a href="#cb44-6"></a>};</span></code></pre></div>
<div class="sourceCode" id="cb45"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb45-1"><a href="#cb45-1"></a>template<class T, class U> constexpr auto operator()(T&& t, U&& u) const</span>
<span id="cb45-2"><a href="#cb45-2"></a> -> decltype(std::forward<T>(t) &= std::forward<U>(u));</span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_17" id="pnum_17">1</a></span> <em>Returns</em>: <code class="sourceCode cpp">std<span class="op">::</span>forward<span class="op"><</span>T<span class="op">>(</span>t<span class="op">)</span> <span class="op">&=</span> std<span class="op">::</span>forward<span class="op"><</span>U<span class="op">>(</span>u<span class="op">)</span></code>.</p>
<h4 id="class-bit_or_equal-compound.operations.bit_or_equal">Class <code class="sourceCode cpp">bit_or_equal</code> [compound.operations.bit_or_equal]<a href="#class-bit_or_equal-compound.operations.bit_or_equal" class="self-link"></a></h4>
<div class="sourceCode" id="cb46"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb46-1"><a href="#cb46-1"></a>struct bit_or_equal {</span>
<span id="cb46-2"><a href="#cb46-2"></a> template<class T, class U> constexpr auto operator()(T&& t, U&& u) const</span>
<span id="cb46-3"><a href="#cb46-3"></a> -> decltype(std::forward<T>(t) |= std::forward<U>(u));</span>
<span id="cb46-4"><a href="#cb46-4"></a></span>
<span id="cb46-5"><a href="#cb46-5"></a> using is_transparent = <em>unspecified</em>;</span>
<span id="cb46-6"><a href="#cb46-6"></a>};</span></code></pre></div>
<div class="sourceCode" id="cb47"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb47-1"><a href="#cb47-1"></a>template<class T, class U> constexpr auto operator()(T&& t, U&& u) const</span>
<span id="cb47-2"><a href="#cb47-2"></a> -> decltype(std::forward<T>(t) |= std::forward<U>(u));</span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_18" id="pnum_18">1</a></span> <em>Returns</em>: <code class="sourceCode cpp">std<span class="op">::</span>forward<span class="op"><</span>T<span class="op">>(</span>t<span class="op">)</span> <span class="op">|=</span> std<span class="op">::</span>forward<span class="op"><</span>U<span class="op">>(</span>u<span class="op">)</span></code>.</p>
<h4 id="class-bit_xor_equal-compound.operations.bit_xor_equal">Class <code class="sourceCode cpp">bit_xor_equal</code> [compound.operations.bit_xor_equal]<a href="#class-bit_xor_equal-compound.operations.bit_xor_equal" class="self-link"></a></h4>
<div class="sourceCode" id="cb48"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb48-1"><a href="#cb48-1"></a>struct bit_xor_equal {</span>
<span id="cb48-2"><a href="#cb48-2"></a> template<class T, class U> constexpr auto operator()(T&& t, U&& u) const</span>
<span id="cb48-3"><a href="#cb48-3"></a> -> decltype(std::forward<T>(t) ^= std::forward<U>(u));</span>
<span id="cb48-4"><a href="#cb48-4"></a></span>
<span id="cb48-5"><a href="#cb48-5"></a> using is_transparent = <em>unspecified</em>;</span>