<!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="2021-11-19" />
  <title>views::chunk_by</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 {
      pre > code.sourceCode { white-space: pre-wrap; }
      pre > code.sourceCode > span { text-indent: -5em; padding-left: 5em; }
      }
      pre.numberSource code
        { counter-reset: source-line 0; }
      pre.numberSource code > span
        { 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;
          -khtml-user-select: none; -moz-user-select: none;
          -ms-user-select: none; user-select: none;
          padding: 0 4px; width: 4em;
          color: #aaaaaa;
        }
      pre.numberSource { margin-left: 3em; border-left: 1px solid #aaaaaa;  padding-left: 4px; }
      div.sourceCode
        {  background-color: #f6f8fa; }
      @media screen {
      pre > code.sourceCode > span > a:first-child::before { text-decoration: underline; }
      }
      code span. { } /* Normal */
      code span.al { color: #ff0000; } /* Alert */
      code span.an { } /* Annotation */
      code span.at { } /* Attribute */
      code span.bn { color: #9f6807; } /* BaseN */
      code span.bu { color: #9f6807; } /* BuiltIn */
      code span.cf { color: #00607c; } /* ControlFlow */
      code span.ch { color: #9f6807; } /* Char */
      code span.cn { } /* Constant */
      code span.co { color: #008000; font-style: italic; } /* Comment */
      code span.cv { color: #008000; font-style: italic; } /* CommentVar */
      code span.do { color: #008000; } /* Documentation */
      code span.dt { color: #00607c; } /* DataType */
      code span.dv { color: #9f6807; } /* DecVal */
      code span.er { color: #ff0000; font-weight: bold; } /* Error */
      code span.ex { } /* Extension */
      code span.fl { color: #9f6807; } /* Float */
      code span.fu { } /* Function */
      code span.im { } /* Import */
      code span.in { color: #008000; } /* Information */
      code span.kw { color: #00607c; } /* Keyword */
      code span.op { color: #af1915; } /* Operator */
      code span.ot { } /* Other */
      code span.pp { color: #6f4e37; } /* Preprocessor */
      code span.re { } /* RegionMarker */
      code span.sc { color: #9f6807; } /* SpecialChar */
      code span.ss { color: #9f6807; } /* SpecialString */
      code span.st { color: #9f6807; } /* String */
      code span.va { } /* Variable */
      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}
  </style>
  <style type="text/css">
body {
margin: 5em;
font-family: serif;

hyphens: auto;
line-height: 1.35;
}
div.wrapper {
max-width: 60em;
margin: auto;
}
ul {
list-style-type: none;
padding-left: 2em;
margin-top: -0.2em;
margin-bottom: -0.2em;
}
a {
text-decoration: none;
color: #4183C4;
}
a.hidden_link {
text-decoration: none;
color: inherit;
}
li {
margin-top: 0.6em;
margin-bottom: 0.6em;
}
h1, h2, h3, h4 {
position: relative;
line-height: 1;
}
a.self-link {
position: absolute;
top: 0;
left: calc(-1 * (3.5rem - 26px));
width: calc(3.5rem - 26px);
height: 2em;
text-align: center;
border: none;
transition: opacity .2s;
opacity: .5;
font-family: sans-serif;
font-weight: normal;
font-size: 83%;
}
a.self-link:hover { opacity: 1; }
a.self-link::before { content: "§"; }
ul > li:before {
content: "\2014";
position: absolute;
margin-left: -1.5em;
}
:target { background-color: #C9FBC9; }
:target .codeblock { background-color: #C9FBC9; }
:target ul { background-color: #C9FBC9; }
.abbr_ref { float: right; }
.folded_abbr_ref { float: right; }
:target .folded_abbr_ref { display: none; }
:target .unfolded_abbr_ref { float: right; display: inherit; }
.unfolded_abbr_ref { display: none; }
.secnum { display: inline-block; min-width: 35pt; }
.header-section-number { display: inline-block; min-width: 35pt; }
.annexnum { display: block; }
div.sourceLinkParent {
float: right;
}
a.sourceLink {
position: absolute;
opacity: 0;
margin-left: 10pt;
}
a.sourceLink:hover {
opacity: 1;
}
a.itemDeclLink {
position: absolute;
font-size: 75%;
text-align: right;
width: 5em;
opacity: 0;
}
a.itemDeclLink:hover { opacity: 1; }
span.marginalizedparent {
position: relative;
left: -5em;
}
li span.marginalizedparent { left: -7em; }
li ul > li span.marginalizedparent { left: -9em; }
li ul > li ul > li span.marginalizedparent { left: -11em; }
li ul > li ul > li ul > li span.marginalizedparent { left: -13em; }
div.footnoteNumberParent {
position: relative;
left: -4.7em;
}
a.marginalized {
position: absolute;
font-size: 75%;
text-align: right;
width: 5em;
}
a.enumerated_item_num {
position: relative;
left: -3.5em;
display: inline-block;
margin-right: -3em;
text-align: right;
width: 3em;
}
div.para { margin-bottom: 0.6em; margin-top: 0.6em; text-align: justify; }
div.section { text-align: justify; }
div.sentence { display: inline; }
span.indexparent {
display: inline;
position: relative;
float: right;
right: -1em;
}
a.index {
position: absolute;
display: none;
}
a.index:before { content: "⟵"; }

a.index:target {
display: inline;
}
.indexitems {
margin-left: 2em;
text-indent: -2em;
}
div.itemdescr {
margin-left: 3em;
}
.bnf {
font-family: serif;
margin-left: 40pt;
margin-top: 0.5em;
margin-bottom: 0.5em;
}
.ncbnf {
font-family: serif;
margin-top: 0.5em;
margin-bottom: 0.5em;
margin-left: 40pt;
}
.ncsimplebnf {
font-family: serif;
font-style: italic;
margin-top: 0.5em;
margin-bottom: 0.5em;
margin-left: 40pt;
background: inherit; 
}
span.textnormal {
font-style: normal;
font-family: serif;
white-space: normal;
display: inline-block;
}
span.rlap {
display: inline-block;
width: 0px;
}
span.descr { font-style: normal; font-family: serif; }
span.grammarterm { font-style: italic; }
span.term { font-style: italic; }
span.terminal { font-family: monospace; font-style: normal; }
span.nonterminal { font-style: italic; }
span.tcode { font-family: monospace; font-style: normal; }
span.textbf { font-weight: bold; }
span.textsc { font-variant: small-caps; }
a.nontermdef { font-style: italic; font-family: serif; }
span.emph { font-style: italic; }
span.techterm { font-style: italic; }
span.mathit { font-style: italic; }
span.mathsf { font-family: sans-serif; }
span.mathrm { font-family: serif; font-style: normal; }
span.textrm { font-family: serif; }
span.textsl { font-style: italic; }
span.mathtt { font-family: monospace; font-style: normal; }
span.mbox { font-family: serif; font-style: normal; }
span.ungap { display: inline-block; width: 2pt; }
span.textit { font-style: italic; }
span.texttt { font-family: monospace; }
span.tcode_in_codeblock { font-family: monospace; font-style: normal; }
span.phantom { color: white; }

span.math { font-style: normal; }
span.mathblock {
display: block;
margin-left: auto;
margin-right: auto;
margin-top: 1.2em;
margin-bottom: 1.2em;
text-align: center;
}
span.mathalpha {
font-style: italic;
}
span.synopsis {
font-weight: bold;
margin-top: 0.5em;
display: block;
}
span.definition {
font-weight: bold;
display: block;
}
.codeblock {
margin-left: 1.2em;
line-height: 127%;
}
.outputblock {
margin-left: 1.2em;
line-height: 127%;
}
div.itemdecl {
margin-top: 2ex;
}
code.itemdeclcode {
white-space: pre;
display: block;
}
span.textsuperscript {
vertical-align: super;
font-size: smaller;
line-height: 0;
}
.footnotenum { vertical-align: super; font-size: smaller; line-height: 0; }
.footnote {
font-size: small;
margin-left: 2em;
margin-right: 2em;
margin-top: 0.6em;
margin-bottom: 0.6em;
}
div.minipage {
display: inline-block;
margin-right: 3em;
}
div.numberedTable {
text-align: center;
margin: 2em;
}
div.figure {
text-align: center;
margin: 2em;
}
table {
border: 1px solid black;
border-collapse: collapse;
margin-left: auto;
margin-right: auto;
margin-top: 0.8em;
text-align: left;
hyphens: none; 
}
td, th {
padding-left: 1em;
padding-right: 1em;
vertical-align: top;
}
td.empty {
padding: 0px;
padding-left: 1px;
}
td.left {
text-align: left;
}
td.right {
text-align: right;
}
td.center {
text-align: center;
}
td.justify {
text-align: justify;
}
td.border {
border-left: 1px solid black;
}
tr.rowsep, td.cline {
border-top: 1px solid black;
}
tr.even, tr.odd {
border-bottom: 1px solid black;
}
tr.capsep {
border-top: 3px solid black;
border-top-style: double;
}
tr.header {
border-bottom: 3px solid black;
border-bottom-style: double;
}
th {
border-bottom: 1px solid black;
}
span.centry {
font-weight: bold;
}
div.table {
display: block;
margin-left: auto;
margin-right: auto;
text-align: center;
width: 90%;
}
span.indented {
display: block;
margin-left: 2em;
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; }
h4:target { background-color: transparent; }
h5:target { background-color: transparent; }
h6:target { background-color: transparent; }
.marginalized: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;
}
table th {
border-bottom: 1px solid black;
text-align: center;
}
table tr:first-child th {
border-top: 0;
}
table tr:last-child td {
border-bottom: 0;
}
table tr td:first-child,
table tr th:first-child {
border-left: 0;
}
table tr td:last-child,
table tr th:last-child {
border-right: 0;
}
table tbody tr:first-child td {
border-top: 1px solid black;
}
#title-block-header td { border: 0; }
@media all {
body {
margin: 2em;
}
}
@media screen and (min-width: 480px) {
body {
margin: 5em;
}
}
#refs code{padding-left: 0px; text-indent: 0px;}
:root {
--diff-ins: #e6ffed;
--diff-strongins: #acf2bd;
--diff-del: #ffdddd;
--diff-strongdel: #ff8888;
}
span.diffins {
background-color: var(--diff-strongins);
}
span.diffdel {
background-color: var(--diff-strongdel);
}
div.rm { text-decoration: line-through; }
div.rm code.sourceCode { text-decoration: line-through; }
div.addu, span.addu {
color: #006e28;
background-color: var(--diff-ins);
}

div.rm pre, div.add pre { background-color: #f6f8fa; }
div.addu pre { background-color: var(--diff-ins); }
div.add, div.add pre, div.add blockquote { background-color: var(--diff-ins); }
div.addu blockquote {
border-left: 4px solid #00a000;
padding: 0 15px;
color: #006e28;
text-decoration: none;
}
div.addu blockquote code.sourceCode { text-decoration: none; }
div.addu blockquote pre { text-decoration: none; }
div.addu blockquote pre code { text-decoration: none; }
code.diff span.va { color: #000000; background-color: var(--diff-ins); }
code.diff span.st { color: #000000; background-color: var(--diff-del); }
blockquote { background-color: #f6f8fa; }
@media (prefers-color-scheme: dark) {
:root {
--diff-ins: #225522;
--diff-strongins: #225522;
--diff-del: #662222;
--diff-strongdel: #662222;
}
body {
background-color: #171717;
color: #b0b0b0;
}
table tr {
background-color: #171717;
}
table tr:nth-child(2n) {
background-color: #252525;
}
#title-block-header > table tr:nth-child(2n) {
background-color: #171717;
}
tr.header {
border-bottom: 3px solid #b0b0b0;
border-bottom-style: double;
}
tr.even, tr.odd {
border-bottom: 1px solid #b0b0b0;
}
table th {
border-bottom: 1px solid #b0b0b0;
}
table tbody tr:first-child td {
border-top: 1px solid #b0b0b0;
}
blockquote { background-color: rgba(255, 255, 255, .03); }
a { color: #549df2; }
div.sourceCode
{ background-color: rgba(255, 255, 255, .03); }
table { border-color: #b0b0b0; }
td.border { border-color: #b0b0b0; }
td.border { border-left-color: #b0b0b0; }
tr.rowsep, td.cline { border-top-color: #b0b0b0; }
tr.capsep { border-top-color: #b0b0b0; }
th { border-bottom-color: #b0b0b0; }
code span.kw { color: #12cabe; }
code span.cf { color: #12cabe; }
code span.op { color: #cf1915; }
code span.pp { color: #b27c58; }
code span.co { color: #35ba00; }
code.diff span.va {
color: #b0b0b0;
}
code.diff span.vd {
color: #b0b0b0;
}
div.add {
color: #d0fddd !important
}
div.rm {
color: #8f3131 !important
}
div.rm pre, div.add pre { background-color: rgba(255, 255, 255, .03); }
}
</style>
  <link href="data:image/x-icon;base64,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" rel="icon" />
  <!--[if lt IE 9]>
    <script src="//cdnjs.cloudflare.com/ajax/libs/html5shiv/3.7.3/html5shiv-printshiv.min.js"></script>
  <![endif]-->
  
</head>
<body>
<div class="wrapper">
<header id="title-block-header">
<h1 class="title" style="text-align:center"><code class="sourceCode cpp">views<span class="op">::</span>chunk_by</code></h1>

<table style="border:none;float:right">
  <tr>
    <td>Document #:</td>
    <td>P2443R1</td>
  </tr>
  <tr>
    <td>Date:</td>
    <td>2021-11-19</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>
      LWG<br>
    </td>
  </tr>
  <tr>
    <td style="vertical-align:top">Reply-to:</td>
    <td>
      Tim Song<br>&lt;<a href="mailto:t.canens.cpp@gmail.com" class="email">t.canens.cpp@gmail.com</a>&gt;<br>
    </td>
  </tr>
</table>

</header>
<div style="clear:both">
<div id="TOC" role="doc-toc">
<h1 id="toctitle">Contents</h1>
<ul>
<li><a href="#revision-history"><span class="toc-section-number">1</span> Revision history<span></span></a></li>
<li><a href="#abstract"><span class="toc-section-number">2</span> Abstract<span></span></a></li>
<li><a href="#example"><span class="toc-section-number">3</span> Example<span></span></a></li>
<li><a href="#design"><span class="toc-section-number">4</span> Design<span></span></a>
<ul>
<li><a href="#predicate-not-equivalence"><span class="toc-section-number">4.1</span> Predicate, not equivalence<span></span></a></li>
<li><a href="#no-input-ranges"><span class="toc-section-number">4.2</span> No input ranges<span></span></a></li>
<li><a href="#properties"><span class="toc-section-number">4.3</span> Properties<span></span></a></li>
<li><a href="#caching"><span class="toc-section-number">4.4</span> Caching<span></span></a></li>
<li><a href="#implementation-experience"><span class="toc-section-number">4.5</span> Implementation experience<span></span></a></li>
</ul></li>
<li><a href="#wording"><span class="toc-section-number">5</span> Wording<span></span></a>
<ul>
<li><a href="#addition-to-ranges"><span class="toc-section-number">5.1</span> Addition to <code class="sourceCode cpp"><span class="op">&lt;</span>ranges<span class="op">&gt;</span></code><span></span></a></li>
<li><a href="#chunk_by"><span class="toc-section-number">5.2</span> <code class="sourceCode cpp">chunk_by</code><span></span></a>
<ul>
<li><a href="#chunk-by-view-range.chunk.by">24.7.? Chunk by view [range.chunk.by]<span></span></a></li>
</ul></li>
<li><a href="#feature-test-macro"><span class="toc-section-number">5.3</span> Feature-test macro<span></span></a></li>
</ul></li>
<li><a href="#bibliography"><span class="toc-section-number">6</span> References<span></span></a></li>
</ul>
</div>
<h1 data-number="1" style="border-bottom:1px solid #cccccc" id="revision-history"><span class="header-section-number">1</span> Revision history<a href="#revision-history" class="self-link"></a></h1>
<ul>
<li>R1: Incorporated LWG review feedback.</li>
</ul>
<h1 data-number="2" style="border-bottom:1px solid #cccccc" id="abstract"><span class="header-section-number">2</span> Abstract<a href="#abstract" class="self-link"></a></h1>
<p>This paper proposes the range adaptor <code class="sourceCode cpp">views<span class="op">::</span>chunk_by</code> as described in section 4.3 of <span class="citation" data-cites="P2214R1">[<a href="#ref-P2214R1" role="doc-biblioref">P2214R1</a>]</span>.</p>
<h1 data-number="3" style="border-bottom:1px solid #cccccc" id="example"><span class="header-section-number">3</span> Example<a href="#example" class="self-link"></a></h1>
<div class="sourceCode" id="cb1"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb1-1"><a href="#cb1-1"></a>std<span class="op">::</span>vector v <span class="op">=</span> <span class="op">{</span><span class="dv">1</span>, <span class="dv">2</span>, <span class="dv">2</span>, <span class="dv">3</span>, <span class="dv">0</span>, <span class="dv">4</span>, <span class="dv">5</span>, <span class="dv">2</span><span class="op">}</span>;</span>
<span id="cb1-2"><a href="#cb1-2"></a>fmt<span class="op">::</span>print<span class="op">(</span><span class="st">&quot;{}</span><span class="sc">\n</span><span class="st">&quot;</span>, v <span class="op">|</span> std<span class="op">::</span>views<span class="op">::</span>chunk_by<span class="op">(</span>ranges<span class="op">::</span>less_equal<span class="op">{}))</span>;   <span class="co">// [[1, 2, 2, 3], [0, 4, 5], [2]]</span></span></code></pre></div>
<h1 data-number="4" style="border-bottom:1px solid #cccccc" id="design"><span class="header-section-number">4</span> Design<a href="#design" class="self-link"></a></h1>
<p>Section 4.3 of <span class="citation" data-cites="P2214R1">[<a href="#ref-P2214R1" role="doc-biblioref">P2214R1</a>]</span> contains an extensive discussion of <code class="sourceCode cpp">chunk_by</code> and similar range algorithms in numerous other languages. The discussion here assumes familiarity with that paper.</p>
<h2 data-number="4.1" id="predicate-not-equivalence"><span class="header-section-number">4.1</span> Predicate, not equivalence<a href="#predicate-not-equivalence" class="self-link"></a></h2>
<p>D’s <code class="sourceCode cpp">chunkBy</code> <a href="https://dlang.org/library/std/algorithm/iteration/chunk_by.html">requires</a> the predicate to be an equivalence relation. The initial implementation of range-v3’s <code class="sourceCode cpp">group_by</code> appeared to tacitly assume this as well, as it was not functional <a href="https://github.com/ericniebler/range-v3/issues/1393">if <code class="sourceCode cpp">pred<span class="op">(*</span>first, <span class="op">*</span>first<span class="op">)</span></code> returns <code class="sourceCode cpp"><span class="kw">false</span></code></a>.</p>
<p>There does not appear to be a compelling reason to require an equivalence relation. Indeed, D provides virtually the same functionality for general predicates under the name <code class="sourceCode cpp">splitWhen</code>. The <code class="sourceCode cpp">chunk_by</code> proposed in this paper therefore does not require equivalence.</p>
<h2 data-number="4.2" id="no-input-ranges"><span class="header-section-number">4.2</span> No input ranges<a href="#no-input-ranges" class="self-link"></a></h2>
<p>Since <code class="sourceCode cpp">chunk_by</code> needs to evaluate the predicate on adjacent elements, it requires forward ranges. Caching elements is not considered a viable approach, essentially for the reasons discussed in section 4.3.4 of <span class="citation" data-cites="P2321R2">[<a href="#ref-P2321R2" role="doc-biblioref">P2321R2</a>]</span>.</p>
<h2 data-number="4.3" id="properties"><span class="header-section-number">4.3</span> Properties<a href="#properties" class="self-link"></a></h2>
<p><code class="sourceCode cpp">chunk_by</code> is bidirectional if the underlying range is; otherwise, it is forward. It is common if the underlying range is. It’s never borrowed or sized.</p>
<h2 data-number="4.4" id="caching"><span class="header-section-number">4.4</span> Caching<a href="#caching" class="self-link"></a></h2>
<p>Similar to <code class="sourceCode cpp">split</code>, <code class="sourceCode cpp">chunk_by</code> calculates the end of the first range in its <code class="sourceCode cpp">begin</code> and caches it to meet the amortized <code class="sourceCode cpp">O<span class="op">(</span><span class="dv">1</span><span class="op">)</span></code> requirement. That means that it does not support const-iteration.</p>
<h2 data-number="4.5" id="implementation-experience"><span class="header-section-number">4.5</span> Implementation experience<a href="#implementation-experience" class="self-link"></a></h2>
<p><code class="sourceCode cpp">views<span class="op">::</span>group_by</code> has long been implemented in range-v3, with the difference that it compares against the first element of the group instead of the previous element. A <a href="https://github.com/ericniebler/range-v3/pull/1648"><code class="sourceCode cpp">views<span class="op">::</span>chunk_by</code></a> with the semantics proposed in this paper (except for bidirectional iteration support) has recently been added to range-v3. I also have implemented a version that directly follows the proposed wording below without issue.</p>
<h1 data-number="5" style="border-bottom:1px solid #cccccc" id="wording"><span class="header-section-number">5</span> Wording<a href="#wording" class="self-link"></a></h1>
<h2 data-number="5.1" id="addition-to-ranges"><span class="header-section-number">5.1</span> Addition to <code class="sourceCode cpp"><span class="op">&lt;</span>ranges<span class="op">&gt;</span></code><a href="#addition-to-ranges" class="self-link"></a></h2>
<p>Add the following to <span>24.2 <a href="https://wg21.link/ranges.syn">[ranges.syn]</a></span>, header <code class="sourceCode cpp"><span class="op">&lt;</span>ranges<span class="op">&gt;</span></code> synopsis:</p>
<div class="sourceCode" id="cb2"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb2-1"><a href="#cb2-1"></a><span class="co">// [...]</span></span>
<span id="cb2-2"><a href="#cb2-2"></a><span class="kw">namespace</span> std<span class="op">::</span>ranges <span class="op">{</span></span>
<span id="cb2-3"><a href="#cb2-3"></a>  <span class="co">// [...]</span></span>
<span id="cb2-4"><a href="#cb2-4"></a></span>
<span id="cb2-5"><a href="#cb2-5"></a>  <span class="co">// [range.chunk.by], chunk by view</span></span>
<span id="cb2-6"><a href="#cb2-6"></a>  <span class="kw">template</span><span class="op">&lt;</span>forward_range V, indirect_binary_predicate<span class="op">&lt;</span>iterator_t<span class="op">&lt;</span>V<span class="op">&gt;</span>, iterator_t<span class="op">&lt;</span>V<span class="op">&gt;&gt;</span> Pred<span class="op">&gt;</span></span>
<span id="cb2-7"><a href="#cb2-7"></a>    <span class="kw">requires</span> view<span class="op">&lt;</span>V<span class="op">&gt;</span> <span class="op">&amp;&amp;</span> is_object_v<span class="op">&lt;</span>Pred<span class="op">&gt;</span></span>
<span id="cb2-8"><a href="#cb2-8"></a>  <span class="kw">class</span> chunk_by_view;</span>
<span id="cb2-9"><a href="#cb2-9"></a></span>
<span id="cb2-10"><a href="#cb2-10"></a>  <span class="kw">namespace</span> views <span class="op">{</span></span>
<span id="cb2-11"><a href="#cb2-11"></a>    <span class="kw">inline</span> <span class="kw">constexpr</span> <em>unspecified</em> chunk_by <span class="op">=</span> <em>unspecified</em>;</span>
<span id="cb2-12"><a href="#cb2-12"></a>  <span class="op">}</span></span>
<span id="cb2-13"><a href="#cb2-13"></a></span>
<span id="cb2-14"><a href="#cb2-14"></a><span class="op">}</span></span></code></pre></div>
<h2 data-number="5.2" id="chunk_by"><span class="header-section-number">5.2</span> <code class="sourceCode cpp">chunk_by</code><a href="#chunk_by" class="self-link"></a></h2>
<p>Add the following subclause to <span>24.7 <a href="https://wg21.link/range.adaptors">[range.adaptors]</a></span>.</p>
<h3 class="unnumbered" data-number id="chunk-by-view-range.chunk.by">24.7.? Chunk by view [range.chunk.by]<a href="#chunk-by-view-range.chunk.by" class="self-link"></a></h3>
<h4 class="unnumbered" data-number id="overview-range.chunk.by.overview">24.7.?.1 Overview [range.chunk.by.overview]<a href="#overview-range.chunk.by.overview" class="self-link"></a></h4>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_1" id="pnum_1">1</a></span> <code class="sourceCode cpp">chunk_by_view</code> takes a <code class="sourceCode cpp">view</code> and a predicate, and splits the view into <code class="sourceCode cpp">subrange</code>s between each pair of adjacent elements for which the predicate returns <code class="sourceCode cpp"><span class="kw">false</span></code>.</p>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_2" id="pnum_2">2</a></span> The name <code class="sourceCode cpp">views<span class="op">::</span>chunk_by</code> denotes a range adaptor object (<span>24.7.2 <a href="https://wg21.link/range.adaptor.object">[range.adaptor.object]</a></span>). Given subexpressions <code class="sourceCode cpp">E</code> and <code class="sourceCode cpp">F</code>, the expression <code class="sourceCode cpp">views<span class="op">::</span>chunk_by<span class="op">(</span>E, F<span class="op">)</span></code> is expression-equivalent to <code class="sourceCode cpp">chunk_by_view<span class="op">(</span>E, F<span class="op">)</span></code>.</p>
<div class="example">
<span>[ <em>Example 1:</em> </span>
<div class="sourceCode" id="cb3"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb3-1"><a href="#cb3-1"></a>vector v <span class="op">=</span> <span class="op">{</span><span class="dv">1</span>, <span class="dv">2</span>, <span class="dv">2</span>, <span class="dv">3</span>, <span class="dv">0</span>, <span class="dv">4</span>, <span class="dv">5</span>, <span class="dv">2</span><span class="op">}</span>;</span>
<span id="cb3-2"><a href="#cb3-2"></a></span>
<span id="cb3-3"><a href="#cb3-3"></a><span class="cf">for</span> <span class="op">(</span><span class="kw">auto</span> r <span class="op">:</span> v <span class="op">|</span> views<span class="op">::</span>chunk_by<span class="op">(</span>ranges<span class="op">::</span>less_equal<span class="op">{}))</span> <span class="op">{</span></span>
<span id="cb3-4"><a href="#cb3-4"></a>  cout <span class="op">&lt;&lt;</span> <span class="ch">&#39;[&#39;</span>;</span>
<span id="cb3-5"><a href="#cb3-5"></a>  <span class="kw">auto</span> sep <span class="op">=</span> <span class="st">&quot;&quot;</span>;</span>
<span id="cb3-6"><a href="#cb3-6"></a>  <span class="cf">for</span><span class="op">(</span><span class="kw">auto</span> i <span class="op">:</span> r<span class="op">)</span> <span class="op">{</span></span>
<span id="cb3-7"><a href="#cb3-7"></a>    cout <span class="op">&lt;&lt;</span> sep <span class="op">&lt;&lt;</span> i;</span>
<span id="cb3-8"><a href="#cb3-8"></a>    sep <span class="op">=</span> <span class="st">&quot;, &quot;</span>;</span>
<span id="cb3-9"><a href="#cb3-9"></a>  <span class="op">}</span></span>
<span id="cb3-10"><a href="#cb3-10"></a>  cout <span class="op">&lt;&lt;</span> <span class="st">&quot;] &quot;</span>;</span>
<span id="cb3-11"><a href="#cb3-11"></a><span class="op">}</span></span>
<span id="cb3-12"><a href="#cb3-12"></a><span class="co">// prints: [1, 2, 2, 3] [0, 4, 5] [2]</span></span></code></pre></div>
<span> — <em>end example</em> ]</span>
</div>
<h4 class="unnumbered" data-number id="class-template-chunk_by_view-range.chunk.by.view">24.7.?.2 Class template <code class="sourceCode cpp">chunk_by_view</code> [range.chunk.by.view]<a href="#class-template-chunk_by_view-range.chunk.by.view" class="self-link"></a></h4>
<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">namespace</span> std<span class="op">::</span>ranges <span class="op">{</span></span>
<span id="cb4-2"><a href="#cb4-2"></a></span>
<span id="cb4-3"><a href="#cb4-3"></a><span class="kw">template</span><span class="op">&lt;</span>forward_range V, indirect_binary_predicate<span class="op">&lt;</span>iterator_t<span class="op">&lt;</span>V<span class="op">&gt;</span>, iterator_t<span class="op">&lt;</span>V<span class="op">&gt;&gt;</span> Pred<span class="op">&gt;</span></span>
<span id="cb4-4"><a href="#cb4-4"></a>  <span class="kw">requires</span> view<span class="op">&lt;</span>V<span class="op">&gt;</span> <span class="op">&amp;&amp;</span> is_object_v<span class="op">&lt;</span>Pred<span class="op">&gt;</span></span>
<span id="cb4-5"><a href="#cb4-5"></a><span class="kw">class</span> chunk_by_view <span class="op">:</span> <span class="kw">public</span> view_interface<span class="op">&lt;</span>chunk_by_view<span class="op">&lt;</span>V, Pred<span class="op">&gt;&gt;{</span></span>
<span id="cb4-6"><a href="#cb4-6"></a>  V <em>base_</em> <span class="op">=</span> V<span class="op">()</span>;                          <span class="co">// exposition only</span></span>
<span id="cb4-7"><a href="#cb4-7"></a>  <em>copyable-box</em><span class="op">&lt;</span>Pred<span class="op">&gt;</span> <em>pred_</em> <span class="op">=</span> Pred<span class="op">()</span>;      <span class="co">// exposition only</span></span>
<span id="cb4-8"><a href="#cb4-8"></a></span>
<span id="cb4-9"><a href="#cb4-9"></a>  <span class="kw">class</span> <em>iterator</em>;                         <span class="co">// exposition only</span></span>
<span id="cb4-10"><a href="#cb4-10"></a></span>
<span id="cb4-11"><a href="#cb4-11"></a><span class="kw">public</span><span class="op">:</span></span>
<span id="cb4-12"><a href="#cb4-12"></a>  chunk_by_view<span class="op">()</span> <span class="kw">requires</span> default_initializable<span class="op">&lt;</span>V<span class="op">&gt;</span> <span class="op">&amp;&amp;</span> default_initializable<span class="op">&lt;</span>Pred<span class="op">&gt;</span> <span class="op">=</span> <span class="cf">default</span>;</span>
<span id="cb4-13"><a href="#cb4-13"></a>  <span class="kw">constexpr</span> <span class="kw">explicit</span> chunk_by_view<span class="op">(</span>V base, Pred pred<span class="op">)</span>;</span>
<span id="cb4-14"><a href="#cb4-14"></a></span>
<span id="cb4-15"><a href="#cb4-15"></a>  <span class="kw">constexpr</span> V base<span class="op">()</span> <span class="kw">const</span> <span class="op">&amp;</span> <span class="kw">requires</span> copy_constructible<span class="op">&lt;</span>V<span class="op">&gt;</span> <span class="op">{</span> <span class="cf">return</span> <em>base_</em>; <span class="op">}</span></span>
<span id="cb4-16"><a href="#cb4-16"></a>  <span class="kw">constexpr</span> V base<span class="op">()</span> <span class="op">&amp;&amp;</span> <span class="op">{</span> <span class="cf">return</span> std<span class="op">::</span>move<span class="op">(</span><em>base_</em><span class="op">)</span>; <span class="op">}</span></span>
<span id="cb4-17"><a href="#cb4-17"></a></span>
<span id="cb4-18"><a href="#cb4-18"></a>  <span class="kw">constexpr</span> <span class="kw">const</span> Pred<span class="op">&amp;</span> pred<span class="op">()</span> <span class="kw">const</span>;</span>
<span id="cb4-19"><a href="#cb4-19"></a></span>
<span id="cb4-20"><a href="#cb4-20"></a>  <span class="kw">constexpr</span> <em>iterator</em> begin<span class="op">()</span>;</span>
<span id="cb4-21"><a href="#cb4-21"></a>  <span class="kw">constexpr</span> <span class="kw">auto</span> end<span class="op">()</span>;</span>
<span id="cb4-22"><a href="#cb4-22"></a></span>
<span id="cb4-23"><a href="#cb4-23"></a>  <span class="kw">constexpr</span> iterator_t<span class="op">&lt;</span>V<span class="op">&gt;</span> <em>find-next</em><span class="op">(</span>iterator_t<span class="op">&lt;</span>V<span class="op">&gt;)</span>; <span class="co">// exposition only</span></span>
<span id="cb4-24"><a href="#cb4-24"></a>  <span class="kw">constexpr</span> iterator_t<span class="op">&lt;</span>V<span class="op">&gt;</span> <em>find-prev</em><span class="op">(</span>iterator_t<span class="op">&lt;</span>V<span class="op">&gt;)</span> <span class="kw">requires</span> bidirectional_range<span class="op">&lt;</span>V<span class="op">&gt;</span>; <span class="co">// exposition only</span></span>
<span id="cb4-25"><a href="#cb4-25"></a><span class="op">}</span>;</span>
<span id="cb4-26"><a href="#cb4-26"></a></span>
<span id="cb4-27"><a href="#cb4-27"></a><span class="kw">template</span><span class="op">&lt;</span><span class="kw">class</span> R, <span class="kw">class</span> Pred<span class="op">&gt;</span></span>
<span id="cb4-28"><a href="#cb4-28"></a>  chunk_by_view<span class="op">(</span>R<span class="op">&amp;&amp;</span>, Pred<span class="op">)</span> <span class="op">-&gt;</span> chunk_by_view<span class="op">&lt;</span>views<span class="op">::</span>all_t<span class="op">&lt;</span>R<span class="op">&gt;</span>, Pred<span class="op">&gt;</span>;</span>
<span id="cb4-29"><a href="#cb4-29"></a></span>
<span id="cb4-30"><a href="#cb4-30"></a><span class="op">}</span></span></code></pre></div>
<div>
<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">constexpr</span> <span class="kw">explicit</span> chunk_by_view<span class="op">(</span>V base, Pred pred<span class="op">)</span>;</span></code></pre></div>
<blockquote>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_3" id="pnum_3">1</a></span> <em>Effects</em>: Initializes <code class="sourceCode cpp"><em>base_</em></code> with <code class="sourceCode cpp">std<span class="op">::</span>move<span class="op">(</span>base<span class="op">)</span></code> and <code class="sourceCode cpp"><em>pred_</em></code> with <code class="sourceCode cpp">std<span class="op">::</span>move<span class="op">(</span>pred<span class="op">)</span></code>.</p>
</blockquote>
<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">constexpr</span> <span class="kw">const</span> Pred<span class="op">&amp;</span> pred<span class="op">()</span> <span class="kw">const</span>;</span></code></pre></div>
<blockquote>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_4" id="pnum_4">2</a></span> <em>Effects</em>: Equivalent to <code class="sourceCode cpp"><span class="cf">return</span> <span class="op">*</span><em>pred_</em>;</code></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="kw">constexpr</span> <em>iterator</em> begin<span class="op">()</span>;</span></code></pre></div>
<blockquote>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_5" id="pnum_5">3</a></span> <em>Preconditions:</em> <code class="sourceCode cpp"><em>pred_</em><span class="op">.</span>has_value<span class="op">()</span></code> is <code class="sourceCode cpp"><span class="kw">true</span></code>.</p>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_6" id="pnum_6">4</a></span> <em>Returns</em>: <code class="sourceCode cpp"><em>iterator</em><span class="op">(*</span><span class="kw">this</span>, ranges<span class="op">::</span>begin<span class="op">(</span><em>base_</em><span class="op">)</span>, <em>find-next</em><span class="op">(</span>ranges<span class="op">::</span>begin<span class="op">(</span><em>base_</em><span class="op">)))</span></code>.</p>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_7" id="pnum_7">5</a></span> <em>Remarks</em>: In order to provide the amortized constant-time complexity required by the <code class="sourceCode cpp">range</code> concept, this function caches the result within the <code class="sourceCode cpp">chunk_by_view</code> for use on subsequent calls.</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="kw">constexpr</span> <span class="kw">auto</span> end<span class="op">()</span>;</span></code></pre></div>
<blockquote>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_8" id="pnum_8">6</a></span> <em>Effects</em>: Equivalent to:</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="cf">if</span> <span class="kw">constexpr</span> <span class="op">(</span>common_range<span class="op">&lt;</span>V<span class="op">&gt;)</span> <span class="op">{</span></span>
<span id="cb9-2"><a href="#cb9-2"></a>  <span class="cf">return</span> <em>iterator</em><span class="op">(*</span><span class="kw">this</span>, ranges<span class="op">::</span>end<span class="op">(</span><em>base_</em><span class="op">)</span>, ranges<span class="op">::</span>end<span class="op">(</span><em>base_</em><span class="op">))</span>;</span>
<span id="cb9-3"><a href="#cb9-3"></a><span class="op">}</span></span>
<span id="cb9-4"><a href="#cb9-4"></a><span class="cf">else</span> <span class="op">{</span></span>
<span id="cb9-5"><a href="#cb9-5"></a>  <span class="cf">return</span> default_sentinel;</span>
<span id="cb9-6"><a href="#cb9-6"></a><span class="op">}</span></span></code></pre></div>
</blockquote>
</blockquote>
<div class="sourceCode" id="cb10"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb10-1"><a href="#cb10-1"></a><span class="kw">constexpr</span> iterator_t<span class="op">&lt;</span>V<span class="op">&gt;</span> <em>find-next</em><span class="op">(</span>iterator_t<span class="op">&lt;</span>V<span class="op">&gt;</span> current<span class="op">)</span>; <span class="co">// exposition only</span></span></code></pre></div>
<blockquote>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_9" id="pnum_9">7</a></span> <em>Preconditions:</em> <code class="sourceCode cpp"><em>pred_</em><span class="op">.</span>has_value<span class="op">()</span></code> is <code class="sourceCode cpp"><span class="kw">true</span></code>.</p>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_10" id="pnum_10">8</a></span> <em>Returns</em>: <code class="sourceCode cpp">ranges<span class="op">::</span>next<span class="op">(</span>ranges<span class="op">::</span>adjacent_find<span class="op">(</span>current, ranges<span class="op">::</span>end<span class="op">(</span><em>base_</em><span class="op">)</span>, not_fn<span class="op">(</span>ref<span class="op">(*</span><em>pred_</em><span class="op">)))</span>, <span class="dv">1</span>, ranges<span class="op">::</span>end<span class="op">(</span><em>base_</em><span class="op">))</span></code>.</p>
</blockquote>
<div class="sourceCode" id="cb11"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb11-1"><a href="#cb11-1"></a><span class="kw">constexpr</span> iterator_t<span class="op">&lt;</span>V<span class="op">&gt;</span> <em>find-prev</em><span class="op">(</span>iterator_t<span class="op">&lt;</span>V<span class="op">&gt;</span> current<span class="op">)</span> <span class="kw">requires</span> bidirectional_range<span class="op">&lt;</span>V<span class="op">&gt;</span>; <span class="co">// exposition only</span></span></code></pre></div>
<blockquote>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_11" id="pnum_11">9</a></span> <em>Preconditions:</em></p>
<ul>
<li><span class="marginalizedparent"><a class="marginalized" href="#pnum_12" id="pnum_12">(9.1)</a></span> <code class="sourceCode cpp">current</code> is not equal to <code class="sourceCode cpp">ranges<span class="op">::</span>begin<span class="op">(</span><em>base_</em><span class="op">)</span></code>.</li>
<li><span class="marginalizedparent"><a class="marginalized" href="#pnum_13" id="pnum_13">(9.2)</a></span> <code class="sourceCode cpp"><em>pred_</em><span class="op">.</span>has_value<span class="op">()</span></code> is <code class="sourceCode cpp"><span class="kw">true</span></code>.</li>
</ul>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_14" id="pnum_14">10</a></span> <em>Returns</em>: An iterator <code class="sourceCode cpp">i</code> in the range <code class="sourceCode cpp"><span class="op">[</span>ranges<span class="op">::</span>begin<span class="op">(</span><em>base_</em><span class="op">)</span>, current<span class="op">)</span></code> such that:</p>
<ul>
<li><span class="marginalizedparent"><a class="marginalized" href="#pnum_15" id="pnum_15">(10.1)</a></span> <code class="sourceCode cpp">ranges<span class="op">::</span>adjacent_find<span class="op">(</span>i, current, not_fn<span class="op">(</span>ref<span class="op">(*</span><em>pred_</em><span class="op">)))</span></code> is equal to <code class="sourceCode cpp">current</code>; and</li>
<li><span class="marginalizedparent"><a class="marginalized" href="#pnum_16" id="pnum_16">(10.2)</a></span> if <code class="sourceCode cpp">i</code> is not equal to <code class="sourceCode cpp">ranges<span class="op">::</span>begin<span class="op">(</span><em>base_</em><span class="op">)</span></code>, then <code class="sourceCode cpp"><span class="dt">bool</span><span class="op">(</span>invoke<span class="op">(*</span><em>pred_</em>, <span class="op">*</span>ranges<span class="op">::</span>prev<span class="op">(</span>i<span class="op">)</span>, <span class="op">*</span>i<span class="op">))</span></code> is <code class="sourceCode cpp"><span class="kw">false</span></code>.</li>
</ul>
<div class="draftnote" style="color: #01796F">
<p>[ Drafting note: Reference implementation:</p>
<div class="sourceCode" id="cb12"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb12-1"><a href="#cb12-1"></a>  <span class="kw">using</span> <span class="kw">namespace</span> std<span class="op">::</span>placeholders;</span>
<span id="cb12-2"><a href="#cb12-2"></a>  reverse_view rv<span class="op">(</span>subrange<span class="op">(</span>ranges<span class="op">::</span>begin<span class="op">(</span>base_<span class="op">)</span>, current<span class="op">))</span>;</span>
<span id="cb12-3"><a href="#cb12-3"></a>  <span class="cf">return</span> ranges<span class="op">::</span>prev<span class="op">(</span>ranges<span class="op">::</span>adjacent_find<span class="op">(</span>rv, not_fn<span class="op">(</span>bind<span class="op">(</span>ref<span class="op">(*</span>pred_<span class="op">)</span>, _2, _1<span class="op">))).</span>base<span class="op">()</span>,</span>
<span id="cb12-4"><a href="#cb12-4"></a>                      <span class="dv">1</span>, ranges<span class="op">::</span>begin<span class="op">(</span>base_<span class="op">))</span>;</span></code></pre></div>
 ]

</div>
</blockquote>
</div>
<h4 class="unnumbered" data-number id="class-chunk_by_viewiterator-range.chunk.by.iter">24.7.?.3 Class <code class="sourceCode cpp">chunk_by_view<span class="op">::</span><em>iterator</em></code> [range.chunk.by.iter]<a href="#class-chunk_by_viewiterator-range.chunk.by.iter" class="self-link"></a></h4>
<div class="sourceCode" id="cb13"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb13-1"><a href="#cb13-1"></a><span class="kw">namespace</span> std<span class="op">::</span>ranges <span class="op">{</span></span>
<span id="cb13-2"><a href="#cb13-2"></a>  <span class="kw">template</span><span class="op">&lt;</span>forward_range V, indirect_binary_predicate<span class="op">&lt;</span>iterator_t<span class="op">&lt;</span>V<span class="op">&gt;</span>, iterator_t<span class="op">&lt;</span>V<span class="op">&gt;&gt;</span> Pred<span class="op">&gt;</span></span>
<span id="cb13-3"><a href="#cb13-3"></a>    <span class="kw">requires</span> view<span class="op">&lt;</span>V<span class="op">&gt;</span> <span class="op">&amp;&amp;</span> is_object_v<span class="op">&lt;</span>Pred<span class="op">&gt;</span></span>
<span id="cb13-4"><a href="#cb13-4"></a>  <span class="kw">class</span> chunk_by_view<span class="op">&lt;</span>V, Pred<span class="op">&gt;::</span><em>iterator</em> <span class="op">{</span></span>
<span id="cb13-5"><a href="#cb13-5"></a>    chunk_by_view<span class="op">*</span> <em>parent_</em> <span class="op">=</span> <span class="kw">nullptr</span>;                       <span class="co">// exposition only</span></span>
<span id="cb13-6"><a href="#cb13-6"></a>    iterator_t<span class="op">&lt;</span>V<span class="op">&gt;</span> <em>current_</em> <span class="op">=</span> iterator_t<span class="op">&lt;</span>V<span class="op">&gt;()</span>;               <span class="co">// exposition only</span></span>
<span id="cb13-7"><a href="#cb13-7"></a>    iterator_t<span class="op">&lt;</span>V<span class="op">&gt;</span> <em>next_</em>    <span class="op">=</span> iterator_t<span class="op">&lt;</span>V<span class="op">&gt;()</span>;               <span class="co">// exposition only</span></span>
<span id="cb13-8"><a href="#cb13-8"></a></span>
<span id="cb13-9"><a href="#cb13-9"></a>    <span class="kw">constexpr</span> <em>iterator</em><span class="op">(</span>chunk_by_view<span class="op">&amp;</span> parent, iterator_t<span class="op">&lt;</span>V<span class="op">&gt;</span> current, iterator_t<span class="op">&lt;</span>V<span class="op">&gt;</span> next<span class="op">)</span>;  <span class="co">// exposition only</span></span>
<span id="cb13-10"><a href="#cb13-10"></a></span>
<span id="cb13-11"><a href="#cb13-11"></a>  <span class="kw">public</span><span class="op">:</span></span>
<span id="cb13-12"><a href="#cb13-12"></a>    <span class="kw">using</span> value_type <span class="op">=</span> subrange<span class="op">&lt;</span>iterator_t<span class="op">&lt;</span>V<span class="op">&gt;&gt;</span>;</span>
<span id="cb13-13"><a href="#cb13-13"></a>    <span class="kw">using</span> difference_type  <span class="op">=</span> range_difference_t<span class="op">&lt;</span>V<span class="op">&gt;</span>;</span>
<span id="cb13-14"><a href="#cb13-14"></a>    <span class="kw">using</span> iterator_category <span class="op">=</span> input_iterator_tag;</span>
<span id="cb13-15"><a href="#cb13-15"></a>    <span class="kw">using</span> iterator_concept <span class="op">=</span> <em>see below</em>;</span>
<span id="cb13-16"><a href="#cb13-16"></a></span>
<span id="cb13-17"><a href="#cb13-17"></a>    <em>iterator</em><span class="op">()</span> <span class="op">=</span> <span class="cf">default</span>;</span>
<span id="cb13-18"><a href="#cb13-18"></a></span>
<span id="cb13-19"><a href="#cb13-19"></a>    <span class="kw">constexpr</span> value_type <span class="kw">operator</span><span class="op">*()</span> <span class="kw">const</span>;</span>
<span id="cb13-20"><a href="#cb13-20"></a>    <span class="kw">constexpr</span> <em>iterator</em><span class="op">&amp;</span> <span class="kw">operator</span><span class="op">++()</span>;</span>
<span id="cb13-21"><a href="#cb13-21"></a>    <span class="kw">constexpr</span> <em>iterator</em> <span class="kw">operator</span><span class="op">++(</span><span class="dt">int</span><span class="op">)</span>;</span>
<span id="cb13-22"><a href="#cb13-22"></a></span>
<span id="cb13-23"><a href="#cb13-23"></a>    <span class="kw">constexpr</span> <em>iterator</em><span class="op">&amp;</span> <span class="kw">operator</span><span class="op">--()</span> <span class="kw">requires</span> bidirectional_range<span class="op">&lt;</span>V<span class="op">&gt;</span>;</span>
<span id="cb13-24"><a href="#cb13-24"></a>    <span class="kw">constexpr</span> <em>iterator</em> <span class="kw">operator</span><span class="op">--(</span><span class="dt">int</span><span class="op">)</span> <span class="kw">requires</span> bidirectional_range<span class="op">&lt;</span>V<span class="op">&gt;</span>;</span>
<span id="cb13-25"><a href="#cb13-25"></a></span>
<span id="cb13-26"><a href="#cb13-26"></a>    <span class="kw">friend</span> <span class="kw">constexpr</span> <span class="dt">bool</span> <span class="kw">operator</span><span class="op">==(</span><span class="kw">const</span> <em>iterator</em><span class="op">&amp;</span> x, <span class="kw">const</span> <em>iterator</em><span class="op">&amp;</span> y<span class="op">)</span>;</span>
<span id="cb13-27"><a href="#cb13-27"></a>    <span class="kw">friend</span> <span class="kw">constexpr</span> <span class="dt">bool</span> <span class="kw">operator</span><span class="op">==(</span><span class="kw">const</span> <em>iterator</em><span class="op">&amp;</span> x, default_sentinel_t<span class="op">)</span>;</span>
<span id="cb13-28"><a href="#cb13-28"></a>  <span class="op">}</span>;</span>
<span id="cb13-29"><a href="#cb13-29"></a><span class="op">}</span></span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_17" id="pnum_17">1</a></span> <code class="sourceCode cpp"><em>iterator</em><span class="op">::</span>iterator_concept</code> is defined as follows:</p>
<ul>
<li><span class="marginalizedparent"><a class="marginalized" href="#pnum_18" id="pnum_18">(1.1)</a></span> If <code class="sourceCode cpp">V</code> models <code class="sourceCode cpp">bidirectional_range</code>, then <code class="sourceCode cpp">iterator_concept</code> denotes <code class="sourceCode cpp">bidirectional_iterator_tag</code>.</li>
<li><span class="marginalizedparent"><a class="marginalized" href="#pnum_19" id="pnum_19">(1.2)</a></span> Otherwise, <code class="sourceCode cpp">iterator_concept</code> denotes <code class="sourceCode cpp">forward_iterator_tag</code>.</li>
</ul>
<div>
<div class="sourceCode" id="cb14"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb14-1"><a href="#cb14-1"></a><span class="kw">constexpr</span> <em>iterator</em><span class="op">(</span>chunk_by_view<span class="op">&amp;</span> parent, iterator_t<span class="op">&lt;</span>V<span class="op">&gt;</span> current, iterator_t<span class="op">&lt;</span>V<span class="op">&gt;</span> next<span class="op">)</span>;</span></code></pre></div>
<blockquote>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_20" id="pnum_20">2</a></span> <em>Effects</em>: Initializes <code class="sourceCode cpp"><em>parent_</em></code> with <code class="sourceCode cpp">addressof<span class="op">(</span>parent<span class="op">)</span></code>, <code class="sourceCode cpp"><em>current_</em></code> with <code class="sourceCode cpp">current</code>, and <code class="sourceCode cpp"><em>next_</em></code> with <code class="sourceCode cpp">next</code>.</p>
</blockquote>
<div class="sourceCode" id="cb15"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb15-1"><a href="#cb15-1"></a><span class="kw">constexpr</span> value_type <span class="kw">operator</span><span class="op">*()</span> <span class="kw">const</span>;</span></code></pre></div>
<blockquote>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_21" id="pnum_21">3</a></span> <em>Preconditions</em>: <code class="sourceCode cpp"><em>current_</em></code> is not equal to <code class="sourceCode cpp"><em>next_</em></code>.</p>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_22" id="pnum_22">4</a></span> <em>Returns</em>: <code class="sourceCode cpp">subrange<span class="op">(</span><em>current_</em>, <em>next_</em><span class="op">)</span></code>.</p>
</blockquote>
<div class="sourceCode" id="cb16"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb16-1"><a href="#cb16-1"></a><span class="kw">constexpr</span> <em>iterator</em><span class="op">&amp;</span> <span class="kw">operator</span><span class="op">++()</span>;</span></code></pre></div>
<blockquote>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_23" id="pnum_23">5</a></span> <em>Preconditions</em>: <code class="sourceCode cpp"><em>current_</em></code> is not equal to <code class="sourceCode cpp"><em>next_</em></code>.</p>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_24" id="pnum_24">6</a></span> <em>Effects:</em> Equivalent to:</p>
<blockquote>
<div class="sourceCode" id="cb17"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb17-1"><a href="#cb17-1"></a>   <em>current_</em> <span class="op">=</span> <em>next_</em>;</span>
<span id="cb17-2"><a href="#cb17-2"></a>   <em>next_</em> <span class="op">=</span> <em>parent_</em><span class="op">-&gt;</span><em>find-next</em><span class="op">(</span><em>current_</em><span class="op">)</span>;</span>
<span id="cb17-3"><a href="#cb17-3"></a>   <span class="cf">return</span> <span class="op">*</span><span class="kw">this</span>;</span></code></pre></div>
</blockquote>
</blockquote>
<div class="sourceCode" id="cb18"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb18-1"><a href="#cb18-1"></a><span class="kw">constexpr</span> <em>iterator</em> <span class="kw">operator</span><span class="op">++(</span><span class="dt">int</span><span class="op">)</span>;</span></code></pre></div>
<blockquote>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_25" id="pnum_25">7</a></span> <em>Effects</em>: Equivalent to:</p>
<blockquote>
<div class="sourceCode" id="cb19"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb19-1"><a href="#cb19-1"></a>  <span class="kw">auto</span> tmp <span class="op">=</span> <span class="op">*</span><span class="kw">this</span>;</span>
<span id="cb19-2"><a href="#cb19-2"></a>  <span class="op">++*</span><span class="kw">this</span>;</span>
<span id="cb19-3"><a href="#cb19-3"></a>  <span class="cf">return</span> tmp;</span></code></pre></div>
</blockquote>
</blockquote>
<div class="sourceCode" id="cb20"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb20-1"><a href="#cb20-1"></a><span class="kw">constexpr</span> <em>iterator</em><span class="op">&amp;</span> <span class="kw">operator</span><span class="op">--()</span> <span class="kw">requires</span> bidirectional_range<span class="op">&lt;</span>V<span class="op">&gt;</span>;</span></code></pre></div>
<blockquote>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_26" id="pnum_26">8</a></span> <em>Effects:</em> Equivalent to:</p>
<blockquote>
<div class="sourceCode" id="cb21"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb21-1"><a href="#cb21-1"></a>   <em>next_</em> <span class="op">=</span> <em>current_</em>;</span>
<span id="cb21-2"><a href="#cb21-2"></a>   <em>current_</em> <span class="op">=</span> <em>parent_</em><span class="op">-&gt;</span><em>find-prev</em><span class="op">(</span><em>next_</em><span class="op">)</span>;</span>
<span id="cb21-3"><a href="#cb21-3"></a>   <span class="cf">return</span> <span class="op">*</span><span class="kw">this</span>;</span></code></pre></div>
</blockquote>
</blockquote>
<div class="sourceCode" id="cb22"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb22-1"><a href="#cb22-1"></a><span class="kw">constexpr</span> <em>iterator</em> <span class="kw">operator</span><span class="op">--(</span><span class="dt">int</span><span class="op">)</span> <span class="kw">requires</span> bidirectional_range<span class="op">&lt;</span>V<span class="op">&gt;</span>;</span></code></pre></div>
<blockquote>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_27" id="pnum_27">9</a></span> <em>Effects</em>: Equivalent to:</p>
<blockquote>
<div class="sourceCode" id="cb23"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb23-1"><a href="#cb23-1"></a>  <span class="kw">auto</span> tmp <span class="op">=</span> <span class="op">*</span><span class="kw">this</span>;</span>
<span id="cb23-2"><a href="#cb23-2"></a>  <span class="op">--*</span><span class="kw">this</span>;</span>
<span id="cb23-3"><a href="#cb23-3"></a>  <span class="cf">return</span> tmp;</span></code></pre></div>
</blockquote>
</blockquote>
<div class="sourceCode" id="cb24"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb24-1"><a href="#cb24-1"></a><span class="kw">friend</span> <span class="kw">constexpr</span> <span class="dt">bool</span> <span class="kw">operator</span><span class="op">==(</span><span class="kw">const</span> <em>iterator</em><span class="op">&amp;</span> x, <span class="kw">const</span> <em>iterator</em><span class="op">&amp;</span> y<span class="op">)</span>;</span></code></pre></div>
<blockquote>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_28" id="pnum_28">10</a></span> <em>Returns:</em> <code class="sourceCode cpp">x<span class="op">.</span><em>current_</em> <span class="op">==</span> y<span class="op">.</span><em>current_</em></code>.</p>
</blockquote>
<div class="sourceCode" id="cb25"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb25-1"><a href="#cb25-1"></a><span class="kw">friend</span> <span class="kw">constexpr</span> <span class="dt">bool</span> <span class="kw">operator</span><span class="op">==(</span><span class="kw">const</span> <em>iterator</em><span class="op">&amp;</span> x, default_sentinel_t<span class="op">)</span>;</span></code></pre></div>
<blockquote>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_29" id="pnum_29">11</a></span> <em>Returns:</em> <code class="sourceCode cpp">x<span class="op">.</span><em>current_</em> <span class="op">==</span> x<span class="op">.</span><em>next_</em></code>.</p>
</blockquote>
</div>
<h2 data-number="5.3" id="feature-test-macro"><span class="header-section-number">5.3</span> Feature-test macro<a href="#feature-test-macro" class="self-link"></a></h2>
<p>Add the following macro definition to <span>17.3.2 <a href="https://wg21.link/version.syn">[version.syn]</a></span>, header <code class="sourceCode cpp"><span class="op">&lt;</span>version<span class="op">&gt;</span></code> synopsis, with the value selected by the editor to reflect the date of adoption of this paper:</p>
<div class="sourceCode" id="cb26"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb26-1"><a href="#cb26-1"></a><span class="pp">#define __cpp_lib_ranges_chunk_by </span><span class="dv">20</span><span class="er">XXXXL</span><span class="pp"> </span><span class="co">// also in &lt;ranges&gt;</span></span></code></pre></div>
<h1 data-number="6" style="border-bottom:1px solid #cccccc" id="bibliography"><span class="header-section-number">6</span> References<a href="#bibliography" class="self-link"></a></h1>
<div id="refs" class="references hanging-indent" role="doc-bibliography">
<div id="ref-P2214R1">
<p>[P2214R1] Barry Revzin, Conor Hoekstra, Tim Song. 2021. A Plan for C++23 Ranges. <br />
<a href="https://wg21.link/p2214r1">https://wg21.link/p2214r1</a></p>
</div>
<div id="ref-P2321R2">
<p>[P2321R2] Tim Song. 2021-06-11. zip. <br />
<a href="https://wg21.link/p2321r2">https://wg21.link/p2321r2</a></p>
</div>
</div>
</div>
</div>
</body>
</html>
