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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="2022-01-28" />
<title>views::join_with</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;
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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; }
}
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code span.wa { color: #008000; font-weight: bold; } /* Warning */
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code.diff span.va {color: #006e28}
code.diff span.st {color: #bf0303}
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a.self-link::before { content: "§"; }
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display: inline-block;
margin-right: 3em;
}
div.numberedTable {
text-align: center;
margin: 2em;
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div.figure {
text-align: center;
margin: 2em;
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table {
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td, th {
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td.border {
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div.table {
display: block;
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display: block;
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margin-bottom: 1em;
margin-top: 1em;
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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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code span.co { font-family: monospace; }
table tr {
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table tr:nth-child(2n) {
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td > div.sourceCode {
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table {
border-collapse: collapse;
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table td, table th {
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table th {
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table tbody tr:first-child td {
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@media all {
body {
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}
}
@media screen and (min-width: 480px) {
body {
margin: 5em;
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}
#refs code{padding-left: 0px; text-indent: 0px;}
:root {
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<h1 class="title" style="text-align:center"><code class="sourceCode cpp">views<span class="op">::</span>join_with</code></h1>
<table style="border:none;float:right">
<tr>
<td>Document #:</td>
<td>P2441R2</td>
</tr>
<tr>
<td>Date:</td>
<td>2022-01-28</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>
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="#revision-history"><span class="toc-section-number">1</span> Revision History<span></span></a></li>
<li><a href="#introduction"><span class="toc-section-number">2</span> Introduction<span></span></a></li>
<li><a href="#design"><span class="toc-section-number">3</span> Design<span></span></a>
<ul>
<li><a href="#naming"><span class="toc-section-number">3.1</span> Naming<span></span></a></li>
<li><a href="#category"><span class="toc-section-number">3.2</span> Category<span></span></a></li>
<li><a href="#value-and-reference-type"><span class="toc-section-number">3.3</span> Value and Reference Type<span></span></a></li>
<li><a href="#various-properties"><span class="toc-section-number">3.4</span> Various Properties<span></span></a>
<ul>
<li><a href="#conditionally-common"><span class="toc-section-number">3.4.1</span> Conditionally Common<span></span></a></li>
<li><a href="#borrowed"><span class="toc-section-number">3.4.2</span> Borrowed<span></span></a></li>
<li><a href="#sized"><span class="toc-section-number">3.4.3</span> Sized<span></span></a></li>
<li><a href="#const-iterable"><span class="toc-section-number">3.4.4</span> <code class="sourceCode cpp"><span class="kw">const</span></code>-iterable<span></span></a></li>
</ul></li>
<li><a href="#implementation-experience"><span class="toc-section-number">3.5</span> Implementation Experience<span></span></a></li>
</ul></li>
<li><a href="#wording"><span class="toc-section-number">4</span> Wording<span></span></a>
<ul>
<li><a href="#addition-to-ranges"><span class="toc-section-number">4.1</span> Addition to <code class="sourceCode cpp"><span class="op"><</span>ranges<span class="op">></span></code><span></span></a></li>
<li><a href="#join_with"><span class="toc-section-number">4.2</span> <code class="sourceCode cpp">join_with</code><span></span></a>
<ul>
<li><a href="#join-with-view-range.join.with">24.7.? Join with view [range.join.with]<span></span></a></li>
</ul></li>
<li><a href="#feature-test-macro"><span class="toc-section-number">4.3</span> Feature-test macro<span></span></a></li>
</ul></li>
<li><a href="#bibliography"><span class="toc-section-number">5</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>
<p>Since <span class="citation" data-cites="P2441R1">[<a href="#ref-P2441R1" role="doc-biblioref">P2441R1</a>]</span>, updated wording.</p>
<p>Since <span class="citation" data-cites="P2441R0">[<a href="#ref-P2441R0" role="doc-biblioref">P2441R0</a>]</span>, added a feature-test macro.</p>
<h1 data-number="2" style="border-bottom:1px solid #cccccc" id="introduction"><span class="header-section-number">2</span> Introduction<a href="#introduction" class="self-link"></a></h1>
<p>C++20 Ranges introduced <code class="sourceCode cpp">views<span class="op">::</span>join</code>: a range adaptor for turning a range of range of <code class="sourceCode cpp">T</code> into a range of <code class="sourceCode cpp">T</code>. This adaptor, however, did not take any delimiter range. So you could not, for instance, join together a range of <code class="sourceCode cpp">string</code>s with a space to then convert that to a longer string. This paper remedies that by producing a <code class="sourceCode cpp">views<span class="op">::</span>join_with</code>, as described in <span class="citation" data-cites="P2214R1">[<a href="#ref-P2214R1" role="doc-biblioref">P2214R1</a>]</span>, section 3.8.</p>
<p>The behavior of <code class="sourceCode cpp">views<span class="op">::</span>join_with</code> is an inverse of <code class="sourceCode cpp">views<span class="op">::</span>split</code>. That is, given a range <code class="sourceCode cpp">r</code> and a pattern <code class="sourceCode cpp">p</code>, <code class="sourceCode cpp">r <span class="op">|</span> views<span class="op">::</span>split<span class="op">(</span>p<span class="op">)</span> <span class="op">|</span> views<span class="op">::</span>join_with<span class="op">(</span>p<span class="op">)</span></code> should yield a range consisting of the same elements as <code class="sourceCode cpp">r</code>.</p>
<h1 data-number="3" style="border-bottom:1px solid #cccccc" id="design"><span class="header-section-number">3</span> Design<a href="#design" class="self-link"></a></h1>
<p>There are several aspects to <code class="sourceCode cpp">join_with</code> that are more complicated than <code class="sourceCode cpp">join</code>, that are worth going over. For convenience, let <code class="sourceCode cpp">Rng</code> denote the range we’re <code class="sourceCode cpp">join</code>ing (i.e. the range of ranges), let <code class="sourceCode cpp">Pattern</code> denote the delimiter pattern, and let <code class="sourceCode cpp">Inner</code> denote the inner range (i.e. <code class="sourceCode cpp">range_reference_t<span class="op"><</span>Rng<span class="op">></span></code>).</p>
<h2 data-number="3.1" id="naming"><span class="header-section-number">3.1</span> Naming<a href="#naming" class="self-link"></a></h2>
<p>Why <code class="sourceCode cpp">views<span class="op">::</span>join_with</code> rather than supporting an extra argument to <code class="sourceCode cpp">views<span class="op">::</span>join</code>? The issue here is ultimately ambiguity. In this potential design where we simply overload <code class="sourceCode cpp">join</code>, <code class="sourceCode cpp">views<span class="op">::</span>join<span class="op">(</span>x<span class="op">)</span></code> could mean either (a) produce a range that joins the ranges of <code class="sourceCode cpp">x</code>, or (b) it is a partial call that produces a range adaptor closure object to where <code class="sourceCode cpp">x</code> is a delimiter for some other range to be provided in the future.</p>
<p>This ambiguity is… rare. <code class="sourceCode cpp">x</code> needs to be a range of ranges (i.e. <code class="sourceCode cpp"><span class="op">[[</span><span class="at">T</span><span class="op">]]</span></code>) in order to be joinable, which means that in order for it to be a delimiter, the range it’s doing needs to be a range of range of ranges (i.e. <code class="sourceCode cpp"><span class="op">[[[</span><span class="at">T</span><span class="op">]]]</span></code>). These don’t come up very often. range-v3 simply treats <code class="sourceCode cpp">join<span class="op">(</span>x<span class="op">)</span></code> if <code class="sourceCode cpp">x</code> is a joinable range (i.e. a range whose reference type is also a range) a request to produce a <code class="sourceCode cpp">join_view</code>. That’s one option.</p>
<p>However, eventually somebody is going to want to join a <code class="sourceCode cpp"><span class="op">[[[</span><span class="at">T</span><span class="op">]]]</span></code> on a <code class="sourceCode cpp"><span class="op">[[</span><span class="at">T</span><span class="op">]]</span></code> and it will end up just not working.</p>
<p>Regardless, joining with a delimiter will produce a different view than joining without a delimiter (it’s <code class="sourceCode cpp">r <span class="op">|</span> views<span class="op">::</span>join</code> does not produce a <code class="sourceCode cpp">join_with_view<span class="op"><</span>all_t<span class="op"><</span>R<span class="op">></span>, empty_view<span class="op"><</span>T<span class="op">>></span></code>, that would be needlessly inefficient… it just produces a <code class="sourceCode cpp">join_with_view<span class="op"><</span>all_t<span class="op"><</span>R<span class="op">>></span></code>), so we don’t gain anything on either the implementation front or the specification front by overloading <code class="sourceCode cpp">join</code>. The only difference of introducing a new name would be that users would have to write <code class="sourceCode cpp">r <span class="op">|</span> views<span class="op">::</span>join_with<span class="op">(</span><span class="ch">' '</span><span class="op">)</span></code> instead of <code class="sourceCode cpp">r <span class="op">|</span> views<span class="op">::</span>join<span class="op">(</span><span class="ch">' '</span><span class="op">)</span></code>. That doesn’t seem like an unreasonable burden on users, at the cost of avoiding any future ambiguity.</p>
<h2 data-number="3.2" id="category"><span class="header-section-number">3.2</span> Category<a href="#category" class="self-link"></a></h2>
<p>Like <code class="sourceCode cpp">views<span class="op">::</span>join</code>, and following <span class="citation" data-cites="P2328R1">[<a href="#ref-P2328R1" role="doc-biblioref">P2328R1</a>]</span>, <code class="sourceCode cpp">views<span class="op">::</span>join_with</code> is input-only if the primary range (the one we’re <code class="sourceCode cpp">join</code>ing) is a range of prvalue non-view ranges.</p>
<p>Otherwise, if <code class="sourceCode cpp">Rng</code>, <code class="sourceCode cpp">Inner</code>, and <code class="sourceCode cpp">Pattern</code> are all bidirectional and <code class="sourceCode cpp">Inner</code> and <code class="sourceCode cpp">Pattern</code> are common, then bidirectional. Otherwise, if <code class="sourceCode cpp">Rng</code>, <code class="sourceCode cpp">Inner</code>, and <code class="sourceCode cpp">Pattern</code> are all forward. Otherwise, input.</p>
<h2 data-number="3.3" id="value-and-reference-type"><span class="header-section-number">3.3</span> Value and Reference Type<a href="#value-and-reference-type" class="self-link"></a></h2>
<p>For <code class="sourceCode cpp">views<span class="op">::</span>join</code>, these are obvious: <code class="sourceCode cpp">Inner</code>’s value and reference, respectively. But now, we have two ranges that we’re joining together: <code class="sourceCode cpp">Inner</code> and <code class="sourceCode cpp">Pattern</code>, an those two may have different value and reference types. range-v3’s implementation allows this, using the folloiwng formation:</p>
<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">using</span> value_type <span class="op">=</span> common_type_t<span class="op"><</span>range_value_t<span class="op"><</span>Inner<span class="op">></span>, range_value_t<span class="op"><</span>Pattern<span class="op">>></span>;</span>
<span id="cb1-2"><a href="#cb1-2"></a><span class="kw">using</span> reference <span class="op">=</span> common_reference_t<span class="op"><</span>range_reference_t<span class="op"><</span>Inner<span class="op">></span>, range_reference_t<span class="op"><</span>Pattern<span class="op">>></span>;</span>
<span id="cb1-3"><a href="#cb1-3"></a><span class="kw">using</span> rvalue_reference <span class="op">=</span> common_reference_t<span class="op"><</span>range_rvalue_reference_t<span class="op"><</span>Inner<span class="op">></span>, range_rvalue_reference_t<span class="op"><</span>Pattern<span class="op">>></span>;</span></code></pre></div>
<p>Those types all existing is an added constraint on constructing a <code class="sourceCode cpp">join_with_view</code>.</p>
<p>I’m not sure I see a need to deviate from the implementation here.</p>
<h2 data-number="3.4" id="various-properties"><span class="header-section-number">3.4</span> Various Properties<a href="#various-properties" class="self-link"></a></h2>
<h3 data-number="3.4.1" id="conditionally-common"><span class="header-section-number">3.4.1</span> Conditionally Common<a href="#conditionally-common" class="self-link"></a></h3>
<p>Like <code class="sourceCode cpp">views<span class="op">::</span>join</code>, <code class="sourceCode cpp">views<span class="op">::</span>join_with</code> can be common when <code class="sourceCode cpp">Rng</code> is a range of glvalue ranges, <code class="sourceCode cpp">Rng</code> and <code class="sourceCode cpp">Inner</code> are both forward and common. Note that we don’t need <code class="sourceCode cpp">Pattern</code> to be common.</p>
<h3 data-number="3.4.2" id="borrowed"><span class="header-section-number">3.4.2</span> Borrowed<a href="#borrowed" class="self-link"></a></h3>
<p>Never.</p>
<h3 data-number="3.4.3" id="sized"><span class="header-section-number">3.4.3</span> Sized<a href="#sized" class="self-link"></a></h3>
<p>Never.</p>
<h3 data-number="3.4.4" id="const-iterable"><span class="header-section-number">3.4.4</span> <code class="sourceCode cpp"><span class="kw">const</span></code>-iterable<a href="#const-iterable" class="self-link"></a></h3>
<p>If <code class="sourceCode cpp">Rng</code> and <code class="sourceCode cpp">Pattern</code> are, and <code class="sourceCode cpp">Inner</code> is glvalue range. This is the same requirement as <code class="sourceCode cpp">join_view</code> has, because if <code class="sourceCode cpp">Inner</code> is not a reference that means we have to store it, which requires state, which implies mutating that state during iteration.</p>
<h2 data-number="3.5" id="implementation-experience"><span class="header-section-number">3.5</span> Implementation Experience<a href="#implementation-experience" class="self-link"></a></h2>
<p>Up until recently, the <code class="sourceCode cpp">join_with_view</code> in range-v3 was input-only, never common, and never const-iterable. I have implemented conditionally-bidirectional support in range-v3 and also implemented <a href="https://godbolt.org/z/b1fdabW3s">this design</a> from scratch.</p>
<h1 data-number="4" style="border-bottom:1px solid #cccccc" id="wording"><span class="header-section-number">4</span> Wording<a href="#wording" class="self-link"></a></h1>
<h2 data-number="4.1" id="addition-to-ranges"><span class="header-section-number">4.1</span> Addition to <code class="sourceCode cpp"><span class="op"><</span>ranges<span class="op">></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"><</span>ranges<span class="op">></span></code> synopsis:</p>
<blockquote>
<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.join.with], join with view</span></span>
<span id="cb2-6"><a href="#cb2-6"></a> <span class="kw">template</span><span class="op"><</span><span class="kw">class</span> R, <span class="kw">class</span> P<span class="op">></span></span>
<span id="cb2-7"><a href="#cb2-7"></a> <span class="kw">concept</span> <em>compatible-joinable-ranges</em> <span class="op">=</span> <em>see below</em>; <span class="co">// exposition only</span></span>
<span id="cb2-8"><a href="#cb2-8"></a></span>
<span id="cb2-9"><a href="#cb2-9"></a> <span class="kw">template</span><span class="op"><</span>input_range V, forward_range Pattern<span class="op">></span></span>
<span id="cb2-10"><a href="#cb2-10"></a> <span class="kw">requires</span> view<span class="op"><</span>V<span class="op">></span></span>
<span id="cb2-11"><a href="#cb2-11"></a> <span class="op">&&</span> input_range<span class="op"><</span>range_reference_t<span class="op"><</span>V<span class="op">>></span></span>
<span id="cb2-12"><a href="#cb2-12"></a> <span class="op">&&</span> view<span class="op"><</span>Pattern<span class="op">></span></span>
<span id="cb2-13"><a href="#cb2-13"></a> <span class="op">&&</span> <em>compatible-joinable-ranges</em><span class="op"><</span>range_reference_t<span class="op"><</span>V<span class="op">></span>, Pattern<span class="op">></span></span>
<span id="cb2-14"><a href="#cb2-14"></a> <span class="kw">class</span> join_with_view;</span>
<span id="cb2-15"><a href="#cb2-15"></a></span>
<span id="cb2-16"><a href="#cb2-16"></a> <span class="kw">namespace</span> views <span class="op">{</span></span>
<span id="cb2-17"><a href="#cb2-17"></a> <span class="kw">inline</span> <span class="kw">constexpr</span> <em>unspecified</em> join_with <span class="op">=</span> <em>unspecified</em>;</span>
<span id="cb2-18"><a href="#cb2-18"></a> <span class="op">}</span></span>
<span id="cb2-19"><a href="#cb2-19"></a><span class="op">}</span></span></code></pre></div>
</blockquote>
<h2 data-number="4.2" id="join_with"><span class="header-section-number">4.2</span> <code class="sourceCode cpp">join_with</code><a href="#join_with" 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="join-with-view-range.join.with">24.7.? Join with view [range.join.with]<a href="#join-with-view-range.join.with" class="self-link"></a></h3>
<h4 class="unnumbered" data-number id="overview-range.join.with.overview">24.7.?.1 Overview [range.join.with.overview]<a href="#overview-range.join.with.overview" class="self-link"></a></h4>
<blockquote>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_1" id="pnum_1">1</a></span> <code class="sourceCode cpp">join_with_view</code> takes a <code class="sourceCode cpp">view</code> and a delimiter, and flattens the <code class="sourceCode cpp">view</code>, inserting every element of the delimiter in between elements of the <code class="sourceCode cpp">view</code>. The delimiter can be a single element or a <code class="sourceCode cpp">view</code> of elements.</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>join_with</code> denotes a range adaptor object ([range.adaptor.object]). 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>join_with<span class="op">(</span>E, F<span class="op">)</span></code> is expression-equivalent to <code class="sourceCode cpp">join_with_view<span class="op">(</span>E, F<span class="op">)</span></code>.</p>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_3" id="pnum_3">3</a></span> [<em>Example</em>:</p>
<div class="sourceCode" id="cb3"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb3-1"><a href="#cb3-1"></a>vector<span class="op"><</span>string<span class="op">></span> vs <span class="op">=</span> <span class="op">{</span><span class="st">"the"</span>, <span class="st">"quick"</span>, <span class="st">"brown"</span>, <span class="st">"fox"</span><span class="op">}</span>;</span>
<span id="cb3-2"><a href="#cb3-2"></a><span class="cf">for</span> <span class="op">(</span><span class="dt">char</span> c <span class="op">:</span> vs <span class="op">|</span> join_with<span class="op">(</span><span class="ch">'-'</span><span class="op">))</span> <span class="op">{</span></span>
<span id="cb3-3"><a href="#cb3-3"></a> cout <span class="op"><<</span> c;</span>
<span id="cb3-4"><a href="#cb3-4"></a><span class="op">}</span></span>
<span id="cb3-5"><a href="#cb3-5"></a><span class="co">// the above prints: the-quick-brown-fox</span></span></code></pre></div>
<p>-<em>end example</em>]</p>
</blockquote>
<h4 class="unnumbered" data-number id="class-template-join_with_view-range.join.with.overview">24.7.?.2 Class template <code class="sourceCode cpp">join_with_view</code> [range.join.with.overview]<a href="#class-template-join_with_view-range.join.with.overview" class="self-link"></a></h4>
<blockquote>
<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 class="kw">template</span><span class="op"><</span><span class="kw">class</span> R, <span class="kw">class</span> P<span class="op">></span></span>
<span id="cb4-3"><a href="#cb4-3"></a> <span class="kw">concept</span> <em>compatible-joinable-ranges</em> <span class="op">=</span> <span class="co">// exposition only</span></span>
<span id="cb4-4"><a href="#cb4-4"></a> common_with<span class="op"><</span>range_value_t<span class="op"><</span>R<span class="op">></span>, range_value_t<span class="op"><</span>P<span class="op">>></span> <span class="op">&&</span></span>
<span id="cb4-5"><a href="#cb4-5"></a> common_reference_with<span class="op"><</span>range_reference_t<span class="op"><</span>R<span class="op">></span>, range_reference_t<span class="op"><</span>P<span class="op">>></span> <span class="op">&&</span></span>
<span id="cb4-6"><a href="#cb4-6"></a> common_reference_with<span class="op"><</span>range_rvalue_reference_t<span class="op"><</span>R<span class="op">></span>, range_rvalue_reference_t<span class="op"><</span>P<span class="op">>></span>;</span>
<span id="cb4-7"><a href="#cb4-7"></a></span>
<span id="cb4-8"><a href="#cb4-8"></a> <span class="kw">template</span> <span class="op"><</span><span class="kw">class</span> R<span class="op">></span></span>
<span id="cb4-9"><a href="#cb4-9"></a> <span class="kw">concept</span> <em>bidirectional-common</em> <span class="op">=</span> bidirectional_range<span class="op"><</span>R<span class="op">></span> <span class="op">&&</span> common_range<span class="op"><</span>R<span class="op">></span>; <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">template</span><span class="op"><</span>input_range V, forward_range Pattern<span class="op">></span></span>
<span id="cb4-12"><a href="#cb4-12"></a> <span class="kw">requires</span> view<span class="op"><</span>V<span class="op">></span></span>
<span id="cb4-13"><a href="#cb4-13"></a> <span class="op">&&</span> input_range<span class="op"><</span>range_reference_t<span class="op"><</span>V<span class="op">>></span></span>
<span id="cb4-14"><a href="#cb4-14"></a> <span class="op">&&</span> view<span class="op"><</span>Pattern<span class="op">></span></span>
<span id="cb4-15"><a href="#cb4-15"></a> <span class="op">&&</span> <em>compatible-joinable-ranges</em><span class="op"><</span>range_reference_t<span class="op"><</span>V<span class="op">></span>, Pattern<span class="op">></span></span>
<span id="cb4-16"><a href="#cb4-16"></a> <span class="kw">class</span> join_with_view <span class="op">:</span> <span class="kw">public</span> view_interface<span class="op"><</span>join_with_view<span class="op"><</span>V, Pattern<span class="op">>></span> <span class="op">{</span></span>
<span id="cb4-17"><a href="#cb4-17"></a> <span class="kw">using</span> <em>InnerRng</em> <span class="op">=</span> range_reference_t<span class="op"><</span>V<span class="op">></span>;</span>
<span id="cb4-18"><a href="#cb4-18"></a></span>
<span id="cb4-19"><a href="#cb4-19"></a> V <em>base_</em> <span class="op">=</span> V<span class="op">()</span>; <span class="co">// exposition only</span></span>
<span id="cb4-20"><a href="#cb4-20"></a> <em>non-propagating-cache</em><span class="op"><</span>remove_cv_t<span class="op"><</span><em>InnerRng</em><span class="op">>></span> <em>inner_</em>; <span class="co">// exposition only, present only</span></span>
<span id="cb4-21"><a href="#cb4-21"></a> <span class="co">// when !is_reference_v<InnerRng></span></span>
<span id="cb4-22"><a href="#cb4-22"></a> Pattern <em>pattern_</em> <span class="op">=</span> Pattern<span class="op">()</span>; <span class="co">// exposition only</span></span>
<span id="cb4-23"><a href="#cb4-23"></a></span>
<span id="cb4-24"><a href="#cb4-24"></a> <span class="kw">template</span><span class="op"><</span><span class="dt">bool</span> Const<span class="op">></span> <span class="kw">struct</span> <em>iterator</em>; <span class="co">// exposition only</span></span>
<span id="cb4-25"><a href="#cb4-25"></a> <span class="kw">template</span><span class="op"><</span><span class="dt">bool</span> Const<span class="op">></span> <span class="kw">struct</span> <em>sentinel</em>; <span class="co">// exposition only</span></span>
<span id="cb4-26"><a href="#cb4-26"></a></span>
<span id="cb4-27"><a href="#cb4-27"></a> <span class="kw">public</span><span class="op">:</span></span>
<span id="cb4-28"><a href="#cb4-28"></a> join_with_view<span class="op">()</span> <span class="kw">requires</span> default_initializable<span class="op"><</span>V<span class="op">></span> <span class="op">&&</span> default_initializable<span class="op"><</span>Pattern<span class="op">></span> <span class="op">=</span> <span class="cf">default</span>;</span>
<span id="cb4-29"><a href="#cb4-29"></a> <span class="kw">constexpr</span> join_with_view<span class="op">(</span>V base, Pattern pattern<span class="op">)</span>;</span>
<span id="cb4-30"><a href="#cb4-30"></a></span>
<span id="cb4-31"><a href="#cb4-31"></a> <span class="kw">template</span><span class="op"><</span>input_range R<span class="op">></span></span>
<span id="cb4-32"><a href="#cb4-32"></a> <span class="kw">requires</span> constructible_from<span class="op"><</span>V, views<span class="op">::</span>all_t<span class="op"><</span>R<span class="op">>></span> <span class="op">&&</span></span>
<span id="cb4-33"><a href="#cb4-33"></a> constructible_from<span class="op"><</span>Pattern, single_view<span class="op"><</span>range_value_t<span class="op"><</span><em>InnerRng</em><span class="op">>>></span></span>
<span id="cb4-34"><a href="#cb4-34"></a> <span class="kw">constexpr</span> join_with_view<span class="op">(</span>R<span class="op">&&</span> r, range_value_t<span class="op"><</span><em>InnerRng</em><span class="op">></span> e<span class="op">)</span>;</span>
<span id="cb4-35"><a href="#cb4-35"></a></span>
<span id="cb4-36"><a href="#cb4-36"></a></span>
<span id="cb4-37"><a href="#cb4-37"></a> <span class="kw">constexpr</span> V base<span class="op">()</span> <span class="kw">const</span><span class="op">&</span> <span class="kw">requires</span> copy_constructible<span class="op"><</span>V<span class="op">></span> <span class="op">{</span> <span class="cf">return</span> <em>base_</em>; <span class="op">}</span></span>
<span id="cb4-38"><a href="#cb4-38"></a> <span class="kw">constexpr</span> V base<span class="op">()</span> <span class="op">&&</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="cb4-39"><a href="#cb4-39"></a></span>
<span id="cb4-40"><a href="#cb4-40"></a> <span class="kw">constexpr</span> <span class="kw">auto</span> begin<span class="op">()</span> <span class="op">{</span></span>
<span id="cb4-41"><a href="#cb4-41"></a> <span class="kw">constexpr</span> <span class="dt">bool</span> use_const <span class="op">=</span> <em>simple-view</em><span class="op"><</span>V<span class="op">></span> <span class="op">&&</span> is_reference_v<span class="op"><</span><em>InnerRng</em><span class="op">></span> <span class="op">&&</span> <em>simple-view</em><span class="op"><</span>Pattern<span class="op">></span>;</span>
<span id="cb4-42"><a href="#cb4-42"></a> <span class="cf">return</span> <em>iterator</em><span class="op"><</span>use_const<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>;</span>
<span id="cb4-43"><a href="#cb4-43"></a> <span class="op">}</span></span>
<span id="cb4-44"><a href="#cb4-44"></a> <span class="kw">constexpr</span> <span class="kw">auto</span> begin<span class="op">()</span> <span class="kw">const</span> <span class="kw">requires</span> input_range<span class="op"><</span><span class="kw">const</span> V<span class="op">></span> <span class="op">&&</span></span>
<span id="cb4-45"><a href="#cb4-45"></a> forward_range<span class="op"><</span><span class="kw">const</span> Pattern<span class="op">></span> <span class="op">&&</span></span>
<span id="cb4-46"><a href="#cb4-46"></a> is_reference_v<span class="op"><</span>range_reference_t<span class="op"><</span><span class="kw">const</span> V<span class="op">>></span> <span class="op">{</span></span>
<span id="cb4-47"><a href="#cb4-47"></a> <span class="cf">return</span> <em>iterator</em><span class="op"><</span><span class="kw">true</span><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>;</span>
<span id="cb4-48"><a href="#cb4-48"></a> <span class="op">}</span></span>
<span id="cb4-49"><a href="#cb4-49"></a></span>
<span id="cb4-50"><a href="#cb4-50"></a> <span class="kw">constexpr</span> <span class="kw">auto</span> end<span class="op">()</span> <span class="op">{</span></span>
<span id="cb4-51"><a href="#cb4-51"></a> <span class="cf">if</span> <span class="kw">constexpr</span> <span class="op">(</span>forward_range<span class="op"><</span>V<span class="op">></span> <span class="op">&&</span></span>
<span id="cb4-52"><a href="#cb4-52"></a> is_reference_v<span class="op"><</span><em>InnerRng</em><span class="op">></span> <span class="op">&&</span> forward_range<span class="op"><</span><em>InnerRng</em><span class="op">></span> <span class="op">&&</span></span>
<span id="cb4-53"><a href="#cb4-53"></a> common_range<span class="op"><</span>V<span class="op">></span> <span class="op">&&</span> common_range<span class="op"><</span><em>InnerRng</em><span class="op">>)</span> <span class="op">{</span></span>
<span id="cb4-54"><a href="#cb4-54"></a> <span class="cf">return</span> <em>iterator</em><span class="op"><</span><em>simple-view</em><span class="op"><</span>V<span class="op">></span> <span class="op">&&</span> <em>simple-view</em><span class="op"><</span>Pattern<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>;</span>
<span id="cb4-55"><a href="#cb4-55"></a> <span class="op">}</span> <span class="cf">else</span> <span class="op">{</span></span>
<span id="cb4-56"><a href="#cb4-56"></a> <span class="cf">return</span> <em>sentinel</em><span class="op"><</span><em>simple-view</em><span class="op"><</span>V<span class="op">></span> <span class="op">&&</span> <em>simple-view</em><span class="op"><</span>Pattern<span class="op">>>{*</span><span class="kw">this</span><span class="op">}</span>;</span>
<span id="cb4-57"><a href="#cb4-57"></a> <span class="op">}</span></span>
<span id="cb4-58"><a href="#cb4-58"></a> <span class="op">}</span></span>
<span id="cb4-59"><a href="#cb4-59"></a> <span class="kw">constexpr</span> <span class="kw">auto</span> end<span class="op">()</span> <span class="kw">const</span> <span class="kw">requires</span> input_range<span class="op"><</span><span class="kw">const</span> V<span class="op">></span> <span class="op">&&</span></span>
<span id="cb4-60"><a href="#cb4-60"></a> forward_range<span class="op"><</span><span class="kw">const</span> Pattern<span class="op">></span> <span class="op">&&</span></span>
<span id="cb4-61"><a href="#cb4-61"></a> is_reference_v<span class="op"><</span>range_reference_t<span class="op"><</span><span class="kw">const</span> V<span class="op">>></span> <span class="op">{</span></span>
<span id="cb4-62"><a href="#cb4-62"></a> <span class="kw">using</span> <em>InnerConstRng</em> <span class="op">=</span> range_reference_t<span class="op"><</span><span class="kw">const</span> V<span class="op">></span>;</span>
<span id="cb4-63"><a href="#cb4-63"></a> <span class="cf">if</span> <span class="kw">constexpr</span> <span class="op">(</span>forward_range<span class="op"><</span><span class="kw">const</span> V<span class="op">></span> <span class="op">&&</span></span>
<span id="cb4-64"><a href="#cb4-64"></a> forward_range<span class="op"><</span><em>InnerConstRng</em><span class="op">></span> <span class="op">&&</span></span>
<span id="cb4-65"><a href="#cb4-65"></a> common_range<span class="op"><</span><span class="kw">const</span> V<span class="op">></span> <span class="op">&&</span> common_range<span class="op"><</span><em>InnerConstRng</em><span class="op">>)</span> <span class="op">{</span></span>
<span id="cb4-66"><a href="#cb4-66"></a> <span class="cf">return</span> <em>iterator</em><span class="op"><</span><span class="kw">true</span><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>;</span>
<span id="cb4-67"><a href="#cb4-67"></a> <span class="op">}</span> <span class="cf">else</span> <span class="op">{</span></span>
<span id="cb4-68"><a href="#cb4-68"></a> <span class="cf">return</span> <em>sentinel</em><span class="op"><</span><span class="kw">true</span><span class="op">>{*</span><span class="kw">this</span><span class="op">}</span>;</span>
<span id="cb4-69"><a href="#cb4-69"></a> <span class="op">}</span></span>
<span id="cb4-70"><a href="#cb4-70"></a> <span class="op">}</span></span>
<span id="cb4-71"><a href="#cb4-71"></a> <span class="op">}</span>;</span>
<span id="cb4-72"><a href="#cb4-72"></a></span>
<span id="cb4-73"><a href="#cb4-73"></a> <span class="kw">template</span><span class="op"><</span><span class="kw">class</span> R, <span class="kw">class</span> P<span class="op">></span></span>
<span id="cb4-74"><a href="#cb4-74"></a> join_with_view<span class="op">(</span>R<span class="op">&&</span>, P<span class="op">&&)</span> <span class="op">-></span> join_with_view<span class="op"><</span>views<span class="op">::</span>all_t<span class="op"><</span>R<span class="op">></span>, views<span class="op">::</span>all_t<span class="op"><</span>P<span class="op">>></span>;</span>
<span id="cb4-75"><a href="#cb4-75"></a></span>
<span id="cb4-76"><a href="#cb4-76"></a> <span class="kw">template</span><span class="op"><</span>input_range R<span class="op">></span></span>
<span id="cb4-77"><a href="#cb4-77"></a> join_with_view<span class="op">(</span>R<span class="op">&&</span>, range_value_t<span class="op"><</span>range_reference_t<span class="op"><</span>R<span class="op">>>)</span></span>
<span id="cb4-78"><a href="#cb4-78"></a> <span class="op">-></span> join_with_view<span class="op"><</span>views<span class="op">::</span>all_t<span class="op"><</span>R<span class="op">></span>, single_view<span class="op"><</span>range_value_t<span class="op"><</span>range_reference_t<span class="op"><</span>R<span class="op">>>>></span>;</span>
<span id="cb4-79"><a href="#cb4-79"></a></span>
<span id="cb4-80"><a href="#cb4-80"></a><span class="op">}</span></span></code></pre></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> join_with_view<span class="op">(</span>V base, Pattern pattern<span class="op">)</span>;</span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_4" id="pnum_4">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>pattern_</em></code> with <code class="sourceCode cpp">std<span class="op">::</span>move<span class="op">(</span>pattern<span class="op">)</span></code>.</p>
<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">template</span><span class="op"><</span>input_range R<span class="op">></span></span>
<span id="cb6-2"><a href="#cb6-2"></a> <span class="kw">requires</span> constructible_from<span class="op"><</span>V, views<span class="op">::</span>all_t<span class="op"><</span>R<span class="op">>></span> <span class="op">&&</span></span>
<span id="cb6-3"><a href="#cb6-3"></a> constructible_from<span class="op"><</span>Pattern, single_view<span class="op"><</span>range_value_t<span class="op"><</span><em>InnerRng</em><span class="op">>>></span></span>
<span id="cb6-4"><a href="#cb6-4"></a><span class="kw">constexpr</span> join_with_view<span class="op">(</span>R<span class="op">&&</span> r, range_value_t<span class="op"><</span><em>InnerRng</em><span class="op">></span> e<span class="op">)</span>;</span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_5" id="pnum_5">2</a></span> <em>Effects</em>: Initializes <code class="sourceCode cpp"><em>base_</em></code> with <code class="sourceCode cpp">views<span class="op">::</span>all<span class="op">(</span>std<span class="op">::</span>forward<span class="op"><</span>R<span class="op">>(</span>r<span class="op">))</span></code> and <code class="sourceCode cpp"><em>pattern_</em></code> with <code class="sourceCode cpp">views<span class="op">::</span>single<span class="op">(</span>std<span class="op">::</span>move<span class="op">(</span>e<span class="op">))</span></code>.</p>
</blockquote>
<h4 class="unnumbered" data-number id="class-template-join_with_viewiterator-range.join.with.iterator">24.7.?.3 Class template <code class="sourceCode cpp">join_with_view<span class="op">::</span><em>iterator</em></code> [range.join.with.iterator]<a href="#class-template-join_with_viewiterator-range.join.with.iterator" class="self-link"></a></h4>
<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">namespace</span> std<span class="op">::</span>ranges <span class="op">{</span></span>
<span id="cb7-2"><a href="#cb7-2"></a> <span class="kw">template</span><span class="op"><</span>input_range V, forward_range Pattern<span class="op">></span></span>
<span id="cb7-3"><a href="#cb7-3"></a> <span class="kw">requires</span> view<span class="op"><</span>V<span class="op">></span></span>
<span id="cb7-4"><a href="#cb7-4"></a> <span class="op">&&</span> input_range<span class="op"><</span>range_reference_t<span class="op"><</span>V<span class="op">>></span></span>
<span id="cb7-5"><a href="#cb7-5"></a> <span class="op">&&</span> view<span class="op"><</span>Pattern<span class="op">></span></span>
<span id="cb7-6"><a href="#cb7-6"></a> <span class="op">&&</span> <em>compatible-joinable-ranges</em><span class="op"><</span>range_reference_t<span class="op"><</span>V<span class="op">></span>, Pattern<span class="op">></span></span>
<span id="cb7-7"><a href="#cb7-7"></a> <span class="kw">template</span><span class="op"><</span><span class="dt">bool</span> Const<span class="op">></span></span>
<span id="cb7-8"><a href="#cb7-8"></a> <span class="kw">class</span> join_with_view<span class="op"><</span>V, Pattern<span class="op">>::</span><em>iterator</em> <span class="op">{</span></span>
<span id="cb7-9"><a href="#cb7-9"></a> <span class="kw">using</span> <em>Parent</em> <span class="op">=</span> <em>maybe-const</em><span class="op"><</span>Const, join_with_view<span class="op">></span>; <span class="co">// exposition only</span></span>
<span id="cb7-10"><a href="#cb7-10"></a> <span class="kw">using</span> <em>Base</em> <span class="op">=</span> <em>maybe-const</em><span class="op"><</span>Const, V<span class="op">></span>; <span class="co">// exposition only</span></span>
<span id="cb7-11"><a href="#cb7-11"></a> <span class="kw">using</span> <em>InnerBase</em> <span class="op">=</span> range_reference_t<span class="op"><</span><em>Base</em><span class="op">></span>; <span class="co">// exposition only</span></span>
<span id="cb7-12"><a href="#cb7-12"></a> <span class="kw">using</span> <em>PatternBase</em> <span class="op">=</span> <em>maybe-const</em><span class="op"><</span>Const, Pattern<span class="op">></span>; <span class="co">// exposition only</span></span>
<span id="cb7-13"><a href="#cb7-13"></a></span>
<span id="cb7-14"><a href="#cb7-14"></a> <span class="kw">using</span> <em>OuterIter</em> <span class="op">=</span> iterator_t<span class="op"><</span><em>Base</em><span class="op">></span>; <span class="co">// exposition only</span></span>
<span id="cb7-15"><a href="#cb7-15"></a> <span class="kw">using</span> <em>InnerIter</em> <span class="op">=</span> iterator_t<span class="op"><</span><em>InnerBase</em><span class="op">></span>; <span class="co">// exposition only</span></span>
<span id="cb7-16"><a href="#cb7-16"></a> <span class="kw">using</span> <em>PatternIter</em> <span class="op">=</span> iterator_t<span class="op"><</span><em>PatternBase</em><span class="op">></span>; <span class="co">// exposition only</span></span>
<span id="cb7-17"><a href="#cb7-17"></a></span>
<span id="cb7-18"><a href="#cb7-18"></a> <span class="kw">static</span> <span class="kw">constexpr</span> <span class="dt">bool</span> <em>ref-is-glvalue</em> <span class="op">=</span> is_reference_v<span class="op"><</span><em>InnerBase</em><span class="op">></span>; <span class="co">// exposition only</span></span>
<span id="cb7-19"><a href="#cb7-19"></a></span>
<span id="cb7-20"><a href="#cb7-20"></a> <em>Parent</em><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="cb7-21"><a href="#cb7-21"></a> <em>OuterIter</em> <em>outer_it_</em> <span class="op">=</span> <em>OuterIter</em><span class="op">()</span>; <span class="co">// exposition only</span></span>
<span id="cb7-22"><a href="#cb7-22"></a> variant<span class="op"><</span><em>PatternIter</em>, <em>InnerIter</em><span class="op">></span> <em>inner_it_</em>; <span class="co">// exposition only</span></span>
<span id="cb7-23"><a href="#cb7-23"></a></span>
<span id="cb7-24"><a href="#cb7-24"></a> <span class="kw">constexpr</span> <em>iterator</em><span class="op">(</span><em>Parent</em><span class="op">&</span> parent, iterator_t<span class="op"><</span><em>Base</em><span class="op">></span> outer<span class="op">)</span>; <span class="co">// exposition only</span></span>
<span id="cb7-25"><a href="#cb7-25"></a> <span class="kw">constexpr</span> <span class="kw">auto</span><span class="op">&&</span> <em>update-inner</em><span class="op">(</span><span class="kw">const</span> <em>OuterIter</em><span class="op">&)</span>; <span class="co">// exposition only</span></span>
<span id="cb7-26"><a href="#cb7-26"></a> <span class="kw">constexpr</span> <span class="kw">auto</span><span class="op">&&</span> <em>get-inner</em><span class="op">(</span><span class="kw">const</span> <em>OuterIter</em><span class="op">&)</span>; <span class="co">// exposition only</span></span>
<span id="cb7-27"><a href="#cb7-27"></a> <span class="kw">constexpr</span> <span class="dt">void</span> <em>satisfy</em><span class="op">()</span>; <span class="co">// exposition only</span></span>
<span id="cb7-28"><a href="#cb7-28"></a> <span class="kw">public</span><span class="op">:</span></span>
<span id="cb7-29"><a href="#cb7-29"></a> <span class="kw">using</span> iterator_concept <span class="op">=</span> <em>see below</em>;</span>
<span id="cb7-30"><a href="#cb7-30"></a> <span class="kw">using</span> iterator_category <span class="op">=</span> <em>see below</em>; <span class="co">// not always present</span></span>
<span id="cb7-31"><a href="#cb7-31"></a> <span class="kw">using</span> value_type <span class="op">=</span> <em>see below</em>;</span>
<span id="cb7-32"><a href="#cb7-32"></a> <span class="kw">using</span> difference_type <span class="op">=</span> <em>see below</em>;</span>
<span id="cb7-33"><a href="#cb7-33"></a></span>
<span id="cb7-34"><a href="#cb7-34"></a> <em>iterator</em><span class="op">()</span> <span class="kw">requires</span> default_initializable<span class="op"><</span><em>OuterIter</em><span class="op">></span> <span class="op">=</span> <span class="cf">default</span>;</span>
<span id="cb7-35"><a href="#cb7-35"></a> <span class="kw">constexpr</span> <em>iterator</em><span class="op">(</span><em>iterator</em><span class="op"><!</span>Const<span class="op">></span> i<span class="op">)</span></span>
<span id="cb7-36"><a href="#cb7-36"></a> <span class="kw">requires</span> Const <span class="op">&&</span></span>
<span id="cb7-37"><a href="#cb7-37"></a> convertible_to<span class="op"><</span>iterator_t<span class="op"><</span>V<span class="op">></span>, <em>OuterIter</em><span class="op">></span> <span class="op">&&</span></span>
<span id="cb7-38"><a href="#cb7-38"></a> convertible_to<span class="op"><</span>iterator_t<span class="op"><</span><em>InnerRng</em><span class="op">></span>, <em>InnerIter</em><span class="op">></span> <span class="op">&&</span></span>
<span id="cb7-39"><a href="#cb7-39"></a> convertible_to<span class="op"><</span>iterator_t<span class="op"><</span><em>Pattern</em><span class="op">></span>, <em>PatternIter</em><span class="op">></span>;</span>
<span id="cb7-40"><a href="#cb7-40"></a></span>
<span id="cb7-41"><a href="#cb7-41"></a> <span class="kw">constexpr</span> <span class="kw">decltype</span><span class="op">(</span><span class="kw">auto</span><span class="op">)</span> <span class="kw">operator</span><span class="op">*()</span> <span class="kw">const</span>;</span>
<span id="cb7-42"><a href="#cb7-42"></a></span>
<span id="cb7-43"><a href="#cb7-43"></a> <span class="kw">constexpr</span> <em>iterator</em><span class="op">&</span> <span class="kw">operator</span><span class="op">++()</span>;</span>
<span id="cb7-44"><a href="#cb7-44"></a> <span class="kw">constexpr</span> <span class="dt">void</span> <span class="kw">operator</span><span class="op">++(</span><span class="dt">int</span><span class="op">)</span>;</span>
<span id="cb7-45"><a href="#cb7-45"></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="cb7-46"><a href="#cb7-46"></a> <span class="kw">requires</span> <em>ref-is-glvalue</em> <span class="op">&&</span> forward_iterator<span class="op"><</span><em>OuterIter</em><span class="op">></span> <span class="op">&&</span></span>
<span id="cb7-47"><a href="#cb7-47"></a> forward_iterator<span class="op"><</span><em>InnerIter</em><span class="op">></span>;</span>
<span id="cb7-48"><a href="#cb7-48"></a></span>
<span id="cb7-49"><a href="#cb7-49"></a> <span class="kw">constexpr</span> <em>iterator</em><span class="op">&</span> <span class="kw">operator</span><span class="op">--()</span></span>
<span id="cb7-50"><a href="#cb7-50"></a> <span class="kw">requires</span> <em>ref-is-glvalue</em> <span class="op">&&</span> bidirectional_range<span class="op"><</span><em>Base</em><span class="op">></span> <span class="op">&&</span></span>
<span id="cb7-51"><a href="#cb7-51"></a> <em>bidirectional-common</em><span class="op"><</span><em>InnerBase</em><span class="op">></span> <span class="op">&&</span> <em>bidirectional-common</em><span class="op"><</span><em>PatternBase</em><span class="op">></span>;</span>
<span id="cb7-52"><a href="#cb7-52"></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="cb7-53"><a href="#cb7-53"></a> <span class="kw">requires</span> <em>ref-is-glvalue</em> <span class="op">&&</span> bidirectional_range<span class="op"><</span><em>Base</em><span class="op">></span> <span class="op">&&</span></span>
<span id="cb7-54"><a href="#cb7-54"></a> <em>bidirectional-common</em><span class="op"><</span><em>InnerBase</em><span class="op">></span> <span class="op">&&</span> <em>bidirectional-common</em><span class="op"><</span><em>PatternBase</em><span class="op">></span>;</span>
<span id="cb7-55"><a href="#cb7-55"></a></span>
<span id="cb7-56"><a href="#cb7-56"></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">&</span> x, <span class="kw">const</span> <em>iterator</em><span class="op">&</span> y<span class="op">)</span></span>
<span id="cb7-57"><a href="#cb7-57"></a> <span class="kw">requires</span> <em>ref-is-glvalue</em> <span class="op">&&</span> equality_comparable<span class="op"><</span><em>OuterIter</em><span class="op">></span> <span class="op">&&</span></span>
<span id="cb7-58"><a href="#cb7-58"></a> equality_comparable<span class="op"><</span><em>InnerIter</em><span class="op">></span>;</span>
<span id="cb7-59"><a href="#cb7-59"></a></span>
<span id="cb7-60"><a href="#cb7-60"></a> <span class="kw">friend</span> <span class="kw">constexpr</span> <span class="kw">decltype</span><span class="op">(</span><span class="kw">auto</span><span class="op">)</span> iter_move<span class="op">(</span><span class="kw">const</span> <em>iterator</em><span class="op">&</span> x<span class="op">)</span></span>
<span id="cb7-61"><a href="#cb7-61"></a> <span class="op">{</span></span>
<span id="cb7-62"><a href="#cb7-62"></a> <span class="kw">using</span> rvalue_reference <span class="op">=</span> common_reference_t<span class="op"><</span></span>
<span id="cb7-63"><a href="#cb7-63"></a> iter_rvalue_reference_t<span class="op"><</span><em>InnerIter</em><span class="op">></span>,</span>
<span id="cb7-64"><a href="#cb7-64"></a> iter_rvalue_reference_t<span class="op"><</span><em>PatternIter</em><span class="op">>></span>;</span>
<span id="cb7-65"><a href="#cb7-65"></a> <span class="cf">return</span> visit<span class="op"><</span>rvalue_reference<span class="op">>(</span>ranges<span class="op">::</span>iter_move, x<span class="op">.</span><em>inner_it_</em><span class="op">)</span>;</span>
<span id="cb7-66"><a href="#cb7-66"></a> <span class="op">}</span></span>
<span id="cb7-67"><a href="#cb7-67"></a></span>
<span id="cb7-68"><a href="#cb7-68"></a> <span class="kw">friend</span> <span class="kw">constexpr</span> <span class="dt">void</span> iter_swap<span class="op">(</span><span class="kw">const</span> <em>iterator</em><span class="op">&</span> x, <span class="kw">const</span> <em>iterator</em><span class="op">&</span> y<span class="op">)</span></span>
<span id="cb7-69"><a href="#cb7-69"></a> <span class="kw">requires</span> indirectly_swappable<span class="op"><</span><em>InnerIter</em>, <em>PatternIter</em><span class="op">></span></span>
<span id="cb7-70"><a href="#cb7-70"></a> <span class="op">{</span></span>
<span id="cb7-71"><a href="#cb7-71"></a> visit<span class="op">(</span>ranges<span class="op">::</span>iter_swap, x<span class="op">.</span><em>inner_it_</em>, y<span class="op">.</span><em>inner_it_</em><span class="op">)</span>;</span>
<span id="cb7-72"><a href="#cb7-72"></a> <span class="op">}</span></span>
<span id="cb7-73"><a href="#cb7-73"></a> <span class="op">}</span>;</span>
<span id="cb7-74"><a href="#cb7-74"></a><span class="op">}</span></span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_6" id="pnum_6">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_7" id="pnum_7">(1.1)</a></span> If <code class="sourceCode cpp"><em>ref-is-glvalue</em></code> is <code class="sourceCode cpp"><span class="kw">true</span></code>, <code class="sourceCode cpp"><em>Base</em></code> models <code class="sourceCode cpp">bidirectional_range</code>, and <code class="sourceCode cpp"><em>InnerBase</em></code> and <code class="sourceCode cpp"><em>PatternBase</em></code> each model <code class="sourceCode cpp"><em>bidirectional-common</em></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_8" id="pnum_8">(1.2)</a></span> Otherwise, if <code class="sourceCode cpp"><em>ref-is-glvalue</em></code> is <code class="sourceCode cpp"><span class="kw">true</span></code> and <code class="sourceCode cpp"><em>Base</em></code> and <code class="sourceCode cpp"><em>InnerBase</em></code> each model <code class="sourceCode cpp">forward_range</code>, then <code class="sourceCode cpp">iterator_concept</code> denotes <code class="sourceCode cpp">forward_iterator_tag</code>.</li>
<li><span class="marginalizedparent"><a class="marginalized" href="#pnum_9" id="pnum_9">(1.3)</a></span> Otherwise, <code class="sourceCode cpp">iterator_concept</code> denotes <code class="sourceCode cpp">input_iterator_tag</code>.</li>
</ul>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_10" id="pnum_10">2</a></span> The member <em>typedef-name</em> <code class="sourceCode cpp">iterator_category</code> is defined if and only if <code class="sourceCode cpp"><em>ref-is-glvalue</em></code> is <code class="sourceCode cpp"><span class="kw">true</span></code>, and <code class="sourceCode cpp"><em>Base</em></code> and <code class="sourceCode cpp"><em>InnerBase</em></code> each model <code class="sourceCode cpp">forward_range</code>. In that case, <code class="sourceCode cpp"><em>iterator</em><span class="op">::</span>iterator_category</code> is defined as follows:</p>
<ul>
<li><span class="marginalizedparent"><a class="marginalized" href="#pnum_11" id="pnum_11">(2.1)</a></span> Let <code class="sourceCode cpp">OUTERC</code> denote <code class="sourceCode cpp">iterator_traits<span class="op"><</span><em>OuterIter</em><span class="op">>::</span>iterator_category</code>. Let <code class="sourceCode cpp">INNERC</code> denote <code class="sourceCode cpp">iterator_traits<span class="op"><</span><em>InnerIter</em><span class="op">>::</span>iterator_category</code>, and let <code class="sourceCode cpp">PATTERNC</code> denote <code class="sourceCode cpp">iterator_traits<span class="op"><</span><em>PatternIter</em><span class="op">>::</span>iterator_category</code>.</li>
<li><span class="marginalizedparent"><a class="marginalized" href="#pnum_12" id="pnum_12">(2.2)</a></span> If <code class="sourceCode cpp">is_lvalue_reference_v<span class="op"><</span>common_reference_t<span class="op"><</span>iter_reference_t<span class="op"><</span><em>InnerIter</em><span class="op">></span>, iter_reference_t<span class="op"><</span><em>PatternIter</em><span class="op">>>></span></code> is <code class="sourceCode cpp"><span class="kw">false</span></code>, <code class="sourceCode cpp">iterator_category</code> denotes <code class="sourceCode cpp">input_iterator_tag</code>.</li>
<li><span class="marginalizedparent"><a class="marginalized" href="#pnum_13" id="pnum_13">(2.3)</a></span> Otherwise, if <code class="sourceCode cpp">OUTERC</code>, <code class="sourceCode cpp">INNERC</code>, and <code class="sourceCode cpp">PATTERNC</code> each model <code class="sourceCode cpp">derived_from<span class="op"><</span>bidirectional_iterator_category<span class="op">></span></code> and <code class="sourceCode cpp"><em>InnerBase</em></code> and <code class="sourceCode cpp"><em>PatternBase</em></code> each model <code class="sourceCode cpp">common_range</code>, <code class="sourceCode cpp">iterator_category</code> denotes <code class="sourceCode cpp">bidirectional_iterator_tag</code>.</li>
<li><span class="marginalizedparent"><a class="marginalized" href="#pnum_14" id="pnum_14">(2.4)</a></span> Otherwise, if <code class="sourceCode cpp">OUTERC</code>, <code class="sourceCode cpp">INNERC</code>, and <code class="sourceCode cpp">PATTERNC</code> each model <code class="sourceCode cpp">derived_from<span class="op"><</span>forward_iterator_tag<span class="op">></span></code>, <code class="sourceCode cpp">iterator_category</code> denotes <code class="sourceCode cpp">forward_iterator_tag</code>.</li>
<li><span class="marginalizedparent"><a class="marginalized" href="#pnum_15" id="pnum_15">(2.5)</a></span> Otherwise, <code class="sourceCode cpp">iterator_category</code> denotes <code class="sourceCode cpp">input_iterator_tag</code>.</li>
</ul>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_16" id="pnum_16">3</a></span> <code class="sourceCode cpp"><em>iterator</em><span class="op">::</span>value_type</code> denotes the type:</p>
<div class="sourceCode" id="cb8"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb8-1"><a href="#cb8-1"></a>common_type_t<span class="op"><</span></span>
<span id="cb8-2"><a href="#cb8-2"></a> iter_value_t<span class="op"><</span><em>InnerIter</em><span class="op">></span>,</span>
<span id="cb8-3"><a href="#cb8-3"></a> iter_value_t<span class="op"><</span><em>PatternIter</em><span class="op">>></span></span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_17" id="pnum_17">4</a></span> <code class="sourceCode cpp"><em>iterator</em><span class="op">::</span>difference_type</code> denotes the type:</p>
<div class="sourceCode" id="cb9"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb9-1"><a href="#cb9-1"></a>common_type_t<span class="op"><</span></span>
<span id="cb9-2"><a href="#cb9-2"></a> iter_difference_t<span class="op"><</span><em>OuterIter</em><span class="op">></span>,</span>
<span id="cb9-3"><a href="#cb9-3"></a> iter_difference_t<span class="op"><</span><em>InnerIter</em><span class="op">></span>,</span>
<span id="cb9-4"><a href="#cb9-4"></a> iter_difference_t<span class="op"><</span><em>PatternIter</em><span class="op">>></span></span></code></pre></div>
<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> <span class="kw">auto</span><span class="op">&&</span> <em>update-inner</em><span class="op">(</span><span class="kw">const</span> <em>OuterIter</em><span class="op">&</span> x<span class="op">)</span>; <span class="co">// exposition only</span></span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_18" id="pnum_18">5</a></span> <em>Effects</em>: Equivalent to:</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="cf">if</span> <span class="kw">constexpr</span> <span class="op">(</span><em>ref-is-glvalue</em><span class="op">)</span> <span class="op">{</span></span>
<span id="cb11-2"><a href="#cb11-2"></a> <span class="cf">return</span> <span class="op">*</span>x;</span>
<span id="cb11-3"><a href="#cb11-3"></a><span class="op">}</span> <span class="cf">else</span> <span class="op">{</span></span>
<span id="cb11-4"><a href="#cb11-4"></a> <span class="cf">return</span> <em>parent_</em><span class="op">-></span><em>inner_</em><span class="op">.</span><em>emplace-deref</em><span class="op">(</span>x<span class="op">)</span>;</span>
<span id="cb11-5"><a href="#cb11-5"></a><span class="op">}</span></span></code></pre></div>
</blockquote>
<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">constexpr</span> <span class="kw">auto</span><span class="op">&&</span> <em>get-inner</em><span class="op">(</span><span class="kw">const</span> <em>OuterIter</em><span class="op">&</span> x<span class="op">)</span>; <span class="co">// exposition only</span></span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_19" id="pnum_19">6</a></span> <em>Effects</em>: Equivalent to:</p>
<blockquote>
<div class="sourceCode" id="cb13"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb13-1"><a href="#cb13-1"></a><span class="cf">if</span> <span class="kw">constexpr</span> <span class="op">(</span><em>ref-is-glvalue</em><span class="op">)</span> <span class="op">{</span></span>
<span id="cb13-2"><a href="#cb13-2"></a> <span class="cf">return</span> <span class="op">*</span>x;</span>
<span id="cb13-3"><a href="#cb13-3"></a><span class="op">}</span> <span class="cf">else</span> <span class="op">{</span></span>
<span id="cb13-4"><a href="#cb13-4"></a> <span class="cf">return</span> <span class="op">*</span><em>parent_</em><span class="op">-></span><em>inner_</em>;</span>
<span id="cb13-5"><a href="#cb13-5"></a><span class="op">}</span></span></code></pre></div>
</blockquote>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_20" id="pnum_20">7</a></span> <code class="sourceCode cpp">join_with_view</code> iterators use the <code class="sourceCode cpp"><em>satisfy</em></code> function to skip over empty inner ranges.</p>
<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> <span class="dt">void</span> <em>satisfy</em><span class="op">()</span>; <span class="co">// exposition only</span></span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_21" id="pnum_21">8</a></span> <em>Effects</em>: Equivalent to:</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="cf">while</span> <span class="op">(</span><span class="kw">true</span><span class="op">)</span> <span class="op">{</span></span>
<span id="cb15-2"><a href="#cb15-2"></a> <span class="cf">if</span> <span class="op">(</span><em>inner_it_</em><span class="op">.</span>index<span class="op">()</span> <span class="op">==</span> <span class="dv">0</span><span class="op">)</span> <span class="op">{</span></span>
<span id="cb15-3"><a href="#cb15-3"></a> <span class="cf">if</span> <span class="op">(</span>std<span class="op">::</span>get<span class="op"><</span><span class="dv">0</span><span class="op">>(</span><em>inner_it_</em><span class="op">)</span> <span class="op">!=</span> ranges<span class="op">::</span>end<span class="op">(</span><em>parent_</em><span class="op">-></span><em>pattern_</em><span class="op">))</span> <span class="op">{</span></span>
<span id="cb15-4"><a href="#cb15-4"></a> <span class="cf">break</span>;</span>
<span id="cb15-5"><a href="#cb15-5"></a> <span class="op">}</span></span>
<span id="cb15-6"><a href="#cb15-6"></a></span>
<span id="cb15-7"><a href="#cb15-7"></a> <span class="kw">auto</span><span class="op">&&</span> inner <span class="op">=</span> <em>update-inner</em><span class="op">(</span><em>outer_it_</em><span class="op">)</span>;</span>
<span id="cb15-8"><a href="#cb15-8"></a> <em>inner_it_</em><span class="op">.</span>emplace<span class="op"><</span><span class="dv">1</span><span class="op">>(</span>ranges<span class="op">::</span>begin<span class="op">(</span>inner<span class="op">))</span>;</span>
<span id="cb15-9"><a href="#cb15-9"></a> <span class="op">}</span> <span class="cf">else</span> <span class="op">{</span></span>
<span id="cb15-10"><a href="#cb15-10"></a> <span class="kw">auto</span><span class="op">&&</span> inner <span class="op">=</span> <em>get-inner</em><span class="op">(</span><em>outer_it_</em><span class="op">)</span>;</span>
<span id="cb15-11"><a href="#cb15-11"></a> <span class="cf">if</span> <span class="op">(</span>std<span class="op">::</span>get<span class="op"><</span><span class="dv">1</span><span class="op">>(</span><em>inner_it_</em><span class="op">)</span> <span class="op">!=</span> ranges<span class="op">::</span>end<span class="op">(</span>inner<span class="op">))</span> <span class="op">{</span></span>
<span id="cb15-12"><a href="#cb15-12"></a> <span class="cf">break</span>;</span>
<span id="cb15-13"><a href="#cb15-13"></a> <span class="op">}</span></span>
<span id="cb15-14"><a href="#cb15-14"></a></span>
<span id="cb15-15"><a href="#cb15-15"></a> <span class="cf">if</span> <span class="op">(++</span><em>outer_it_</em> <span class="op">==</span> ranges<span class="op">::</span>end<span class="op">(</span><em>parent_</em><span class="op">-></span><em>base_</em><span class="op">))</span> <span class="op">{</span></span>
<span id="cb15-16"><a href="#cb15-16"></a> <span class="cf">if</span> <span class="kw">constexpr</span> <span class="op">(</span><em>ref-is-glvalue</em><span class="op">)</span> <span class="op">{</span></span>
<span id="cb15-17"><a href="#cb15-17"></a> <em>inner_it_</em><span class="op">.</span>emplace<span class="op"><</span><span class="dv">0</span><span class="op">>()</span>;</span>
<span id="cb15-18"><a href="#cb15-18"></a> <span class="op">}</span></span>
<span id="cb15-19"><a href="#cb15-19"></a> <span class="cf">break</span>;</span>
<span id="cb15-20"><a href="#cb15-20"></a> <span class="op">}</span></span>
<span id="cb15-21"><a href="#cb15-21"></a></span>
<span id="cb15-22"><a href="#cb15-22"></a> <em>inner_it_</em><span class="op">.</span>emplace<span class="op"><</span><span class="dv">0</span><span class="op">>(</span>ranges<span class="op">::</span>begin<span class="op">(</span><em>parent_</em><span class="op">-></span><em>pattern_</em><span class="op">))</span>;</span>
<span id="cb15-23"><a href="#cb15-23"></a> <span class="op">}</span></span>
<span id="cb15-24"><a href="#cb15-24"></a><span class="op">}</span></span></code></pre></div>
</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">(</span><em>Parent</em><span class="op">&</span> parent, iterator_t<span class="op"><</span><em>Base</em><span class="op">></span> outer<span class="op">)</span>;</span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_22" id="pnum_22">9</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> and <code class="sourceCode cpp"><em>outer_it_</em></code> with <code class="sourceCode cpp">std<span class="op">::</span>move<span class="op">(</span>outer<span class="op">)</span></code>. Then, 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><span class="cf">if</span> <span class="op">(</span><em>outer_it_</em> <span class="op">!=</span> ranges<span class="op">::</span>end<span class="op">(</span><em>parent_</em><span class="op">-></span><em>base_</em><span class="op">))</span> <span class="op">{</span></span>
<span id="cb17-2"><a href="#cb17-2"></a> <span class="kw">auto</span><span class="op">&&</span> inner <span class="op">=</span> <em>update-inner</em><span class="op">(</span><em>outer_it_</em><span class="op">)</span>;</span>
<span id="cb17-3"><a href="#cb17-3"></a> <em>inner_it_</em><span class="op">.</span>emplace<span class="op"><</span><span class="dv">1</span><span class="op">>(</span>ranges<span class="op">::</span>begin<span class="op">(</span>inner<span class="op">))</span>;</span>
<span id="cb17-4"><a href="#cb17-4"></a> <em>satisfy</em><span class="op">()</span>;</span>
<span id="cb17-5"><a href="#cb17-5"></a><span class="op">}</span></span></code></pre></div>
</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="op">(</span><em>iterator</em><span class="op"><!</span>Const<span class="op">></span> i<span class="op">)</span></span>
<span id="cb18-2"><a href="#cb18-2"></a> <span class="kw">requires</span> Const <span class="op">&&</span></span>
<span id="cb18-3"><a href="#cb18-3"></a> convertible_to<span class="op"><</span>iterator_t<span class="op"><</span>V<span class="op">></span>, <em>OuterIter</em><span class="op">></span> <span class="op">&&</span></span>
<span id="cb18-4"><a href="#cb18-4"></a> convertible_to<span class="op"><</span>iterator_t<span class="op"><</span><em>InnerRng</em><span class="op">></span>, <em>InnerIter</em><span class="op">></span> <span class="op">&&</span></span>
<span id="cb18-5"><a href="#cb18-5"></a> convertible_to<span class="op"><</span>iterator_t<span class="op"><</span><em>Pattern</em><span class="op">></span>, <em>PatternIter</em><span class="op">></span>;</span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_23" id="pnum_23">10</a></span> <em>Effects</em>: Initializes <code class="sourceCode cpp"><em>outer_it_</em></code> with <code class="sourceCode cpp">std<span class="op">::</span>move<span class="op">(</span>i<span class="op">.</span><em>outer_it_</em><span class="op">)</span></code> and <code class="sourceCode cpp"><em>parent_</em></code> with <code class="sourceCode cpp">i<span class="op">.</span><em>parent_</em></code>. Then, 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="cf">if</span> <span class="op">(</span>i<span class="op">.</span><em>inner_it_</em><span class="op">.</span>index<span class="op">()</span> <span class="op">==</span> <span class="dv">0</span><span class="op">)</span> <span class="op">{</span></span>
<span id="cb19-2"><a href="#cb19-2"></a> <em>inner_it_</em><span class="op">.</span>emplace<span class="op"><</span><span class="dv">0</span><span class="op">>(</span>std<span class="op">::</span>get<span class="op"><</span><span class="dv">0</span><span class="op">>(</span>std<span class="op">::</span>move<span class="op">(</span>i<span class="op">.</span><em>inner_it_</em><span class="op">)))</span>;</span>
<span id="cb19-3"><a href="#cb19-3"></a><span class="op">}</span> <span class="cf">else</span> <span class="op">{</span></span>
<span id="cb19-4"><a href="#cb19-4"></a> <em>inner_it_</em><span class="op">.</span>emplace<span class="op"><</span><span class="dv">1</span><span class="op">>(</span>std<span class="op">::</span>get<span class="op"><</span><span class="dv">1</span><span class="op">>(</span>std<span class="op">::</span>move<span class="op">(</span>i<span class="op">.</span><em>inner_it_</em><span class="op">)))</span>;</span>
<span id="cb19-5"><a href="#cb19-5"></a><span class="op">}</span></span></code></pre></div>
</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> <span class="kw">decltype</span><span class="op">(</span><span class="kw">auto</span><span class="op">)</span> <span class="kw">operator</span><span class="op">*()</span> <span class="kw">const</span>;</span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_24" id="pnum_24">11</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><span class="kw">using</span> reference <span class="op">=</span> common_reference_t<span class="op"><</span></span>
<span id="cb21-2"><a href="#cb21-2"></a> iter_reference_t<span class="op"><</span><em>InnerIter</em><span class="op">></span>,</span>
<span id="cb21-3"><a href="#cb21-3"></a> iter_reference_t<span class="op"><</span><em>PatternIter</em><span class="op">>></span>;</span>
<span id="cb21-4"><a href="#cb21-4"></a><span class="cf">return</span> visit<span class="op">([](</span><span class="kw">auto</span><span class="op">&</span> it<span class="op">)</span> <span class="op">-></span> reference <span class="op">{</span> <span class="cf">return</span> <span class="op">*</span>it; <span class="op">}</span>, <em>inner_it_</em><span class="op">)</span>;</span></code></pre></div>
</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="op">&</span> <span class="kw">operator</span><span class="op">++()</span>;</span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_25" id="pnum_25">12</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>visit<span class="op">([](</span><span class="kw">auto</span><span class="op">&</span> it<span class="op">){</span> <span class="op">++</span>it; <span class="op">}</span>, <em>inner_it_</em><span class="op">)</span>;</span>
<span id="cb23-2"><a href="#cb23-2"></a><em>satisfy</em><span class="op">()</span>;</span>
<span id="cb23-3"><a href="#cb23-3"></a><span class="cf">return</span> <span class="op">*</span><span class="kw">this</span>;</span></code></pre></div>
</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">constexpr</span> <span class="dt">void</span> <span class="kw">operator</span><span class="op">++(</span><span class="dt">int</span><span class="op">)</span>;</span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_26" id="pnum_26">13</a></span> <em>Effects</em>: Equivalent to <code class="sourceCode cpp"><span class="op">++*</span><span class="kw">this</span>;</code></p>
<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">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="cb25-2"><a href="#cb25-2"></a> <span class="kw">requires</span> <em>ref-is-glvalue</em> <span class="op">&&</span> forward_iterator<span class="op"><</span><em>OuterIter</em><span class="op">></span> <span class="op">&&</span></span>
<span id="cb25-3"><a href="#cb25-3"></a> forward_iterator<span class="op"><</span><em>InnerIter</em><span class="op">></span>;</span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_27" id="pnum_27">14</a></span> <em>Effects</em>: Equivalent to:</p>
<blockquote>
<div class="sourceCode" id="cb26"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb26-1"><a href="#cb26-1"></a><em>iterator</em> tmp <span class="op">=</span> <span class="op">*</span><span class="kw">this</span>;</span>
<span id="cb26-2"><a href="#cb26-2"></a><span class="op">++*</span><span class="kw">this</span>;</span>
<span id="cb26-3"><a href="#cb26-3"></a><span class="cf">return</span> tmp;</span></code></pre></div>
</blockquote>
<div class="sourceCode" id="cb27"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb27-1"><a href="#cb27-1"></a><span class="kw">constexpr</span> <em>iterator</em><span class="op">&</span> <span class="kw">operator</span><span class="op">--()</span></span>
<span id="cb27-2"><a href="#cb27-2"></a> <span class="kw">requires</span> <em>ref-is-glvalue</em> <span class="op">&&</span> bidirectional_range<span class="op"><</span><em>Base</em><span class="op">></span> <span class="op">&&</span></span>
<span id="cb27-3"><a href="#cb27-3"></a> <em>bidirectional-common</em><span class="op"><</span><em>InnerBase</em><span class="op">></span> <span class="op">&&</span> <em>bidirectional-common</em><span class="op"><</span><em>PatternBase</em><span class="op">></span>;</span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_28" id="pnum_28">15</a></span> <em>Effects</em>: Equivalent to:</p>
<blockquote>
<div class="sourceCode" id="cb28"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb28-1"><a href="#cb28-1"></a><span class="cf">if</span> <span class="op">(</span><em>outer_it_</em> <span class="op">==</span> ranges<span class="op">::</span>end<span class="op">(</span><em>parent_</em><span class="op">-></span><em>base_</em><span class="op">))</span> <span class="op">{</span></span>
<span id="cb28-2"><a href="#cb28-2"></a> <span class="kw">auto</span><span class="op">&&</span> inner <span class="op">=</span> <span class="op">*--</span><em>outer_it_</em>;</span>
<span id="cb28-3"><a href="#cb28-3"></a> <em>inner_it_</em><span class="op">.</span>emplace<span class="op"><</span><span class="dv">1</span><span class="op">>(</span>ranges<span class="op">::</span>end<span class="op">(</span>inner<span class="op">))</span>;</span>
<span id="cb28-4"><a href="#cb28-4"></a><span class="op">}</span></span>
<span id="cb28-5"><a href="#cb28-5"></a></span>
<span id="cb28-6"><a href="#cb28-6"></a><span class="cf">while</span> <span class="op">(</span><span class="kw">true</span><span class="op">)</span> <span class="op">{</span></span>
<span id="cb28-7"><a href="#cb28-7"></a> <span class="cf">if</span> <span class="op">(</span><em>inner_it_</em><span class="op">.</span>index<span class="op">()</span> <span class="op">==</span> <span class="dv">0</span><span class="op">)</span> <span class="op">{</span></span>
<span id="cb28-8"><a href="#cb28-8"></a> <span class="kw">auto</span><span class="op">&</span> it <span class="op">=</span> std<span class="op">::</span>get<span class="op"><</span><span class="dv">0</span><span class="op">>(</span><em>inner_it_</em><span class="op">)</span>;</span>
<span id="cb28-9"><a href="#cb28-9"></a> <span class="cf">if</span> <span class="op">(</span>it <span class="op">==</span> ranges<span class="op">::</span>begin<span class="op">(</span><em>parent_</em><span class="op">-></span><em>pattern_</em><span class="op">))</span> <span class="op">{</span></span>
<span id="cb28-10"><a href="#cb28-10"></a> <span class="kw">auto</span><span class="op">&&</span> inner <span class="op">=</span> <span class="op">*--</span><em>outer_it_</em>;</span>
<span id="cb28-11"><a href="#cb28-11"></a> <em>inner_it_</em><span class="op">.</span>emplace<span class="op"><</span><span class="dv">1</span><span class="op">>(</span>ranges<span class="op">::</span>end<span class="op">(</span>inner<span class="op">))</span>;</span>
<span id="cb28-12"><a href="#cb28-12"></a> <span class="op">}</span> <span class="cf">else</span> <span class="op">{</span></span>
<span id="cb28-13"><a href="#cb28-13"></a> <span class="cf">break</span>;</span>
<span id="cb28-14"><a href="#cb28-14"></a> <span class="op">}</span></span>
<span id="cb28-15"><a href="#cb28-15"></a> <span class="op">}</span> <span class="cf">else</span> <span class="op">{</span></span>
<span id="cb28-16"><a href="#cb28-16"></a> <span class="kw">auto</span><span class="op">&</span> it <span class="op">=</span> std<span class="op">::</span>get<span class="op"><</span><span class="dv">1</span><span class="op">>(</span><em>inner_it_</em><span class="op">)</span>;</span>
<span id="cb28-17"><a href="#cb28-17"></a> <span class="kw">auto</span><span class="op">&&</span> inner <span class="op">=</span> <span class="op">*</span><em>outer_it_</em>;</span>
<span id="cb28-18"><a href="#cb28-18"></a> <span class="cf">if</span> <span class="op">(</span>it <span class="op">==</span> ranges<span class="op">::</span>begin<span class="op">(</span>inner<span class="op">))</span> <span class="op">{</span></span>
<span id="cb28-19"><a href="#cb28-19"></a> <em>inner_it_</em><span class="op">.</span>emplace<span class="op"><</span><span class="dv">0</span><span class="op">>(</span>ranges<span class="op">::</span>end<span class="op">(</span><em>parent_</em><span class="op">-></span><em>pattern_</em><span class="op">))</span>;</span>
<span id="cb28-20"><a href="#cb28-20"></a> <span class="op">}</span> <span class="cf">else</span> <span class="op">{</span></span>
<span id="cb28-21"><a href="#cb28-21"></a> <span class="cf">break</span>;</span>
<span id="cb28-22"><a href="#cb28-22"></a> <span class="op">}</span></span>
<span id="cb28-23"><a href="#cb28-23"></a> <span class="op">}</span></span>
<span id="cb28-24"><a href="#cb28-24"></a><span class="op">}</span></span>
<span id="cb28-25"><a href="#cb28-25"></a></span>
<span id="cb28-26"><a href="#cb28-26"></a>visit<span class="op">([](</span><span class="kw">auto</span><span class="op">&</span> it<span class="op">){</span> <span class="op">--</span>it; <span class="op">}</span>, <em>inner_it_</em><span class="op">)</span>;</span>
<span id="cb28-27"><a href="#cb28-27"></a><span class="cf">return</span> <span class="op">*</span><span class="kw">this</span>;</span></code></pre></div>
</blockquote>
<div class="sourceCode" id="cb29"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb29-1"><a href="#cb29-1"></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>
<span id="cb29-2"><a href="#cb29-2"></a> <span class="kw">requires</span> <em>ref-is-glvalue</em> <span class="op">&&</span> bidirectional_range<span class="op"><</span><em>Base</em><span class="op">></span> <span class="op">&&</span></span>
<span id="cb29-3"><a href="#cb29-3"></a> <em>bidirectional-common</em><span class="op"><</span><em>InnerBase</em><span class="op">></span> <span class="op">&&</span> <em>bidirectional-common</em><span class="op"><</span><em>PatternBase</em><span class="op">></span>;</span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_29" id="pnum_29">16</a></span> <em>Effects</em>: Equivalent to:</p>
<blockquote>
<div class="sourceCode" id="cb30"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb30-1"><a href="#cb30-1"></a><em>iterator</em> tmp <span class="op">=</span> <span class="op">*</span><span class="kw">this</span>;</span>
<span id="cb30-2"><a href="#cb30-2"></a><span class="op">--*</span><span class="kw">this</span>;</span>
<span id="cb30-3"><a href="#cb30-3"></a><span class="cf">return</span> tmp;</span></code></pre></div>
</blockquote>
<div class="sourceCode" id="cb31"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb31-1"><a href="#cb31-1"></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">&</span> x, <span class="kw">const</span> <em>iterator</em><span class="op">&</span> y<span class="op">)</span></span>
<span id="cb31-2"><a href="#cb31-2"></a> <span class="kw">requires</span> <em>ref-is-glvalue</em> <span class="op">&&</span> equality_comparable<span class="op"><</span><em>OuterIter</em><span class="op">></span> <span class="op">&&</span></span>
<span id="cb31-3"><a href="#cb31-3"></a> equality_comparable<span class="op"><</span><em>InnerIter</em><span class="op">></span>;</span></code></pre></div>
<p><span class="marginalizedparent"><a class="marginalized" href="#pnum_30" id="pnum_30">17</a></span> <em>Effects</em>: Equivalent to <code class="sourceCode cpp"><span class="cf">return</span> x<span class="op">.</span><em>outer_it_</em> <span class="op">==</span> y<span class="op">.</span><em>outer_it_</em> <span class="op">&&</span> x<span class="op">.</span><em>inner_it_</em> <span class="op">==</span> y<span class="op">.</span><em>inner_it_</em></code>;</p>
</blockquote>
<h4 class="unnumbered" data-number id="class-template-join_with_viewsentinel-range.join.with.sentinel">24.7.?.3 Class template <code class="sourceCode cpp">join_with_view<span class="op">::</span><em>sentinel</em></code> [range.join.with.sentinel]<a href="#class-template-join_with_viewsentinel-range.join.with.sentinel" class="self-link"></a></h4>
<blockquote>
<div class="sourceCode" id="cb32"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb32-1"><a href="#cb32-1"></a><span class="kw">namespace</span> std<span class="op">::</span>ranges <span class="op">{</span></span>