<!doctype html><html lang="en">
 <head>
  <meta content="text/html; charset=utf-8" http-equiv="Content-Type">
  <meta content="width=device-width, initial-scale=1, shrink-to-fit=no" name="viewport">
  <title>P2494R2: Relaxing range adaptors to allow for move only types</title>
<style data-fill-with="stylesheet">/******************************************************************************
 *                   Style sheet for the W3C specifications                   *
 *
 * Special classes handled by this style sheet include:
 *
 * Indices
 *   - .toc for the Table of Contents (<ol class="toc">)
 *     + <span class="secno"> for the section numbers
 *   - #toc for the Table of Contents (<nav id="toc">)
 *   - ul.index for Indices (<a href="#ref">term</a><span>, in § N.M</span>)
 *   - table.index for Index Tables (e.g. for properties or elements)
 *
 * Structural Markup
 *   - table.data for general data tables
 *     -> use 'scope' attribute, <colgroup>, <thead>, and <tbody> for best results !
 *     -> use <table class='complex data'> for extra-complex tables
 *     -> use <td class='long'> for paragraph-length cell content
 *     -> use <td class='pre'> when manual line breaks/indentation would help readability
 *   - dl.switch for switch statements
 *   - ol.algorithm for algorithms (helps to visualize nesting)
 *   - .figure and .caption (HTML4) and figure and figcaption (HTML5)
 *     -> .sidefigure for right-floated figures
 *   - ins/del
 *     -> ins/del.c### for candidate and proposed changes (amendments)
 *
 * Code
 *   - pre and code
 *
 * Special Sections
 *   - .note       for informative notes             (div, p, span, aside, details)
 *   - .example    for informative examples          (div, p, pre, span)
 *   - .issue      for issues                        (div, p, span)
 *   - .advisement for loud normative statements     (div, p, strong)
 *   - .annoying-warning for spec obsoletion notices (div, aside, details)
 *   - .correction for "candidate corrections"       (div, aside, details, section)
 *   - .addition   for "candidate additions"         (div, aside, details, section)
 *   - .correction.proposed for "proposed corrections" (div, aside, details, section)
 *   - .addition.proposed   for "proposed additions"   (div, aside, details, section)
 *
 * Definition Boxes
 *   - pre.def   for WebIDL definitions
 *   - table.def for tables that define other entities (e.g. CSS properties)
 *   - dl.def    for definition lists that define other entitles (e.g. HTML elements)
 *
 * Numbering
 *   - .secno for section numbers in .toc and headings (<span class='secno'>3.2</span>)
 *   - .marker for source-inserted example/figure/issue numbers (<span class='marker'>Issue 4</span>)
 *   - ::before styled for CSS-generated issue/example/figure numbers:
 *     -> Documents wishing to use this only need to add
 *        figcaption::before,
 *        .caption::before { content: "Figure "  counter(figure) " ";  }
 *        .example::before { content: "Example " counter(example) " "; }
 *        .issue::before   { content: "Issue "   counter(issue) " ";   }
 *
 * Header Stuff (ignore, just don't conflict with these classes)
 *   - .head for the header
 *   - .copyright for the copyright
 *
 * Outdated warning for old specs
 *
 * Miscellaneous
 *   - .overlarge for things that should be as wide as possible, even if
 *     that overflows the body text area. This can be used on an item or
 *     on its container, depending on the effect desired.
 *     Note that this styling basically doesn't help at all when printing,
 *     since A4 paper isn't much wider than the max-width here.
 *     It's better to design things to fit into a narrower measure if possible.
 *
 *   - js-added ToC jump links (see fixup.js)
 *
 ******************************************************************************/

/* color variables included separately for reliability */

/******************************************************************************/
/*                                    Body                                    */
/******************************************************************************/

	html {
	}

	body {
		counter-reset: example figure issue;

		/* Layout */
		max-width: 50em;			  /* limit line length to 50em for readability   */
		margin: 0 auto;				/* center text within page                    */
		padding: 1.6em 1.5em 2em 50px; /* assume 16px font size for downlevel clients */
		padding: 1.6em 1.5em 2em calc(26px + 1.5em); /* leave space for status flag    */

		/* Typography */
		line-height: 1.5;
		font-family: sans-serif;
		widows: 2;
		orphans: 2;
		word-wrap: break-word;
		overflow-wrap: break-word;
		hyphens: auto;

		color: black;
		color: var(--text);
		background: white top left fixed no-repeat;
		background: var(--bg) top left fixed no-repeat;
		background-size: 25px auto;
	}


/******************************************************************************/
/*                         Front Matter & Navigation                          */
/******************************************************************************/

/** Header ********************************************************************/

	div.head { margin-bottom: 1em; }
	div.head hr { border-style: solid; }

	div.head h1 {
		font-weight: bold;
		margin: 0 0 .1em;
		font-size: 220%;
	}

	div.head h2 { margin-bottom: 1.5em;}

/** W3C Logo ******************************************************************/

	.head .logo {
		float: right;
		margin: 0.4rem 0 0.2rem .4rem;
	}

	.head img[src*="logos/W3C"] {
		display: block;
		border: solid #1a5e9a;
		border: solid var(--logo-bg);
		border-width: .65rem .7rem .6rem;
		border-radius: .4rem;
		background: #1a5e9a;
		background: var(--logo-bg);
		color: white;
		color: var(--logo-text);
		font-weight: bold;
	}

	.head a:hover > img[src*="logos/W3C"],
	.head a:focus > img[src*="logos/W3C"] {
		opacity: .8;
	}

	.head a:active > img[src*="logos/W3C"] {
		background: #c00;
		background: var(--logo-active-bg);
		border-color: #c00;
		border-color: var(--logo-active-bg);
	}

	/* see also additional rules in Link Styling section */

/** Copyright *****************************************************************/

	p.copyright,
	p.copyright small { font-size: small; }

/** Back to Top / ToC Toggle **************************************************/

	@media print {
		#toc-nav {
			display: none;
		}
	}
	@media not print {
		#toc-nav {
			position: fixed;
			z-index: 3;
			bottom: 0; left: 0;
			margin: 0;
			min-width: 1.33em;
			border-top-right-radius: 2rem;
			box-shadow: 0 0 2px;
			font-size: 1.5em;
		}
		#toc-nav > a {
			display: block;
			white-space: nowrap;

			height: 1.33em;
			padding: .1em 0.3em;
			margin: 0;

			box-shadow: 0 0 2px;
			border: none;
			border-top-right-radius: 1.33em;

			color: #707070;
			color: var(--tocnav-normal-text);
			background: white;
			background: var(--tocnav-normal-bg);
		}
		#toc-nav > a:hover,
		#toc-nav > a:focus {
			color: black;
			color: var(--tocnav-hover-text);
			background: #f8f8f8;
			background: var(--tocnav-hover-bg);
		}
		#toc-nav > a:active {
			color: #c00;
			color: var(--tocnav-active-text);
			background: white;
			background: var(--tocnav-active-bg);
		}

		#toc-nav > #toc-jump {
			padding-bottom: 2em;
			margin-bottom: -1.9em;
		}

		/* statusbar gets in the way on keyboard focus; remove once browsers fix */
		#toc-nav > a[href="#toc"]:not(:hover):focus:last-child {
			padding-bottom: 1.5rem;
		}

		#toc-nav:not(:hover) > a:not(:focus) > span + span {
			/* Ideally this uses :focus-within on #toc-nav */
			display: none;
		}
		#toc-nav > a > span + span {
			padding-right: 0.2em;
		}
	}

/** ToC Sidebar ***************************************************************/

	/* Floating sidebar */
	@media screen {
		body.toc-sidebar #toc {
			position: fixed;
			top: 0; bottom: 0;
			left: 0;
			width: 23.5em;
			max-width: 80%;
			max-width: calc(100% - 2em - 26px);
			overflow: auto;
			padding: 0 1em;
			padding-left: 42px;
			padding-left: calc(1em + 26px);
			color: black;
			color: var(--tocsidebar-text);
			background: inherit;
			background-color: #f7f8f9;
			background-color: var(--tocsidebar-bg);
			z-index: 1;
			box-shadow: -.1em 0 .25em rgba(0,0,0,.1) inset;
			box-shadow: -.1em 0 .25em var(--tocsidebar-shadow) inset;
		}
		body.toc-sidebar #toc h2 {
			margin-top: .8rem;
			font-variant: small-caps;
			font-variant: all-small-caps;
			text-transform: lowercase;
			font-weight: bold;
			color: gray;
			color: hsla(203,20%,40%,.7);
			color: var(--tocsidebar-heading-text);
		}
		body.toc-sidebar #toc-jump:not(:focus) {
			width: 0;
			height: 0;
			padding: 0;
			position: absolute;
			overflow: hidden;
		}
	}
	/* Hide main scroller when only the ToC is visible anyway */
	@media screen and (max-width: 28em) {
		body.toc-sidebar {
			overflow: hidden;
		}
	}

	/* Sidebar with its own space */
	@media screen and (min-width: 78em) {
		body:not(.toc-inline) #toc {
			position: fixed;
			top: 0; bottom: 0;
			left: 0;
			width: 23.5em;
			overflow: auto;
			padding: 0 1em;
			padding-left: 42px;
			padding-left: calc(1em + 26px);
			color: black;
			color: var(--tocsidebar-text);
			background: inherit;
			background-color: #f7f8f9;
			background-color: var(--tocsidebar-bg);
			z-index: 1;
			box-shadow: -.1em 0 .25em rgba(0,0,0,.1) inset;
			box-shadow: -.1em 0 .25em var(--tocsidebar-shadow) inset;
		}
		body:not(.toc-inline) #toc h2 {
			margin-top: .8rem;
			font-variant: small-caps;
			font-variant: all-small-caps;
			text-transform: lowercase;
			font-weight: bold;
			color: gray;
			color: hsla(203,20%,40%,.7);
			color: var(--tocsidebar-heading-text);
		}

		body:not(.toc-inline) {
			padding-left: 29em;
		}
		/* See also Overflow section at the bottom */

		body:not(.toc-inline) #toc-jump:not(:focus) {
			width: 0;
			height: 0;
			padding: 0;
			position: absolute;
			overflow: hidden;
		}
	}
	@media screen and (min-width: 90em) {
		body:not(.toc-inline) {
			margin: 0 4em;
		}
	}

/******************************************************************************/
/*                                Sectioning                                  */
/******************************************************************************/

/** Headings ******************************************************************/

	h1, h2, h3, h4, h5, h6, dt {
		page-break-after: avoid;
		page-break-inside: avoid;
		font: 100% sans-serif;   /* Reset all font styling to clear out UA styles */
		font-family: inherit;	/* Inherit the font family. */
		line-height: 1.2;		/* Keep wrapped headings compact */
		hyphens: manual;		/* Hyphenated headings look weird */
	}

	h2, h3, h4, h5, h6 {
		margin-top: 3rem;
	}

	h1, h2, h3 {
		color: #005A9C;
		color: var(--heading-text);
	}

	h1 { font-size: 170%; }
	h2 { font-size: 140%; }
	h3 { font-size: 120%; }
	h4 { font-weight: bold; }
	h5 { font-style: italic; }
	h6 { font-variant: small-caps; }
	dt { font-weight: bold; }

/** Subheadings ***************************************************************/

	h1 + h2,
	#profile-and-date {
		/* #profile-and-date is a subtitle in an H2 under the H1 */
		margin-top: 0;
	}
	h2 + h3,
	h3 + h4,
	h4 + h5,
	h5 + h6 {
		margin-top: 1.2em; /* = 1 x line-height */
	}

/** Section divider ***********************************************************/

	:not(.head) > :not(.head) + hr {
		font-size: 1.5em;
		text-align: center;
		margin: 1em auto;
		height: auto;
		color: black;
		color: var(--hr-text);
		border: transparent solid 0;
		background: transparent;
	}
	:not(.head) > hr::before {
		content: "\2727\2003\2003\2727\2003\2003\2727";
	}

/******************************************************************************/
/*                            Paragraphs and Lists                            */
/******************************************************************************/

	p {
		margin: 1em 0;
	}

	dd > p:first-child,
	li > p:first-child {
		margin-top: 0;
	}

	ul, ol {
		margin-left: 0;
		padding-left: 2em;
	}

	li {
		margin: 0.25em 0 0.5em;
		padding: 0;
	}

	dl dd {
		margin: 0 0 .5em 2em;
	}

	.head dd + dd { /* compact for header */
		margin-top: -.5em;
	}

	/* Style for algorithms */
	ol.algorithm ol:not(.algorithm),
	.algorithm > ol ol:not(.algorithm) {
	border-left: 0.5em solid #DEF;
	border-left: 0.5em solid var(--algo-border);
	}

	/* Put nice boxes around each algorithm. */
	[data-algorithm]:not(.heading) {
	 padding: .5em;
	 border: thin solid #ddd;
	 border: thin solid var(--algo-border);
	 border-radius: .5em;
	 margin: .5em calc(-0.5em - 1px);
	}
	[data-algorithm]:not(.heading) > :first-child {
	 margin-top: 0;
	}
	[data-algorithm]:not(.heading) > :last-child {
	 margin-bottom: 0;
	}

	/* Style for switch/case <dl>s */
	dl.switch > dd > ol.only,
	dl.switch > dd > .only > ol {
	margin-left: 0;
	}
	dl.switch > dd > ol.algorithm,
	dl.switch > dd > .algorithm > ol {
	margin-left: -2em;
	}
	dl.switch {
	padding-left: 2em;
	}
	dl.switch > dt {
	text-indent: -1.5em;
	margin-top: 1em;
	}
	dl.switch > dt + dt {
	margin-top: 0;
	}
	dl.switch > dt::before {
	content: '\21AA';
	padding: 0 0.5em 0 0;
	display: inline-block;
	width: 1em;
	text-align: right;
	line-height: 0.5em;
	}

/** Terminology Markup ********************************************************/


/******************************************************************************/
/*                                 Inline Markup                              */
/******************************************************************************/

/** Terminology Markup ********************************************************/
	dfn   { /* Defining instance */
		font-weight: bolder;
	}
	a > i { /* Instance of term */
		font-style: normal;
	}
	dt dfn code, code.idl {
		font-size: inherit;
	}
	dfn var {
		font-style: normal;
	}

/** Change Marking ************************************************************/

	del {
		color: #aa0000;
		color: var(--del-text);
		background: transparent;
		background: var(--del-bg);
		text-decoration: line-through;
	}
	ins {
		color: #006100;
		color: var(--ins-text);
		background: transparent;
		background: var(--ins-bg);
		text-decoration: underline;
	}

	/* for amendments (candidate/proposed changes) */

	.amendment ins, .correction ins, .addition ins,
	ins[class^=c] {
		text-decoration-style: dotted;
	}
	.amendment del, .correction del, .addition del,
	del[class^=c] {
		text-decoration-style: dotted;
	}
	.amendment.proposed ins, .correction.proposed ins, .addition.proposed ins,
	ins[class^=c].proposed {
		text-decoration-style: double;
	}
	.amendment.proposed del, .correction.proposed del, .addition.proposed del,
	del[class^=c].proposed {
		text-decoration-style: double;
	}

/** Miscellaneous improvements to inline formatting ***************************/

	sup {
		vertical-align: super;
		font-size: 80%
	}

/******************************************************************************/
/*                                    Code                                    */
/******************************************************************************/

/** General monospace/pre rules ***********************************************/

	pre, code, samp {
		font-family: Menlo, Consolas, "DejaVu Sans Mono", Monaco, monospace;
		font-size: .9em;
		hyphens: none;
		text-transform: none;
		text-align: left;
		text-align: start;
		font-variant: normal;
		orphans: 3;
		widows: 3;
		page-break-before: avoid;
	}
	pre code,
	code code {
		font-size: 100%;
	}

	pre {
		margin-top: 1em;
		margin-bottom: 1em;
		overflow: auto;
	}

/** Inline Code fragments *****************************************************/

	/* Do something nice. */

/******************************************************************************/
/*                                    Links                                   */
/******************************************************************************/

/** General Hyperlinks ********************************************************/

	/* We hyperlink a lot, so make it less intrusive */
	a[href] {
		color: #034575;
		color: var(--a-normal-text);
		text-decoration: underline #707070;
		text-decoration: underline var(--a-normal-underline);
		text-decoration-skip-ink: none;
	}
	a:visited {
		color: #034575;
		color: var(--a-visited-text);
		text-decoration-color: #bbb;
		text-decoration-color: var(--a-visited-underline);
	}

	/* Indicate interaction with the link */
	a[href]:focus,
	a[href]:hover {
		text-decoration-thickness: 2px;
	}
	a[href]:active {
		color: #c00;
		color: var(--a-active-text);
		text-decoration-color: #c00;
		text-decoration-color: var(--a-active-underline);
	}

	/* Backout above styling for W3C logo */
	.head .logo,
	.head .logo a {
		border: none;
		text-decoration: none;
		background: transparent;
	}

/******************************************************************************/
/*                                    Images                                  */
/******************************************************************************/

	img {
		border-style: none;
	}

	img, svg {
		/* Intentionally not color-scheme aware. */
		background: white;
	}

	/* For autogen numbers, add
	  .caption::before, figcaption::before { content: "Figure " counter(figure) ". "; }
	*/

	figure, .figure, .sidefigure {
		page-break-inside: avoid;
		text-align: center;
		margin: 2.5em 0;
	}
	.figure img,	.sidefigure img,	figure img,
	.figure object, .sidefigure object, figure object {
		max-width: 100%;
		margin: auto;
		height: auto;
	}
	.figure pre, .sidefigure pre, figure pre {
		text-align: left;
		display: table;
		margin: 1em auto;
	}
	.figure table, figure table {
		margin: auto;
	}
	@media screen and (min-width: 20em) {
		.sidefigure {
			float: right;
			width: 50%;
			margin: 0 0 0.5em 0.5em;
		}
	}
	.caption, figcaption, caption {
		font-style: italic;
		font-size: 90%;
	}
	.caption::before, figcaption::before, figcaption > .marker {
		font-weight: bold;
	}
	.caption, figcaption {
		counter-increment: figure;
	}

	/* DL list is indented 2em, but figure inside it is not */
	dd > .figure, dd > figure { margin-left: -2em; }

/******************************************************************************/
/*                             Colored Boxes                                  */
/******************************************************************************/

	.issue, .note, .example, .assertion, .advisement, blockquote,
	.amendment, .correction, .addition {
		margin: 1em auto;
		padding: .5em;
		border: .5em;
		border-left-style: solid;
		page-break-inside: avoid;
	}
	span.issue, span.note {
		padding: .1em .5em .15em;
		border-right-style: solid;
	}

	blockquote > :first-child,
	.note  > p:first-child,
	.issue > p:first-child,
	.amendment > p:first-child,
	.correction > p:first-child,
	.addition > p:first-child {
		margin-top: 0;
	}
	blockquote > :last-child,
	.note  > p:last-child,
	.issue > p:last-child,
	.amendment > p:last-child,
	.correction > p:last-child,
	.addition > p:last-child {
		margin-bottom: 0;
	}


	.issue::before, .issue > .marker,
	.example::before, .example > .marker,
	.note::before, .note > .marker,
	details.note > summary > .marker,
	.amendment::before, .amendment > .marker,
	details.amendment > summary > .marker,
	.addition::before, .addition > .marker,
	addition.amendment > summary > .marker,
	.correction::before, .correction > .marker,
	correction.amendment > summary > .marker
	{
		text-transform: uppercase;
		padding-right: 1em;
	}

	.example::before, .example > .marker {
		display: block;
		padding-right: 0em;
	}

/** Blockquotes ***************************************************************/

	blockquote {
		border-color: silver;
		border-color: var(--blockquote-border);
		background: transparent;
		background: var(--blockquote-bg);
		color: currentcolor;
		color: var(--blockquote-text);
	}

/** Open issue ****************************************************************/

	.issue {
		border-color: #e05252;
		border-color: var(--issue-border);
		background: #fbe9e9;
		background: var(--issue-bg);
		color: black;
		color: var(--issue-text);
		counter-increment: issue;
		overflow: auto;
	}
	.issue::before, .issue > .marker {
		color: #831616;
		color: var(--issueheading-text);
	}
	/* Add .issue::before { content: "Issue " counter(issue) " "; } for autogen numbers,
	  or use class="marker" to mark up the issue number in source. */

/** Example *******************************************************************/

	.example {
		border-color: #e0cb52;
		border-color: var(--example-border);
		background: #fcfaee;
		background: var(--example-bg);
		color: black;
		color: var(--example-text);
		counter-increment: example;
		overflow: auto;
		clear: both;
	}
	.example::before, .example > .marker {
		color: #574b0f;
		color: var(--exampleheading-text);
	}
	/* Add .example::before { content: "Example " counter(example) " "; } for autogen numbers,
	  or use class="marker" to mark up the example number in source. */

/** Non-normative Note ********************************************************/

	.note {
		border-color: #52e052;
		border-color: var(--note-border);
		background: #e9fbe9;
		background: var(--note-bg);
		color: black;
		color: var(--note-text);
		overflow: auto;
	}

	.note::before, .note > .marker,
	details.note > summary {
		color: hsl(120, 70%, 30%);
		color: var(--noteheading-text);
	}
	/* Add .note::before { content: "Note "; } for autogen label,
	  or use class="marker" to mark up the label in source. */

	details.note[open] > summary {
		border-bottom: 1px silver solid;
		border-bottom: 1px var(--notesummary-underline) solid;
	}

/** Assertion Box *************************************************************/
	/*  for assertions in algorithms */

	.assertion {
		border-color: #AAA;
		border-color: var(--assertion-border);
		background: #EEE;
		background: var(--assertion-bg);
		color: black;
		color: var(--assertion-text);
	}

/** Advisement Box ************************************************************/
	/*  for attention-grabbing normative statements */

	.advisement {
		border-color: orange;
		border-color: var(--advisement-border);
		border-style: none solid;
		background: #fec;
		background: var(--advisement-bg);
		color: black;
		color: var(--advisement-text);
	}
	strong.advisement {
		display: block;
		text-align: center;
	}
	.advisement::before, .advisement > .marker {
		color: #b35f00;
		color: var(--advisementheading-text);
	}

/** Amendment Box *************************************************************/

	.amendment, .correction, .addition {
		border-color: #330099;
		border-color: var(--amendment-border);
		background: #F5F0FF;
		background: var(--amendment-bg);
		color: black;
		color: var(--amendment-text);
	}
	.amendment.proposed, .correction.proposed, .addition.proposed {
		border-style: solid;
		border-block-width: 0.25em;
	}
	.amendment::before, .amendment > .marker,
	details.amendment > summary::before, details.amendment > summary > .marker,
	.correction::before, .correction > .marker,
	details.correction > summary::before, details.correction > summary > .marker,
	.addition::before, .addition > .marker,
	details.addition > summary::before, details.addition > summary > .marker {
		color: #220066;
		color: var(--amendmentheading-text);
	}
	.amendment.proposed::before, .amendment.proposed > .marker,
	details.amendment.proposed > summary::before, details.amendment.proposed > summary > .marker,
	.correction.proposed::before, .correction.proposed > .marker,
	details.correction.proposed > summary::before, details.correction.proposed > summary > .marker,
	.addition.proposed::before, .addition.proposed > .marker,
	details.addition.proposed > summary::before, details.addition.proposed > summary > .marker {
		font-weight: bold;
	}

/** Spec Obsoletion Notice ****************************************************/
	/* obnoxious obsoletion notice for older/abandoned specs. */

	details {
		display: block;
	}
	summary {
		font-weight: bolder;
	}

	.annoying-warning:not(details),
	details.annoying-warning:not([open]) > summary,
	details.annoying-warning[open] {
		background: hsla(40,100%,50%,0.95);
		background: var(--warning-bg);
		color: black;
		color: var(--warning-text);
		padding: .75em 1em;
		border: red;
		border: var(--warning-border);
		border-style: solid none;
		box-shadow: 0 2px 8px black;
		text-align: center;
	}
	.annoying-warning :last-child {
		margin-bottom: 0;
	}

@media not print {
	details.annoying-warning[open] {
		position: fixed;
		left: 0;
		right: 0;
		bottom: 2em;
		z-index: 1000;
	}
}

	details.annoying-warning:not([open]) > summary {
		text-align: center;
	}

/** Entity Definition Boxes ***************************************************/

	.def {
		padding: .5em 1em;
		background: #def;
		background: var(--def-bg);
		margin: 1.2em 0;
		border-left: 0.5em solid #8ccbf2;
		border-left: 0.5em solid var(--def-border);
		color: black;
		color: var(--def-text);
	}

/******************************************************************************/
/*                                    Tables                                  */
/******************************************************************************/

	th, td {
		text-align: left;
		text-align: start;
	}

/** Property/Descriptor Definition Tables *************************************/

	table.def {
		/* inherits .def box styling, see above */
		width: 100%;
		border-spacing: 0;
	}

	table.def td,
	table.def th {
		padding: 0.5em;
		vertical-align: baseline;
		border-bottom: 1px solid #bbd7e9;
		border-bottom: 1px solid var(--defrow-border);
	}

	table.def > tbody > tr:last-child th,
	table.def > tbody > tr:last-child td {
		border-bottom: 0;
	}

	table.def th {
		font-style: italic;
		font-weight: normal;
		padding-left: 1em;
		width: 3em;
	}

	/* For when values are extra-complex and need formatting for readability */
	table td.pre {
		white-space: pre-wrap;
	}

	/* A footnote at the bottom of a def table */
	table.def td.footnote {
		padding-top: 0.6em;
	}
	table.def td.footnote::before {
		content: " ";
		display: block;
		height: 0.6em;
		width: 4em;
		border-top: thin solid;
	}

/** Data tables (and properly marked-up index tables) *************************/
	/*
		<table class="data"> highlights structural relationships in a table
		when correct markup is used (e.g. thead/tbody, th vs. td, scope attribute)

		Use class="complex data" for particularly complicated tables --
		(This will draw more lines: busier, but clearer.)

		Use class="long" on table cells with paragraph-like contents
		(This will adjust text alignment accordingly.)
		Alternately use class="longlastcol" on tables, to have the last column assume "long".
	*/

	table {
		word-wrap: normal;
		overflow-wrap: normal;
		hyphens: manual;
	}

	table.data,
	table.index {
		margin: 1em auto;
		border-collapse: collapse;
		border: hidden;
		width: 100%;
	}
	table.data caption,
	table.index caption {
		max-width: 50em;
		margin: 0 auto 1em;
	}

	table.data td,  table.data th,
	table.index td, table.index th {
		padding: 0.5em 1em;
		border-width: 1px;
		border-color: silver;
		border-color: var(--datacell-border);
		border-top-style: solid;
	}

	table.data thead td:empty {
		padding: 0;
		border: 0;
	}

	table.data  thead,
	table.index thead,
	table.data  tbody,
	table.index tbody {
		border-bottom: 2px solid;
	}

	table.data colgroup,
	table.index colgroup {
		border-left: 2px solid;
	}

	table.data  tbody th:first-child,
	table.index tbody th:first-child  {
		border-right: 2px solid;
		border-top: 1px solid silver;
		border-top: 1px solid var(--datacell-border);
		padding-right: 1em;
	}

	table.data th[colspan],
	table.data td[colspan] {
		text-align: center;
	}

	table.complex.data th,
	table.complex.data td {
		border: 1px solid silver;
		border: 1px solid var(--datacell-border);
		text-align: center;
	}

	table.data.longlastcol td:last-child,
	table.data td.long {
		vertical-align: baseline;
		text-align: left;
	}

	table.data img {
		vertical-align: middle;
	}


/*
Alternate table alignment rules

	table.data,
	table.index {
		text-align: center;
	}

	table.data  thead th[scope="row"],
	table.index thead th[scope="row"] {
		text-align: right;
	}

	table.data  tbody th:first-child,
	table.index tbody th:first-child  {
		text-align: right;
	}

Possible extra rowspan handling

	table.data  tbody th[rowspan]:not([rowspan='1']),
	table.index tbody th[rowspan]:not([rowspan='1']),
	table.data  tbody td[rowspan]:not([rowspan='1']),
	table.index tbody td[rowspan]:not([rowspan='1']) {
		border-left: 1px solid silver;
	}

	table.data  tbody th[rowspan]:first-child,
	table.index tbody th[rowspan]:first-child,
	table.data  tbody td[rowspan]:first-child,
	table.index tbody td[rowspan]:first-child{
		border-left: 0;
		border-right: 1px solid silver;
	}
*/

/******************************************************************************/
/*                                  Indices                                   */
/******************************************************************************/


/** Table of Contents *********************************************************/

	.toc a {
		/* More spacing; use padding to make it part of the click target. */
		padding: 0.1rem 1px 0;
		/* Larger, more consistently-sized click target */
		display: block;
		/* Switch to using border-bottom for underlines */
		text-decoration: none;
		border-bottom: 1px solid;
		/* Reverse color scheme */
		color: black;
		color: var(--toclink-text);
		border-color: #3980b5;
		border-color: var(--toclink-underline);
	}
	.toc a:visited {
		color: black;
		color: var(--toclink-visited-text);
		border-color: #054572;
		border-color: var(--toclink-visited-underline);
	}
	.toc a:focus,
	.toc a:hover {
		background: rgba(75%, 75%, 75%, .25);
		background: var(--a-hover-bg);
		border-bottom-width: 3px;
		margin-bottom: -2px;
	}
	.toc a:not(:focus):not(:hover) {
		/* Allow colors to cascade through from link styling */
		border-bottom-color: transparent;
	}

	.toc, .toc ol, .toc ul, .toc li {
		list-style: none; /* Numbers must be inlined into source */
		/* because generated content isn't search/selectable and markers can't do multilevel yet */
		margin:  0;
		padding: 0;
	}
	.toc {
		line-height: 1.1em;
	}

	/* ToC not indented until third level, but font style & margins show hierarchy */
	.toc > li			{ font-weight: bold;   }
	.toc > li li		 { font-weight: normal; }
	.toc > li li li	  { font-size:   95%;	}
	.toc > li li li li	{ font-size:   90%;	}
	.toc > li li li li li { font-size:   85%;	}

	/* @supports not (display:grid) { */
		.toc > li			{ margin: 1.5rem 0;	}
		.toc > li li		 { margin: 0.3rem 0;	}
		.toc > li li li	  { margin-left: 2rem;   }

		/* Section numbers in a column of their own */
		.toc .secno {
			float: left;
			width: 4rem;
			white-space: nowrap;
		}
		.toc > li li li li .secno { font-size: 85%; }
		.toc > li li li li li .secno { font-size: 100%; }

		.toc li {
			clear: both;
		}

		:not(li) > .toc			 { margin-left:  5rem; }
		.toc .secno				 { margin-left: -5rem; }
		.toc > li li li .secno	  { margin-left: -7rem; }
		.toc > li li li li .secno	{ margin-left: -9rem; }
		.toc > li li li li li .secno { margin-left: -11rem; }

		/* Tighten up indentation in narrow ToCs */
		@media (max-width: 30em) {
			:not(li) > .toc			 { margin-left:  4rem; }
			.toc .secno				 { margin-left: -4rem; }
			.toc > li li li			 { margin-left:  1rem; }
			.toc > li li li .secno	  { margin-left: -5rem; }
			.toc > li li li li .secno	{ margin-left: -6rem; }
			.toc > li li li li li .secno { margin-left: -7rem; }
		}
		/* Loosen it on wide screens */
		@media screen and (min-width: 78em) {
			body:not(.toc-inline) :not(li) > .toc			 { margin-left:  4rem; }
			body:not(.toc-inline) .toc .secno				 { margin-left: -4rem; }
			body:not(.toc-inline) .toc > li li li			 { margin-left:  1rem; }
			body:not(.toc-inline) .toc > li li li .secno	  { margin-left: -5rem; }
			body:not(.toc-inline) .toc > li li li li .secno	{ margin-left: -6rem; }
			body:not(.toc-inline) .toc > li li li li li .secno { margin-left: -7rem; }
	}
	/* } */

	@supports (display:grid) and (display:contents) {
		/* Use #toc over .toc to override non-@supports rules. */
		#toc {
			display: grid;
			align-content: start;
			grid-template-columns: auto 1fr;
			grid-column-gap: 1rem;
			column-gap: 1rem;
			grid-row-gap: .6rem;
			row-gap: .6rem;
		}
		#toc h2 {
			grid-column: 1 / -1;
			margin-bottom: 0;
		}
		#toc ol,
		#toc li,
		#toc a {
			display: contents;
			/* Switch <a> to subgrid when supported */
		}
		#toc span {
			margin: 0;
		}
		#toc > .toc > li > a > span {
			/* The spans of the top-level list,
			  comprising the first items of each top-level section. */
			margin-top: 1.1rem;
		}
		#toc#toc .secno { /* Ugh, need more specificity to override base.css */
			grid-column: 1;
			width: auto;
			margin-left: 0;
		}
		#toc .content {
			grid-column: 2;
			width: auto;
			margin-right: 1rem;
		}
		#toc .content:hover,
		#toc .content:focus {
			background: rgba(75%, 75%, 75%, .25);
			background: var(--a-hover-bg);
			border-bottom: 3px solid #054572;
			border-bottom: 3px solid var(--toclink-underline);
			margin-bottom: -3px;
		}
		#toc li li li .content {
			margin-left: 1rem;
		}
		#toc li li li li .content {
			margin-left: 2rem;
		}
	}


/** Index *********************************************************************/

	/* Index Lists: Layout */
	ul.index	  { margin-left: 0; columns: 15em; text-indent: 1em hanging; }
	ul.index li	{ margin-left: 0; list-style: none; break-inside: avoid; }
	ul.index li li { margin-left: 1em; }
	ul.index dl	{ margin-top: 0; }
	ul.index dt	{ margin: .2em 0 .2em 20px;}
	ul.index dd	{ margin: .2em 0 .2em 40px;}
	/* Index Lists: Typography */
	ul.index ul,
	ul.index dl { font-size: smaller; }
	@media not print {
		ul.index li span:not(.dfn-paneled) {
			white-space: nowrap;
			color: transparent; }
		ul.index li a:hover + span,
		ul.index li a:focus + span {
			color: #707070;
			color: var(--indexinfo-text);
		}
	}

/** Index Tables *****************************************************/
	/* See also the data table styling section, which this effectively subclasses */

	table.index {
		font-size: small;
		border-collapse: collapse;
		border-spacing: 0;
		text-align: left;
		margin: 1em 0;
	}

	table.index td,
	table.index th {
		padding: 0.4em;
	}

	table.index tr:hover td:not([rowspan]),
	table.index tr:hover th:not([rowspan]) {
		color: black;
		color: var(--indextable-hover-text);
		background: #f7f8f9;
		background: var(--indextable-hover-bg);
	}

	/* The link in the first column in the property table (formerly a TD) */
	table.index th:first-child a {
		font-weight: bold;
	}

/** Outdated warning **********************************************************/

.outdated-spec {
	color: black;
	color: var(--outdatedspec-text);
	background-color: rgba(0,0,0,0.5);
	background-color: var(--outdatedspec-bg);
}

.outdated-warning {
	position: fixed;
	bottom: 50%;
	left: 0;
	right: 0;
	margin: 0 auto;
	width: 50%;
	background: maroon;
	background: var(--outdated-bg);
	color: white;
	color: var(--outdated-text);
	border-radius: 1em;
	box-shadow: 0 0 1em red;
	box-shadow: 0 0 1em var(--outdated-shadow);
	padding: 2em;
	text-align: center;
	z-index: 2;
}

.outdated-warning a {
	color: currentcolor;
	background: transparent;
}

.edited-rec-warning {
	background: darkorange;
	background: var(--editedrec-bg);
	box-shadow: 0 0 1em;
}

.outdated-warning button {
	color: var(--outdated-text);
	border-radius: 1em;
	box-shadow: 0 0 1em red;
	box-shadow: 0 0 1em var(--outdated-shadow);
	padding: 2em;
	text-align: center;
	z-index: 2;
}

.outdated-warning a {
	color: currentcolor;
	background: transparent;
}

.edited-rec-warning {
	background: darkorange;
	background: var(--editedrec-bg);
	box-shadow: 0 0 1em;
}

.outdated-warning button {
	position: absolute;
	top: 0;
	right:0;
	margin: 0;
	border: 0;
	padding: 0.25em 0.5em;
	background: transparent;
	color: white;
	color: var(--outdated-text);
	font:1em sans-serif;
	text-align:center;
}

.outdated-warning span {
	display: block;
}

.outdated-collapsed {
	bottom: 0;
	border-radius: 0;
	width: 100%;
	padding: 0;
}

/******************************************************************************/
/*                                    Print                                   */
/******************************************************************************/

	@media print {
		/* Pages have their own margins. */
		html {
			margin: 0;
		}
		/* Serif for print. */
		body {
			font-family: serif;
		}

		.outdated-warning {
			position: absolute;
			border-style: solid;
			border-color: red;
		}

		.outdated-warning input {
			display: none;
		}
	}
	@page {
		margin: 1.5cm 1.1cm;
	}



/******************************************************************************/
/*                             Overflow Control                               */
/******************************************************************************/

	.figure .caption, .sidefigure .caption, figcaption {
		/* in case figure is overlarge, limit caption to 50em */
		max-width: 50rem;
		margin-left: auto;
		margin-right: auto;
	}
	.overlarge {
		/* Magic to create good item positioning:
		  "content column" is 50ems wide at max; less on smaller screens.
		  Extra space (after ToC + content) is empty on the right.

		  1. When item < content column, centers item in column.
		  2. When content < item < available, left-aligns.
		  3. When item > available, fills available + scroll bar.
		*/
		display: grid;
		grid-template-columns: minmax(0, 50em);
	}
	.overlarge > table {
		/* limit preferred width of table */
		max-width: 50em;
		margin-left: auto;
		margin-right: auto;
	}

	@media (min-width: 55em) {
		.overlarge {
			margin-right: calc(13px + 26.5rem - 50vw);
			max-width: none;
		}
	}
	@media screen and (min-width: 78em) {
		body:not(.toc-inline) .overlarge {
			/* 30.5em body padding 50em content area */
			margin-right: calc(40em - 50vw) !important;
		}
	}
	@media screen and (min-width: 90em) {
		body:not(.toc-inline) .overlarge {
			/* 4em html margin 30.5em body padding 50em content area */
			margin-right: calc(84.5em - 100vw) !important;
		}
	}

	@media not print {
		.overlarge {
			overflow-x: auto;
			/* See Lea Verou's explanation background-attachment:
			* http://lea.verou.me/2012/04/background-attachment-local/
			*
			background: top left  / 4em 100% linear-gradient(to right,  #ffffff, rgba(255, 255, 255, 0)) local,
						top right / 4em 100% linear-gradient(to left, #ffffff, rgba(255, 255, 255, 0)) local,
						top left  / 1em 100% linear-gradient(to right,  #c3c3c5, rgba(195, 195, 197, 0)) scroll,
						top right / 1em 100% linear-gradient(to left, #c3c3c5, rgba(195, 195, 197, 0)) scroll,
						white;
			background-repeat: no-repeat;
			*/
		}
	}
</style>
<style type="text/css">
    table, th, td {
      border: 1px solid black;
      border-collapse: collapse;
      vertical-align: top;
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    th, td {
      border-left: none;
      border-right: none;
      padding: 0px 10px;
    }
    th {
      text-align: center;
    }

    del { background: #fcc; color: #000; text-decoration: line-through; }
    ins { background: #cfc; color: #000; }
    blockquote .highlight:not(.idl) { background: initial; margin: initial; padding: 0.5em }
    blockquote ul { background: inherit; }
    blockquote code.highlight:not(.idl) { padding: initial; }
    blockquote c-[a] { color: inherit; } /* Keyword.Declaration */
    blockquote c-[b] { color: inherit; } /* Keyword.Type */
    blockquote c-[c] { color: inherit; } /* Comment */
    blockquote c-[d] { color: inherit; } /* Comment.Multiline */
    blockquote c-[e] { color: inherit; } /* Name.Attribute */
    blockquote c-[f] { color: inherit; } /* Name.Tag */
    blockquote c-[g] { color: inherit; } /* Name.Variable */
    blockquote c-[k] { color: inherit; } /* Keyword */
    blockquote c-[l] { color: inherit; } /* Literal */
    blockquote c-[m] { color: inherit; } /* Literal.Number */
    blockquote c-[n] { color: inherit; } /* Name */
    blockquote c-[o] { color: inherit; } /* Operator */
    blockquote c-[p] { color: inherit; } /* Punctuation */
    blockquote c-[s] { color: inherit; } /* Literal.String */
    blockquote c-[t] { color: inherit; } /* Literal.String.Single */
    blockquote c-[u] { color: inherit; } /* Literal.String.Double */
    blockquote c-[cp] { color: inherit; } /* Comment.Preproc */
    blockquote c-[c1] { color: inherit; } /* Comment.Single */
    blockquote c-[cs] { color: inherit; } /* Comment.Special */
    blockquote c-[kc] { color: inherit; } /* Keyword.Constant */
    blockquote c-[kn] { color: inherit; } /* Keyword.Namespace */
    blockquote c-[kp] { color: inherit; } /* Keyword.Pseudo */
    blockquote c-[kr] { color: inherit; } /* Keyword.Reserved */
    blockquote c-[ld] { color: inherit; } /* Literal.Date */
    blockquote c-[nc] { color: inherit; } /* Name.Class */
    blockquote c-[no] { color: inherit; } /* Name.Constant */
    blockquote c-[nd] { color: inherit; } /* Name.Decorator */
    blockquote c-[ni] { color: inherit; } /* Name.Entity */
    blockquote c-[ne] { color: inherit; } /* Name.Exception */
    blockquote c-[nf] { color: inherit; } /* Name.Function */
    blockquote c-[nl] { color: inherit; } /* Name.Label */
    blockquote c-[nn] { color: inherit; } /* Name.Namespace */
    blockquote c-[py] { color: inherit; } /* Name.Property */
    blockquote c-[ow] { color: inherit; } /* Operator.Word */
    blockquote c-[mb] { color: inherit; } /* Literal.Number.Bin */
    blockquote c-[mf] { color: inherit; } /* Literal.Number.Float */
    blockquote c-[mh] { color: inherit; } /* Literal.Number.Hex */
    blockquote c-[mi] { color: inherit; } /* Literal.Number.Integer */
    blockquote c-[mo] { color: inherit; } /* Literal.Number.Oct */
    blockquote c-[sb] { color: inherit; } /* Literal.String.Backtick */
    blockquote c-[sc] { color: inherit; } /* Literal.String.Char */
    blockquote c-[sd] { color: inherit; } /* Literal.String.Doc */
    blockquote c-[se] { color: inherit; } /* Literal.String.Escape */
    blockquote c-[sh] { color: inherit; } /* Literal.String.Heredoc */
    blockquote c-[si] { color: inherit; } /* Literal.String.Interpol */
    blockquote c-[sx] { color: inherit; } /* Literal.String.Other */
    blockquote c-[sr] { color: inherit; } /* Literal.String.Regex */
    blockquote c-[ss] { color: inherit; } /* Literal.String.Symbol */
    blockquote c-[vc] { color: inherit; } /* Name.Variable.Class */
    blockquote c-[vg] { color: inherit; } /* Name.Variable.Global */
    blockquote c-[vi] { color: inherit; } /* Name.Variable.Instance */
    blockquote c-[il] { color: inherit; } /* Literal.Number.Integer.Long */
  </style>
  <meta content="Bikeshed version fb1e763a4, updated Tue Mar 1 13:13:50 2022 -0800" name="generator">
  <link href="https://wg21.link/P2494" rel="canonical">
  <link href="https://isocpp.org/favicon.ico" rel="icon">
<style>
pre {
  margin-top: 0px;
  margin-bottom: 0px;
}
table, th, tr, td {
  border: 2px solid black !important;
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 <body class="h-entry">
  <div class="head">
   <p data-fill-with="logo"></p>
   <h1 class="p-name no-ref" id="title">P2494R2<br>Relaxing range adaptors to allow for move only types</h1>
   <h2 class="no-num no-toc no-ref heading settled" id="profile-and-date"><span class="content">Published Proposal, <time class="dt-updated" datetime="2022-07-13">2022-07-13</time></span></h2>
   <div data-fill-with="spec-metadata">
    <dl>
     <dt class="editor">Author:
     <dd class="editor p-author h-card vcard"><a class="p-name fn u-email email" href="mailto:griwes@griwes.info">Michał Dominiak</a>
     <dt>Project:
     <dd>ISO/IEC JTC1/SC22/WG21 14882: Programming Language — C++
     <dt>Audience:
     <dd>LWG
    </dl>
   </div>
   <div data-fill-with="warning"></div>
   <hr title="Separator for header">
  </div>
  <nav data-fill-with="table-of-contents" id="toc">
   <h2 class="no-num no-toc no-ref" id="contents">Table of Contents</h2>
   <ol class="toc" role="directory">
    <li><a href="#into"><span class="secno">1</span> <span class="content">Introduction</span></a>
    <li>
     <a href="#history"><span class="secno">2</span> <span class="content">Revision history</span></a>
     <ol class="toc">
      <li><a href="#r1"><span class="secno">2.1</span> <span class="content">R1</span></a>
      <li><a href="#r0"><span class="secno">2.2</span> <span class="content">R0</span></a>
     </ol>
    <li>
     <a href="#design"><span class="secno">3</span> <span class="content">Design</span></a>
     <ol class="toc">
      <li><a href="#design-abi"><span class="secno">3.1</span> <span class="content">ABI compatibility</span></a>
      <li><a href="#design-ftm"><span class="secno">3.2</span> <span class="content">Feature test macro</span></a>
      <li><a href="#design-experience"><span class="secno">3.3</span> <span class="content">Implementation experience</span></a>
     </ol>
    <li>
     <a href="#wording"><span class="secno">4</span> <span class="content">Wording</span></a>
     <ol class="toc">
      <li><a href="#wording-ranges.syn"><span class="secno">4.1</span> <span class="content">Header <code class="highlight"><c- o>&lt;</c-><c- n>ranges</c-><c- o>></c-></code> synopsis</span></a>
      <li>
       <a href="#wording-range.factories"><span class="secno">4.2</span> <span class="content">Range factories</span></a>
       <ol class="toc">
        <li><a href="#wording-range.single.view"><span class="secno">4.2.1</span> <span class="content">Class template <code class="highlight"><c- n>single_view</c-></code></span></a>
        <li><a href="#wording-range.iota.view"><span class="secno">4.2.2</span> <span class="content">Class template <code class="highlight"><c- n>iota_view</c-></code></span></a>
       </ol>
      <li>
       <a href="#wording-range.adaptors"><span class="secno">4.3</span> <span class="content">Range adaptors</span></a>
       <ol class="toc">
        <li><a href="#wording-range.copy.wrap"><span class="secno">4.3.1</span> <span class="content">Copyable wrapper</span></a>
        <li><a href="#wording-range.filter.view"><span class="secno">4.3.2</span> <span class="content">Class template <code class="highlight"><c- n>filter_view</c-></code></span></a>
        <li><a href="#wording-range.transform.view"><span class="secno">4.3.3</span> <span class="content">Class template <code class="highlight"><c- n>transform_view</c-></code></span></a>
        <li><a href="#wording-range.take.while.view"><span class="secno">4.3.4</span> <span class="content">Class template <code class="highlight"><c- n>take_while_view</c-></code></span></a>
        <li><a href="#wording-range.drop.while.view"><span class="secno">4.3.5</span> <span class="content">Class template <code class="highlight"><c- n>drop_while_view</c-></code></span></a>
        <li><a href="#wording-range.zip.transform.view"><span class="secno">4.3.6</span> <span class="content">Class template <code class="highlight"><c- n>zip_transform_view</c-></code></span></a>
        <li><a href="#wording-range.adjacent.transform.view"><span class="secno">4.3.7</span> <span class="content">Class template <code class="highlight"><c- n>adjacent_transform_view</c-></code></span></a>
       </ol>
      <li><a href="#wording-ftm"><span class="secno">4.4</span> <span class="content">Feature test macro</span></a>
     </ol>
    <li><a href="#wording-p2474"><span class="secno">5</span> <span class="content">Modifications to P2474</span></a>
    <li><a href="#acks"><span class="secno">6</span> <span class="content">Acknowledgements</span></a>
    <li>
     <a href="#references"><span class="secno"></span> <span class="content">References</span></a>
     <ol class="toc">
      <li><a href="#informative"><span class="secno"></span> <span class="content">Informative References</span></a>
     </ol>
   </ol>
  </nav>
  <main>
   <h2 class="heading settled" data-level="1" id="into"><span class="secno">1. </span><span class="content">Introduction</span><a class="self-link" href="#into"></a></h2>
   <p>Currently, many range adaptors require that the user-provided types they store must be copy constructible, which is also required by the assignment wrapper they use, <i><code class="highlight"><c- n>copyable</c-><c- o>-</c-><c- n>box</c-></code></i>. This is a consequence of <a data-link-type="biblio" href="#biblio-p1456r1">[P1456R1]</a> and <a data-link-type="biblio" href="#biblio-p2325r3">[P2325R3]</a> not being integrated together so far. The author believes that this paper is a logical next step from these two papers.</p>
   <p>This paper exists, because while writing a paper proposing <code class="highlight"><c- n>views</c-><c- o>::</c-><c- n>repeat</c-></code> (P2474), the author had a desire to make it support move-only types, and needed the tools to specify it. He tried to use the approach in <span>[P2483R0]</span>, but has found that approach to not solve the problem correctly.</p>
   <h2 class="heading settled" data-level="2" id="history"><span class="secno">2. </span><span class="content">Revision history</span><a class="self-link" href="#history"></a></h2>
   <h3 class="heading settled" data-level="2.1" id="r1"><span class="secno">2.1. </span><span class="content">R1</span><a class="self-link" href="#r1"></a></h3>
   <p>Apply the SG10 recommendation for handling the feature test macro for this change.</p>
   <p>Adjust the wording changes to P2474, to align with the wording of a new revision of that paper.</p>
   <h3 class="heading settled" data-level="2.2" id="r0"><span class="secno">2.2. </span><span class="content">R0</span><a class="self-link" href="#r0"></a></h3>
   <p>Initial revision.</p>
   <h2 class="heading settled" data-level="3" id="design"><span class="secno">3. </span><span class="content">Design</span><a class="self-link" href="#design"></a></h2>
   <p>Similarly to how <a data-link-type="biblio" href="#biblio-p2325r3">[P2325R3]</a> turned <code class="highlight"><c- n>semiregular</c-><c- o>-</c-><c- n>box</c-></code> into <code class="highlight"><c- n>copyable</c-><c- o>-</c-><c- n>box</c-></code>, this paper proposes to turn <code class="highlight"><c- n>copyable</c-><c- o>-</c-><c- n>box</c-></code> into <code class="highlight"><c- n>movable</c-><c- o>-</c-><c- n>box</c-></code>. This name is probably not ideal, because it still turns types that happen to be copy constructible into copyable types, but it follows from the prior changes to the wrapper.</p>
   <p>The reason why the approach in <span>[P2483R0]</span> is incorrect is that it does not handle types that are copy constructible, but not copy assignable: if a type is copyable, then it works with the wrapper, but if it misses copy assignment, then it does not. The approach taken in this paper solves this issue.</p>
   <p><span>[P2483R0]</span> also suggests future work to relax the requirements on the predicate types stored by standard views. This paper does <em>not</em> perform this relaxation, as the copy constructibility requirement is enshrined in the indirect callable concepts ([indirectcallable.indirectinvocable]). Thus, while this paper modifies the views that currently use <code class="highlight"><c- n>copyable</c-><c- o>-</c-><c- n>box</c-></code> for user provided predicates, it only does so to apply the rename of the exposition-only type to <code class="highlight"><c- n>movable</c-><c- o>-</c-><c- n>box</c-></code>; it does not change any of the constraints on those views. It does, however, relax the requirements on invocables accepted by the transform family of views, because those are not constrained using the indirect callable concepts.</p>
   <p>In effect, the only views whose constraints are changed by this paper are:</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>single_view</c-></code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>transform_view</c-></code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>zip_transform_view</c-></code>, and</p>
    <li data-md>
     <p><code class="highlight"><c- n>adjacent_transform_view</c-></code>.</p>
   </ul>
   <p>Additionally, this paper proposes to modify the changes in P2474 in this same way. If both this paper and P2474 are accepted, we should make <code class="highlight"><c- n>views</c-><c- o>::</c-><c- n>repeat</c-></code> have the same constraints as <code class="highlight"><c- n>views</c-><c- o>::</c-><c- n>single</c-></code>.</p>
   <h3 class="heading settled" data-level="3.1" id="design-abi"><span class="secno">3.1. </span><span class="content">ABI compatibility</span><a class="self-link" href="#design-abi"></a></h3>
   <p>The author is not aware of any ABI concerns of this proposal; the question of whether changing constraints on a primary class template has been run by the ABI Review Group, and the responses indicated that constraints are only mangled in for overloadable templates on the major implementations of C++.</p>
   <h3 class="heading settled" data-level="3.2" id="design-ftm"><span class="secno">3.2. </span><span class="content">Feature test macro</span><a class="self-link" href="#design-ftm"></a></h3>
   <p>After asking for SG10’s opinion on the topic on the group’s mailing list, this paper proposes to not introduce a new feature test macro for the proposed feature, and rather increment the value of <code class="highlight"><c- n>__cpp_lib_ranges</c-></code> - which is consistent with how prior changes of similar nature have been handled.</p>
   <h3 class="heading settled" data-level="3.3" id="design-experience"><span class="secno">3.3. </span><span class="content">Implementation experience</span><a class="self-link" href="#design-experience"></a></h3>
   <p>The author has implemented the changes to <code class="highlight"><c- n>single_view</c-></code> and <code class="highlight"><c- n>transform_view</c-></code> in <a href="https://github.com/CaseyCarter/cmcstl2">CMCSTL2</a>. The changes to the box type were not necessary. CMCSTL2 still contains a <code class="highlight"><c- n>semiregular_box</c-></code>, from before the change to <code class="highlight"><c- n>copyable</c-><c- o>-</c-><c- n>box</c-></code>, but its semiregular box is relaxed to allow for move-only types. Thanks to that, the entire change is replacing "copy" with "move" in the two views mentioned earlier (CMCSTL2 does not include <code class="highlight"><c- n>zip_transform_view</c-></code> and <code class="highlight"><c- n>adjacent_transform_view</c-></code>). All the preexisting tests pass with the changes.</p>
   <h2 class="heading settled" data-level="4" id="wording"><span class="secno">4. </span><span class="content">Wording</span><a class="self-link" href="#wording"></a></h2>
   <h3 class="heading settled" data-level="4.1" id="wording-ranges.syn"><span class="secno">4.1. </span><span class="content">Header <code class="highlight"><c- o>&lt;</c-><c- n>ranges</c-><c- o>></c-></code> synopsis</span><a class="self-link" href="#wording-ranges.syn"></a></h3>
   <p>Modify Header <code class="highlight"><c- o>&lt;</c-><c- n>ranges</c-><c- o>></c-></code> synopsis [ranges.syn] as follows:</p>
<pre class="highlight"><c- c1>// ...</c->

<c- c1>// [range.single], single view</c->
<c- k>template</c-><c- o>&lt;</c-><del><c- n>copy_constructible</c-></del><ins><c- n>move_constructible</c-></ins> <c- n>T</c-><c- o>></c->
    <c- k>requires</c-> <c- n>is_object_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c->
<c- k>class</c-> <c- nc>single_view</c-><c- p>;</c->

<c- c1>// ...</c->

<c- c1>// [range.transform], transform view</c->
<c- k>template</c-><c- o>&lt;</c-><c- n>input_range</c-> <c- n>V</c-><c- p>,</c-> <del><c- n>copy_constructible</c-></del><ins><c- n>move_constructible</c-></ins> <c- n>F</c-><c- o>></c->
<c- k>requires</c-> <c- n>view</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c-> <c- o>&amp;&amp;</c-> <c- n>is_object_v</c-><c- o>&lt;</c-><c- n>F</c-><c- o>></c-> <c- o>&amp;&amp;</c->
         <c- n>regular_invocable</c-><c- o>&lt;</c-><c- n>F</c-><c- o>&amp;</c-><c- p>,</c-> <c- n>range_reference_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>>></c-> <c- o>&amp;&amp;</c->
         <c- n>can</c-><c- o>-</c-><c- n>reference</c-><c- o>&lt;</c-><c- n>invoke_result_t</c-><c- o>&lt;</c-><c- n>F</c-><c- o>&amp;</c-><c- p>,</c-> <c- n>range_reference_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>>>></c->
<c- k>class</c-> <c- nc>transform_view</c-><c- p>;</c->

<c- c1>// ...</c->

<c- c1>// [range.zip.transform], zip transform view</c->
<c- k>template</c-><c- o>&lt;</c-><del><c- n>copy_constructible</c-></del><ins><c- n>move_constructible</c-></ins> <c- n>F</c-><c- p>,</c-> <c- n>input_range</c-><c- p>...</c-> <c- n>Views</c-><c- o>></c->
<c- k>requires</c-> <c- p>(</c-><c- n>view</c-><c- o>&lt;</c-><c- n>Views</c-><c- o>></c-> <c- o>&amp;&amp;</c-> <c- p>...)</c-> <c- o>&amp;&amp;</c-> <c- p>(</c-><c- k>sizeof</c-><c- p>...(</c-><c- n>Views</c-><c- p>)</c-> <c- o>></c-> <c- mi>0</c-><c- p>)</c-> <c- o>&amp;&amp;</c-> <c- n>is_object_v</c-><c- o>&lt;</c-><c- n>F</c-><c- o>></c-> <c- o>&amp;&amp;</c->
            <c- n>regular_invocable</c-><c- o>&lt;</c-><c- n>F</c-><c- o>&amp;</c-><c- p>,</c-> <c- n>range_reference_t</c-><c- o>&lt;</c-><c- n>Views</c-><c- o>></c-><c- p>...</c-><c- o>></c-> <c- o>&amp;&amp;</c->
            <c- n>can</c-><c- o>-</c-><c- n>reference</c-><c- o>&lt;</c-><c- n>invoke_result_t</c-><c- o>&lt;</c-><c- n>F</c-><c- o>&amp;</c-><c- p>,</c-> <c- n>range_reference_t</c-><c- o>&lt;</c-><c- n>Views</c-><c- o>></c-><c- p>...</c-><c- o>>></c->
<c- k>class</c-> <c- nc>zip_transform_view</c-><c- p>;</c->

<c- c1>// ...</c->

<c- c1>// [range.adjacent.transform], adjacent transform view</c->
<c- k>template</c-><c- o>&lt;</c-><c- n>forward_range</c-> <c- n>V</c-><c- p>,</c-> <del><c- n>copy_constructible</c-></del><ins><c- n>move_constructible</c-></ins> <c- n>F</c-><c- p>,</c-> <c- b>size_t</c-> <c- n>N</c-><c- o>></c->
  <c- k>requires</c-> <i><c- n>see</c-> <c- n>below</c-></i>
<c- k>class</c-> <c- nc>adjacent_transform_view</c-><c- p>;</c->

<c- c1>// ...</c->
</pre>
   <h3 class="heading settled" data-level="4.2" id="wording-range.factories"><span class="secno">4.2. </span><span class="content">Range factories</span><a class="self-link" href="#wording-range.factories"></a></h3>
   <h4 class="heading settled" data-level="4.2.1" id="wording-range.single.view"><span class="secno">4.2.1. </span><span class="content">Class template <code class="highlight"><c- n>single_view</c-></code></span><a class="self-link" href="#wording-range.single.view"></a></h4>
   <p>Modify Class template <code class="highlight"><c- n>single_view</c-></code> [range.single.view] as follows:</p>
<pre class="highlight"><c- k>namespace</c-> <c- nn>std</c-><c- o>::</c-><c- nn>ranges</c-> <c- p>{</c->
  <c- k>template</c-><c- o>&lt;</c-><del><c- n>copy_constructible</c-></del><ins><c- n>move_constructible</c-></ins> <c- n>T</c-><c- o>></c->
    <c- k>requires</c-> <c- n>is_object_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c->
  <c- k>class</c-> <c- nc>single_view</c-> <c- o>:</c-> <c- k>public</c-> <c- n>view_interface</c-><c- o>&lt;</c-><c- n>single_view</c-><c- o>&lt;</c-><c- n>T</c-><c- o>>></c-> <c- p>{</c->
  <c- k>private</c-><c- o>:</c->
    <i><del><c- n>copyable</c-><c- o>-</c-><c- n>box</c-></del><ins><c- n>movable</c-><c- o>-</c-><c- n>box</c-></ins></i><c- o>&lt;</c-><c- n>T</c-><c- o>></c-> <c- n>value_</c-><c- p>;</c-> <c- c1>// exposition only (see [range.</c-><del><c- c1>copy</c-></del><ins><c- c1>move</c-></ins><c- c1>.wrap])</c->

  <c- k>public</c-><c- o>:</c->
    <c- n>single_view</c-><c- p>()</c-> <c- k>requires</c-> <c- n>default_</c->­<c- n>initializable</c-><t> <c- o>=</c-> <c- k>default</c-><c- p>;</c->
    <c- k>constexpr</c-> <c- k>explicit</c-> <c- n>single_view</c-><c- p>(</c-><c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>t</c-><c- p>)</c-> <ins><c- k>requires</c-> <c- n>copy_constructible</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></ins><c- p>;</c->
    <c- k>constexpr</c-> <c- k>explicit</c-> <c- n>single_view</c-><c- p>(</c-><c- n>T</c-><c- o>&amp;&amp;</c-> <c- n>t</c-><c- p>);</c->

    <c- c1>// ...</c->
</t></pre>
<pre class="highlight"><c- k>constexpr</c-> <c- k>explicit</c-> <c- n>single_view</c-><c- p>(</c-><c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>t</c-><c- p>)</c-> <ins><c- k>requires</c-> <c- n>copy_constructible</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></ins><c- p>;</c->
</pre>
   <ol start="11">
    <li data-md>
     <p><em>Effects</em>: Initializes <code class="highlight"><c- n>value_</c-></code>­ with <code class="highlight"><c- n>t</c-></code>.</p>
   </ol>
   <h4 class="heading settled" data-level="4.2.2" id="wording-range.iota.view"><span class="secno">4.2.2. </span><span class="content">Class template <code class="highlight"><c- n>iota_view</c-></code></span><a class="self-link" href="#wording-range.iota.view"></a></h4>
   <p>Do not modify <code class="highlight"><c- n>iota_view</c-></code>, which explicitly requires <code class="highlight"><c- n>copyable</c-></code>, and creates copies of the user-provided types as part of its operation.</p>
   <h3 class="heading settled" data-level="4.3" id="wording-range.adaptors"><span class="secno">4.3. </span><span class="content">Range adaptors</span><a class="self-link" href="#wording-range.adaptors"></a></h3>
   <h4 class="heading settled" data-level="4.3.1" id="wording-range.copy.wrap"><span class="secno">4.3.1. </span><span class="content">Copyable wrapper</span><a class="self-link" href="#wording-range.copy.wrap"></a></h4>
   <p>Replace the section Copyable wrapper [range.copy.wrap] with a new section Movable wrapper [range.move.wrap]. The following diff can be applied to the body of [range.copy.wrap] to produce the body of the new [range.move.wrap] section:</p>
   <ol>
    <li data-md>
     <p>Many types in this subclause are specified in terms of an exposition-only class template <i><del>copyable-box</del><ins>movable-box</ins></i>. <i><del>copyable-box</del><ins>movable-box</ins></i><code class="highlight"><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> behaves exactly like <code class="highlight"><c- n>optional</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> with the following differences:</p>
     <ol>
      <li data-md>
       <p><i><del>copyable-box</del><ins>movable-box</ins></i><code class="highlight"><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> constrains its type parameter <code class="highlight"><c- n>T</c-></code> with <code class="highlight"><del><c- n>copy_constructible</c-></del><ins><c- n>move_constructible</c-></ins><c- o>&lt;</c-><c- n>T</c-><c- o>></c-> <c- o>&amp;&amp;</c-> <c- n>is_object_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code>.</p>
      <li data-md>
       <p>The default constructor of <i><del>copyable-box</del><ins>movable-box</ins></i><code class="highlight"><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is equivalent to:</p>
<pre class="highlight"><c- k>constexpr</c-> <i><del><c- n>copyable</c-><c- o>-</c-><c- n>box</c-></del><ins><c- n>movable</c-><c- o>-</c-><c- n>box</c-></ins></i><c- p>()</c-> <c- k>noexcept</c-><c- p>(</c-><c- n>is_nothrow_default_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>)</c->
    <c- k>requires</c-> <c- n>default_initializable</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c->
  <c- o>:</c-> <i><del><c- n>copyable</c-><c- o>-</c-><c- n>box</c-></del><ins><c- n>movable</c-><c- o>-</c-><c- n>box</c-></ins></i><c- p>{</c-><c- n>in_place</c-><c- p>}</c-> <c- p>{}</c->
</pre>
      <li data-md>
       <p>If <code class="highlight"><c- n>copyable</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is not modeled, the copy assignment operator is equivalent to:</p>
<pre class="highlight"><c- k>constexpr</c-> <i><del><c- n>copyable</c-><c- o>-</c-><c- n>box</c-></del><ins><c- n>movable</c-><c- o>-</c-><c- n>box</c-></ins></i><c- o>&amp;</c-> <c- k>operator</c-><c- o>=</c-><c- p>(</c-><c- k>const</c-> <i><del><c- n>copyable</c-><c- o>-</c-><c- n>box</c-></del><ins><c- n>movable</c-><c- o>-</c-><c- n>box</c-></ins></i><c- o>&amp;</c-> <c- n>that</c-><c- p>)</c->
  <c- k>noexcept</c-><c- p>(</c-><c- n>is_nothrow_copy_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>)</c-><ins> 
  <c- k>requires</c-> <c- n>copy_constructible</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></ins> <c- p>{</c->
  <c- k>if</c-> <c- p>(</c-><c- k>this</c-> <c- o>!=</c-> <c- n>addressof</c-><c- p>(</c-><c- n>that</c-><c- p>))</c-> <c- p>{</c->
    <c- k>if</c-> <c- p>(</c-><c- n>that</c-><c- p>)</c-> <c- n>emplace</c-><c- p>(</c-><c- o>*</c-><c- n>that</c-><c- p>);</c->
    <c- k>else</c-> <c- n>reset</c-><c- p>();</c->
  <c- p>}</c->
  <c- k>return</c-> <c- o>*</c-><c- k>this</c-><c- p>;</c->
<c- p>}</c->
</pre>
      <li data-md>
       <p>If <code class="highlight"><c- n>movable</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is not modeled, the move assignment operator is equivalent to:</p>
<pre class="highlight"><c- k>constexpr</c-> <i><del><c- n>copyable</c-><c- o>-</c-><c- n>box</c-></del><ins><c- n>movable</c-><c- o>-</c-><c- n>box</c-></ins></i><c- o>&amp;</c-> <c- k>operator</c-><c- o>=</c-><c- p>(</c-><i><del><c- n>copyable</c-><c- o>-</c-><c- n>box</c-></del><ins><c- n>movable</c-><c- o>-</c-><c- n>box</c-></ins></i><c- o>&amp;&amp;</c-> <c- n>that</c-><c- p>)</c->
  <c- k>noexcept</c-><c- p>(</c-><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>)</c-> <c- p>{</c->
  <c- k>if</c-> <c- p>(</c-><c- k>this</c-> <c- o>!=</c-> <c- n>addressof</c-><c- p>(</c-><c- n>that</c-><c- p>))</c-> <c- p>{</c->
    <c- k>if</c-> <c- p>(</c-><c- n>that</c-><c- p>)</c-> <c- n>emplace</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- o>*</c-><c- n>that</c-><c- p>));</c->
    <c- k>else</c-> <c- n>reset</c-><c- p>();</c->
  <c- p>}</c->
  <c- k>return</c-> <c- o>*</c-><c- k>this</c-><c- p>;</c->
<c- p>}</c->
</pre>
     </ol>
    <li data-md>
     <p>
      <em>Recommended practice</em>: 
      <del><i>copyable-box</i><code class="highlight"><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> should store only a <code class="highlight"><c- n>T</c-></code> if either <code class="highlight"><c- n>T</c-></code> models <code class="highlight"><c- n>copyable</c-></code> or <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-> <c- o>&amp;&amp;</c-> <c- n>is_nothrow_copy_constructible_</c->­<c- n>v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code>.</del>
     </p>
     <ins>
      <ol>
       <li data-md>
        <p>If <code class="highlight"><c- n>copy_constructible</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code>, <i>movable-box</i><code class="highlight"><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> should store only a <code class="highlight"><c- n>T</c-></code> if either <code class="highlight"><c- n>T</c-></code> models <code class="highlight"><c- n>copyable</c-></code>, or <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-> <c- o>&amp;&amp;</c-> <c- n>is_nothrow_copy_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
       <li data-md>
        <p>Otherwise, <i>movable-box</i><code class="highlight"><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> should store only a <code class="highlight"><c- n>T</c-></code> if either <code class="highlight"><c- n>T</c-></code> models <code class="highlight"><c- n>movable</c-></code> or <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
      </ol>
     </ins>
   </ol>
   <h4 class="heading settled" data-level="4.3.2" id="wording-range.filter.view"><span class="secno">4.3.2. </span><span class="content">Class template <code class="highlight"><c- n>filter_view</c-></code></span><a class="self-link" href="#wording-range.filter.view"></a></h4>
   <p>Modify Class template <code class="highlight"><c- n>filter_view</c-></code> [range.filter.view] as follows:</p>
<pre class="highlight"><c- k>namespace</c-> <c- nn>std</c-><c- o>::</c-><c- nn>ranges</c-> <c- p>{</c->
  <c- k>template</c-><c- o>&lt;</c-><c- n>input_range</c-> <c- n>V</c-><c- p>,</c-> <c- n>indirect_unary_predicate</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>>></c-> <c- n>Pred</c-><c- o>></c->
    <c- k>requires</c-> <c- n>view</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c-> <c- o>&amp;&amp;</c-> <c- n>is_object_v</c-><c- o>&lt;</c-><c- n>Pred</c-><c- o>></c->
  <c- k>class</c-> <c- nc>filter_view</c-> <c- o>:</c-> <c- k>public</c-> <c- n>view_interface</c-><c- o>&lt;</c-><c- n>filter_view</c-><c- o>&lt;</c-><c- n>V</c-><c- p>,</c-> <c- n>Pred</c-><c- o>>></c-> <c- p>{</c->
  <c- k>private</c-><c- o>:</c->
    <c- n>V</c-> <c- n>base_</c-> <c- o>=</c-> <c- n>V</c-><c- p>();</c->                              <c- c1>// exposition only</c->
    <i><del><c- n>copyable</c-><c- o>-</c-><c- n>box</c-></del><ins><c- n>movable</c-><c- o>-</c-><c- n>box</c-></ins></i><c- o>&lt;</c-><c- n>Pred</c-><c- o>></c-> <c- n>pred_</c-><c- p>;</c->        <c- c1>// exposition only</c->

    <c- c1>// ...</c->
</pre>
   <h4 class="heading settled" data-level="4.3.3" id="wording-range.transform.view"><span class="secno">4.3.3. </span><span class="content">Class template <code class="highlight"><c- n>transform_view</c-></code></span><a class="self-link" href="#wording-range.transform.view"></a></h4>
   <p>Modify Class template <code class="highlight"><c- n>transform_view</c-></code> [range.transform.view] as follows:</p>
<pre class="highlight"><c- k>namespace</c-> <c- nn>std</c-><c- o>::</c-><c- nn>ranges</c-> <c- p>{</c->
  <c- k>template</c-><c- o>&lt;</c-><c- n>input_range</c-> <c- n>V</c-><c- p>,</c-> <del><c- n>copy_constructible</c-></del><ins><c- n>move_constructible</c-></ins> <c- n>F</c-><c- o>></c->
    <c- k>requires</c-> <c- n>view</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c-> <c- o>&amp;&amp;</c-> <c- n>is_object_v</c-><c- o>&lt;</c-><c- n>F</c-><c- o>></c-> <c- o>&amp;&amp;</c->
             <c- n>regular_invocable</c-><c- o>&lt;</c-><c- n>F</c-><c- o>&amp;</c-><c- p>,</c-> <c- n>range_reference_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>>></c-> <c- o>&amp;&amp;</c->
             <c- n>can</c-><c- o>-</c-><c- n>reference</c-><c- o>&lt;</c-><c- n>invoke_result_t</c-><c- o>&lt;</c-><c- n>F</c-><c- o>&amp;</c-><c- p>,</c-> <c- n>range_reference_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>>>></c->
  <c- k>class</c-> <c- nc>transform_view</c-> <c- o>:</c-> <c- k>public</c-> <c- n>view_interface</c-><c- o>&lt;</c-><c- n>transform_view</c-><c- o>&lt;</c-><c- n>V</c-><c- p>,</c-> <c- n>F</c-><c- o>>></c-> <c- p>{</c->
  <c- k>private</c-><c- o>:</c->
    <c- c1>// [range.transform.iterator], class template transform_view::iterator</c->
    <c- k>template</c-><c- o>&lt;</c-><c- b>bool</c-><c- o>></c-> <c- k>struct</c-> <c- nc>iterator</c-><c- p>;</c->             <c- c1>// exposition only</c->

    <c- c1>// [range.transform.sentinel], class template transform_view::sentinel</c->
    <c- k>template</c-><c- o>&lt;</c-><c- b>bool</c-><c- o>></c-> <c- k>struct</c-> <c- nc>sentinel</c-><c- p>;</c->             <c- c1>// exposition only</c->

    <c- n>V</c-> <c- n>base_</c-> <c- o>=</c-> <c- n>V</c-><c- p>();</c->                              <c- c1>// exposition only</c->
    <i><del><c- n>copyable</c-><c- o>-</c-><c- n>box</c-></del><ins><c- n>movable</c-><c- o>-</c-><c- n>box</c-></ins></i><c- o>&lt;</c-><c- n>F</c-><c- o>></c-> <c- n>fun_</c-><c- p>;</c->            <c- c1>// exposition only</c->

    <c- c1>// ...</c->
</pre>
   <h4 class="heading settled" data-level="4.3.4" id="wording-range.take.while.view"><span class="secno">4.3.4. </span><span class="content">Class template <code class="highlight"><c- n>take_while_view</c-></code></span><a class="self-link" href="#wording-range.take.while.view"></a></h4>
   <p>Modify Class template <code class="highlight"><c- n>take_while_view</c-></code> [range.take.while.view] as follows:</p>
<pre class="highlight"><c- k>namespace</c-> <c- nn>std</c-><c- o>::</c-><c- nn>ranges</c-> <c- p>{</c->
  <c- k>template</c-><c- o>&lt;</c-><c- n>view</c-> <c- n>V</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Pred</c-><c- o>></c->
    <c- k>requires</c-> <c- n>input_range</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c-> <c- o>&amp;&amp;</c-> <c- n>is_object_v</c-><c- o>&lt;</c-><c- n>Pred</c-><c- o>></c-> <c- o>&amp;&amp;</c->
             <c- n>indirect_unary_predicate</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>Pred</c-><c- p>,</c-> <c- n>iterator_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>>></c->
  <c- k>class</c-> <c- nc>take_while_view</c-> <c- o>:</c-> <c- k>public</c-> <c- n>view_interface</c-><c- o>&lt;</c-><c- n>take_while_view</c-><c- o>&lt;</c-><c- n>V</c-><c- p>,</c-> <c- n>Pred</c-><c- o>>></c-> <c- p>{</c->
    <c- c1>// [range.take.while.sentinel], class template take_while_view::sentinel</c->
    <c- k>template</c-><c- o>&lt;</c-><c- b>bool</c-><c- o>></c-> <c- k>class</c-> <c- nc>sentinel</c-><c- p>;</c->                      <c- c1>// exposition only</c->

    <c- n>V</c-> <c- n>base_</c-> <c- o>=</c-> <c- n>V</c-><c- p>();</c->                                      <c- c1>// exposition only</c->
    <i><del><c- n>copyable</c-><c- o>-</c-><c- n>box</c-></del><ins><c- n>movable</c-><c- o>-</c-><c- n>box</c-></ins></i><c- o>&lt;</c-><c- n>Pred</c-><c- o>></c-> <c- n>pred_</c-><c- p>;</c->                <c- c1>// exposition only</c->

    <c- c1>// ...</c->
</pre>
   <h4 class="heading settled" data-level="4.3.5" id="wording-range.drop.while.view"><span class="secno">4.3.5. </span><span class="content">Class template <code class="highlight"><c- n>drop_while_view</c-></code></span><a class="self-link" href="#wording-range.drop.while.view"></a></h4>
<pre class="highlight"><c- k>namespace</c-> <c- nn>std</c-><c- o>::</c-><c- nn>ranges</c-> <c- p>{</c->
  <c- k>template</c-><c- o>&lt;</c-><c- n>view</c-> <c- n>V</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Pred</c-><c- o>></c->
    <c- k>requires</c-> <c- n>input_range</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c-> <c- o>&amp;&amp;</c-> <c- n>is_object_v</c-><c- o>&lt;</c-><c- n>Pred</c-><c- o>></c-> <c- o>&amp;&amp;</c->
             <c- n>indirect_unary_predicate</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>Pred</c-><c- p>,</c-> <c- n>iterator_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>>></c->
  <c- k>class</c-> <c- nc>drop_while_view</c-> <c- o>:</c-> <c- k>public</c-> <c- n>view_interface</c-><c- o>&lt;</c-><c- n>drop_while_view</c-><c- o>&lt;</c-><c- n>V</c-><c- p>,</c-> <c- n>Pred</c-><c- o>>></c-> <c- p>{</c->
  <c- k>public</c-><c- o>:</c->
    <c- n>drop_while_view</c-><c- p>()</c-> <c- k>requires</c-> <c- n>default_initializable</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c-> <c- o>&amp;&amp;</c-> <c- n>default_initializable</c-><c- o>&lt;</c-><c- n>Pred</c-><c- o>></c-> <c- o>=</c-> <c- k>default</c-><c- p>;</c->
    <c- k>constexpr</c-> <c- n>drop_while_view</c-><c- p>(</c-><c- n>V</c-> <c- n>base</c-><c- p>,</c-> <c- n>Pred</c-> <c- n>pred</c-><c- p>);</c->

    <c- k>constexpr</c-> <c- n>V</c-> <c- nf>base</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;</c-> <c- k>requires</c-> <c- n>copy_constructible</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c-> <c- p>{</c-> <c- k>return</c-> <c- n>base_</c-><c- p>;</c-> <c- p>}</c->
    <c- k>constexpr</c-> <c- n>V</c-> <c- nf>base</c-><c- p>()</c-> <c- o>&amp;&amp;</c-> <c- p>{</c-> <c- k>return</c-> <c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>base_</c-><c- p>);</c-> <c- p>}</c->

    <c- k>constexpr</c-> <c- k>const</c-> <c- n>Pred</c-><c- o>&amp;</c-> <c- nf>pred</c-><c- p>()</c-> <c- k>const</c-><c- p>;</c->

    <c- k>constexpr</c-> <c- k>auto</c-> <c- n>begin</c-><c- p>();</c->

    <c- k>constexpr</c-> <c- k>auto</c-> <c- n>end</c-><c- p>()</c-> <c- p>{</c-> <c- k>return</c-> <c- n>ranges</c-><c- o>::</c-><c- n>end</c-><c- p>(</c-><c- n>base_</c-><c- p>);</c-> <c- p>}</c->

  <c- k>private</c-><c- o>:</c->
    <c- n>V</c-> <c- n>base_</c-> <c- o>=</c-> <c- n>V</c-><c- p>();</c->                                      <c- c1>// exposition only</c->
    <i><del><c- n>copyable</c-><c- o>-</c-><c- n>box</c-></del><ins><c- n>movable</c-><c- o>-</c-><c- n>box</c-></ins></i><c- o>&lt;</c-><c- n>Pred</c-><c- o>></c-> <c- n>pred_</c-><c- p>;</c->                <c- c1>// exposition only</c->

    <c- c1>// ...</c->
</pre>
   <h4 class="heading settled" data-level="4.3.6" id="wording-range.zip.transform.view"><span class="secno">4.3.6. </span><span class="content">Class template <code class="highlight"><c- n>zip_transform_view</c-></code></span><a class="self-link" href="#wording-range.zip.transform.view"></a></h4>
   <p>Modify Class template <code class="highlight"><c- n>zip_transform_view</c-></code> [range.zip.transform.view] as follows:</p>
<pre class="highlight"><c- k>namespace</c-> <c- nn>std</c-><c- o>::</c-><c- nn>ranges</c-> <c- p>{</c->
  <c- k>template</c-><c- o>&lt;</c-><del><c- n>copy_constructible</c-></del><ins><c- n>move_constructible</c-></ins> <c- n>F</c-><c- p>,</c-> <c- n>input_range</c-><c- p>...</c-> <c- n>Views</c-><c- o>></c->
    <c- k>requires</c-> <c- p>(</c-><c- n>view</c-><c- o>&lt;</c-><c- n>Views</c-><c- o>></c-> <c- o>&amp;&amp;</c-> <c- p>...)</c-> <c- o>&amp;&amp;</c-> <c- p>(</c-><c- k>sizeof</c-><c- p>...(</c-><c- n>Views</c-><c- p>)</c-> <c- o>></c-> <c- mi>0</c-><c- p>)</c-> <c- o>&amp;&amp;</c-> <c- n>is_object_v</c-><c- o>&lt;</c-><c- n>F</c-><c- o>></c-> <c- o>&amp;&amp;</c->
              <c- n>regular_invocable</c-><c- o>&lt;</c-><c- n>F</c-><c- o>&amp;</c-><c- p>,</c-> <c- n>range_reference_t</c-><c- o>&lt;</c-><c- n>Views</c-><c- o>></c-><c- p>...</c-><c- o>></c-> <c- o>&amp;&amp;</c->
              <c- n>can</c-><c- o>-</c-><c- n>reference</c-><c- o>&lt;</c-><c- n>invoke_result_t</c-><c- o>&lt;</c-><c- n>F</c-><c- o>&amp;</c-><c- p>,</c-> <c- n>range_reference_t</c-><c- o>&lt;</c-><c- n>Views</c-><c- o>></c-><c- p>...</c-><c- o>>></c->
  <c- k>class</c-> <c- nc>zip_transform_view</c-> <c- o>:</c-> <c- k>public</c-> <c- n>view_interface</c-><c- o>&lt;</c-><c- n>zip_transform_view</c-><c- o>&lt;</c-><c- n>F</c-><c- p>,</c-> <c- n>Views</c-><c- p>...</c-><c- o>>></c-> <c- p>{</c->
    <i><del><c- n>copyable</c-><c- o>-</c-><c- n>box</c-></del><ins><c- n>movable</c-><c- o>-</c-><c- n>box</c-></ins></i><c- o>&lt;</c-><c- n>F</c-><c- o>></c-> <c- n>fun_</c-><c- p>;</c->        <c- c1>// exposition only</c->

    <c- c1>// ...</c->
</pre>
   <h4 class="heading settled" data-level="4.3.7" id="wording-range.adjacent.transform.view"><span class="secno">4.3.7. </span><span class="content">Class template <code class="highlight"><c- n>adjacent_transform_view</c-></code></span><a class="self-link" href="#wording-range.adjacent.transform.view"></a></h4>
   <p>Modify Class template <code class="highlight"><c- n>adjacent_transform_view</c-></code> [range.adjacent.transform.view] as follows:</p>
<pre class="highlight"><c- k>namespace</c-> <c- nn>std</c-><c- o>::</c-><c- nn>ranges</c-> <c- p>{</c->
  <c- k>template</c-><c- o>&lt;</c-><c- n>forward_range</c-> <c- n>V</c-><c- p>,</c-> <del><c- n>copy_constructible</c-></del><ins><c- n>move_constructible</c-></ins> <c- n>F</c-><c- p>,</c-> <c- b>size_t</c-> <c- n>N</c-><c- o>></c->
   <c- k>requires</c-> <c- n>view</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c-> <c- o>&amp;&amp;</c-> <c- p>(</c-><c- n>N</c-> <c- o>></c-> <c- mi>0</c-><c- p>)</c-> <c- o>&amp;&amp;</c-> <c- n>is_object_v</c-><c- o>&lt;</c-><c- n>F</c-><c- o>></c-> <c- o>&amp;&amp;</c->
            <c- n>regular_invocable</c-><c- o>&lt;</c-><c- n>F</c-><c- o>&amp;</c-><c- p>,</c-> <c- n>REPEAT</c-><c- p>(</c-><c- n>range_reference_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c-><c- p>,</c-> <c- n>N</c-><c- p>)...</c-><c- o>></c-> <c- o>&amp;&amp;</c->
            <c- n>can</c-><c- o>-</c-><c- n>reference</c-><c- o>&lt;</c-><c- n>invoke_result_t</c-><c- o>&lt;</c-><c- n>F</c-><c- o>&amp;</c-><c- p>,</c-> <c- n>REPEAT</c-><c- p>(</c-><c- n>range_reference_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c-><c- p>,</c-> <c- n>N</c-><c- p>)...</c-><c- o>>></c->
  <c- k>class</c-> <c- nc>adjacent_transform_view</c-> <c- o>:</c-> <c- k>public</c-> <c- n>view_interface</c-><c- o>&lt;</c-><c- n>adjacent_transform_view</c-><c- o>&lt;</c-><c- n>V</c-><c- p>,</c-> <c- n>F</c-><c- p>,</c-> <c- n>N</c-><c- o>>></c-> <c- p>{</c->
    <i><del><c- n>copyable</c-><c- o>-</c-><c- n>box</c-></del><ins><c- n>movable</c-><c- o>-</c-><c- n>box</c-></ins></i><c- o>&lt;</c-><c- n>F</c-><c- o>></c-> <c- n>fun_</c-><c- p>;</c->            <c- c1>// exposition only</c->

    <c- c1>// ...</c->
</pre>
   <h3 class="heading settled" data-level="4.4" id="wording-ftm"><span class="secno">4.4. </span><span class="content">Feature test macro</span><a class="self-link" href="#wording-ftm"></a></h3>
   <p>Bump the Ranges feature-test macro in 17.3.2 [version.syn], Header <code class="highlight"><c- o>&lt;</c-><c- n>version</c-><c- o>></c-></code> synopsis, with the value selected by the editor to reflect the date of adoption of this paper:</p>
<pre class="highlight"><c- cp>#define __cpp_lib_ranges </c-><del><c- cp>202110L</c-></del><ins><c- cp>20XXXXL</c-></ins>
</pre>
   <h2 class="heading settled" data-level="5" id="wording-p2474"><span class="secno">5. </span><span class="content">Modifications to P2474</span><a class="self-link" href="#wording-p2474"></a></h2>
   <p class="note" role="note"><span>Note:</span> these changes should be applied to the Working Draft if both this paper and P2474 are approved.</p>
   <p>Modify Header <code class="highlight"><c- o>&lt;</c-><c- n>ranges</c-><c- o>></c-></code> synopsis [ranges.syn] as follows:</p>
<pre class="highlight"><c- k>namespace</c-> <c- nn>std</c-><c- o>::</c-><c- nn>ranges</c-> <c- p>{</c->
  <c- c1>// ...</c->

  <c- c1>// [range.repeat], repeat view</c->
  <c- k>template</c-><c- o>&lt;</c-><del><c- n>copy_constructible</c-></del><ins><c- n>move_constructible</c-></ins> <c- n>W</c-><c- p>,</c-> <c- n>semiregular</c-> <c- n>Bound</c-> <c- o>=</c-> <c- n>unreachable_sentinel_t</c-><c- o>></c->
    <c- k>requires</c-> <c- p>(</c-><c- n>is_object_v</c-><c- o>&lt;</c-><c- n>W</c-><c- o>></c-> <c- o>&amp;&amp;</c-> <c- n>same_as</c-><c- o>&lt;</c-><c- n>W</c-><c- p>,</c-> <c- n>remove_cv_t</c-><c- o>&lt;</c-><c- n>W</c-><c- o>>></c->
      <c- o>&amp;&amp;</c-> <c- p>(</c-><c- n>is</c-><c- o>-</c-><c- n>integer</c-><c- o>-</c-><c- n>like</c-><c- o>&lt;</c-><c- n>Bound</c-><c- o>></c-> <c- o>||</c-> <c- n>same_as</c-><c- o>&lt;</c-><c- n>Bound</c-><c- p>,</c-> <c- n>unreachable_sentinel_t</c-><c- o>></c-><c- p>))</c->
  <c- k>class</c-> <c- nc>repeat_view</c-><c- p>;</c->

  <c- c1>// ...</c->
<c- p>}</c->
</pre>
   <p>Modify Class template <code class="highlight"><c- n>repeat_view</c-></code> [range.repeat.view] as follows:</p>
<pre class="highlight"><c- k>namespace</c-> <c- nn>std</c-><c- o>::</c-><c- nn>ranges</c-> <c- p>{</c->
  <c- k>template</c-><c- o>&lt;</c-><del><c- n>copy_constructible</c-></del><ins><c- n>move_constructible</c-></ins> <c- n>W</c-><c- p>,</c-> <c- n>semiregular</c-> <c- n>Bound</c-> <c- o>=</c-> <c- n>unreachable_sentinel_t</c-><c- o>></c->
    <c- k>requires</c-> <c- p>(</c-><c- n>is_object_v</c-><c- o>&lt;</c-><c- n>W</c-><c- o>></c-> <c- o>&amp;&amp;</c-> <c- n>same_as</c-><c- o>&lt;</c-><c- n>W</c-><c- p>,</c-> <c- n>remove_cv_t</c-><c- o>&lt;</c-><c- n>W</c-><c- o>>></c->
      <c- o>&amp;&amp;</c-> <c- p>(</c-><c- n>is</c-><c- o>-</c-><c- n>integer</c-><c- o>-</c-><c- n>like</c-><c- o>&lt;</c-><c- n>Bound</c-><c- o>></c-> <c- o>||</c-> <c- n>same_as</c-><c- o>&lt;</c-><c- n>Bound</c-><c- p>,</c-> <c- n>unreachable_sentinel_t</c-><c- o>></c-><c- p>))</c->
  <c- k>class</c-> <c- nc>repeat_view</c-> <c- o>:</c-> <c- k>public</c-> <c- n>view_interface</c-><c- o>&lt;</c-><c- n>repeat_view</c-><c- o>&lt;</c-><c- n>W</c-><c- p>,</c-> <c- n>Bound</c-><c- o>>></c-> <c- p>{</c->
  <c- k>private</c-><c- o>:</c->
    <c- c1>// [range.repeat.iterator], class range_view::iterator</c->
    <c- k>struct</c-> <c- nc>iterator</c-><c- p>;</c->

    <i><del><c- n>copyable</c-><c- o>-</c-><c- n>box</c-></del><ins><c- n>movable</c-><c- o>-</c-><c- n>box</c-></ins></i><c- o>&lt;</c-><c- n>W</c-><c- o>></c-> <c- n>value_</c-> <c- o>=</c-> <c- n>W</c-><c- p>();</c-> <c- c1>// exposition only (see [range.</c-><del><c- c1>copy</c-></del><ins><c- c1>move</c-></ins><c- c1>.wrap])</c->
    <c- n>Bound</c-> <c- n>bound_</c-> <c- o>=</c-> <c- n>Bound</c-><c- p>();</c-> <c- c1>// exposition only</c->

  <c- k>public</c-><c- o>:</c->
    <c- n>repeat_view</c-><c- p>()</c-> <c- k>requires</c-> <c- n>default_initializable</c-><c- o>&lt;</c-><c- n>W</c-><c- o>></c-> <c- o>=</c-> <c- k>default</c-><c- p>;</c->

    <c- k>constexpr</c-> <c- k>explicit</c-> <c- n>repeat_view</c-><c- p>(</c-><c- k>const</c-> <c- n>W</c-> <c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Bound</c-> <c- n>bound</c-> <c- o>=</c-> <c- n>Bound</c-><c- p>())</c->
      <ins><c- k>requires</c-> <c- n>copy_constructible</c-><c- o>&lt;</c-><c- n>W</c-><c- o>></c-></ins><c- p>;</c->

    <c- c1>// ...</c->
</pre>
<pre class="highlight"><c- k>constexpr</c-> <c- k>explicit</c-> <c- n>repeat_view</c-><c- p>(</c-><c- k>const</c-> <c- n>W</c-> <c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Bound</c-> <c- n>bound</c-> <c- o>=</c-> <c- n>Bound</c-><c- p>())</c->
  <ins><c- k>requires</c-> <c- n>copy_constructible</c-><c- o>&lt;</c-><c- n>W</c-><c- o>></c-></ins><c- p>;</c->
</pre>
   <ol>
    <li data-md>
     <p><em>Effects</em>: Initializes <code class="highlight"><c- n>value_</c-></code> with <code class="highlight"><c- n>value</c-></code> and <code class="highlight"><c- n>bound_</c-></code> with <code class="highlight"><c- n>bound</c-></code>.</p>
   </ol>
   <h2 class="heading settled" data-level="6" id="acks"><span class="secno">6. </span><span class="content">Acknowledgements</span><a class="self-link" href="#acks"></a></h2>
   <p>Thanks to Christopher Di Bella, Corentin Jabot, and Casey Carter for a review and comments of this paper. Thanks to Hui Xie for authoring <span>[P2483R0]</span>.</p>
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  <h2 class="no-num no-ref heading settled" id="references"><span class="content">References</span><a class="self-link" href="#references"></a></h2>
  <h3 class="no-num no-ref heading settled" id="informative"><span class="content">Informative References</span><a class="self-link" href="#informative"></a></h3>
  <dl>
   <dt id="biblio-p1456r1">[P1456R1]
   <dd>Casey Carter. <a href="https://wg21.link/p1456r1"><cite>Move-only views</cite></a>. 12 November 2019. URL: <a href="https://wg21.link/p1456r1">https://wg21.link/p1456r1</a>
   <dt id="biblio-p2325r3">[P2325R3]
   <dd>Barry Revzin. <a href="https://wg21.link/p2325r3"><cite>Views should not be required to be default constructible</cite></a>. 14 May 2021. URL: <a href="https://wg21.link/p2325r3">https://wg21.link/p2325r3</a>
  </dl>