<!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>P3660R0: Improve reference_wrapper Ergonomics</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;
			border-bottom: 3px solid transparent;
			margin-bottom: -3px;
		}
		#toc .content:hover,
		#toc .content:focus {
			background: rgba(75%, 75%, 75%, .25);
			background: var(--a-hover-bg);
			border-bottom-color: #054572;
			border-bottom-color: var(--toclink-underline);
		}
		#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 a + span {
			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>
    table, th, td {
      border: 1px solid black;
      border-collapse: collapse;
      vertical-align: top;
    }
    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 */
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    blockquote c-[t] { color: inherit; } /* Literal.String.Single */
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    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 */
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    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 b25686b9f, updated Fri Mar 14 14:15:20 2025 -0700" name="generator">
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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">P3660R0<br>Improve <code class="highlight"><c- n>reference_wrapper</c-></code> Ergonomics</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="2025-03-12">2025-03-12</time></span></h2>
   <div data-fill-with="spec-metadata">
    <dl>
     <dt>This version:
     <dd><a class="u-url" href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3660r0.html">https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3660r0.html</a>
     <dt class="editor">Author:
     <dd class="editor p-author h-card vcard"><a class="p-name fn u-email email" href="mailto:jeremy@rifkin.dev">Jeremy Rifkin</a>
     <dt>Audience:
     <dd>SG18
     <dt>Project:
     <dd>ISO/IEC 14882 Programming Languages — C++, ISO/IEC JTC1/SC22/WG21
     <dt>Source:
     <dd><a href="https://github.com/jeremy-rifkin/proposals/blob/main/cpp/reference-wrapper-improvements.bs">https://github.com/jeremy-rifkin/proposals/blob/main/cpp/reference-wrapper-improvements.bs</a>
    </dl>
   </div>
   <div data-fill-with="warning"></div>
   <hr title="Separator for header">
  </div>
  <div class="p-summary" data-fill-with="abstract">
   <h2 class="no-num no-toc no-ref heading settled" id="abstract"><span class="content">Abstract</span></h2>
   <p><code class="highlight"><c- n>reference_wrapper</c-></code> is an existing practice to fill a gap between nullability and reassignability while also providing a well-behaved reference object. This paper proposes a small set of ergonomic improvements.</p>
  </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="#introduction"><span class="secno">1</span> <span class="content">Introduction</span></a>
    <li><a href="#motivation"><span class="secno">2</span> <span class="content">Motivation</span></a>
    <li><a href="#alternatives"><span class="secno">3</span> <span class="content">Alternatives</span></a>
    <li><a href="#proposal"><span class="secno">4</span> <span class="content">Proposal</span></a>
    <li><a href="#proposed-wording"><span class="secno">5</span> <span class="content">Proposed Wording</span></a>
    <li>
     <a href="#references"><span class="secno"></span> <span class="content">References</span></a>
     <ol class="toc">
      <li><a href="#normative"><span class="secno"></span> <span class="content">Normative References</span></a>
      <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="introduction"><span class="secno">1. </span><span class="content">Introduction</span><a class="self-link" href="#introduction"></a></h2>
   <p>References in C++ are aliases to objects. They are not guaranteed to occupy storage, cannot be reassigned, and are not
objects themselves. Pointers, on the other hand, point to objects while being reassignable objects. While references and
pointers serve much the same purpose, references provide an important guarantee that they will never refer to a null
object. Thus, there is a gap in core language and library support for representing non-nullable but reassignable
indirection:</p>
   <center>
    <table>
     <tbody>
      <tr>
       <th>
       <th>Not reassignable
       <th>Reassignable
      <tr>
       <th>Nullable
       <td><code class="highlight"><c- n>T</c-><c- o>*</c-> <c- k>const</c-></code>
       <td><code class="highlight"><c- n>T</c-><c- o>*</c-></code>
      <tr>
       <th>Non-nullable
       <td><code class="highlight"><c- n>T</c-><c- o>&amp;</c-></code>
       <td>-
    </table>
   </center>
   <p>When faced with a problem where such a non-nullable reassignable reference type would be useful, developers must either
switch to pointers or use another wrapper type with these properties. Due to its availability, <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>reference_wrapper</c-></code> has emerged as an existing practice for this use case. However, because it was designed for certain metaprogramming uses
requiring references that behave like regular objects as opposed to serving as a more general utility type, it is not
very ergonomic. The two most notable shortcomings are that the name is long and cumbersome and the only ways to access
the referenced object are a conversion operator or <code class="highlight"><c- p>.</c-><c- n>get</c-><c- p>()</c-></code> instead of a forwarding member access operator.</p>
   <p>Ergonomic limitations of <code class="highlight"><c- n>reference_wrapper</c-></code> have led some developers to create their own reference wrapper-like types
that are more ergonomic in lieu of <code class="highlight"><c- n>reference_wrapper</c-></code>’s shortcomings. For example, Barry Revzin shared on the <code class="highlight"><c- n>std</c-><c- o>-</c-><c- n>proposals</c-></code> mailing list in <a href="https://lists.isocpp.org/std-proposals/2024/09/11280.php">September 2024</a>:</p>
   <blockquote>
    <p><i>In reply to a question asking if <code class="highlight"><c- p>.</c-><c- n>get</c-><c- p>()</c-></code> was not already sufficient:</i></p>
    <p>For what it’s worth, we have a template that inherits from <code class="highlight"><c- n>reference_wrapper</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> specifically for this reason. After a lot of use, <code class="highlight"><c- n>r</c-><c- p>.</c-><c- n>get</c-><c- p>().</c-><c- n>f</c-><c- p>()</c-></code> is pretty verbose compared to <code class="highlight"><c- n>r</c-><c- o>-></c-><c- n>f</c-><c- p>()</c-></code>.</p>
    <p>Well that and the name <code class="highlight"><c- n>reference_wrapper</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is also very verbose so ours is
just <code class="highlight"><c- n>Ref</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code>.</p>
   </blockquote>
   <p>Both the name and constantly having to call <code class="highlight"><c- p>.</c-><c- n>get</c-><c- p>()</c-></code> results in this utility being quite cumbersome to use. <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>optional</c-></code> would be similarly cumbersome if developers had to constantly call <code class="highlight"><c- p>.</c-><c- n>value</c-><c- p>()</c-></code> as opposed to being able
to use <code class="highlight"><c- k>operator</c-><c- o>-></c-></code> for member access.</p>
   <p>This paper proposes a small set of ergonomic improvements to address these limitations and transform the type from a
metaprogramming utility to a more broadly applicable vocabulary type that closes the gap between nullability and
reassignability.</p>
   <h2 class="heading settled" data-level="2" id="motivation"><span class="secno">2. </span><span class="content">Motivation</span><a class="self-link" href="#motivation"></a></h2>
   <p>References are often preferred in C++ because they do not require careful thought about nullability. However, there are
times when references can’t be used due to not behaving like objects and not being reassignable. For example, it’s
generally not possible to implement a copy or move assignment operator for a class with non-static reference members and
implicitly-declared copy and move assignment operators are defined as deleted. Additionally, due to not behaving like
normal objects, all of the following are ill-formed: <code class="highlight"><c- b>int</c-><c- o>&amp;</c-> <c- n>arr</c-><c- p>[</c-><c- mi>2</c-><c- p>]</c-></code>, <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>array</c-><c- o>&lt;</c-><c- b>int</c-><c- o>&amp;</c-><c- p>,</c-> <c- mi>2</c-><c- o>></c-></code>, <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>vector</c-><c- o>&lt;</c-><c- b>int</c-><c- o>&amp;></c-></code>, <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>variant</c-><c- o>&lt;</c-><c- b>int</c-><c- o>&amp;</c-><c- p>,</c-> <c- b>float</c-><c- o>&amp;></c-></code>, and <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>initializer_list</c-><c- o>&lt;</c-><c- b>int</c-><c- o>&amp;></c-></code>. Notably, <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>optional</c-><c- o>&lt;</c-><c- n>T</c-><c- o>&amp;></c-></code> is also ill-formed,
however, <a data-link-type="biblio" href="#biblio-p2988" title="std::optional<T&amp;>">[P2988]</a> is on track for acceptance. Whenever any of the aforementioned constructs are desired, or a
programmer would simply like to reassign a <code class="highlight"><c- n>T</c-><c- o>&amp;</c-> <c- n>ref</c-></code>, the limitations of references result in either needing to switch to
a pointer or another wrapper type.</p>
   <p>Pointers work as replacements for references when object-like behavior or reassignability is desirable. However, they
do not reflect non-nullability in the type system. Losing this valuable information in the type system has implications
with bug-proneness and may also lead to unnecessary null checks out of an abundance of caution in code paths where
non-nullability cannot be readily shown. This can increase complexity and clutter code.</p>
   <p>The desire for a non-nullable, reassignable, well-behaved reference has led many to reach for <code class="highlight"><c- n>reference_wrapper</c-></code> as a
standard utility with these semantics. For example, a highly upvoted comment on <a href="https://stackoverflow.com/q/26858034/15675011">Why does std::optional not have a specialization for reference types?</a> mentions using <code class="highlight"><c- n>reference_wrapper</c-></code> as a workaround.</p>
   <p>While <code class="highlight"><c- n>reference_wrapper</c-></code> was initially added for certain metaprogramming uses, it has become a fairly widespread
pattern that can be seen in codebases ranging from hobby projects to large and established codebases such as Chromium. A
cursory GitHub code search for <code class="highlight"><c- n>reference_wrapper</c-></code> in open-source C++ code at the time of writing yields 45k results: <a href="https://github.com/search?type=code&amp;q=%2Fstd%3A%3Areference_wrapper%2F+-is%3Afork+language%3Ac%2B%2B">Code Search</a>.
Many of these uses are:</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>reference_wrapper</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> as a non-static data member</p>
    <li data-md>
     <p><code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>vector</c-><c- o>&lt;</c-><c- n>std</c-><c- o>::</c-><c- n>reference_wrapper</c-><c- o>&lt;</c-><c- n>T</c-><c- o>>></c-></code></p>
    <li data-md>
     <p><code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>optional</c-><c- o>&lt;</c-><c- n>std</c-><c- o>::</c-><c- n>reference_wrapper</c-><c- o>&lt;</c-><c- n>T</c-><c- o>>></c-></code></p>
    <li data-md>
     <p><code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>map</c-><c- o>&lt;</c-><c- n>K</c-><c- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>reference_wrapper</c-><c- o>&lt;</c-><c- n>V</c-><c- o>>></c-></code></p>
    <li data-md>
     <p>Use in <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>variant</c-></code></p>
    <li data-md>
     <p>Use in other containers</p>
   </ul>
   <p>The first few pages of results suggest these categories account for the vast majority of use of <code class="highlight"><c- n>reference_wrapper</c-></code> in
open-source C++ code.</p>
   <p>Due to its semantics and status as an existing practice for this use case, it’s fitting to expand the intended use case
of <code class="highlight"><c- n>reference_wrapper</c-></code> and improve its ergonomics as a general utility instead of introducing a new vocabulary type for
this use case.</p>
   <h2 class="heading settled" data-level="3" id="alternatives"><span class="secno">3. </span><span class="content">Alternatives</span><a class="self-link" href="#alternatives"></a></h2>
   <p>Alternatives to <code class="highlight"><c- n>reference_wrapper</c-></code> for this use case include:</p>
   <ol>
    <li data-md>
     <p>Tell developers to just use pointers</p>
    <li data-md>
     <p>Add a <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>not_null</c-></code> pointer wrapper to fill the gap instead</p>
     <center>
      <table>
       <tbody>
        <tr>
         <th>
         <th>Not reassignable
         <th>Reassignable
        <tr>
         <th>Nullable
         <td><code class="highlight"><c- n>T</c-><c- o>*</c-> <c- k>const</c-></code>
         <td><code class="highlight"><c- n>T</c-><c- o>*</c-></code>
        <tr>
         <th>Non-nullable
         <td><code class="highlight"><c- n>T</c-><c- o>&amp;</c-></code>
         <td><code class="highlight"><c- n>reference_wrapper</c-></code>, <code class="highlight"><c- n>not_null</c-></code>
      </table>
     </center>
    <li data-md>
     <p>Add first-order language support for reassignable references or references that behave as normal objects</p>
   </ol>
   <p>Pointers are undesirable for reasons mentioned earlier.</p>
   <p>There is prior art for <code class="highlight"><c- n>not_null</c-></code> in the form of <code class="highlight"><c- n>gsl</c-><c- o>::</c-><c- n>not_null</c-></code>. This wrapper type fundamentally mimics a pointer,
though, and has constructors taking pointers that are null-checked at runtime. <code class="highlight"><c- n>reference_wrapper</c-></code>, on the other hand,
is designed to model a reference: It’s constructed only by a reference, and thus, non-nullability is ensured as an
invariant at the type system level.</p>
   <p>First-order language support for references that behave like objects and are assignable is a possibility, but, it would
be a massive change to the language. Instead, improving <code class="highlight"><c- n>reference_wrapper</c-></code> for this use case seems preferable.</p>
   <h2 class="heading settled" data-level="4" id="proposal"><span class="secno">4. </span><span class="content">Proposal</span><a class="self-link" href="#proposal"></a></h2>
   <p>This paper proposes three changes:</p>
   <ol>
    <li data-md>
     <p>Add <code class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>typename</c-> <c- nc>T</c-><c- o>></c-> <c- k>using</c-> <c- n>reference</c-> <c- o>=</c-> <c- n>reference_wrapper</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>;</c-></code> as an alias</p>
    <li data-md>
     <p>Add an <code class="highlight"><c- k>operator</c-><c- o>-></c-></code> overload for forwarding member access as well as an <code class="highlight"><c- k>operator</c-><c- o>*</c-></code> overload for symmetry</p>
    <li data-md>
     <p>Provide <code class="highlight"><c- n>reference_wrapper</c-></code> and the <code class="highlight"><c- n>reference</c-></code> alias through the <code class="highlight"><c- o>&lt;</c-><c- n>utility</c-><c- o>></c-></code> header</p>
   </ol>
   <p><code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>reference</c-></code> is chosen as a shorter alias for <code class="highlight"><c- n>reference_wrapper</c-></code> due to <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ref</c-></code> already being used.</p>
   <p>Expanding the forwarding operations for <code class="highlight"><c- n>reference_wrapper</c-></code> follows the precedent of <a data-link-type="biblio" href="#biblio-p2944" title="Comparisons for reference_wrapper">[P2944]</a>, which added forwarding
comparison operators to <code class="highlight"><c- n>reference_wrapper</c-></code>. While <code class="highlight"><c- k>operator</c-><c- o>-></c-></code> is typically associated with pointers and pointer-like
types (such as iterators or smart pointers), it is the only option for member access forwarding in lieu of <code class="highlight"><c- k>operator</c-><c- p>.</c-></code>.
This use of <code class="highlight"><c- k>operator</c-><c- o>-></c-></code> isn’t without precedent, and it isn’t uncommon even for types that aren’t pointer-like. For
example, all of the following have <code class="highlight"><c- k>operator</c-><c- o>-></c-></code> overloads for convenience: <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>optional</c-></code>, <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>expected</c-></code>, or types
like <code class="highlight"><c- n>proxy_holder</c-></code>/<code class="highlight"><c- n>arrow_proxy</c-></code> (<a href="https://stackoverflow.com/a/26496041/15675011">stackoverflow</a>) or <code class="highlight"><c- n>pilfered</c-></code> (<a href="https://github.com/boostorg/json/blob/0b1048adf7571b42ae9f684b63e4383241b9e4a1/include/boost/json/pilfer.hpp">boost json</a>, <a data-link-type="biblio" href="#biblio-p0308" title="Valueless Variants Considered Harmful">[P0308]</a>). <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>optional</c-></code> is arguably similar to a pointer in that it is nullable; however, <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>expected</c-></code> and the proxy/wrapper
types are less so. Fundamentally, the main commonality between all these types isn’t nullability but rather serving as
proxies to other objects via either wrapping or indirection. As such, <code class="highlight"><c- k>operator</c-><c- o>-></c-></code> is fitting for <code class="highlight"><c- n>reference_wrapper</c-></code>.</p>
   <p>With the expanded use case for <code class="highlight"><c- n>reference_wrapper</c-></code>, it is better provided through <code class="highlight"><c- o>&lt;</c-><c- n>utility</c-><c- o>></c-></code> so that <code class="highlight"><c- o>&lt;</c-><c- n>functional</c-><c- o>></c-></code> does not have to be pulled in just to use the type. This follows the precedent of <a data-link-type="biblio" href="#biblio-p0472" title="Put std::monostate in <utility>">[P0472]</a>, which added <code class="highlight"><c- n>monostate</c-></code> to <code class="highlight"><c- o>&lt;</c-><c- n>utility</c-><c- o>></c-></code>. This will require that implementations either <code class="highlight"><c- cp>#include</c-> &lt;utility></code> from <code class="highlight"><c- o>&lt;</c-><c- n>functional</c-><c- o>></c-></code> or put <code class="highlight"><c- n>reference_wrapper</c-></code> in a common implementation header that can be included in both places.</p>
   <h2 class="heading settled" data-level="5" id="proposed-wording"><span class="secno">5. </span><span class="content">Proposed Wording</span><a class="self-link" href="#proposed-wording"></a></h2>
   <p>Proposed wording relative to <a data-link-type="biblio" href="#biblio-n4950" title="Working Draft, Standard for Programming Language C++">[N4950]</a>:</p>
   <p>Move [refwrap] and subsections to [utility.refwrap].</p>
   <p>Move from [functional.syn] to [utility.syn]:</p>
<pre class="highlight"><c- c1>// [</c-><ins><c- c1>utility.</c-></ins><c- c1>refwrap], reference_wrapper</c->
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- o>></c-> <c- k>class</c-> <c- nc>reference_wrapper</c-><c- p>;</c->                                        <c- c1>// freestanding</c->

<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- o>></c-> <c- k>constexpr</c-> <c- n>reference_wrapper</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-> <c- n>ref</c-><c- p>(</c-><c- n>T</c-><c- o>&amp;</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->                <c- c1>// freestanding</c->
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- o>></c-> <c- k>constexpr</c-> <c- n>reference_wrapper</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>T</c-><c- o>></c-> <c- n>cref</c-><c- p>(</c-><c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->   <c- c1>// freestanding</c->
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- o>></c-> <c- b>void</c-> <c- n>ref</c-><c- p>(</c-><c- k>const</c-> <c- n>T</c-><c- o>&amp;&amp;</c-><c- p>)</c-> <c- o>=</c-> <c- k>delete</c-><c- p>;</c->                                   <c- c1>// freestanding</c->
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- o>></c-> <c- b>void</c-> <c- n>cref</c-><c- p>(</c-><c- k>const</c-> <c- n>T</c-><c- o>&amp;&amp;</c-><c- p>)</c-> <c- o>=</c-> <c- k>delete</c-><c- p>;</c->                                  <c- c1>// freestanding</c->

<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>reference_wrapper</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-> <c- n>ref</c-><c- p>(</c-><c- n>reference_wrapper</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->              <c- c1>// freestanding</c->
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>reference_wrapper</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>T</c-><c- o>></c-> <c- n>cref</c-><c- p>(</c-><c- n>reference_wrapper</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->       <c- c1>// freestanding</c->

<c- c1>// [</c-><ins><c- c1>utility.</c-></ins><c- c1>refwrap.common.ref], common_reference related specializations</c->
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>R</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-> <c- k>template</c-><c- o>&lt;</c-><c- k>class</c-><c- o>></c-> <c- k>class</c-> <c- nc>RQual</c-><c- p>,</c-> <c- k>template</c-><c- o>&lt;</c-><c- k>class</c-><c- o>></c-> <c- k>class</c-> <c- nc>TQual</c-><c- o>></c->
  <c- k>requires</c-> <c- n>see</c-> <c- n>below</c->
<c- k>struct</c-> <c- nc>basic_common_reference</c-><c- o>&lt;</c-><c- n>R</c-><c- p>,</c-> <c- n>T</c-><c- p>,</c-> <c- n>RQual</c-><c- p>,</c-> <c- n>TQual</c-><c- o>></c-><c- p>;</c->

<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- p>,</c-> <c- k>class</c-> <c- nc>R</c-><c- p>,</c-> <c- k>template</c-><c- o>&lt;</c-><c- k>class</c-><c- o>></c-> <c- k>class</c-> <c- nc>TQual</c-><c- p>,</c-> <c- k>template</c-><c- o>&lt;</c-><c- k>class</c-><c- o>></c-> <c- k>class</c-> <c- nc>RQual</c-><c- o>></c->
  <c- k>requires</c-> <c- n>see</c-> <c- n>below</c->
<c- k>struct</c-> <c- nc>basic_common_reference</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>R</c-><c- p>,</c-> <c- n>TQual</c-><c- p>,</c-> <c- n>RQual</c-><c- o>></c-><c- p>;</c->
</pre>
   <p>Add to [utility.syn]:</p>
<pre class="highlight"><c- c1>// [utility.refwrap], reference_wrapper</c->
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- o>></c-> <c- k>class</c-> <c- nc>reference_wrapper</c-><c- p>;</c->                                        <c- c1>// freestanding</c->

<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- o>></c-> <c- k>constexpr</c-> <c- n>reference_wrapper</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-> <c- n>ref</c-><c- p>(</c-><c- n>T</c-><c- o>&amp;</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->                <c- c1>// freestanding</c->
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- o>></c-> <c- k>constexpr</c-> <c- n>reference_wrapper</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>T</c-><c- o>></c-> <c- n>cref</c-><c- p>(</c-><c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->   <c- c1>// freestanding</c->
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- o>></c-> <c- b>void</c-> <c- n>ref</c-><c- p>(</c-><c- k>const</c-> <c- n>T</c-><c- o>&amp;&amp;</c-><c- p>)</c-> <c- o>=</c-> <c- k>delete</c-><c- p>;</c->                                   <c- c1>// freestanding</c->
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- o>></c-> <c- b>void</c-> <c- n>cref</c-><c- p>(</c-><c- k>const</c-> <c- n>T</c-><c- o>&amp;&amp;</c-><c- p>)</c-> <c- o>=</c-> <c- k>delete</c-><c- p>;</c->                                  <c- c1>// freestanding</c->

<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>reference_wrapper</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-> <c- n>ref</c-><c- p>(</c-><c- n>reference_wrapper</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->              <c- c1>// freestanding</c->
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>reference_wrapper</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>T</c-><c- o>></c-> <c- n>cref</c-><c- p>(</c-><c- n>reference_wrapper</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->       <c- c1>// freestanding</c->

<ins><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- o>></c-> <c- k>using</c-> <c- n>reference</c-> <c- o>=</c-> <c- n>reference_wrapper</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>;</c->                         <c- c1>// freestanding</c-></ins>

<c- c1>// [utility.refwrap.common.ref], common_reference related specializations</c->
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>R</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-> <c- k>template</c-><c- o>&lt;</c-><c- k>class</c-><c- o>></c-> <c- k>class</c-> <c- nc>RQual</c-><c- p>,</c-> <c- k>template</c-><c- o>&lt;</c-><c- k>class</c-><c- o>></c-> <c- k>class</c-> <c- nc>TQual</c-><c- o>></c->
  <c- k>requires</c-> <c- n>see</c-> <c- n>below</c->
<c- k>struct</c-> <c- nc>basic_common_reference</c-><c- o>&lt;</c-><c- n>R</c-><c- p>,</c-> <c- n>T</c-><c- p>,</c-> <c- n>RQual</c-><c- p>,</c-> <c- n>TQual</c-><c- o>></c-><c- p>;</c->

<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- p>,</c-> <c- k>class</c-> <c- nc>R</c-><c- p>,</c-> <c- k>template</c-><c- o>&lt;</c-><c- k>class</c-><c- o>></c-> <c- k>class</c-> <c- nc>TQual</c-><c- p>,</c-> <c- k>template</c-><c- o>&lt;</c-><c- k>class</c-><c- o>></c-> <c- k>class</c-> <c- nc>RQual</c-><c- o>></c->
  <c- k>requires</c-> <c- n>see</c-> <c- n>below</c->
<c- k>struct</c-> <c- nc>basic_common_reference</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>R</c-><c- p>,</c-> <c- n>TQual</c-><c- p>,</c-> <c- n>RQual</c-><c- o>></c-><c- p>;</c->
</pre>
   <p>Add a paragraph at the end of [functional.syn]:</p>
   <blockquote>
    <ins> The class templates, function templates, and alias template defined in [utility.refwrap] are available when <code class="highlight"><c- o>&lt;</c-><c- n>functional</c-><c- o>></c-></code> is included. </ins>
   </blockquote>
   <p>Add to [utility.refwrap.general]:</p>
<pre class="highlight"><c- k>namespace</c-> <c- nn>std</c-> <c- p>{</c->
  <c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- o>></c-> <c- k>class</c-> <c- nc>reference_wrapper</c-> <c- p>{</c->
  <c- k>public</c-><c- o>:</c->
    <c- c1>// types</c->
    <c- k>using</c-> <c- n>type</c-> <c- o>=</c-> <c- n>T</c-><c- p>;</c->

    <c- c1>// [utility.refwrap.const], constructors</c->
    <c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>U</c-><c- o>></c->
      <c- k>constexpr</c-> <c- n>reference_wrapper</c-><c- p>(</c-><c- n>U</c-><c- o>&amp;&amp;</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>);</c->
    <c- k>constexpr</c-> <c- n>reference_wrapper</c-><c- p>(</c-><c- k>const</c-> <c- n>reference_wrapper</c-><c- o>&amp;</c-> <c- n>x</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->

    <c- c1>// [utility.refwrap.assign], assignment</c->
    <c- k>constexpr</c-> <c- n>reference_wrapper</c-><c- o>&amp;</c-> <c- k>operator</c-><c- o>=</c-><c- p>(</c-><c- k>const</c-> <c- n>reference_wrapper</c-><c- o>&amp;</c-> <c- n>x</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->

    <c- c1>// [utility.refwrap.access], access</c->
    <c- k>constexpr</c-> <c- k>operator</c-> <c- n>T</c-><c- o>&amp;</c-> <c- p>()</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->
    <c- k>constexpr</c-> <c- n>T</c-><c- o>&amp;</c-> <c- nf>get</c-><c- p>()</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->
    <ins><c- k>constexpr</c-> <c- n>T</c-><c- o>*</c-> <c- k>operator</c-><c- o>-></c-><c- p>()</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c-></ins>
    <ins><c- k>constexpr</c-> <c- n>T</c-><c- o>&amp;</c-> <c- k>operator</c-><c- o>*</c-><c- p>()</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c-></ins>

    <c- c1>// [utility.refwrap.invoke], invocation</c->
    <c- k>template</c-><c- o>&lt;</c-><c- k>class</c-><c- p>...</c-> <c- n>ArgTypes</c-><c- o>></c->
      <c- k>constexpr</c-> <c- n>invoke_result_t</c-><c- o>&lt;</c-><c- n>T</c-><c- o>&amp;</c-><c- p>,</c-> <c- n>ArgTypes</c-><c- p>...</c-><c- o>></c-> <c- k>operator</c-><c- p>()(</c-><c- n>ArgTypes</c-><c- o>&amp;&amp;</c-><c- p>...)</c-> <c- k>const</c->
        <c- k>noexcept</c-><c- p>(</c-><c- n>is_nothrow_invocable_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>&amp;</c-><c- p>,</c-> <c- n>ArgTypes</c-><c- p>...</c-><c- o>></c-><c- p>);</c->

    <c- c1>// [utility.refwrap.comparisons], comparisons</c->
    <c- k>friend</c-> <c- k>constexpr</c-> <c- b>bool</c-> <c- k>operator</c-><c- o>==</c-><c- p>(</c-><c- n>reference_wrapper</c-><c- p>,</c-> <c- n>reference_wrapper</c-><c- p>);</c->
    <c- k>friend</c-> <c- k>constexpr</c-> <c- b>bool</c-> <c- k>operator</c-><c- o>==</c-><c- p>(</c-><c- n>reference_wrapper</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-><c- p>);</c->
    <c- k>friend</c-> <c- k>constexpr</c-> <c- b>bool</c-> <c- k>operator</c-><c- o>==</c-><c- p>(</c-><c- n>reference_wrapper</c-><c- p>,</c-> <c- n>reference_wrapper</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>T</c-><c- o>></c-><c- p>);</c->

    <c- k>friend</c-> <c- k>constexpr</c-> <c- k>auto</c-> <c- k>operator</c-><c- o>&lt;=></c-><c- p>(</c-><c- n>reference_wrapper</c-><c- p>,</c-> <c- n>reference_wrapper</c-><c- p>);</c->
    <c- k>friend</c-> <c- k>constexpr</c-> <c- k>auto</c-> <c- k>operator</c-><c- o>&lt;=></c-><c- p>(</c-><c- n>reference_wrapper</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-><c- p>);</c->
    <c- k>friend</c-> <c- k>constexpr</c-> <c- k>auto</c-> <c- k>operator</c-><c- o>&lt;=></c-><c- p>(</c-><c- n>reference_wrapper</c-><c- p>,</c-> <c- n>reference_wrapper</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>T</c-><c- o>></c-><c- p>);</c->
  <c- p>};</c->

  <c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- o>></c->
    <c- n>reference_wrapper</c-><c- p>(</c-><c- n>T</c-><c- o>&amp;</c-><c- p>)</c-> <c- o>-></c-> <c- n>reference_wrapper</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>;</c->
<c- p>}</c->
</pre>
   <p>Add to [utility.refwrap.access]:</p>
   <div class="insall">
    <p><code class="highlight"><c- k>constexpr</c-> <c- n>T</c-><c- o>*</c-> <c- k>operator</c-><c- o>-></c-><c- p>()</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c-></code></p>
    <p class="indent"><em>Returns</em>: <code class="highlight"><c- n>addressof</c-><c- p>(</c-><c- n>get</c-><c- p>())</c-></code>.</p>
    <p><code class="highlight"><c- k>constexpr</c-> <c- n>T</c-><c- o>&amp;</c-> <c- k>operator</c-><c- o>*</c-><c- p>()</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c-></code></p>
    <p class="indent"><em>Returns</em>: The stored reference.</p>
   </div>
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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="normative"><span class="content">Normative References</span><a class="self-link" href="#normative"></a></h3>
  <dl>
   <dt id="biblio-n4950">[N4950]
   <dd>Thomas Köppe. <a href="https://wg21.link/n4950"><cite>Working Draft, Standard for Programming Language C++</cite></a>. 10 May 2023. URL: <a href="https://wg21.link/n4950">https://wg21.link/n4950</a>
  </dl>
  <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-p0308">[P0308]
   <dd><a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0308r0.html"><cite>Valueless Variants Considered Harmful</cite></a>. URL: <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0308r0.html">https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0308r0.html</a>
   <dt id="biblio-p0472">[P0472]
   <dd><a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p0472r3.pdf"><cite>Put std::monostate in &lt;utility></cite></a>. URL: <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p0472r3.pdf">https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p0472r3.pdf</a>
   <dt id="biblio-p2944">[P2944]
   <dd><a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p2944r3.html"><cite>Comparisons for reference_wrapper</cite></a>. URL: <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p2944r3.html">https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p2944r3.html</a>
   <dt id="biblio-p2988">[P2988]
   <dd><a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p2988r8.pdf"><cite>std::optional&lt;T&amp;></cite></a>. URL: <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p2988r8.pdf">https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p2988r8.pdf</a>
  </dl>