<!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>P2266R2: Simpler implicit move</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;
    }
    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 4f053d00e, updated Tue Aug 10 14:13:32 2021 -0700" name="generator">
  <link href="https://isocpp.org/favicon.ico" rel="icon">
<style>
hilite  {background-color: #FFFF00; font-weight: bold;}
ins  {background-color: #CCFFCC; text-decoration: underline;}
del  {background-color: #FFCACA; text-decoration: line-through;}
</style>
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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">P2266R2<br>Simpler implicit move</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="2021-08-31">2021-08-31</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:arthur.j.odwyer@gmail.com">Arthur O'Dwyer</a>
     <dt>Audience:
     <dd>EWG
     <dt>Project:
     <dd>ISO/IEC JTC1/SC22/WG21 14882: Programming Language — C++
     <dt>Current Source:
     <dd><a href="https://github.com/Quuxplusone/draft/blob/gh-pages/d2266-implicit-move-rvalue-ref.bs">github.com/Quuxplusone/draft/blob/gh-pages/d2266-implicit-move-rvalue-ref.bs</a>
     <dt>Current:
     <dd><a href="https://rawgit.com/Quuxplusone/draft/gh-pages/d2266-implicit-move-rvalue-ref.html">rawgit.com/Quuxplusone/draft/gh-pages/d2266-implicit-move-rvalue-ref.html</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>In C++20, return statements can <i>implicitly move</i> from local variables of rvalue reference type; but a defect in the wording means that <i>implicit move</i> fails to apply to functions that return references.
  C++20’s implicit move is specified via a complicated process involving two overload resolutions,
  which is hard to implement, causing implementation divergence.
  We fix the defect and simplify the spec by saying that a returned move-eligible
  id-expression is <i>always</i> an xvalue.</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="#changelog"><span class="secno">1</span> <span class="content">Changelog</span></a>
    <li><a href="#background"><span class="secno">2</span> <span class="content">Background</span></a>
    <li>
     <a href="#problems"><span class="secno">3</span> <span class="content">Problems remaining in C++20</span></a>
     <ol class="toc">
      <li><a href="#conversion-operator"><span class="secno">3.1</span> <span class="content">Conversion operators are treated inconsistently</span></a>
      <li>
       <a href="#perfect-backwarding"><span class="secno">3.2</span> <span class="content">"Perfect backwarding" is treated inconsistently</span></a>
       <ol class="toc">
        <li><a href="#decltype-auto"><span class="secno">3.2.1</span> <span class="content">Interaction with <code class="highlight"><c- k>decltype</c-></code> and <code class="highlight"><c- k>decltype</c-><c- p>(</c-><c- k>auto</c-><c- p>)</c-></code></span></a>
       </ol>
      <li><a href="#two-resolutions"><span class="secno">3.3</span> <span class="content">Two overload resolutions are overly confusing</span></a>
      <li><a href="#refwrap"><span class="secno">3.4</span> <span class="content">A specific case involving <code class="highlight"><c- n>reference_wrapper</c-></code></span></a>
     </ol>
    <li>
     <a href="#polls"><span class="secno">4</span> <span class="content">Straw polls</span></a>
     <ol class="toc">
      <li><a href="#taken-polls-2021-03-17"><span class="secno">4.1</span> <span class="content">Polls taken in EWG telecon on 2021-03-17</span></a>
     </ol>
    <li>
     <a href="#experience"><span class="secno">5</span> <span class="content">Implementation experience</span></a>
     <ol class="toc">
      <li><a href="#exp-getline"><span class="secno">5.1</span> <span class="content">Microsoft’s rvalue <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>getline</c-></code></span></a>
      <li><a href="#exp-ostring"><span class="secno">5.2</span> <span class="content">LibreOffice <code class="highlight"><c- n>OString</c-></code> constructor</span></a>
      <li><a href="#exp-o3tl"><span class="secno">5.3</span> <span class="content">LibreOffice <code class="highlight"><c- n>o3tl</c-><c- o>::</c-><c- n>temporary</c-></code></span></a>
     </ol>
    <li>
     <a href="#wording"><span class="secno">6</span> <span class="content">Proposed wording relative to N4861</span></a>
     <ol class="toc">
      <li><a href="#wording-nn"><span class="secno">6.1</span> <span class="content">Non-normative clarifications</span></a>
     </ol>
    <li><a href="#acknowledgments"><span class="secno">7</span> <span class="content">Acknowledgments</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="changelog"><span class="secno">1. </span><span class="content">Changelog</span><a class="self-link" href="#changelog"></a></h2>
   <ul>
    <li data-md>
     <p>R2:</p>
     <ul>
      <li data-md>
       <p>Merged the drive-by bugfix into the main "proposed wording" section.</p>
      <li data-md>
       <p>Added new wording for the note in [basic.lval]/4.</p>
      <li data-md>
       <p>Added feature-test macro <code class="highlight"><c- n>__cpp_implicit_move</c-></code>.</p>
      <li data-md>
       <p>Added straw poll results.</p>
      <li data-md>
       <p>Added a section on "Implementation Experience", mentioning <a data-link-type="biblio" href="#biblio-d99005">[D99005]</a>.</p>
     </ul>
    <li data-md>
     <p>R1:</p>
     <ul>
      <li data-md>
       <p>Added the drive-by bugfix about lambda-expressions.</p>
     </ul>
   </ul>
   <h2 class="heading settled" data-level="2" id="background"><span class="secno">2. </span><span class="content">Background</span><a class="self-link" href="#background"></a></h2>
   <p>Starting in C++11, <em>implicit move</em> (<a href="https://timsong-cpp.github.io/cppwp/n4861/class.copy.elision#3">[class.copy.elision]/3</a>)
permits us to return move-only types by value:</p>
<pre class="language-c++ highlight"><c- k>struct</c-> <c- nc>Widget</c-> <c- p>{</c->
    <c- n>Widget</c-><c- p>(</c-><c- n>Widget</c-><c- o>&amp;&amp;</c-><c- p>);</c->
<c- p>};</c->

<c- n>Widget</c-> <c- nf>one</c-><c- p>(</c-><c- n>Widget</c-> <c- n>w</c-><c- p>)</c-> <c- p>{</c->
    <c- k>return</c-> <c- n>w</c-><c- p>;</c->  <c- c1>// OK since C++11</c->
<c- p>}</c->
</pre>
   <p>This wording was amended by <a data-link-type="biblio" href="#biblio-cwg1579">[CWG1579]</a>, which made it
legal to call converting constructors accepting an rvalue reference of the
returned expression’s type.</p>
<pre class="language-c++ highlight"><c- k>struct</c-> <c- nc>RRefTaker</c-> <c- p>{</c->
    <c- n>RRefTaker</c-><c- p>(</c-><c- n>Widget</c-><c- o>&amp;&amp;</c-><c- p>);</c->
<c- p>};</c->
<c- n>RRefTaker</c-> <c- nf>two</c-><c- p>(</c-><c- n>Widget</c-> <c- n>w</c-><c- p>)</c-> <c- p>{</c->
    <c- k>return</c-> <c- n>w</c-><c- p>;</c->  <c- c1>// OK since C++11 + CWG1579</c->
<c- p>}</c->
</pre>
   <p>C++20 adopted <a data-link-type="biblio" href="#biblio-p1825">[P1825]</a>, a wording paper created by merging <a data-link-type="biblio" href="#biblio-p0527">[P0527]</a> and <a data-link-type="biblio" href="#biblio-p1155">[P1155]</a>. The former introduced the category of "implicitly movable entities,"
and extended that category to include automatic variables of
rvalue reference type. The latter increased the scope of the "implicit move"
optimization beyond converting constructors — now, in C++20, the rule is
simply that the first overload resolution to initialize the returned object is done
by treating <code class="highlight"><c- n>w</c-></code> as an rvalue. (The resolution may now produce candidates such
as conversion operators and constructors-taking-<code class="highlight"><c- n>Base</c-><c- o>&amp;&amp;</c-></code>.) Of these two
changes, P0527’s was the more drastic:</p>
<pre class="language-c++ highlight"><c- n>RRefTaker</c-> <c- nf>three</c-><c- p>(</c-><c- n>Widget</c-><c- o>&amp;&amp;</c-> <c- n>w</c-><c- p>)</c-> <c- p>{</c->
    <c- k>return</c-> <c- n>w</c-><c- p>;</c->  <c- c1>// OK since C++20 because P0527</c->
<c- p>}</c->
</pre>
   <p>However, due to the placement of P1825’s new wording in <a href="https://timsong-cpp.github.io/cppwp/n4861/class.copy.elision#3">[class.copy.elision]/3</a>,
the new wording about "implicitly movable entities" is triggered <em>only when
initializing a return object.</em> Functions that do not return objects, do not
benefit from this wording. This leads to a surprising result:</p>
<pre class="language-c++ highlight"><c- n>Widget</c-><c- o>&amp;&amp;</c-> <c- nf>four</c-><c- p>(</c-><c- n>Widget</c-><c- o>&amp;&amp;</c-> <c- n>w</c-><c- p>)</c-> <c- p>{</c->
    <c- k>return</c-> <c- n>w</c-><c- p>;</c->  <c- c1>// Error</c->
<c- p>}</c->
</pre>
   <p>In <code class="highlight"><c- k>return</c-> <c- n>w</c-></code>, the implicitly movable entity <code class="highlight"><c- n>w</c-></code> is treated as an rvalue
when the return type of the function is <code class="highlight"><c- n>RRefTaker</c-></code> as in example <code class="highlight"><c- n>three</c-></code>,
but it is treated as an lvalue when the return type of the function is <code class="highlight"><c- n>Widget</c-><c- o>&amp;&amp;</c-></code> as in example <code class="highlight"><c- n>four</c-></code>.</p>
   <h2 class="heading settled" data-level="3" id="problems"><span class="secno">3. </span><span class="content">Problems remaining in C++20</span><a class="self-link" href="#problems"></a></h2>
   <h3 class="heading settled" data-level="3.1" id="conversion-operator"><span class="secno">3.1. </span><span class="content">Conversion operators are treated inconsistently</span><a class="self-link" href="#conversion-operator"></a></h3>
<pre class="language-c++ highlight"><c- k>struct</c-> <c- nc>Mutt</c-> <c- p>{</c->
    <c- n>operator</c-> <c- b>int</c-><c- o>*</c-><c- p>()</c-> <c- o>&amp;&amp;</c-><c- p>;</c->
<c- p>};</c->
<c- k>struct</c-> <c- nc>Jeff</c-> <c- p>{</c->
    <c- n>operator</c-> <c- b>int</c-><c- o>&amp;</c-><c- p>()</c-> <c- o>&amp;&amp;</c-><c- p>;</c->
<c- p>};</c->

<c- b>int</c-><c- o>*</c-> <c- nf>five</c-><c- p>(</c-><c- n>Mutt</c-> <c- n>x</c-><c- p>)</c-> <c- p>{</c->
    <c- k>return</c-> <c- n>x</c-><c- p>;</c->  <c- c1>// OK since C++20 because P1155</c->
<c- p>}</c->

<c- b>int</c-><c- o>&amp;</c-> <c- nf>six</c-><c- p>(</c-><c- n>Jeff</c-> <c- n>x</c-><c- p>)</c-> <c- p>{</c->
    <c- k>return</c-> <c- n>x</c-><c- p>;</c->  <c- c1>// Error</c->
<c- p>}</c->
</pre>
   <p>(<code class="highlight"><c- n>Mutt</c-></code> here is isomorphic to example <code class="highlight"><c- n>nine</c-></code> from <a data-link-type="biblio" href="#biblio-p1155">[P1155]</a>. P1155 did not
explicitly consider <code class="highlight"><c- n>Jeff</c-></code> because, at the time, Arthur hadn’t realized that
the difference between <code class="highlight"><c- n>Mutt</c-></code> and <code class="highlight"><c- n>Jeff</c-></code> was significant to the wording.)</p>
   <h3 class="heading settled" data-level="3.2" id="perfect-backwarding"><span class="secno">3.2. </span><span class="content">"Perfect backwarding" is treated inconsistently</span><a class="self-link" href="#perfect-backwarding"></a></h3>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>T</c-><c- o>></c->
<c- n>T</c-><c- o>&amp;&amp;</c-> <c- n>seven</c-><c- p>(</c-><c- n>T</c-><c- o>&amp;&amp;</c-> <c- n>x</c-><c- p>)</c-> <c- p>{</c-> <c- k>return</c-> <c- n>x</c-><c- p>;</c-> <c- p>}</c->

<c- b>void</c-> <c- n>test_seven</c-><c- p>(</c-><c- n>Widget</c-> <c- n>w</c-><c- p>)</c-> <c- p>{</c->
    <c- n>Widget</c-><c- o>&amp;</c-> <c- n>r</c-> <c- o>=</c-> <c- n>seven</c-><c- p>(</c-><c- n>w</c-><c- p>);</c->               <c- c1>// OK</c->
    <c- n>Widget</c-><c- o>&amp;&amp;</c-> <c- n>rr</c-> <c- o>=</c-> <c- n>seven</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>w</c-><c- p>));</c->  <c- c1>// Error</c->
<c- p>}</c->
</pre>
   <p>The line marked "Error" instantiates <code class="highlight"><c- n>seven</c-><c- o>&lt;</c-><c- n>Widget</c-><c- o>></c-></code>, with the signature <code class="highlight"><c- n>Widget</c-><c- o>&amp;&amp;</c-> <c- n>seven</c-><c- p>(</c-><c- n>Widget</c-><c- o>&amp;&amp;</c-> <c- n>x</c-><c- p>)</c-></code>. The rvalue-reference parameter <code class="highlight"><c- n>x</c-></code> is an implicitly
movable entity according to C++20; but, because the return type is not an
object type, implicit move fails to happen — the return type <code class="highlight"><c- n>Widget</c-><c- o>&amp;&amp;</c-></code> cannot
bind to the lvalue <em>id-expression</em> <code class="highlight"><c- n>x</c-></code>.</p>
   <p>The same surprise occurs with <code class="highlight"><c- k>decltype</c-><c- p>(</c-><c- k>auto</c-><c- p>)</c-></code> return types:</p>
<pre class="highlight"><c- n>Widget</c-> <c- nf>val</c-><c- p>();</c->
<c- n>Widget</c-><c- o>&amp;</c-> <c- nf>lref</c-><c- p>();</c->
<c- n>Widget</c-><c- o>&amp;&amp;</c-> <c- nf>rref</c-><c- p>();</c->

<c- k>decltype</c-><c- p>(</c-><c- k>auto</c-><c- p>)</c-> <c- n>eight</c-><c- p>()</c-> <c- p>{</c->
    <c- k>decltype</c-><c- p>(</c-><c- k>auto</c-><c- p>)</c-> <c- n>x</c-> <c- o>=</c-> <c- n>val</c-><c- p>();</c->  <c- c1>// OK, x is Widget</c->
    <c- k>return</c-> <c- n>x</c-><c- p>;</c->  <c- c1>// OK, return type is Widget, we get copy elision</c->
<c- p>}</c->

<c- k>decltype</c-><c- p>(</c-><c- k>auto</c-><c- p>)</c-> <c- n>nine</c-><c- p>()</c-> <c- p>{</c->
    <c- k>decltype</c-><c- p>(</c-><c- k>auto</c-><c- p>)</c-> <c- n>x</c-> <c- o>=</c-> <c- n>lref</c-><c- p>();</c->  <c- c1>// OK, x is Widget&amp;</c->
    <c- k>return</c-> <c- n>x</c-><c- p>;</c->  <c- c1>// OK, return type is Widget&amp;</c->
<c- p>}</c->

<c- k>decltype</c-><c- p>(</c-><c- k>auto</c-><c- p>)</c-> <c- n>ten</c-><c- p>()</c-> <c- p>{</c->
    <c- k>decltype</c-><c- p>(</c-><c- k>auto</c-><c- p>)</c-> <c- n>x</c-> <c- o>=</c-> <c- n>rref</c-><c- p>();</c->  <c- c1>// OK, x is Widget&amp;&amp;</c->
    <c- k>return</c-> <c- n>x</c-><c- p>;</c->  <c- c1>// Error, return type is Widget&amp;&amp;, cannot bind to x</c->
<c- p>}</c->
</pre>
   <p>We propose to make <code class="highlight"><c- n>ten</c-></code> work, by permitting — in fact <em>requiring</em> —<wbr>the move-eligible <em>id-expression</em> <code class="highlight"><c- n>x</c-></code> to be treated as an rvalue.</p>
   <h4 class="heading settled" data-level="3.2.1" id="decltype-auto"><span class="secno">3.2.1. </span><span class="content">Interaction with <code class="highlight"><c- k>decltype</c-></code> and <code class="highlight"><c- k>decltype</c-><c- p>(</c-><c- k>auto</c-><c- p>)</c-></code></span><a class="self-link" href="#decltype-auto"></a></h4>
   <p>We do not propose to change any of the rules around
the deduction of <code class="highlight"><c- k>decltype</c-><c- p>(</c-><c- k>auto</c-><c- p>)</c-></code> itself.
However, functions with <code class="highlight"><c- k>decltype</c-><c- p>(</c-><c- k>auto</c-><c- p>)</c-></code> return types have some subtlety
to them.</p>
   <p>Consider this extremely contrived example:</p>
<pre class="language-c++ highlight"><c- n>decltype</c-><c- p>(</c-><c- k>auto</c-><c- p>)</c-> <c- n>eleven</c-><c- p>(</c-><c- n>Widget</c-><c- o>&amp;&amp;</c-> <c- n>x</c-><c- p>)</c-> <c- p>{</c->
    <c- k>return</c-> <c- p>(</c-><c- n>x</c-><c- p>);</c->
<c- p>}</c->
</pre>
   <p>Here, the return type of <code class="highlight"><c- n>eleven</c-></code> is the decltype of the expression <code class="highlight"><c- p>(</c-><c- n>x</c-><c- p>)</c-></code>.
This is governed by <a href="https://eel.is/c++draft/dcl.spec.auto#dcl.type.auto.deduct-5">[dcl.type.auto.deduct]/5</a>:</p>
   <blockquote>
    <p>If the <em>placeholder-type-specifier</em> is of the form <i>type-constraint<sub>opt</sub></i> <code class="highlight"><c- k>decltype</c-><c- p>(</c-><c- k>auto</c-><c- p>)</c-></code>, <code class="highlight"><c- n>T</c-></code> shall be the placeholder alone. The type deduced for <code class="highlight"><c- n>T</c-></code> is determined as described in <a href="https://eel.is/c++draft/dcl.type.decltype">[dcl.type.decltype]</a>,
as though <em>E</em> had been the operand of the decltype.</p>
   </blockquote>
   <p>In C++17, the decltype of <code class="highlight"><c- p>(</c-><c- n>x</c-><c- p>)</c-></code> was <code class="highlight"><c- b>int</c-><c- o>&amp;</c-></code>. No implicit move happened, because <code class="highlight"><c- n>x</c-></code> (being a reference) was not an implicitly movable entity. The lvalue expression <code class="highlight"><c- p>(</c-><c- n>x</c-><c- p>)</c-></code> happily binds to the function return type <code class="highlight"><c- b>int</c-><c- o>&amp;</c-></code>, and the code compiles OK.</p>
   <p>In C++20, the decltype of <code class="highlight"><c- p>(</c-><c- n>x</c-><c- p>)</c-></code> is <code class="highlight"><c- b>int</c-><c- o>&amp;</c-></code>. <code class="highlight"><c- n>x</c-></code> now <em>is</em> an implicitly movable entity,
but (because the return type is not an object type) implicit move does not apply.
The lvalue expression <code class="highlight"><c- p>(</c-><c- n>x</c-><c- p>)</c-></code> happily binds to the function return type <code class="highlight"><c- b>int</c-><c- o>&amp;</c-></code>, and
the code compiles OK.</p>
   <p>We propose to change the behavior of <code class="highlight"><c- n>eleven</c-></code>!</p>
   <p>Under our proposal, the <em>id-expression</em> <code class="highlight"><c- n>x</c-></code> (as the operand of <code class="highlight"><c- k>return</c-></code>) is <em>move-eligible</em>, which means it is an xvalue.
The function return type is deduced as <code class="highlight"><c- k>decltype</c-><c- p>(</c-></code><i>E</i><code class="highlight"><c- p>)</c-></code>, which is to say, <code class="highlight"><c- b>int</c-><c- o>&amp;&amp;</c-></code> since <em>E</em> is an xvalue.
The xvalue expression <code class="highlight"><c- p>(</c-><c- n>x</c-><c- p>)</c-></code> happily binds to the function return type <code class="highlight"><c- b>int</c-><c- o>&amp;&amp;</c-></code>, and the code compiles OK. <b>But now it returns <code class="highlight"><c- b>int</c-><c- o>&amp;&amp;</c-></code>, not <code class="highlight"><c- b>int</c-><c- o>&amp;</c-></code>.</b></p>
   <p>This does produce surprising inconsistencies in the handling of parentheses; for example,</p>
<pre class="language-c++ highlight"><c- k>auto</c-> <c- nf>f1</c-><c- p>(</c-><c- b>int</c-> <c- n>x</c-><c- p>)</c-> <c- o>-></c-> <c- n>decltype</c-><c- p>(</c-><c- n>x</c-><c- p>)</c-> <c- p>{</c-> <c- k>return</c-> <c- p>(</c-><c- n>x</c-><c- p>);</c-> <c- p>}</c->     <c- c1>// int</c->
<c- k>auto</c-> <c- nf>f2</c-><c- p>(</c-><c- b>int</c-> <c- n>x</c-><c- p>)</c-> <c- o>-></c-> <c- n>decltype</c-><c- p>((</c-><c- n>x</c-><c- p>))</c-> <c- p>{</c-> <c- k>return</c-> <c- p>(</c-><c- n>x</c-><c- p>);</c-> <c- p>}</c->   <c- c1>// int&amp;</c->
<c- k>auto</c-> <c- nf>f3</c-><c- p>(</c-><c- b>int</c-> <c- n>x</c-><c- p>)</c-> <c- o>-></c-> <c- n>decltype</c-><c- p>(</c-><c- k>auto</c-><c- p>)</c-> <c- p>{</c-> <c- k>return</c-> <c- p>(</c-><c- n>x</c-><c- p>);</c-> <c- p>}</c->  <c- c1>// C++20: int&amp;. Proposed: int&amp;&amp;</c->
<c- k>auto</c-> <c- nf>g1</c-><c- p>(</c-><c- b>int</c-> <c- n>x</c-><c- p>)</c-> <c- o>-></c-> <c- n>decltype</c-><c- p>(</c-><c- n>x</c-><c- p>)</c-> <c- p>{</c-> <c- k>return</c-> <c- n>x</c-><c- p>;</c-> <c- p>}</c->       <c- c1>// int</c->
<c- k>auto</c-> <c- nf>g2</c-><c- p>(</c-><c- b>int</c-> <c- n>x</c-><c- p>)</c-> <c- o>-></c-> <c- n>decltype</c-><c- p>((</c-><c- n>x</c-><c- p>))</c-> <c- p>{</c-> <c- k>return</c-> <c- n>x</c-><c- p>;</c-> <c- p>}</c->     <c- c1>// int&amp;</c->
<c- k>auto</c-> <c- nf>g3</c-><c- p>(</c-><c- b>int</c-> <c- n>x</c-><c- p>)</c-> <c- o>-></c-> <c- n>decltype</c-><c- p>(</c-><c- k>auto</c-><c- p>)</c-> <c- p>{</c-> <c- k>return</c-> <c- n>x</c-><c- p>;</c-> <c- p>}</c->    <c- c1>// int</c->
</pre>
   <p>Note that <code class="highlight"><c- n>f2</c-></code> and <code class="highlight"><c- n>g2</c-></code> are well-formed in C++20, but we propose to make <code class="highlight"><c- n>f2</c-></code> and <code class="highlight"><c- n>g2</c-></code> ill-formed,
because they attempt to bind an lvalue reference to a <em>move-eligible</em> xvalue expression.</p>
   <p>However, C++ users already know to be wary of parentheses anywhere in the vicinity of <code class="highlight"><c- k>decltype</c-></code> or <code class="highlight"><c- k>decltype</c-><c- p>(</c-><c- k>auto</c-><c- p>)</c-></code>. We don’t think we’re adding any significant amount
of surprise in this already-arcane area.</p>
   <h3 class="heading settled" data-level="3.3" id="two-resolutions"><span class="secno">3.3. </span><span class="content">Two overload resolutions are overly confusing</span><a class="self-link" href="#two-resolutions"></a></h3>
   <p>Implicit move is currently expressed
in terms of two separate overload resolutions: one treating the operand as an rvalue,
and then (if that resolution fails) another one treating the operand as an lvalue.</p>
   <p>As far as I know, this is the only place in the language where two separate resolutions
are done on the same operand. This mechanism has some counterintuitive ramifications —<wbr>not <em>problems</em> per se, but surprising and subtle quirks that would be nice to simplify
out of the language.</p>
<pre class="language-c++ highlight"><c- k>struct</c-> <c- nc>Sam</c-> <c- p>{</c->
    <c- n>Sam</c-><c- p>(</c-><c- n>Widget</c-><c- o>&amp;</c-><c- p>);</c->        <c- c1>// #1</c->
    <c- n>Sam</c-><c- p>(</c-><c- k>const</c-> <c- n>Widget</c-><c- o>&amp;</c-><c- p>);</c->  <c- c1>// #2</c->
<c- p>};</c->

<c- n>Sam</c-> <c- nf>twelve</c-><c- p>()</c-> <c- p>{</c->
    <c- n>Widget</c-> <c- n>w</c-><c- p>;</c->
    <c- k>return</c-> <c- n>w</c-><c- p>;</c->  <c- c1>// calls #2 since C++20 because P1155</c->
<c- p>}</c->
</pre>
   <p class="note" role="note"><span>Note:</span> In C++17 (prior to P1155), #2 would not be found by the first pass because
its argument type is not exactly <code class="highlight"><c- n>Widget</c-><c- o>&amp;&amp;</c-></code>. The comment in <code class="highlight"><c- n>twelve</c-></code> matches the
current Standard wording, and matches the behavior of MSVC, Clang 13+, and GCC 7 through 10.
(As of this writing, GCC 11+ have regressed and lost the correct behavior.)</p>
   <p>The first overload resolution succeeds, and selects a candidate (#2) that is
a <em>worse match</em> than the candidate that would have been selected by the second
overload resolution. This is a surprising quirk, which was discussed internally around
the time P1825 was adopted (see <a data-link-type="biblio" href="#biblio-corereflector">[CoreReflector]</a>); that discussion petered out with
no conclusion except a general sense that the alternative mechanisms
discussed (such as introducing a notion of "lvalues that preferentially bind
to rvalue references" or "rvalues that reluctantly bind to lvalue references")
were strictly worse than the status quo.</p>
<pre class="language-c++ highlight"><c- k>struct</c-> <c- nc>Frodo</c-> <c- p>{</c->
    <c- n>Frodo</c-><c- p>(</c-><c- n>Widget</c-><c- o>&amp;</c-><c- p>);</c->
    <c- n>Frodo</c-><c- p>(</c-><c- n>Widget</c-><c- o>&amp;&amp;</c-><c- p>)</c-> <c- o>=</c-> <c- n>delete</c-><c- p>;</c->
<c- p>};</c->

<c- n>Frodo</c-> <c- nf>thirteen</c-><c- p>()</c-> <c- p>{</c->
    <c- n>Widget</c-> <c- n>w</c-><c- p>;</c->
    <c- k>return</c-> <c- n>w</c-><c- p>;</c->  <c- c1>// Error: the first overload resolution selects a deleted function</c->
<c- p>}</c->
</pre>
   <p>Here the first pass uniquely finds <code class="highlight"><c- n>Frodo</c-><c- p>(</c-><c- n>Widget</c-><c- o>&amp;&amp;</c-><c- p>)</c-></code>,
which is a deleted function; does this count as "the first overload resolution fails,"
or does it count as a success and thus produce an error when we try to use that deleted
function? Vendors currently disagree, but <a href="https://eel.is/c++draft/over.match.general#3">[over.match.general]/3</a> is clear:</p>
   <blockquote>
    <p>If a best viable function exists and is unique, overload resolution succeeds
and produces it as the result. Otherwise overload resolution fails
and the invocation is ill-formed. [...] Overload resolution
results in a <em>usable candidate</em> if overload resolution succeeds and
the selected candidate is either not a function ([over.built]), or is a function
that is not deleted and is accessible from the context in which overload resolution
was performed.</p>
   </blockquote>
   <p>
    <b>Error from use of deleted function:</b> GCC 5,6,7; GCC 11+ with 
    <tt>-std=c++20</tt>
    ; MSVC; ICC
   </p>
   <p>
    <b>Non-conforming fallback to <code class="highlight"><c- n>Frodo</c-><c- p>(</c-><c- n>Widget</c-><c- o>&amp;</c-><c- p>)</c-></code>:</b> GCC 8,9,10; GCC 11+ with 
    <tt>-std=c++17</tt>
    ; Clang before <a data-link-type="biblio" href="#biblio-d92936">[D92936]</a>
   </p>
   <p>This implementation divergence would be less likely to exist, if the specification
were simplified to avoid relying on the precise formal meaning of "failure."
We propose that simplification.</p>
   <p>Another example of vendors misinterpreting the meaning of "failure":</p>
<pre class="language-c++ highlight"><c- k>struct</c-> <c- nc>Merry</c-> <c- p>{};</c->
<c- k>struct</c-> <c- nc>Pippin</c-> <c- p>{};</c->
<c- k>struct</c-> <c- nc>Together</c-> <c- o>:</c-> <c- n>Merry</c-><c- p>,</c-> <c- n>Pippin</c-> <c- p>{};</c->
<c- k>struct</c-> <c- nc>Quest</c-> <c- p>{</c->
    <c- n>Quest</c-><c- p>(</c-><c- n>Merry</c-><c- o>&amp;&amp;</c-><c- p>);</c->
    <c- n>Quest</c-><c- p>(</c-><c- n>Pippin</c-><c- o>&amp;&amp;</c-><c- p>);</c->
    <c- n>Quest</c-><c- p>(</c-><c- n>Together</c-><c- o>&amp;</c-><c- p>);</c->
<c- p>};</c->

<c- n>Quest</c-> <c- nf>fourteen</c-><c- p>()</c-> <c- p>{</c->
    <c- n>Together</c-> <c- n>t</c-><c- p>;</c->
    <c- k>return</c-> <c- n>t</c-><c- p>;</c->  <c- c1>// C++20: calls Quest(Together&amp;). Proposed: ill-formed</c->
<c- p>}</c->
</pre>
   <p>Here the first pass finds both <code class="highlight"><c- n>Quest</c-><c- p>(</c-><c- n>Merry</c-><c- o>&amp;&amp;</c-><c- p>)</c-></code> and <code class="highlight"><c- n>Quest</c-><c- p>(</c-><c- n>Pippin</c-><c- o>&amp;&amp;</c-><c- p>)</c-></code>. <a href="https://eel.is/c++draft/over.match.general#3">[over.match.general]/3</a> is clear
that ambiguity <em>is</em> an overload resolution failure and the second resolution must
be performed. However, EDG’s front-end disagrees.</p>
   <p><b>Fallback to <code class="highlight"><c- n>Quest</c-><c- p>(</c-><c- n>Together</c-><c- o>&amp;</c-><c- p>)</c-></code>:</b> GCC; Clang; MSVC</p>
   <p><b>Non-conforming error due to ambiguity in the first pass:</b> ICC</p>
   <h3 class="heading settled" data-level="3.4" id="refwrap"><span class="secno">3.4. </span><span class="content">A specific case involving <code class="highlight"><c- n>reference_wrapper</c-></code></span><a class="self-link" href="#refwrap"></a></h3>
   <p>Consider this dangerous function:</p>
<pre class="language-c++ highlight"><c- n>std</c-><c- o>::</c-><c- n>reference_wrapper</c-><c- o>&lt;</c-><c- n>Widget</c-><c- o>></c-> <c- n>fifteen</c-><c- p>()</c-> <c- p>{</c->
    <c- n>Widget</c-> <c- n>w</c-><c- p>;</c->
    <c- k>return</c-> <c- n>w</c-><c- p>;</c->  <c- c1>// OK until CWG1579; OK after LWG2993. Proposed: ill-formed</c->
<c- p>}</c->
</pre>
   <p>Prior to <a data-link-type="biblio" href="#biblio-cwg1579">[CWG1579]</a> (circa 2014), implicit move was not done, and so <code class="highlight"><c- n>w</c-></code> was treated
as an lvalue and <code class="highlight"><c- n>fifteen</c-></code> was well-formed — it returned a dangling reference to automatic
variable <code class="highlight"><c- n>w</c-></code>.</p>
   <p>CWG1579 made <code class="highlight"><c- n>fifteen</c-></code> ill-formed (except on the non-conforming compilers listed above),
because now the first overload resolution step would find <code class="highlight"><c- n>reference_wrapper</c-><c- p>(</c-><c- n>type</c-><c- o>&amp;&amp;</c-><c- p>)</c-> <c- o>=</c-> <c- k>delete</c-></code> and hard-error.</p>
   <p>Then, <a data-link-type="biblio" href="#biblio-lwg2993">[LWG2993]</a> eliminated this deleted constructor from <code class="highlight"><c- n>reference_wrapper</c-></code> and
replaced it with a SFINAE-constrained constructor from <code class="highlight"><c- n>U</c-><c- o>&amp;&amp;</c-></code>. Now, the first overload
resolution step legitimately fails (it finds no viable candidates), and so the second
overload resolution is performed and finds a usable candidate — it returns a dangling
reference to automatic variable <code class="highlight"><c- n>w</c-></code>. This is how the situation stands today in C++20.</p>
   <p>We propose to simplify <a href="https://timsong-cpp.github.io/cppwp/n4861/class.copy.elision#3">[class.copy.elision]/3</a> by eliminating the second "fallback" overload resolution.
If this proposal is adopted, <code class="highlight"><c- n>fifteen</c-></code> will once again become ill-formed.</p>
   <p>In the internal discussion of P1825 (<a data-link-type="biblio" href="#biblio-corereflector">[CoreReflector]</a>) one participant opined that
making <code class="highlight"><c- n>fifteen</c-></code> ill-formed is a good thing, because it correctly diagnoses
the dangling reference. The existing two-step mechanism works to defeat
the clear intent of <code class="highlight"><c- n>reference_wrapper</c-></code>'s SFINAE-constrained constructor
and permit the returning of dangling references when in fact we don’t want that.</p>
   <h2 class="heading settled" data-level="4" id="polls"><span class="secno">4. </span><span class="content">Straw polls</span><a class="self-link" href="#polls"></a></h2>
   <h3 class="heading settled" data-level="4.1" id="taken-polls-2021-03-17"><span class="secno">4.1. </span><span class="content">Polls taken in EWG telecon on 2021-03-17</span><a class="self-link" href="#taken-polls-2021-03-17"></a></h3>
   <p>Arthur O’Dwyer presented P2266R1. The following straw polls were taken.
The second poll was interpreted as consensus, but with the strong "Against" vote indicating
that implementation experience (and an updated paper) was needed before sending P2266 to electronic polling.
(Two days later, the first draft of Clang patch <a data-link-type="biblio" href="#biblio-d99005">[D99005]</a> became available.)</p>
   <table class="def">
    <tbody>
     <tr>
      <th style="width: 70%;">
      <th><strong>SF</strong>
      <th><strong>F</strong>
      <th><strong>N</strong>
      <th><strong>A</strong>
      <th><strong>SA</strong>
     <tr>
      <th><small>We are interested in addressing the issue raised in P2266 (as proposed, or in another manner).</small>
      <th> 13 
      <th> 9 
      <th> 1 
      <th> 0 
      <th> 0 
     <tr>
      <th><small>Send P2266 (with minor wording fixes) to electronic polling, then CWG, targeting C++23.</small>
      <th> 5 
      <th> 6 
      <th> 7 
      <th> 2 
      <th> 1 
     <tr>
      <th><small>Treat P2266 as a “Defect Report” against prior versions of C++ (i.e. not just C++23).</small>
      <th> 1 
      <th> 2 
      <th> 5 
      <th> 7 
      <th> 5 
   </table>
   <h2 class="heading settled" data-level="5" id="experience"><span class="secno">5. </span><span class="content">Implementation experience</span><a class="self-link" href="#experience"></a></h2>
   <p>
    In June 2021, P2266R1 was implemented as the default behavior in Clang’s 
    <tt>-std=c++2b</tt>
     mode. This was
shipped in the Clang 13 release (July 2021). We are aware of three pieces of industry code that broke
as a result of this change. All three have been treated as "dubious code, worth patching" and have been
patched already. These are the <em>only</em> three breakages we have seen from deployment of
Clang 13’s 
    <tt>-std=c++2b</tt>
     mode. See <a data-link-type="biblio" href="#biblio-fieldtesting">[FieldTesting]</a> for full details.
The executive summary of the three breakages is:
   </p>
   <h3 class="heading settled" data-level="5.1" id="exp-getline"><span class="secno">5.1. </span><span class="content">Microsoft’s rvalue <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>getline</c-></code></span><a class="self-link" href="#exp-getline"></a></h3>
<pre class="language-c++ highlight"><c- n>std</c-><c- o>::</c-><c- n>istream</c-><c- o>&amp;</c-> <c- n>getline</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>istream</c-><c- o>&amp;&amp;</c-> <c- n>in</c-><c- p>,</c-> <c- o>~~~</c-><c- p>)</c-> <c- p>{</c->
    <c- o>~~~</c->
    <c- k>return</c-> <c- n>in</c-><c- p>;</c->
<c- p>}</c->
</pre>
   <p><a href="https://github.com/microsoft/STL/pull/2025">was changed</a> to</p>
<pre class="language-c++ highlight"><c- n>std</c-><c- o>::</c-><c- n>istream</c-><c- o>&amp;</c-> <c- n>getline</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>istream</c-><c- o>&amp;&amp;</c-> <c- n>in</c-><c- p>,</c-> <c- o>~~~</c-><c- p>)</c-> <c- p>{</c->
    <c- o>~~~</c->
    <c- k>return</c-> <c- n>static_cast</c-><c- o>&lt;</c-><c- n>std</c-><c- o>::</c-><c- n>istream</c-><c- o>&amp;></c-><c- p>(</c-><c- n>in</c-><c- p>);</c->
<c- p>}</c->
</pre>
   <h3 class="heading settled" data-level="5.2" id="exp-ostring"><span class="secno">5.2. </span><span class="content">LibreOffice <code class="highlight"><c- n>OString</c-></code> constructor</span><a class="self-link" href="#exp-ostring"></a></h3>
   <p>This is a subtle one, but it boils down to the fact that</p>
<pre class="language-c++ highlight"><c- k>struct</c-> <c- nc>X</c-> <c- p>{</c->
    <c- n>X</c-><c- p>(</c-><c- k>auto</c-><c- o>&amp;</c-><c- p>);</c->
<c- p>};</c->

<c- n>X</c-> <c- nf>f</c-><c- p>()</c-> <c- p>{</c->
    <c- b>char</c-> <c- n>a</c-><c- p>[</c-><c- mi>10</c-><c- p>];</c->
    <c- k>return</c-> <c- n>a</c-><c- p>;</c->
<c- p>}</c->
</pre>
   <p>compiles in C++20 (deducing <code class="highlight"><c- n>X</c-><c- p>(</c-><c- b>char</c-> <c- p>(</c-><c- o>&amp;</c-><c- p>)[</c-><c- mi>10</c-><c- p>])</c-></code>) but not after P2266
(because the returned expression now has type <code class="highlight"><c- b>char</c-> <c- p>(</c-><c- o>&amp;&amp;</c-><c- p>)[</c-><c- mi>10</c-><c- p>]</c-></code>, which
cannot bind to <code class="highlight"><c- k>auto</c-><c- o>&amp;</c-></code>). The solution <a href="https://git.libreoffice.org/core/+/433ab39b2175bdadb4916373cd2dc8e1aabc08a5%5E%21">was to change it</a> by making the return convert explicitly rather than implicitly:</p>
<pre class="highlight"><c- n>X</c-> <c- nf>f</c-><c- p>()</c-> <c- p>{</c->
    <c- b>char</c-> <c- n>a</c-><c- p>[</c-><c- mi>10</c-><c- p>];</c->
    <c- k>return</c-> <c- n>X</c-><c- p>(</c-><c- n>a</c-><c- p>);</c->
<c- p>}</c->
</pre>
   <h3 class="heading settled" data-level="5.3" id="exp-o3tl"><span class="secno">5.3. </span><span class="content">LibreOffice <code class="highlight"><c- n>o3tl</c-><c- o>::</c-><c- n>temporary</c-></code></span><a class="self-link" href="#exp-o3tl"></a></h3>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>T</c-><c- o>></c->
<c- n>T</c-><c- o>&amp;</c-> <c- n>temporary</c-><c- p>(</c-><c- n>T</c-><c- o>&amp;&amp;</c-> <c- n>x</c-><c- p>)</c-> <c- p>{</c-> <c- k>return</c-> <c- n>x</c-><c- p>;</c-> <c- p>}</c->
</pre>
   <p><a href="https://git.libreoffice.org/core/+/21da7d80aa1ee0f9661dcde37bc4629d5eb9d50e%5E%21">was changed</a> to</p>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>T</c-><c- o>></c->
<c- n>T</c-><c- o>&amp;</c-> <c- n>temporary</c-><c- p>(</c-><c- n>T</c-><c- o>&amp;&amp;</c-> <c- n>x</c-><c- p>)</c-> <c- p>{</c-> <c- k>return</c-> <c- n>static_cast</c-><c- o>&lt;</c-><c- n>T</c-><c- o>&amp;></c-><c- p>(</c-><c- n>x</c-><c- p>);</c-> <c- p>}</c->
</pre>
   <h2 class="heading settled" data-level="6" id="wording"><span class="secno">6. </span><span class="content">Proposed wording relative to N4861</span><a class="self-link" href="#wording"></a></h2>
   <p>Consensus is that [class.copy.elision] is no longer the best place to explain
"implicit move."
We propose to move the wording from [class.copy.elision] to [expr.prim.id.unqual],
and introduce the term "move-eligible <em>id-expression</em>" for id-expressions that are xvalues.</p>
   <p>Modify <a href="https://timsong-cpp.github.io/cppwp/n4861/expr.prim.id.unqual#2">[expr.prim.id.unqual]/2</a> as follows:</p>
   <blockquote>
    <p>
     The expression is 
     <ins>an xvalue if it is move-eligible (see below);</ins>
      an lvalue if the entity is a function, variable, structured binding,
data member, or template parameter object
     <ins>;</ins>
      and a prvalue otherwise;
it is a bit-field if the identifier designates a bit-field.
    </p>
    <ins>An <em>implicitly movable entity</em> is a variable of automatic storage duration that is either
a non-volatile object or an rvalue reference to a non-volatile object type. In the following
contexts, an <em>id-expression</em> is <em>move-eligible</em>:</ins>
    <ul>
     <li data-md>
      <ins>If the <em>id-expression</em> (possibly parenthesized) is the operand of
a <code class="highlight"><c- k>return</c-></code> or <code class="highlight"><c- k>co_return</c-></code> statement, and
names an implicitly movable entity declared in the body or <em>parameter-declaration-clause</em> of the innermost enclosing function or <em>lambda-expression</em>, or</ins>
     <li data-md>
      <ins>
       if the <em>id-expression</em> (possibly parenthesized) is the operand of
a <em>throw-expression</em>, and
names an implicitly movable entity that belongs to a scope that does not contain the <em>compound-statement</em> of the innermost 
       <ins><em>lambda-expression</em>,</ins>
        <em>try-block</em> 
       <ins>,</ins>
        or <em>function-try-block</em> (if any)
whose <em>compound-statement</em> or <em>ctor-initializer</em> encloses the <em>throw-expression</em>.
      </ins>
    </ul>
   </blockquote>
   <p>Eliminate <a href="https://timsong-cpp.github.io/cppwp/n4861/class.copy.elision#3">[class.copy.elision]/3</a>:</p>
   <blockquote>
    <del>An <em>implicitly movable entity</em> is a variable of automatic storage duration that is either
a non-volatile object or an rvalue reference to a non-volatile object type. In the following copy-initialization
contexts, a move operation is first considered before attempting a copy
operation:</del>
    <ul>
     <li data-md>
      <del>If the <em>expression</em> in
a <code class="highlight"><c- k>return</c-></code> or <code class="highlight"><c- k>co_return</c-></code> statement is a (possibly parenthesized) <em>id-expression</em> that names an implicitly movable entity declared in the body or <em>parameter-declaration-clause</em> of the innermost enclosing function or <em>lambda-expression</em>, or</del>
     <li data-md>
      <del>if the operand of a <em>throw-expression</em> is a (possibly parenthesized) <em>id-expression</em> that names an implicitly movable entity that belongs to a scope that does not contain the <em>compound-statement</em> of the innermost <em>try-block</em> or <em>function-try-block</em> (if any)
whose <em>compound-statement</em> or <em>ctor-initializer</em> encloses the <em>throw-expression</em>,</del>
    </ul>
    <del>overload resolution to select the constructor for the copy or the <code class="highlight"><c- n>return_value</c-></code> overload to call is first performed as if the expression or operand were an rvalue.
If the first overload resolution fails or was not performed, overload resolution
is performed again, considering the expression or operand as an lvalue.</del>
    <del>[<em>Note 3:</em> This two-stage overload resolution is performed
regardless of whether copy elision will occur. It determines the constructor
or the <code class="highlight"><c- n>return_value</c-></code> overload to be called if elision is not performed,
and the selected constructor or <code class="highlight"><c- n>return_value</c-></code> overload
must be accessible even if the call is elided. — <em>end note</em>]</del>
   </blockquote>
   <p>Also change the definition of <code class="highlight"><c- n>g</c-><c- p>()</c-></code> in <a href="https://timsong-cpp.github.io/cppwp/n4861/class.copy.elision#4">[class.copy.elision]/4</a>:</p>
   <p><small></small></p>
   <blockquote>
    <p></p>
    <small> <pre class="highlight"><c- k>struct</c-> <c- nc>Weird</c-> <c- p>{</c->
  <c- n>Weird</c-><c- p>();</c->
  <c- n>Weird</c-><c- p>(</c-><c- n>Weird</c-><c- o>&amp;</c-><c- p>);</c->
<c- p>};</c->

<del><c- n>Weird</c-> <c- nf>g</c-><c- p>()</c-> <c- p>{</c-></del>
  <del><c- n>Weird</c-> <c- n>w</c-><c- p>;</c-></del>
  <del><c- k>return</c-> <c- n>w</c-><c- p>;</c->  <c- c1>// OK: first overload resolution fails, second overload resolution selects Weird(Weird&amp;)</c-></del>
<del><c- p>}</c-></del>
<ins><c- n>Weird</c-> <c- nf>g</c-><c- p>(</c-><c- b>bool</c-> <c- n>b</c-><c- p>)</c-> <c- p>{</c-></ins>
  <ins><c- k>static</c-> <c- n>Weird</c-> <c- n>w1</c-><c- p>;</c-></ins>
  <ins><c- n>Weird</c-> <c- n>w2</c-><c- p>;</c-></ins>
  <ins><c- k>if</c-> <c- p>(</c-><c- n>b</c-><c- p>)</c-> <c- p>{</c-></ins>
    <ins><c- k>return</c-> <c- n>w1</c-><c- p>;</c->  <c- c1>// OK: Weird(Weird&amp;)</c-></ins>
  <ins><c- p>}</c-> <c- k>else</c-> <c- p>{</c-></ins>
    <ins><c- k>return</c-> <c- n>w2</c-><c- p>;</c->  <c- c1>// error: w2 in this context is an xvalue</c-></ins>
  <ins><c- p>}</c-></ins>
<ins><c- p>}</c-></ins>
</pre></small>
   </blockquote>
   <p>Add a feature-test macro in <a href="https://timsong-cpp.github.io/cppwp/n4861/cpp.predefined#tab:cpp.predefined.ft">[cpp.predefined]</a>:</p>
   <blockquote>
<pre class="highlight"><ins><c- n>__cpp_implicit_move</c->     <i><c- n>DATE</c-><c- o>-</c-><c- n>OF</c-><c- o>-</c-><c- n>ADOPTION</c-></i></ins></pre>
   </blockquote>
   <h3 class="heading settled" data-level="6.1" id="wording-nn"><span class="secno">6.1. </span><span class="content">Non-normative clarifications</span><a class="self-link" href="#wording-nn"></a></h3>
   <p>Modify <a href="https://timsong-cpp.github.io/cppwp/n4861/basic.lval#4">[basic.lval]/4</a> as follows:</p>
   <blockquote>
     [<em>Note:</em> An expression is an xvalue if it is: 
    <ul>
     <li data-md>
      <ins>a move-eligible <i>id-expression</i> ([expr.prim.id.unqual]),</ins>
     <li data-md>
      <p>the result of calling a function, whether implicitly or explicitly, whose return type is an rvalue reference to object type,</p>
     <li data-md>
      <p>a cast to an rvalue reference to object type,</p>
     <li data-md>
      <p>a subscripting operation with an xvalue array operand,</p>
     <li data-md>
      <p>a class member access expression designating a non-static data member of non-reference type in which the object expression is an xvalue, or</p>
     <li data-md>
      <p>a <code class="highlight"><c- p>.</c-><c- o>*</c-></code> pointer-to-member expression in which the first operand is an xvalue and the second operand is a pointer to data member.</p>
    </ul>
    <p>In general, the effect of this rule is that named rvalue references are treated as lvalues and unnamed rvalue references to objects
are treated as xvalues; rvalue references to functions are treated as lvalues whether named or not. — <em>end note</em>]</p>
   </blockquote>
   <p>Modify <a href="https://timsong-cpp.github.io/cppwp/n4861/dcl.type.auto.deduct#5">[dcl.type.auto.deduct]/5</a> as follows:</p>
   <blockquote>
     If the <em>placeholder-type-specifier</em> is of the form <i>type-constraint<sub>opt</sub></i> <code class="highlight"><c- k>decltype</c-><c- p>(</c-><c- k>auto</c-><c- p>)</c-></code>, <code class="highlight"><c- n>T</c-></code> shall be the placeholder alone. The type deduced for <code class="highlight"><c- n>T</c-></code> is determined as described in [dcl.type.decltype],
as though <em>E</em> had been the operand of the <code class="highlight"><c- k>decltype</c-></code>. 
    <ins>[<em>Example:</em></ins>
     <small><pre class="highlight">    <ins><c- k>auto</c-> <c- nf>f</c-><c- p>(</c-><c- b>int</c-> <c- n>x</c-><c- p>)</c-> <c- o>-></c-> <c- k>decltype</c-><c- p>((</c-><c- n>x</c-><c- p>))</c-> <c- p>{</c-> <c- k>return</c-> <c- p>(</c-><c- n>x</c-><c- p>);</c-> <c- p>}</c->   <c- c1>// return type is "int&amp;"</c-></ins>
    <ins><c- k>auto</c-> <c- nf>g</c-><c- p>(</c-><c- b>int</c-> <c- n>x</c-><c- p>)</c-> <c- o>-></c-> <c- k>decltype</c-><c- p>(</c-><c- k>auto</c-><c- p>)</c-> <c- p>{</c-> <c- k>return</c-> <c- p>(</c-><c- n>x</c-><c- p>);</c-> <c- p>}</c->  <c- c1>// return type is "int&amp;&amp;"</c-></ins>
</pre></small> 
    <ins>— <em>end example</em>]</ins>
   </blockquote>
   <p>Add yet more examples to <a href="https://timsong-cpp.github.io/cppwp/n4861/class.copy.elision#4">[class.copy.elision]/4</a>,
showing how the new wording affects functions that return references:</p>
   <p><small></small></p>
   <blockquote>
    <p></p>
    <small> <pre class="highlight"><ins><c- b>int</c-><c- o>&amp;</c-> <c- nf>h</c-><c- p>(</c-><c- b>bool</c-> <c- n>b</c-><c- p>,</c-> <c- b>int</c-> <c- n>i</c-><c- p>)</c-> <c- p>{</c-></ins>
  <ins><c- k>static</c-> <c- b>int</c-> <c- n>s</c-><c- p>;</c-></ins>
  <ins><c- k>if</c-> <c- p>(</c-><c- n>b</c-><c- p>)</c-> <c- p>{</c-></ins>
    <ins><c- k>return</c-> <c- n>s</c-><c- p>;</c->  <c- c1>// OK</c-></ins>
  <ins><c- p>}</c-> <c- k>else</c-> <c- p>{</c-></ins>
    <ins><c- k>return</c-> <c- n>i</c-><c- p>;</c->  <c- c1>// error: i is an xvalue</c-></ins>
  <ins><c- p>}</c-></ins>
<ins><c- p>}</c-></ins>

<ins><c- k>decltype</c-><c- p>(</c-><c- k>auto</c-><c- p>)</c-> <c- n>h2</c-><c- p>(</c-><c- n>Thing</c-> <c- n>t</c-><c- p>)</c-> <c- p>{</c-></ins>
  <ins><c- k>return</c-> <c- n>t</c-><c- p>;</c->  <c- c1>// OK: t is an xvalue and h2’s return type is Thing</c-></ins>
<ins><c- p>}</c-></ins>

<ins><c- k>decltype</c-><c- p>(</c-><c- k>auto</c-><c- p>)</c-> <c- n>h3</c-><c- p>(</c-><c- n>Thing</c-> <c- n>t</c-><c- p>)</c-> <c- p>{</c-></ins>
  <ins><c- k>return</c-> <c- p>(</c-><c- n>t</c-><c- p>);</c->  <c- c1>// OK: (t) is an xvalue and h3’s return type is Thing&amp;&amp;</c-></ins>
<ins><c- p>}</c-></ins>
</pre></small>
   </blockquote>
   <p>Add a note after <a href="https://timsong-cpp.github.io/cppwp/n4861/dcl.init#ref-5.4.4">[dcl.init.ref]/5.4.4</a>:</p>
   <blockquote>
    <p>if the reference is an rvalue reference, the initializer expression shall not be an lvalue.</p>
    <ins>[<em>Note:</em> This can be affected by whether the initializer expression
is move-eligible ([expr.prim.id.unqual]). — <em>end note</em>]</ins>
   </blockquote>
   <h2 class="heading settled" data-level="7" id="acknowledgments"><span class="secno">7. </span><span class="content">Acknowledgments</span><a class="self-link" href="#acknowledgments"></a></h2>
   <ul>
    <li data-md>
     <p>Thanks to Ville Voutilainen for recommending Arthur write this paper.</p>
    <li data-md>
     <p>Thanks to Aaron Puchert for inspiring <code class="highlight"><c- n>fourteen</c-></code> via his comments on <a data-link-type="biblio" href="#biblio-d68845">[D68845]</a>.</p>
    <li data-md>
     <p>Thanks to Richard Smith and Jens Maurer for their feedback, and to Jens for proposing the term "move-eligible."</p>
   </ul>
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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-corereflector">[CoreReflector]
   <dd>CWG internal email discussion. <a href="https://lists.isocpp.org/core/2020/02/8455.php"><cite>[isocpp-core] P1825 (more implicit moves) surprise</cite></a>. February 2020. URL: <a href="https://lists.isocpp.org/core/2020/02/8455.php">https://lists.isocpp.org/core/2020/02/8455.php</a>
   <dt id="biblio-cwg1579">[CWG1579]
   <dd>Jeffrey Yasskin. <a href="http://open-std.org/JTC1/SC22/WG21/docs/cwg_defects.html#1579"><cite>Return by converting move constructor</cite></a>. October 2012. URL: <a href="http://open-std.org/JTC1/SC22/WG21/docs/cwg_defects.html#1579">http://open-std.org/JTC1/SC22/WG21/docs/cwg_defects.html#1579</a>
   <dt id="biblio-d68845">[D68845]
   <dd>Aaron Puchert. <a href="https://reviews.llvm.org/D68845"><cite>Don't emit unwanted constructor calls in co_return statements</cite></a>. October 2019. URL: <a href="https://reviews.llvm.org/D68845">https://reviews.llvm.org/D68845</a>
   <dt id="biblio-d92936">[D92936]
   <dd>Yang Fan. <a href="https://reviews.llvm.org/D92936"><cite>[Sema] Fix deleted function problem in implicitly movable test</cite></a>. December 2020. URL: <a href="https://reviews.llvm.org/D92936">https://reviews.llvm.org/D92936</a>
   <dt id="biblio-d99005">[D99005]
   <dd>Matheus Izvekov. <a href="https://reviews.llvm.org/D99005"><cite>[clang] Implement P2266 Simpler implicit move</cite></a>. March 2021. URL: <a href="https://reviews.llvm.org/D99005">https://reviews.llvm.org/D99005</a>
   <dt id="biblio-fieldtesting">[FieldTesting]
   <dd>Arthur O'Dwyer. <a href="https://quuxplusone.github.io/blog/2021/08/07/p2266-field-test-results/"><cite>Field-testing P2266 'Simpler Implicit Move'</cite></a>. August 2021. URL: <a href="https://quuxplusone.github.io/blog/2021/08/07/p2266-field-test-results/">https://quuxplusone.github.io/blog/2021/08/07/p2266-field-test-results/</a>
   <dt id="biblio-lwg2993">[LWG2993]
   <dd>Tim Song. <a href="https://cplusplus.github.io/LWG/issue2993"><cite>reference_wrapper&lt;T> conversion from T&amp;&amp;</cite></a>. November 2017. URL: <a href="https://cplusplus.github.io/LWG/issue2993">https://cplusplus.github.io/LWG/issue2993</a>
   <dt id="biblio-p0527">[P0527]
   <dd>David Stone. <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0527r1.html"><cite>Implicitly move from rvalue references in return statements</cite></a>. November 2017. URL: <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0527r1.html">http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0527r1.html</a>
   <dt id="biblio-p1155">[P1155]
   <dd>Arthur O'Dwyer; David Stone. <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1155r3.html"><cite>More implicit moves</cite></a>. June 2019. URL: <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1155r3.html">http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1155r3.html</a>
   <dt id="biblio-p1825">[P1825]
   <dd>David Stone. <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1825r0.html"><cite>Merged wording for P0527R1 and P1155R3</cite></a>. July 2019. URL: <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1825r0.html">http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1825r0.html</a>
  </dl>