<!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>P3055R0: Relax wording to permit relocation optimizations in the STL</title>
<style data-fill-with="stylesheet">/******************************************************************************
 *                   Style sheet for the W3C specifications                   *
 *
 * Special classes handled by this style sheet include:
 *
 * Indices
 *   - .toc for the Table of Contents (<ol class="toc">)
 *     + <span class="secno"> for the section numbers
 *   - #toc for the Table of Contents (<nav id="toc">)
 *   - ul.index for Indices (<a href="#ref">term</a><span>, in § N.M</span>)
 *   - table.index for Index Tables (e.g. for properties or elements)
 *
 * Structural Markup
 *   - table.data for general data tables
 *     -> use 'scope' attribute, <colgroup>, <thead>, and <tbody> for best results !
 *     -> use <table class='complex data'> for extra-complex tables
 *     -> use <td class='long'> for paragraph-length cell content
 *     -> use <td class='pre'> when manual line breaks/indentation would help readability
 *   - dl.switch for switch statements
 *   - ol.algorithm for algorithms (helps to visualize nesting)
 *   - .figure and .caption (HTML4) and figure and figcaption (HTML5)
 *     -> .sidefigure for right-floated figures
 *   - ins/del
 *     -> ins/del.c### for candidate and proposed changes (amendments)
 *
 * Code
 *   - pre and code
 *
 * Special Sections
 *   - .note       for informative notes             (div, p, span, aside, details)
 *   - .example    for informative examples          (div, p, pre, span)
 *   - .issue      for issues                        (div, p, span)
 *   - .advisement for loud normative statements     (div, p, strong)
 *   - .annoying-warning for spec obsoletion notices (div, aside, details)
 *   - .correction for "candidate corrections"       (div, aside, details, section)
 *   - .addition   for "candidate additions"         (div, aside, details, section)
 *   - .correction.proposed for "proposed corrections" (div, aside, details, section)
 *   - .addition.proposed   for "proposed additions"   (div, aside, details, section)
 *
 * Definition Boxes
 *   - pre.def   for WebIDL definitions
 *   - table.def for tables that define other entities (e.g. CSS properties)
 *   - dl.def    for definition lists that define other entitles (e.g. HTML elements)
 *
 * Numbering
 *   - .secno for section numbers in .toc and headings (<span class='secno'>3.2</span>)
 *   - .marker for source-inserted example/figure/issue numbers (<span class='marker'>Issue 4</span>)
 *   - ::before styled for CSS-generated issue/example/figure numbers:
 *     -> Documents wishing to use this only need to add
 *        figcaption::before,
 *        .caption::before { content: "Figure "  counter(figure) " ";  }
 *        .example::before { content: "Example " counter(example) " "; }
 *        .issue::before   { content: "Issue "   counter(issue) " ";   }
 *
 * Header Stuff (ignore, just don't conflict with these classes)
 *   - .head for the header
 *   - .copyright for the copyright
 *
 * Outdated warning for old specs
 *
 * Miscellaneous
 *   - .overlarge for things that should be as wide as possible, even if
 *     that overflows the body text area. This can be used on an item or
 *     on its container, depending on the effect desired.
 *     Note that this styling basically doesn't help at all when printing,
 *     since A4 paper isn't much wider than the max-width here.
 *     It's better to design things to fit into a narrower measure if possible.
 *
 *   - js-added ToC jump links (see fixup.js)
 *
 ******************************************************************************/

/* color variables included separately for reliability */

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

	html {
	}

	body {
		counter-reset: example figure issue;

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

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

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


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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

	p {
		margin: 1em 0;
	}

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

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

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

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

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

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

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

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

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


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

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

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

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

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

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

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

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

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

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

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

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

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

	/* Do something nice. */

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

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

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

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

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

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

	img {
		border-style: none;
	}

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

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

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

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

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

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

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


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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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


/*
Alternate table alignment rules

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

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

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

Possible extra rowspan handling

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

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

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


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

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

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

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

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

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

		.toc li {
			clear: both;
		}

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

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

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


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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

.outdated-warning span {
	display: block;
}

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

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

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

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

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



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

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

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

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

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

    del { background: #fcc; color: #000; text-decoration: line-through; }
    ins { background: #cfc; color: #000; }
    blockquote .highlight:not(.idl) { background: initial; margin: initial; padding: 0.5em }
    blockquote ul { background: inherit; }
    blockquote code.highlight:not(.idl) { padding: initial; }
    blockquote c-[a] { color: inherit; } /* Keyword.Declaration */
    blockquote c-[b] { color: inherit; } /* Keyword.Type */
    blockquote c-[c] { color: inherit; } /* Comment */
    blockquote c-[d] { color: inherit; } /* Comment.Multiline */
    blockquote c-[e] { color: inherit; } /* Name.Attribute */
    blockquote c-[f] { color: inherit; } /* Name.Tag */
    blockquote c-[g] { color: inherit; } /* Name.Variable */
    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 82ce88815, updated Thu Sep 7 16:33:55 2023 -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>
<style>/* Boilerplate: style-autolinks */
.css.css, .property.property, .descriptor.descriptor {
    color: var(--a-normal-text);
    font-size: inherit;
    font-family: inherit;
}
.css::before, .property::before, .descriptor::before {
    content: "‘";
}
.css::after, .property::after, .descriptor::after {
    content: "’";
}
.property, .descriptor {
    /* Don't wrap property and descriptor names */
    white-space: nowrap;
}
.type { /* CSS value <type> */
    font-style: italic;
}
pre .property::before, pre .property::after {
    content: "";
}
[data-link-type="property"]::before,
[data-link-type="propdesc"]::before,
[data-link-type="descriptor"]::before,
[data-link-type="value"]::before,
[data-link-type="function"]::before,
[data-link-type="at-rule"]::before,
[data-link-type="selector"]::before,
[data-link-type="maybe"]::before {
    content: "‘";
}
[data-link-type="property"]::after,
[data-link-type="propdesc"]::after,
[data-link-type="descriptor"]::after,
[data-link-type="value"]::after,
[data-link-type="function"]::after,
[data-link-type="at-rule"]::after,
[data-link-type="selector"]::after,
[data-link-type="maybe"]::after {
    content: "’";
}

[data-link-type].production::before,
[data-link-type].production::after,
.prod [data-link-type]::before,
.prod [data-link-type]::after {
    content: "";
}

[data-link-type=element],
[data-link-type=element-attr] {
    font-family: Menlo, Consolas, "DejaVu Sans Mono", monospace;
    font-size: .9em;
}
[data-link-type=element]::before { content: "<" }
[data-link-type=element]::after  { content: ">" }

[data-link-type=biblio] {
    white-space: pre;
}

@media (prefers-color-scheme: dark) {
    :root {
        --selflink-text: black;
        --selflink-bg: silver;
        --selflink-hover-text: white;
    }
}
</style>
<style>/* Boilerplate: style-colors */

/* Any --*-text not paired with a --*-bg is assumed to have a transparent bg */
:root {
    color-scheme: light dark;

    --text: black;
    --bg: white;

    --unofficial-watermark: url(https://www.w3.org/StyleSheets/TR/2016/logos/UD-watermark);

    --logo-bg: #1a5e9a;
    --logo-active-bg: #c00;
    --logo-text: white;

    --tocnav-normal-text: #707070;
    --tocnav-normal-bg: var(--bg);
    --tocnav-hover-text: var(--tocnav-normal-text);
    --tocnav-hover-bg: #f8f8f8;
    --tocnav-active-text: #c00;
    --tocnav-active-bg: var(--tocnav-normal-bg);

    --tocsidebar-text: var(--text);
    --tocsidebar-bg: #f7f8f9;
    --tocsidebar-shadow: rgba(0,0,0,.1);
    --tocsidebar-heading-text: hsla(203,20%,40%,.7);

    --toclink-text: var(--text);
    --toclink-underline: #3980b5;
    --toclink-visited-text: var(--toclink-text);
    --toclink-visited-underline: #054572;

    --heading-text: #005a9c;

    --hr-text: var(--text);

    --algo-border: #def;

    --del-text: red;
    --del-bg: transparent;
    --ins-text: #080;
    --ins-bg: transparent;

    --a-normal-text: #034575;
    --a-normal-underline: #bbb;
    --a-visited-text: var(--a-normal-text);
    --a-visited-underline: #707070;
    --a-hover-bg: rgba(75%, 75%, 75%, .25);
    --a-active-text: #c00;
    --a-active-underline: #c00;

    --blockquote-border: silver;
    --blockquote-bg: transparent;
    --blockquote-text: currentcolor;

    --issue-border: #e05252;
    --issue-bg: #fbe9e9;
    --issue-text: var(--text);
    --issueheading-text: #831616;

    --example-border: #e0cb52;
    --example-bg: #fcfaee;
    --example-text: var(--text);
    --exampleheading-text: #574b0f;

    --note-border: #52e052;
    --note-bg: #e9fbe9;
    --note-text: var(--text);
    --noteheading-text: hsl(120, 70%, 30%);
    --notesummary-underline: silver;

    --assertion-border: #aaa;
    --assertion-bg: #eee;
    --assertion-text: black;

    --advisement-border: orange;
    --advisement-bg: #fec;
    --advisement-text: var(--text);
    --advisementheading-text: #b35f00;

    --warning-border: red;
    --warning-bg: hsla(40,100%,50%,0.95);
    --warning-text: var(--text);

    --amendment-border: #330099;
    --amendment-bg: #F5F0FF;
    --amendment-text: var(--text);
    --amendmentheading-text: #220066;

    --def-border: #8ccbf2;
    --def-bg: #def;
    --def-text: var(--text);
    --defrow-border: #bbd7e9;

    --datacell-border: silver;

    --indexinfo-text: #707070;

    --indextable-hover-text: black;
    --indextable-hover-bg: #f7f8f9;

    --outdatedspec-bg: rgba(0, 0, 0, .5);
    --outdatedspec-text: black;
    --outdated-bg: maroon;
    --outdated-text: white;
    --outdated-shadow: red;

    --editedrec-bg: darkorange;
}

@media (prefers-color-scheme: dark) {
    :root {
        --text: #ddd;
        --bg: black;

        --unofficial-watermark: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='400' height='400'%3E%3Cg fill='%23100808' transform='translate(200 200) rotate(-45) translate(-200 -200)' stroke='%23100808' stroke-width='3'%3E%3Ctext x='50%25' y='220' style='font: bold 70px sans-serif; text-anchor: middle; letter-spacing: 6px;'%3EUNOFFICIAL%3C/text%3E%3Ctext x='50%25' y='305' style='font: bold 70px sans-serif; text-anchor: middle; letter-spacing: 6px;'%3EDRAFT%3C/text%3E%3C/g%3E%3C/svg%3E");

        --logo-bg: #1a5e9a;
        --logo-active-bg: #c00;
        --logo-text: white;

        --tocnav-normal-text: #999;
        --tocnav-normal-bg: var(--bg);
        --tocnav-hover-text: var(--tocnav-normal-text);
        --tocnav-hover-bg: #080808;
        --tocnav-active-text: #f44;
        --tocnav-active-bg: var(--tocnav-normal-bg);

        --tocsidebar-text: var(--text);
        --tocsidebar-bg: #080808;
        --tocsidebar-shadow: rgba(255,255,255,.1);
        --tocsidebar-heading-text: hsla(203,20%,40%,.7);

        --toclink-text: var(--text);
        --toclink-underline: #6af;
        --toclink-visited-text: var(--toclink-text);
        --toclink-visited-underline: #054572;

        --heading-text: #8af;

        --hr-text: var(--text);

        --algo-border: #456;

        --del-text: #f44;
        --del-bg: transparent;
        --ins-text: #4a4;
        --ins-bg: transparent;

        --a-normal-text: #6af;
        --a-normal-underline: #555;
        --a-visited-text: var(--a-normal-text);
        --a-visited-underline: var(--a-normal-underline);
        --a-hover-bg: rgba(25%, 25%, 25%, .2);
        --a-active-text: #f44;
        --a-active-underline: var(--a-active-text);

        --borderedblock-bg: rgba(255, 255, 255, .05);

        --blockquote-border: silver;
        --blockquote-bg: var(--borderedblock-bg);
        --blockquote-text: currentcolor;

        --issue-border: #e05252;
        --issue-bg: var(--borderedblock-bg);
        --issue-text: var(--text);
        --issueheading-text: hsl(0deg, 70%, 70%);

        --example-border: hsl(50deg, 90%, 60%);
        --example-bg: var(--borderedblock-bg);
        --example-text: var(--text);
        --exampleheading-text: hsl(50deg, 70%, 70%);

        --note-border: hsl(120deg, 100%, 35%);
        --note-bg: var(--borderedblock-bg);
        --note-text: var(--text);
        --noteheading-text: hsl(120, 70%, 70%);
        --notesummary-underline: silver;

        --assertion-border: #444;
        --assertion-bg: var(--borderedblock-bg);
        --assertion-text: var(--text);

        --advisement-border: orange;
        --advisement-bg: #222218;
        --advisement-text: var(--text);
        --advisementheading-text: #f84;

        --warning-border: red;
        --warning-bg: hsla(40,100%,20%,0.95);
        --warning-text: var(--text);

        --amendment-border: #330099;
        --amendment-bg: #080010;
        --amendment-text: var(--text);
        --amendmentheading-text: #cc00ff;

        --def-border: #8ccbf2;
        --def-bg: #080818;
        --def-text: var(--text);
        --defrow-border: #136;

        --datacell-border: silver;

        --indexinfo-text: #aaa;

        --indextable-hover-text: var(--text);
        --indextable-hover-bg: #181818;

        --outdatedspec-bg: rgba(255, 255, 255, .5);
        --outdatedspec-text: black;
        --outdated-bg: maroon;
        --outdated-text: white;
        --outdated-shadow: red;

        --editedrec-bg: darkorange;
    }
    /* In case a transparent-bg image doesn't expect to be on a dark bg,
       which is quite common in practice... */
    img { background: white; }
}
</style>
<style>/* Boilerplate: style-counters */
body {
    counter-reset: example figure issue;
}
.issue {
    counter-increment: issue;
}
.issue:not(.no-marker)::before {
    content: "Issue " counter(issue);
}

.example {
    counter-increment: example;
}
.example:not(.no-marker)::before {
    content: "Example " counter(example);
}
.invalid.example:not(.no-marker)::before,
.illegal.example:not(.no-marker)::before {
    content: "Invalid Example" counter(example);
}

figcaption {
    counter-increment: figure;
}
figcaption:not(.no-marker)::before {
    content: "Figure " counter(figure) " ";
}
</style>
<style>/* Boilerplate: style-issues */
a[href].issue-return {
    float: right;
    float: inline-end;
    color: var(--issueheading-text);
    font-weight: bold;
    text-decoration: none;
}
</style>
<style>/* Boilerplate: style-md-lists */
/* This is a weird hack for me not yet following the commonmark spec
   regarding paragraph and lists. */
[data-md] > :first-child {
    margin-top: 0;
}
[data-md] > :last-child {
    margin-bottom: 0;
}
</style>
<style>/* Boilerplate: style-selflinks */

:root {
    --selflink-text: white;
    --selflink-bg: gray;
    --selflink-hover-text: black;
}
.heading, .issue, .note, .example, li, dt {
    position: relative;
}
a.self-link {
    position: absolute;
    top: 0;
    left: calc(-1 * (3.5rem - 26px));
    width: calc(3.5rem - 26px);
    height: 2em;
    text-align: center;
    border: none;
    transition: opacity .2s;
    opacity: .5;
}
a.self-link:hover {
    opacity: 1;
}
.heading > a.self-link {
    font-size: 83%;
}
.example > a.self-link,
.note > a.self-link,
.issue > a.self-link {
    /* These blocks are overflow:auto, so positioning outside
       doesn't work. */
    left: auto;
    right: 0;
}
li > a.self-link {
    left: calc(-1 * (3.5rem - 26px) - 2em);
}
dfn > a.self-link {
    top: auto;
    left: auto;
    opacity: 0;
    width: 1.5em;
    height: 1.5em;
    background: var(--selflink-bg);
    color: var(--selflink-text);
    font-style: normal;
    transition: opacity .2s, background-color .2s, color .2s;
}
dfn:hover > a.self-link {
    opacity: 1;
}
dfn > a.self-link:hover {
    color: var(--selflink-hover-text);
}

a.self-link::before            { content: "¶"; }
.heading > a.self-link::before { content: "§"; }
dfn > a.self-link::before      { content: "#"; }
</style>
<style>/* Boilerplate: style-syntax-highlighting */

code.highlight { padding: .1em; border-radius: .3em; }
pre.highlight, pre > code.highlight { display: block; padding: 1em; margin: .5em 0; overflow: auto; border-radius: 0; }

.highlight:not(.idl) { background: rgba(0, 0, 0, .03); }
c-[a] { color: #990055 } /* Keyword.Declaration */
c-[b] { color: #990055 } /* Keyword.Type */
c-[c] { color: #708090 } /* Comment */
c-[d] { color: #708090 } /* Comment.Multiline */
c-[e] { color: #0077aa } /* Name.Attribute */
c-[f] { color: #669900 } /* Name.Tag */
c-[g] { color: #222222 } /* Name.Variable */
c-[k] { color: #990055 } /* Keyword */
c-[l] { color: #000000 } /* Literal */
c-[m] { color: #000000 } /* Literal.Number */
c-[n] { color: #0077aa } /* Name */
c-[o] { color: #999999 } /* Operator */
c-[p] { color: #999999 } /* Punctuation */
c-[s] { color: #a67f59 } /* Literal.String */
c-[t] { color: #a67f59 } /* Literal.String.Single */
c-[u] { color: #a67f59 } /* Literal.String.Double */
c-[cp] { color: #708090 } /* Comment.Preproc */
c-[c1] { color: #708090 } /* Comment.Single */
c-[cs] { color: #708090 } /* Comment.Special */
c-[kc] { color: #990055 } /* Keyword.Constant */
c-[kn] { color: #990055 } /* Keyword.Namespace */
c-[kp] { color: #990055 } /* Keyword.Pseudo */
c-[kr] { color: #990055 } /* Keyword.Reserved */
c-[ld] { color: #000000 } /* Literal.Date */
c-[nc] { color: #0077aa } /* Name.Class */
c-[no] { color: #0077aa } /* Name.Constant */
c-[nd] { color: #0077aa } /* Name.Decorator */
c-[ni] { color: #0077aa } /* Name.Entity */
c-[ne] { color: #0077aa } /* Name.Exception */
c-[nf] { color: #0077aa } /* Name.Function */
c-[nl] { color: #0077aa } /* Name.Label */
c-[nn] { color: #0077aa } /* Name.Namespace */
c-[py] { color: #0077aa } /* Name.Property */
c-[ow] { color: #999999 } /* Operator.Word */
c-[mb] { color: #000000 } /* Literal.Number.Bin */
c-[mf] { color: #000000 } /* Literal.Number.Float */
c-[mh] { color: #000000 } /* Literal.Number.Hex */
c-[mi] { color: #000000 } /* Literal.Number.Integer */
c-[mo] { color: #000000 } /* Literal.Number.Oct */
c-[sb] { color: #a67f59 } /* Literal.String.Backtick */
c-[sc] { color: #a67f59 } /* Literal.String.Char */
c-[sd] { color: #a67f59 } /* Literal.String.Doc */
c-[se] { color: #a67f59 } /* Literal.String.Escape */
c-[sh] { color: #a67f59 } /* Literal.String.Heredoc */
c-[si] { color: #a67f59 } /* Literal.String.Interpol */
c-[sx] { color: #a67f59 } /* Literal.String.Other */
c-[sr] { color: #a67f59 } /* Literal.String.Regex */
c-[ss] { color: #a67f59 } /* Literal.String.Symbol */
c-[vc] { color: #0077aa } /* Name.Variable.Class */
c-[vg] { color: #0077aa } /* Name.Variable.Global */
c-[vi] { color: #0077aa } /* Name.Variable.Instance */
c-[il] { color: #000000 } /* Literal.Number.Integer.Long */


@media (prefers-color-scheme: dark) {
    .highlight:not(.idl) { background: rgba(255, 255, 255, .05); }

    c-[a] { color: #d33682 } /* Keyword.Declaration */
    c-[b] { color: #d33682 } /* Keyword.Type */
    c-[c] { color: #2aa198 } /* Comment */
    c-[d] { color: #2aa198 } /* Comment.Multiline */
    c-[e] { color: #268bd2 } /* Name.Attribute */
    c-[f] { color: #b58900 } /* Name.Tag */
    c-[g] { color: #cb4b16 } /* Name.Variable */
    c-[k] { color: #d33682 } /* Keyword */
    c-[l] { color: #657b83 } /* Literal */
    c-[m] { color: #657b83 } /* Literal.Number */
    c-[n] { color: #268bd2 } /* Name */
    c-[o] { color: #657b83 } /* Operator */
    c-[p] { color: #657b83 } /* Punctuation */
    c-[s] { color: #6c71c4 } /* Literal.String */
    c-[t] { color: #6c71c4 } /* Literal.String.Single */
    c-[u] { color: #6c71c4 } /* Literal.String.Double */
    c-[ch] { color: #2aa198 } /* Comment.Hashbang */
    c-[cp] { color: #2aa198 } /* Comment.Preproc */
    c-[cpf] { color: #2aa198 } /* Comment.PreprocFile */
    c-[c1] { color: #2aa198 } /* Comment.Single */
    c-[cs] { color: #2aa198 } /* Comment.Special */
    c-[kc] { color: #d33682 } /* Keyword.Constant */
    c-[kn] { color: #d33682 } /* Keyword.Namespace */
    c-[kp] { color: #d33682 } /* Keyword.Pseudo */
    c-[kr] { color: #d33682 } /* Keyword.Reserved */
    c-[ld] { color: #657b83 } /* Literal.Date */
    c-[nc] { color: #268bd2 } /* Name.Class */
    c-[no] { color: #268bd2 } /* Name.Constant */
    c-[nd] { color: #268bd2 } /* Name.Decorator */
    c-[ni] { color: #268bd2 } /* Name.Entity */
    c-[ne] { color: #268bd2 } /* Name.Exception */
    c-[nf] { color: #268bd2 } /* Name.Function */
    c-[nl] { color: #268bd2 } /* Name.Label */
    c-[nn] { color: #268bd2 } /* Name.Namespace */
    c-[py] { color: #268bd2 } /* Name.Property */
    c-[ow] { color: #657b83 } /* Operator.Word */
    c-[mb] { color: #657b83 } /* Literal.Number.Bin */
    c-[mf] { color: #657b83 } /* Literal.Number.Float */
    c-[mh] { color: #657b83 } /* Literal.Number.Hex */
    c-[mi] { color: #657b83 } /* Literal.Number.Integer */
    c-[mo] { color: #657b83 } /* Literal.Number.Oct */
    c-[sa] { color: #6c71c4 } /* Literal.String.Affix */
    c-[sb] { color: #6c71c4 } /* Literal.String.Backtick */
    c-[sc] { color: #6c71c4 } /* Literal.String.Char */
    c-[dl] { color: #6c71c4 } /* Literal.String.Delimiter */
    c-[sd] { color: #6c71c4 } /* Literal.String.Doc */
    c-[se] { color: #6c71c4 } /* Literal.String.Escape */
    c-[sh] { color: #6c71c4 } /* Literal.String.Heredoc */
    c-[si] { color: #6c71c4 } /* Literal.String.Interpol */
    c-[sx] { color: #6c71c4 } /* Literal.String.Other */
    c-[sr] { color: #6c71c4 } /* Literal.String.Regex */
    c-[ss] { color: #6c71c4 } /* Literal.String.Symbol */
    c-[fm] { color: #268bd2 } /* Name.Function.Magic */
    c-[vc] { color: #cb4b16 } /* Name.Variable.Class */
    c-[vg] { color: #cb4b16 } /* Name.Variable.Global */
    c-[vi] { color: #cb4b16 } /* Name.Variable.Instance */
    c-[vm] { color: #cb4b16 } /* Name.Variable.Magic */
    c-[il] { color: #657b83 } /* Literal.Number.Integer.Long */
}
</style>
 <body class="h-entry">
  <div class="head">
   <p data-fill-with="logo"></p>
   <h1 class="p-name no-ref" id="title">P3055R0<br>Relax wording to permit relocation optimizations in the STL</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="2023-12-09">2023-12-09</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>LEWG
     <dt>Project:
     <dd>ISO/IEC 14882 Programming Languages — C++, ISO/IEC JTC1/SC22/WG21
     <dt>Draft Revision:
     <dd>3
    </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>We catalog the STL containers and algorithms that could benefit from

  optimizations related to relocation (P1144, P2786), and propose to loosen
  their current overspecification so that such optimizations become legal
  (but not mandatory), even in the absence of a standardized vocabulary
  for relocation.</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="#proposal"><span class="secno">2</span> <span class="content">Motivation and proposal</span></a>
     <ol class="toc">
      <li><a href="#benchmark"><span class="secno">2.1</span> <span class="content">Benchmark</span></a>
     </ol>
    <li><a href="#breakage"><span class="secno">3</span> <span class="content">Breakage of existing code</span></a>
    <li><a href="#experience"><span class="secno">4</span> <span class="content">Implementation experience</span></a>
    <li>
     <a href="#wording"><span class="secno">5</span> <span class="content">Proposed wording</span></a>
     <ol class="toc">
      <li><a href="#wording-vector.modifiers"><span class="secno">5.1</span> <span class="content">[vector.modifiers]</span></a>
      <li><a href="#wording-deque.modifiers"><span class="secno">5.2</span> <span class="content">[deque.modifiers]</span></a>
      <li><a href="#wording-alg.rotate"><span class="secno">5.3</span> <span class="content">[alg.rotate]</span></a>
      <li><a href="#wording-alg.swap"><span class="secno">5.4</span> <span class="content">[alg.swap]</span></a>
      <li><a href="#wording-utility.swap"><span class="secno">5.5</span> <span class="content">[utility.swap] (unchanged)</span></a>
      <li><a href="#wording-iterator.cust.swap"><span class="secno">5.6</span> <span class="content">[iterator.cust.swap] (unchanged)</span></a>
     </ol>
    <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>R0:</p>
     <ul>
      <li data-md>
       <p>Initial revision.</p>
     </ul>
   </ul>
   <h2 class="heading settled" data-level="2" id="proposal"><span class="secno">2. </span><span class="content">Motivation and proposal</span><a class="self-link" href="#proposal"></a></h2>
   <p>We have two largely similar active proposals for "trivial relocation" in C++: Arthur’s <a data-link-type="biblio" href="#biblio-p1144" title="std::is_trivially_relocatable">[P1144]</a>,
and Bloomberg’s <a data-link-type="biblio" href="#biblio-p2786" title="Trivial relocatability for C++26">[P2786]</a> / <a data-link-type="biblio" href="#biblio-p2959" title="Relocation within containers">[P2959]</a> / <a data-link-type="biblio" href="#biblio-p2967" title="Relocation has a library interface">[P2967]</a>. We also have two recent proposals
for "non-trivial relocation" as a new fundamental operation: Bloomberg’s <a data-link-type="biblio" href="#biblio-p2839" title="Non-trivial relocation via a new owning reference type">[P2839]</a> (rejected by EWG
in Varna) and Bini and Catmur’s <a data-link-type="biblio" href="#biblio-p2785" title="Relocating prvalues">[P2785]</a> (still active).</p>
   <p>A major motivation for "(trivial) relocation" is that it allows library authors to choose "fast paths"
for (trivially) relocatable types. For example, <code class="highlight"><c- n>vector</c-><c- o>::</c-><c- n>erase</c-><c- p>(</c-><c- n>it</c-><c- p>)</c-></code> for non-relocatable <code class="highlight"><c- n>T</c-></code> must
use <code class="highlight"><c- k>operator</c-><c- o>=</c-></code> in a loop (represented here by <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-></code>), but for trivially relocatable <code class="highlight"><c- n>T</c-></code> it can avoid <code class="highlight"><c- k>operator</c-><c- o>=</c-></code> and use the moral equivalent of memcpy
(represented here by P1144 <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>uninitialized_relocate</c-></code>).</p>
<pre class="language-c++ highlight"><c- b>void</c-> <c- nf>erase</c-><c- p>(</c-><c- n>iterator</c-> <c- n>it</c-><c- p>)</c-> <c- p>{</c->
    <c- k>if</c-> <c- n>constexpr</c-> <c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>is_trivially_relocatable_v</c-><c- o>&lt;</c-><c- n>value_type</c-><c- o>></c-><c- p>)</c-> <c- p>{</c->
        <c- n>std</c-><c- o>::</c-><c- n>destroy_at</c-><c- p>(</c-><c- n>it</c-><c- p>);</c->
        <c- n>std</c-><c- o>::</c-><c- n>uninitialized_relocate</c-><c- p>(</c-><c- n>it</c-> <c- o>+</c-> <c- mi>1</c-><c- p>,</c-> <c- n>end_</c-><c- p>,</c-> <c- n>it</c-><c- p>);</c->
    <c- p>}</c-> <c- k>else</c-> <c- p>{</c->
        <c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>it</c-> <c- o>+</c-> <c- mi>1</c-><c- p>,</c-> <c- n>end_</c-><c- p>,</c-> <c- n>it</c-><c- p>);</c-> <c- c1>// operator=</c->
        <c- n>std</c-><c- o>::</c-><c- n>destroy_at</c-><c- p>(</c-><c- n>end_</c-> <c- o>-</c-> <c- mi>1</c-><c- p>);</c->
    <c- p>}</c->
    <c- o>--</c-><c- n>end_</c-><c- p>;</c->
<c- p>}</c->
</pre>
   <p>The exact details of that snippet are up for debate: should the library provide a trait <code class="highlight"><c- n>is_nothrow_relocatable_v</c-></code>? should <code class="highlight"><c- n>uninitialized_relocate</c-></code> be guaranteed, or merely encouraged,
to use memcpy instead of move-and-destroy-in-a-loop? and so on. This paper P3055 considers all
those little details to be "out of scope"; they don’t affect the gist of this paper.</p>
   <p>This paper concerns itself with one giant problem — anything like the above implementation
is, formally, forbidden by the current Standard! To permit the above implementation, we must
loosen the specification of <code class="highlight"><c- n>vector</c-><c- o>::</c-><c- n>erase</c-></code> (<a href="https://eel.is/c++draft/vector.modifiers">[vector.modifiers]/3</a>)
along these lines:</p>
   <p><small></small></p>
   <blockquote>
    <p></p>
    <small> <pre class="highlight"><c- k>constexpr</c-> <c- n>iterator</c-> <c- nf>erase</c-><c- p>(</c-><c- n>const_iterator</c-> <c- n>position</c-><c- p>);</c->
<c- k>constexpr</c-> <c- n>iterator</c-> <c- nf>erase</c-><c- p>(</c-><c- n>const_iterator</c-> <c- n>first</c-><c- p>,</c-> <c- n>const_iterator</c-> <c- n>last</c-><c- p>);</c->
<c- k>constexpr</c-> <c- b>void</c-> <c- nf>pop_back</c-><c- p>();</c->
</pre><p>3․ <i>Effects:</i> Invalidates iterators and references at or after the point of the erase. </p><p>4․ <i>Throws:</i> Nothing unless an exception is thrown by the assignment operator or move assignment operator of <code class="highlight"><c- n>T</c-></code>. </p><p>5․ <i>Complexity:</i> <del>The destructor of <code class="highlight"><c- n>T</c-></code> is called the number of times equal to the number of the elements erased,
but the assignment operator of <code class="highlight"><c- n>T</c-></code> is called the number of times equal to the number of elements in the vector after the
erased elements.</del> <ins>Linear in the number of elements following the first erased element in the original vector.</ins> </p></small>
   </blockquote>
   <p>This change would be consistent with LWG’s wording choices in the modern era:
it specifies the complexity only in terms of big-O, and does not directly mandate any particular implementation
strategy. So for example it would become legal for the implementation to do just this:</p>
<pre class="language-c++ highlight"><c- b>void</c-> <c- nf>erase</c-><c- p>(</c-><c- n>iterator</c-> <c- n>it</c-><c- p>)</c-> <c- p>{</c->
    <c- n>std</c-><c- o>::</c-><c- n>rotate</c-><c- p>(</c-><c- n>it</c-><c- p>,</c-> <c- n>it</c-> <c- o>+</c-> <c- mi>1</c-><c- p>,</c-> <c- n>end_</c-><c- p>);</c->
    <c- n>std</c-><c- o>::</c-><c- n>destroy_at</c-><c- p>(</c-><c- n>end_</c-><c- o>--</c-><c- p>);</c->
<c- p>}</c->
</pre>
   <p>according to <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>rotate</c-></code>’s current wording. But furthermore, we propose to loosen <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>rotate</c-></code>’s wording
(<a href="https://eel.is/c++draft/alg.rotate">[alg.rotate]</a>) too:</p>
   <p><small></small></p>
   <blockquote>
    <p></p>
    <small> <p>1․ <i>Preconditions:</i> <code class="highlight"><c- p>[</c-><c- n>first</c-><c- p>,</c-> <c- n>middle</c-><c- p>)</c-></code> and <code class="highlight"><c- p>[</c-><c- n>middle</c-><c- p>,</c-> <c- n>last</c-><c- p>)</c-></code> are valid ranges.
For the overloads in namespace <code class="highlight"><c- n>std</c-></code>, <code class="highlight"><c- n>ForwardIterator</c-></code> meets the <em>Cpp17ValueSwappable</em> requirements ([swappable.requirements]),
and the type of <code class="highlight"><c- o>*</c-><c- n>first</c-></code> meets the <em>Cpp17MoveConstructible</em> (Table 31) and <em>Cpp17MoveAssignable</em> (Table 33) requirements. </p><p>2․ <i>Effects:</i> For each non-negative integer <code class="highlight"><c- n>i</c-> <c- o>&lt;</c-> <c- p>(</c-><c- n>last</c-> <c- o>-</c-> <c- n>first</c-><c- p>)</c-></code>, places the element from the position <code class="highlight"><c- n>first</c-> <c- o>+</c-> <c- n>i</c-></code> into position <code class="highlight"><c- n>first</c-> <c- o>+</c-> <c- p>(</c-><c- n>i</c-> <c- o>+</c-> <c- p>(</c-><c- n>last</c-> <c- o>-</c-> <c- n>middle</c-><c- p>))</c-> <c- o>%</c-> <c- p>(</c-><c- n>last</c-> <c- o>-</c-> <c- n>first</c-><c- p>)</c-></code>. [<i>Note:</i> This is a left rotate. <i>— end note</i>] </p><p>3․ <i>Returns:</i> </p><ul><li data-md><p><code class="highlight"><c- n>first</c-> <c- o>+</c-> <c- p>(</c-><c- n>last</c-> <c- o>-</c-> <c- n>middle</c-><c- p>)</c-></code> for the overloads in namespace <code class="highlight"><c- n>std</c-></code>.</p> </li><li data-md><p><code class="highlight"><c- p>{</c-><c- n>first</c-> <c- o>+</c-> <c- p>(</c-><c- n>last</c-> <c- o>-</c-> <c- n>middle</c-><c- p>),</c-> <c- n>last</c-><c- p>}</c-></code> for the overload in namespace <code class="highlight"><c- n>ranges</c-></code>.</p> </li></ul> <p>4․ <i>Complexity:</i> <del>At most <code class="highlight"><c- n>last</c-> <c- o>-</c-> <c- n>first</c-></code> swaps.</del> <ins>Linear in <code class="highlight"><c- n>last</c-> <c- o>-</c-> <c- n>first</c-></code>.</ins> </p></small>
   </blockquote>
   <p><code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>rotate</c-></code>’s previous wording was defined in terms of "swaps." Look at the specification for <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>swap</c-></code> (<a href="https://eel.is/c++draft/utility.swap">[utility.swap]</a>):</p>
   <p><small></small></p>
   <blockquote>
    <p></p>
    <small> <pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- o>></c->
  <c- k>constexpr</c-> <c- b>void</c-> <c- n>swap</c-><c- p>(</c-><c- n>T</c-><c- o>&amp;</c-> <c- n>a</c-><c- p>,</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>b</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>(</c-><i><c- n>see</c-> <c- n>below</c-></i><c- p>);</c->
</pre><p>1․ <i>Constraints:</i> <code class="highlight"><c- n>is_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_move_assignable_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code>. </p><p>2․ <i>Preconditions:</i> Type <code class="highlight"><c- n>T</c-></code> meets the <em>Cpp17MoveConstructible</em> (Table 31) and <em>Cpp17MoveAssignable</em> (Table 33) requirements. </p><p>3․ <i>Effects:</i> Exchanges values stored in two locations. </p><p>4․ <i>Remarks:</i> The exception specification is equivalent to: <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-> <c- o>&amp;&amp;</c-> <c- n>is_nothrow_move_assignable_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code>. </p></small>
   </blockquote>
   <p>Here the status quo is sufficiently loose to permit an efficient implementation by means of relocation,
and in fact Arthur’s libc++ fork does exactly that
(<a href="https://github.com/Quuxplusone/llvm-project/blob/trivially-relocatable-v88/libcxx/include/__utility/swap.h#L67-L86">source</a>, <a href="https://godbolt.org/z/EWzKqq5s3">Godbolt</a>). The following code omits details such as <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>is_constant_evaluated</c-><c- p>()</c-></code> which are present in the actual library.</p>
<pre class="language-c++ highlight"><c- b>void</c-> <c- nf>swap</c-><c- p>(</c-><c- n>T</c-><c- o>&amp;</c-> <c- n>a</c-><c- p>,</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>b</c-><c- p>)</c->
    <c- n>noexcept</c-><c- p>(</c-><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-> <c- o>&amp;&amp;</c-> <c- n>is_nothrow_move_assignable_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>)</c->
<c- p>{</c->
    <c- k>if</c-> <c- n>constexpr</c-> <c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>is_trivially_relocatable_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>)</c-> <c- p>{</c->
        <c- n>__builtin_memswap</c-><c- p>(</c-><c- o>&amp;</c-><c- n>a</c-><c- p>,</c-> <c- o>&amp;</c-><c- n>b</c-><c- p>,</c-> <c- n>__datasizeof</c-><c- p>(</c-><c- n>T</c-><c- p>));</c->
    <c- p>}</c-> <c- k>else</c-> <c- p>{</c->
        <c- n>T</c-> <c- n>temp</c-> <c- o>=</c-> <c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>a</c-><c- p>);</c->
        <c- n>a</c-> <c- o>=</c-> <c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>b</c-><c- p>);</c->
        <c- n>b</c-> <c- o>=</c-> <c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>temp</c-><c- p>);</c->
    <c- p>}</c->
<c- p>}</c->
</pre>
   <p>In other words, this paper P3055 is needed, even after P1144/P2786. If one of those papers
is adopted without P3055, then conforming implementations will still be technically forbidden to do
the optimizations we want to enable (which are already done by <code class="highlight"><c- n>bsl</c-><c- o>::</c-><c- n>vector</c-></code>, <code class="highlight"><c- n>folly</c-><c- o>::</c-><c- n>FBVector</c-></code>, etc).
Vice versa, as soon as P3055 is adopted (even without P1144/P2786), a conforming implementation will
be able to use these optimizations on types it knows to be trivially relocatable
(e.g. <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>deque</c-><c- o>&lt;</c-><c- b>int</c-><c- o>></c-></code>), even if we continue to lack a standardized vocabulary
for relocatable user-defined types.</p>
   <h3 class="heading settled" data-level="2.1" id="benchmark"><span class="secno">2.1. </span><span class="content">Benchmark</span><a class="self-link" href="#benchmark"></a></h3>
   <p>Trivial relocation is an "infinitely valuable optimization"
in the same sense as C++11 move semantics. For the following type <code class="highlight"><c- n>S</c-></code>,
mainline libc++ compiles <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>swap</c-></code> into 74 lines of assembly.
Arthur’s P1144 fork of libc++ compiles it into 18 lines. (<a href="https://godbolt.org/z/EWzKqq5s3">Godbolt.</a>)</p>
<pre class="language-c++ highlight"><c- k>struct</c-> <c- nc>S</c-> <c- p>{</c->
    <c- n>S</c-><c- p>();</c->
    <c- n>std</c-><c- o>::</c-><c- n>unique_ptr</c-><c- o>&lt;</c-><c- b>int</c-><c- o>></c-> <c- n>p</c-><c- p>;</c->
    <c- n>std</c-><c- o>::</c-><c- n>shared_ptr</c-><c- o>&lt;</c-><c- b>int</c-><c- o>></c-> <c- n>q</c-><c- p>;</c->
    <c- b>bool</c-> <c- n>b</c-><c- p>;</c->
<c- p>};</c->

<c- b>void</c-> <c- nf>test</c-><c- p>(</c-><c- n>S</c-><c- o>&amp;</c-> <c- n>a</c-><c- p>,</c-> <c- n>S</c-><c- o>&amp;</c-> <c- n>b</c-><c- p>)</c-> <c- p>{</c->
    <c- n>std</c-><c- o>::</c-><c- n>swap</c-><c- p>(</c-><c- n>a</c-><c- p>,</c-> <c- n>b</c-><c- p>);</c->
<c- p>}</c->
</pre>
   <p>This propagates back up the call-stack as high as we’re willing to let it propagate.
Arthur’s libc++ effectively applies this paper P3055’s proposed wording already,
permitting <code class="highlight"><c- n>rotate</c-></code> to be implemented in terms of <code class="highlight"><c- n>swap</c-></code> and <code class="highlight"><c- n>erase</c-></code> to be implemented
in terms of <code class="highlight"><c- n>rotate</c-></code>.</p>
   <table>
    <tbody>
     <tr>
      <th>Operation
      <th>Mainline libc++ LOC
      <th>P1144 libc++ LOC
     <tr>
      <td><a href="https://godbolt.org/z/EWzKqq5s3"><pre class="highlight"><c- n>std</c-><c- o>::</c-><c- n>swap</c-><c- p>(</c-><c- n>S</c-><c- o>&amp;</c-><c- p>,</c-> <c- n>S</c-><c- o>&amp;</c-><c- p>)</c-></pre></a>
      <td>74
      <td>18
     <tr>
      <td><a href="https://godbolt.org/z/7cs1WrvjP"><pre class="highlight"><c- n>std</c-><c- o>::</c-><c- n>rotate</c-><c- p>(</c-><c- n>S</c-><c- o>*</c-><c- p>,</c-> <c- n>S</c-><c- o>*</c-><c- p>,</c-> <c- n>S</c-><c- o>*</c-><c- p>)</c-></pre></a>
      <td>145
      <td>122
     <tr>
      <td><a href="https://godbolt.org/z/E5vobhhd1"><pre class="highlight"><c- n>vector</c-><c- o>&lt;</c-><c- n>S</c-><c- o>>::</c-><c- n>erase</c-><c- p>(</c-><c- n>it</c-><c- p>)</c-></pre></a>
      <td>108
      <td>39
   </table>
   <h2 class="heading settled" data-level="3" id="breakage"><span class="secno">3. </span><span class="content">Breakage of existing code</span><a class="self-link" href="#breakage"></a></h2>
   <p>Since the proposed wording is looser than the existing wording, all vendors already conform to it by definition;
we’re not asking any vendor to change their implementation for C++26. However, a vendor who takes advantage of
the new freedom may change the behavior of certain algorithms and containers for non-regular types.
Following <a data-link-type="biblio" href="#biblio-p2959" title="Relocation within containers">[P2959]</a>, we’ll use <code class="highlight"><c- n>tuple</c-><c- o>&lt;</c-><c- b>int</c-><c- o>&amp;></c-></code> as our canonical example. <code class="highlight"><c- n>tuple</c-><c- o>&lt;</c-><c- b>int</c-><c- o>&amp;></c-></code> assigns-through on
assignment and swap; it never rebinds (except on initial construction). This is the polar opposite of <code class="highlight"><c- n>reference_wrapper</c-><c- o>&lt;</c-><c- b>int</c-><c- o>></c-></code>, which rebinds on assignment and swap, and never assigns-through. In P1144’s
terminology, <code class="highlight"><c- n>reference_wrapper</c-><c- o>&lt;</c-><c- b>int</c-><c- o>></c-></code> is trivially relocatable and <code class="highlight"><c- n>tuple</c-><c- o>&lt;</c-><c- b>int</c-><c- o>&amp;></c-></code> is not trivially relocatable.
(<a href="https://godbolt.org/z/4nqY1GTrx">Godbolt.</a>)</p>
   <p>Recall that <code class="highlight"><c- n>swap</c-></code> is already loosely specified — it "exchanges the values"  of its arguments — so
our proposal leaves the following example untouched:</p>
<pre class="language-c++ highlight"><c- b>int</c-> <c- n>i</c-> <c- o>=</c-> <c- mi>1</c-><c- p>,</c-> <c- n>j</c-> <c- o>=</c-> <c- mi>2</c-><c- p>;</c->
<c- n>std</c-><c- o>::</c-><c- n>tuple</c-><c- o>&lt;</c-><c- b>int</c-><c- o>&amp;></c-> <c- n>a</c-> <c- o>=</c-> <c- p>{</c-><c- n>i</c-><c- p>},</c-> <c- n>b</c-> <c- o>=</c-> <c- p>{</c-><c- n>j</c-><c- p>};</c->
<c- n>std</c-><c- o>::</c-><c- n>swap</c-><c- p>(</c-><c- n>a</c-><c- p>,</c-> <c- n>b</c-><c- p>);</c->
<c- n>assert</c-><c- p>(</c-><c- n>i</c-> <c- o>==</c-> <c- mi>2</c-> <c- o>&amp;&amp;</c-> <c- n>j</c-> <c- o>==</c-> <c- mi>1</c-><c- p>);</c->
</pre>
   <p><code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>rotate</c-></code>’s <i>Effects</i> are specified via the phrase "places the element from position <em>x</em> into position <em>y</em>";
its semantics are coupled to <code class="highlight"><c- n>swap</c-></code> only through the phrase "At most <em>n</em> swaps" in the <i>Complexity</i> element,
which we propose to remove. After that change, a vendor might reasonably construe that this old behavior...</p>
<pre class="language-c++ highlight"><c- b>int</c-> <c- n>a</c-><c- p>[</c-><c- mi>3</c-><c- p>]</c-> <c- o>=</c-> <c- p>{</c-><c- mi>1</c-><c- p>,</c-><c- mi>2</c-><c- p>,</c-><c- mi>3</c-><c- p>};</c->
<c- n>std</c-><c- o>::</c-><c- n>tuple</c-><c- o>&lt;</c-><c- b>int</c-><c- o>&amp;></c-> <c- n>ts</c-><c- p>[</c-><c- mi>3</c-><c- p>]</c-> <c- o>=</c-> <c- p>{{</c-><c- n>a</c-><c- p>[</c-><c- mi>0</c-><c- p>]},</c-> <c- p>{</c-><c- n>a</c-><c- p>[</c-><c- mi>1</c-><c- p>]},</c-> <c- p>{</c-><c- n>a</c-><c- p>[</c-><c- mi>2</c-><c- p>]}};</c->
<c- n>std</c-><c- o>::</c-><c- n>rotate</c-><c- p>(</c-><c- n>ts</c-><c- p>,</c-> <c- n>ts</c-><c- o>+</c-><c- mi>1</c-><c- p>,</c-> <c- n>ts</c-><c- o>+</c-><c- mi>3</c-><c- p>);</c->
<c- n>assert</c-><c- p>(</c-><c- n>a</c-><c- p>[</c-><c- mi>0</c-><c- p>]</c-> <c- o>==</c-> <c- mi>2</c-> <c- o>&amp;&amp;</c-> <c- n>a</c-><c- p>[</c-><c- mi>1</c-><c- p>]</c-> <c- o>==</c-> <c- mi>3</c-> <c- o>&amp;&amp;</c-> <c- n>a</c-><c- p>[</c-><c- mi>2</c-><c- p>]</c-> <c- o>==</c-> <c- mi>1</c-><c- p>);</c->
</pre>
   <p>...was no longer strictly mandated. They might choose to "place" the <code class="highlight"><c- n>tuple</c-><c- o>&lt;</c-><c- b>int</c-><c- o>&amp;></c-></code>s as-if-by relocation, rebinding
each <code class="highlight"><c- n>tuple</c-><c- o>&lt;</c-><c- b>int</c-><c- o>&amp;></c-></code> and leaving the array <code class="highlight"><c- n>a</c-></code> untouched. (However, Arthur’s libc++ doesn’t change this behavior,
because Arthur’s libc++ optimizes only trivially relocatable types, and <code class="highlight"><c- n>tuple</c-><c- o>&lt;</c-><c- b>int</c-><c- o>&amp;></c-></code> is not trivially relocatable.)</p>
   <p>Consider <code class="highlight"><c- n>vector</c-><c- o>::</c-><c- n>erase</c-></code>, whose semantics are coupled to <code class="highlight"><c- k>operator</c-><c- o>=</c-></code> only through wording in its <i>Complexity</i> element
which we propose to remove. After that change, a vendor might reasonably construe that this old behavior...</p>
<pre class="language-c++ highlight"><c- b>int</c-> <c- n>a</c-><c- p>[</c-><c- mi>3</c-><c- p>]</c-> <c- o>=</c-> <c- p>{</c-><c- mi>1</c-><c- p>,</c-><c- mi>2</c-><c- p>,</c-><c- mi>3</c-><c- p>};</c->
<c- n>std</c-><c- o>::</c-><c- n>vector</c-><c- o>&lt;</c-><c- n>std</c-><c- o>::</c-><c- n>tuple</c-><c- o>&lt;</c-><c- b>int</c-><c- o>&amp;>></c-> <c- n>ts</c-> <c- o>=</c-> <c- p>{{</c-><c- n>a</c-><c- p>[</c-><c- mi>0</c-><c- p>]},</c-> <c- p>{</c-><c- n>a</c-><c- p>[</c-><c- mi>1</c-><c- p>]},</c-> <c- p>{</c-><c- n>a</c-><c- p>[</c-><c- mi>2</c-><c- p>]}};</c->
<c- n>ts</c-><c- p>.</c-><c- n>erase</c-><c- p>(</c-><c- n>ts</c-><c- p>.</c-><c- n>begin</c-><c- p>());</c->
<c- n>assert</c-><c- p>(</c-><c- n>a</c-><c- p>[</c-><c- mi>0</c-><c- p>]</c-> <c- o>==</c-> <c- mi>2</c-> <c- o>&amp;&amp;</c-> <c- n>a</c-><c- p>[</c-><c- mi>1</c-><c- p>]</c-> <c- o>==</c-> <c- mi>3</c-> <c- o>&amp;&amp;</c-> <c- n>a</c-><c- p>[</c-><c- mi>2</c-><c- p>]</c-> <c- o>==</c-> <c- mi>3</c-><c- p>);</c->
</pre>
   <p>...was no longer strictly mandated. They might choose to "erase the element pointed to"
(<a href="https://eel.is/c++draft/sequence.reqmts#47">[sequence.reqmts]/47</a>) as-if-by relocation,
rebinding each <code class="highlight"><c- n>tuple</c-><c- o>&lt;</c-><c- b>int</c-><c- o>&amp;></c-></code> and leaving the array <code class="highlight"><c- n>a</c-></code> untouched. As <a data-link-type="biblio" href="#biblio-p2959" title="Relocation within containers">[P2959]</a> points out, this is
exactly what happens anyway if you switch out <code class="highlight"><c- n>vector</c-></code> for <code class="highlight"><c- n>list</c-></code>. (Again, Arthur’s libc++ doesn’t change
this behavior, because <code class="highlight"><c- n>tuple</c-><c- o>&lt;</c-><c- b>int</c-><c- o>&amp;></c-></code> is not trivially relocatable; but we certainly have no desire to
continue mandating the old behavior.)</p>
   <h2 class="heading settled" data-level="4" id="experience"><span class="secno">4. </span><span class="content">Implementation experience</span><a class="self-link" href="#experience"></a></h2>
   <p>Since the proposed wording is looser than the existing wording, all vendors already conform to it
by definition; we’re not asking any vendor to change their implementation for C++26.</p>
   <p>Arthur has implemented trivial-relocation optimizations in his fork of libc++, and used it to compile
both LLVM/Clang/libc++ and another large C++17 codebase. No problems were found (naturally).</p>
   <h2 class="heading settled" data-level="5" id="wording"><span class="secno">5. </span><span class="content">Proposed wording</span><a class="self-link" href="#wording"></a></h2>
   <p class="note" role="note"><span class="marker">Note:</span> We’re trying to eliminate places where the <i>Effects</i> and <i>Complexity</i> elements specifically mention
assignment. We don’t mind e.g. when [deque.modifiers] specifies that <code class="highlight"><c- n>push_back</c-></code> "causes a single call to a constructor of <code class="highlight"><c- n>T</c-></code>,"
because that’s still correct even if we’re optimizing trivially relocatable types. We don’t even mind when
[vector.modifiers] specifies that <code class="highlight"><c- n>erase</c-></code> calls <code class="highlight"><c- n>T</c-></code>’s destructor "the number of times equal to the number of the elements erased,"
because of course it does; but we propose to remove that sentence anyway because it is redundant. We also don’t
mind when an operation says "<i>Throws:</i> Nothing unless an exception is thrown from the assignment operator
of <code class="highlight"><c- n>T</c-></code>," because our new trivial-relocation "happy path" will never throw. Such a <i>Throws</i> element continues
to describe the circumstances under which the operation <i>might</i> throw. We never propose to loosen any <i>Throws</i> element.</p>
   <h3 class="heading settled" data-level="5.1" id="wording-vector.modifiers"><span class="secno">5.1. </span><span class="content">[vector.modifiers]</span><a class="self-link" href="#wording-vector.modifiers"></a></h3>
   <p>Modify <a href="https://eel.is/c++draft/vector.modifiers">[vector.modifiers]</a> as follows:</p>
   <p><small></small></p>
   <blockquote>
    <p></p>
    <small> <pre class="highlight"><c- k>constexpr</c-> <c- n>iterator</c-> <c- nf>insert</c-><c- p>(</c-><c- n>const_iterator</c-> <c- n>position</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>x</c-><c- p>);</c->
<c- k>constexpr</c-> <c- n>iterator</c-> <c- nf>insert</c-><c- p>(</c-><c- n>const_iterator</c-> <c- n>position</c-><c- p>,</c-> <c- n>T</c-><c- o>&amp;&amp;</c-> <c- n>x</c-><c- p>);</c->
<c- k>constexpr</c-> <c- n>iterator</c-> <c- nf>insert</c-><c- p>(</c-><c- n>const_iterator</c-> <c- n>position</c-><c- p>,</c-> <c- n>size_type</c-> <c- n>n</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>x</c-><c- p>);</c->
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>InputIterator</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>iterator</c-> <c- n>insert</c-><c- p>(</c-><c- n>const_iterator</c-> <c- n>position</c-><c- p>,</c-> <c- n>InputIterator</c-> <c- n>first</c-><c- p>,</c-> <c- n>InputIterator</c-> <c- n>last</c-><c- p>);</c->
<c- k>template</c-><c- o>&lt;</c-><i><c- n>container</c-><c- o>-</c-><c- n>compatible</c-><c- o>-</c-><c- n>range</c-></i><c- o>&lt;</c-><c- n>T</c-><c- o>></c-> <c- n>R</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>iterator</c-> <c- n>insert_range</c-><c- p>(</c-><c- n>const_iterator</c-> <c- n>position</c-><c- p>,</c-> <c- n>R</c-><c- o>&amp;&amp;</c-> <c- n>rg</c-><c- p>);</c->
<c- k>constexpr</c-> <c- n>iterator</c-> <c- nf>insert</c-><c- p>(</c-><c- n>const_iterator</c-> <c- n>position</c-><c- p>,</c-> <c- n>initializer_list</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>);</c->

<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c-> <c- k>constexpr</c-> <c- n>reference</c-> <c- n>emplace_back</c-><c- p>(</c-><c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...</c-> <c- n>args</c-><c- p>);</c->
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c-> <c- k>constexpr</c-> <c- n>iterator</c-> <c- n>emplace</c-><c- p>(</c-><c- n>const_iterator</c-> <c- n>position</c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...</c-> <c- n>args</c-><c- p>);</c->
<c- k>constexpr</c-> <c- b>void</c-> <c- nf>push_back</c-><c- p>(</c-><c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>x</c-><c- p>);</c->
<c- k>constexpr</c-> <c- b>void</c-> <c- nf>push_back</c-><c- p>(</c-><c- n>T</c-><c- o>&amp;&amp;</c-> <c- n>x</c-><c- p>);</c->
<c- k>template</c-><c- o>&lt;</c-><i><c- n>container</c-><c- o>-</c-><c- n>compatible</c-><c- o>-</c-><c- n>range</c-></i><c- o>&lt;</c-><c- n>T</c-><c- o>></c-> <c- n>R</c-><c- o>></c->
  <c- k>constexpr</c-> <c- b>void</c-> <c- n>append_range</c-><c- p>(</c-><c- n>R</c-><c- o>&amp;&amp;</c-> <c- n>rg</c-><c- p>);</c->
</pre><p>1. <i>Complexity:</i> If reallocation happens, linear in the number of elements of the resulting vector;
otherwise, linear in the number of elements inserted plus the distance to the end of the vector. </p><p>2. <em>Remarks:</em> Causes reallocation if the new size is greater than the old capacity. Reallocation invalidates
all the references, pointers, and iterators referring to the elements in the sequence, as well as the past-the-end iterator.
If no reallocation happens, then references, pointers, and iterators before the insertion point remain valid but those at
or after the insertion point, including the past-the-end iterator, are invalidated. If an exception is thrown other than
by the copy constructor, move constructor, assignment operator, or move assignment operator of <code class="highlight"><c- n>T</c-></code> or by any <code class="highlight"><c- n>InputIterator</c-></code> operation there are no effects. If an exception is thrown while inserting a single element at the end and <code class="highlight"><c- n>T</c-></code> is <em>Cpp17CopyInsertable</em> or <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code>, there are no effects.
Otherwise, if an exception is thrown by the move constructor of a non-<i>Cpp17CopyInsertable</i> <code class="highlight"><c- n>T</c-></code>, the effects are unspecified. </p><pre class="highlight"><c- k>constexpr</c-> <c- n>iterator</c-> <c- nf>erase</c-><c- p>(</c-><c- n>const_iterator</c-> <c- n>position</c-><c- p>);</c->
<c- k>constexpr</c-> <c- n>iterator</c-> <c- nf>erase</c-><c- p>(</c-><c- n>const_iterator</c-> <c- n>first</c-><c- p>,</c-> <c- n>const_iterator</c-> <c- n>last</c-><c- p>);</c->
<c- k>constexpr</c-> <c- b>void</c-> <c- nf>pop_back</c-><c- p>();</c->
</pre><p>3. <em>Effects:</em> Invalidates iterators and references at or after the point of the erase. </p><p>4. <em>Throws:</em> Nothing unless an exception is thrown by the assignment operator or move assignment operator of <code class="highlight"><c- n>T</c-></code>. </p><p>5. <em>Complexity:</em> <del>The destructor of <code class="highlight"><c- n>T</c-></code> is called the number of times equal to the number of the elements erased,
but the assignment operator of <code class="highlight"><c- n>T</c-></code> is called the number of times equal to the number of elements in the vector after
the erased elements.</del> <ins>Linear in the number of elements after the first erased element in the original vector.</ins> </p></small>
   </blockquote>
   <h3 class="heading settled" data-level="5.2" id="wording-deque.modifiers"><span class="secno">5.2. </span><span class="content">[deque.modifiers]</span><a class="self-link" href="#wording-deque.modifiers"></a></h3>
   <p>Modify <a href="https://eel.is/c++draft/deque.modifiers">[deque.modifiers]</a> as follows:</p>
   <p><small></small></p>
   <blockquote>
    <p></p>
    <small> <pre class="highlight"><c- n>iterator</c-> <c- nf>insert</c-><c- p>(</c-><c- n>const_iterator</c-> <c- n>position</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>x</c-><c- p>);</c->
<c- n>iterator</c-> <c- nf>insert</c-><c- p>(</c-><c- n>const_iterator</c-> <c- n>position</c-><c- p>,</c-> <c- n>T</c-><c- o>&amp;&amp;</c-> <c- n>x</c-><c- p>);</c->
<c- n>iterator</c-> <c- nf>insert</c-><c- p>(</c-><c- n>const_iterator</c-> <c- n>position</c-><c- p>,</c-> <c- n>size_type</c-> <c- n>n</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>x</c-><c- p>);</c->
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>InputIterator</c-><c- o>></c->
  <c- n>iterator</c-> <c- n>insert</c-><c- p>(</c-><c- n>const_iterator</c-> <c- n>position</c-><c- p>,</c->
                  <c- n>InputIterator</c-> <c- n>first</c-><c- p>,</c-> <c- n>InputIterator</c-> <c- n>last</c-><c- p>);</c->
<c- k>template</c-><c- o>&lt;</c-><i><c- n>container</c-><c- o>-</c-><c- n>compatible</c-><c- o>-</c-><c- n>range</c-></i><c- o>&lt;</c-><c- n>T</c-><c- o>></c-> <c- n>R</c-><c- o>></c->
  <c- n>iterator</c-> <c- n>insert_range</c-><c- p>(</c-><c- n>const_iterator</c-> <c- n>position</c-><c- p>,</c-> <c- n>R</c-><c- o>&amp;&amp;</c-> <c- n>rg</c-><c- p>);</c->
<c- n>iterator</c-> <c- nf>insert</c-><c- p>(</c-><c- n>const_iterator</c-> <c- n>position</c-><c- p>,</c-> <c- n>initializer_list</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>);</c->

<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c-> <c- n>reference</c-> <c- n>emplace_front</c-><c- p>(</c-><c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...</c-> <c- n>args</c-><c- p>);</c->
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c-> <c- n>reference</c-> <c- n>emplace_back</c-><c- p>(</c-><c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...</c-> <c- n>args</c-><c- p>);</c->
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c-> <c- n>iterator</c-> <c- n>emplace</c-><c- p>(</c-><c- n>const_iterator</c-> <c- n>position</c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...</c-> <c- n>args</c-><c- p>);</c->
<c- b>void</c-> <c- nf>push_front</c-><c- p>(</c-><c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>x</c-><c- p>);</c->
<c- b>void</c-> <c- nf>push_front</c-><c- p>(</c-><c- n>T</c-><c- o>&amp;&amp;</c-> <c- n>x</c-><c- p>);</c->
<c- k>template</c-><c- o>&lt;</c-><i><c- n>container</c-><c- o>-</c-><c- n>compatible</c-><c- o>-</c-><c- n>range</c-></i><c- o>&lt;</c-><c- n>T</c-><c- o>></c-> <c- n>R</c-><c- o>></c->
  <c- b>void</c-> <c- n>prepend_range</c-><c- p>(</c-><c- n>R</c-><c- o>&amp;&amp;</c-> <c- n>rg</c-><c- p>);</c->
<c- b>void</c-> <c- nf>push_back</c-><c- p>(</c-><c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>x</c-><c- p>);</c->
<c- b>void</c-> <c- nf>push_back</c-><c- p>(</c-><c- n>T</c-><c- o>&amp;&amp;</c-> <c- n>x</c-><c- p>);</c->
<c- k>template</c-><c- o>&lt;</c-><i><c- n>container</c-><c- o>-</c-><c- n>compatible</c-><c- o>-</c-><c- n>range</c-></i><c- o>&lt;</c-><c- n>T</c-><c- o>></c-> <c- n>R</c-><c- o>></c->
  <c- b>void</c-> <c- n>append_range</c-><c- p>(</c-><c- n>R</c-><c- o>&amp;&amp;</c-> <c- n>rg</c-><c- p>);</c->
</pre><p>1. <i>Effects:</i> An insertion in the middle of the deque invalidates all the iterators and references to elements of the deque.
An insertion at either end of the deque invalidates all the iterators to the deque, but has no effect on the validity of references to elements of the deque. </p><p>2. <i>Complexity:</i> <del>The complexity is linear</del> <ins>Linear</ins> in the number of elements inserted plus the lesser of the distances
to the beginning and end of the deque. Inserting a single element at either the beginning or end of a deque always takes constant time
and causes a single call to a constructor of <code class="highlight"><c- n>T</c-></code>. </p><p>3. <i>Remarks:</i> If an exception is thrown other than by the copy constructor, move constructor, assignment operator, or move assignment operator of <code class="highlight"><c- n>T</c-></code> there are no effects. If an exception is thrown while inserting a single element at either end, there are no effects. Otherwise, if an exception is thrown
by the move constructor of a non-<i>Cpp17CopyInsertable</i> <code class="highlight"><c- n>T</c-></code>, the effects are unspecified. </p><pre class="highlight"><c- n>iterator</c-> <c- nf>erase</c-><c- p>(</c-><c- n>const_iterator</c-> <c- n>position</c-><c- p>);</c->
<c- n>iterator</c-> <c- nf>erase</c-><c- p>(</c-><c- n>const_iterator</c-> <c- n>first</c-><c- p>,</c-> <c- n>const_iterator</c-> <c- n>last</c-><c- p>);</c->
<c- b>void</c-> <c- nf>pop_front</c-><c- p>();</c->
<c- b>void</c-> <c- nf>pop_back</c-><c- p>();</c->
</pre><p>4. <i>Effects:</i> An erase operation that erases the last element of a deque invalidates only the past-the-end iterator
and all iterators and references to the erased elements. An erase operation that erases the first element of a deque but not
the last element invalidates only iterators and references to the erased elements. An erase operation that erases neither the
first element nor the last element of a deque invalidates the past-the-end iterator and all iterators and references to all the elements of the deque.
[<i>Note:</i> <code class="highlight"><c- n>pop_front</c-></code> and <code class="highlight"><c- n>pop_back</c-></code> are erase operations. <i>— end note</i>] </p><p>5. <i>Throws:</i> Nothing unless an exception is thrown by the assignment operator of <code class="highlight"><c- n>T</c-></code>. </p><p>6. <i>Complexity:</i> <del>The number of calls to the destructor of <code class="highlight"><c- n>T</c-></code> is the same as the number of elements erased,
but the number of calls to the assignment operator of <code class="highlight"><c- n>T</c-></code> is no more than the lesser of the number of elements before the erased elements
and the number of elements after the erased elements.</del> <ins>Linear in the lesser of the number of elements after the first erased element
and the number of elements before the last erased element in the original deque.</ins> </p></small>
   </blockquote>
   <h3 class="heading settled" data-level="5.3" id="wording-alg.rotate"><span class="secno">5.3. </span><span class="content">[alg.rotate]</span><a class="self-link" href="#wording-alg.rotate"></a></h3>
   <p>Modify <a href="https://eel.is/c++draft/alg.rotate">[alg.rotate]</a> as follows:</p>
   <p><small></small></p>
   <blockquote>
    <p></p>
    <small> <pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>ForwardIterator</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>ForwardIterator</c->
    <c- n>rotate</c-><c- p>(</c-><c- n>ForwardIterator</c-> <c- n>first</c-><c- p>,</c-> <c- n>ForwardIterator</c-> <c- n>middle</c-><c- p>,</c-> <c- n>ForwardIterator</c-> <c- n>last</c-><c- p>);</c->
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>ExecutionPolicy</c-><c- p>,</c-> <c- k>class</c-> <c- nc>ForwardIterator</c-><c- o>></c->
  <c- n>ForwardIterator</c->
    <c- n>rotate</c-><c- p>(</c-><c- n>ExecutionPolicy</c-><c- o>&amp;&amp;</c-> <c- n>exec</c-><c- p>,</c->
           <c- n>ForwardIterator</c-> <c- n>first</c-><c- p>,</c-> <c- n>ForwardIterator</c-> <c- n>middle</c-><c- p>,</c-> <c- n>ForwardIterator</c-> <c- n>last</c-><c- p>);</c->
<c- k>template</c-><c- o>&lt;</c-><c- n>permutable</c-> <c- n>I</c-><c- p>,</c-> <c- n>sentinel_for</c-><c- o>&lt;</c-><c- n>I</c-><c- o>></c-> <c- n>S</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>subrange</c-><c- o>&lt;</c-><c- n>I</c-><c- o>></c-> <c- n>ranges</c-><c- o>::</c-><c- n>rotate</c-><c- p>(</c-><c- n>I</c-> <c- n>first</c-><c- p>,</c-> <c- n>I</c-> <c- n>middle</c-><c- p>,</c-> <c- n>S</c-> <c- n>last</c-><c- p>);</c->
</pre><p>1. <i>Preconditions:</i> <code class="highlight"><c- p>[</c-><c- n>first</c-><c- p>,</c-> <c- n>middle</c-><c- p>)</c-></code> and <code class="highlight"><c- p>[</c-><c- n>middle</c-><c- p>,</c-> <c- n>last</c-><c- p>)</c-></code> are valid ranges. For the overloads in namespace <code class="highlight"><c- n>std</c-></code>, <code class="highlight"><c- n>ForwardIterator</c-></code> meets the Cpp17ValueSwappable requirements ([swappable.requirements]), and the type of <code class="highlight"><c- o>*</c-><c- n>first</c-></code> meets
the <em>Cpp17MoveConstructible</em> (Table 31) and <em>Cpp17MoveAssignable</em> (Table 33) requirements. </p><p>2. <i>Effects:</i> For each non-negative integer <code class="highlight"><c- n>i</c-> <c- o>&lt;</c-> <c- p>(</c-><c- n>last</c-> <c- o>-</c-> <c- n>first</c-><c- p>)</c-></code>, places the element from the position <code class="highlight"><c- n>first</c-> <c- o>+</c-> <c- n>i</c-></code> into
position <code class="highlight"><c- n>first</c-> <c- o>+</c-> <c- p>(</c-><c- n>i</c-> <c- o>+</c-> <c- p>(</c-><c- n>last</c-> <c- o>-</c-> <c- n>middle</c-><c- p>))</c-> <c- o>%</c-> <c- p>(</c-><c- n>last</c-> <c- o>-</c-> <c- n>first</c-><c- p>)</c-></code>. [<i>Note:</i> This is a left rotate. <i>— end note</i>] </p><p>3. Returns: </p><ul><li data-md><p><code class="highlight"><c- n>first</c-> <c- o>+</c-> <c- p>(</c-><c- n>last</c-> <c- o>-</c-> <c- n>middle</c-><c- p>)</c-></code> for the overloads in namespace <code class="highlight"><c- n>std</c-></code>.</p> </li><li data-md><p><code class="highlight"><c- p>{</c-><c- n>first</c-> <c- o>+</c-> <c- p>(</c-><c- n>last</c-> <c- o>-</c-> <c- n>middle</c-><c- p>),</c-> <c- n>last</c-><c- p>}</c-></code> for the overload in namespace <code class="highlight"><c- n>ranges</c-></code>.</p> </li></ul> <p>4. <i>Complexity:</i> <del>At most <code class="highlight"><c- n>last</c-> <c- o>-</c-> <c- n>first</c-></code> swaps.</del> <ins>Linear in <code class="highlight"><c- n>last</c-> <c- o>-</c-> <c- n>first</c-></code>.</ins> </p></small>
   </blockquote>
   <h3 class="heading settled" data-level="5.4" id="wording-alg.swap"><span class="secno">5.4. </span><span class="content">[alg.swap]</span><a class="self-link" href="#wording-alg.swap"></a></h3>
   <p>Modify <a href="https://eel.is/c++draft/alg.swap">[alg.swap]</a> as follows:</p>
   <p><small></small></p>
   <blockquote>
    <p></p>
    <small> <pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>ForwardIterator1</c-><c- p>,</c-> <c- k>class</c-> <c- nc>ForwardIterator2</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>ForwardIterator2</c->
    <c- n>swap_ranges</c-><c- p>(</c-><c- n>ForwardIterator1</c-> <c- n>first1</c-><c- p>,</c-> <c- n>ForwardIterator1</c-> <c- n>last1</c-><c- p>,</c->
                <c- n>ForwardIterator2</c-> <c- n>first2</c-><c- p>);</c->
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>ExecutionPolicy</c-><c- p>,</c-> <c- k>class</c-> <c- nc>ForwardIterator1</c-><c- p>,</c-> <c- k>class</c-> <c- nc>ForwardIterator2</c-><c- o>></c->
  <c- n>ForwardIterator2</c->
    <c- n>swap_ranges</c-><c- p>(</c-><c- n>ExecutionPolicy</c-><c- o>&amp;&amp;</c-> <c- n>exec</c-><c- p>,</c->
                <c- n>ForwardIterator1</c-> <c- n>first1</c-><c- p>,</c-> <c- n>ForwardIterator1</c-> <c- n>last1</c-><c- p>,</c->
                <c- n>ForwardIterator2</c-> <c- n>first2</c-><c- p>);</c->

<c- k>template</c-><c- o>&lt;</c-><c- n>input_iterator</c-> <c- n>I1</c-><c- p>,</c-> <c- n>sentinel_for</c-><c- o>&lt;</c-><c- n>I1</c-><c- o>></c-> <c- n>S1</c-><c- p>,</c-> <c- n>input_iterator</c-> <c- n>I2</c-><c- p>,</c-> <c- n>sentinel_for</c-><c- o>&lt;</c-><c- n>I2</c-><c- o>></c-> <c- n>S2</c-><c- o>></c->
  <c- k>requires</c-> <c- n>indirectly_swappable</c-><c- o>&lt;</c-><c- n>I1</c-><c- p>,</c-> <c- n>I2</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>ranges</c-><c- o>::</c-><c- n>swap_ranges_result</c-><c- o>&lt;</c-><c- n>I1</c-><c- p>,</c-> <c- n>I2</c-><c- o>></c->
    <c- n>ranges</c-><c- o>::</c-><c- n>swap_ranges</c-><c- p>(</c-><c- n>I1</c-> <c- n>first1</c-><c- p>,</c-> <c- n>S1</c-> <c- n>last1</c-><c- p>,</c-> <c- n>I2</c-> <c- n>first2</c-><c- p>,</c-> <c- n>S2</c-> <c- n>last2</c-><c- p>);</c->
<c- k>template</c-><c- o>&lt;</c-><c- n>input_range</c-> <c- n>R1</c-><c- p>,</c-> <c- n>input_range</c-> <c- n>R2</c-><c- o>></c->
  <c- k>requires</c-> <c- n>indirectly_swappable</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R1</c-><c- o>></c-><c- p>,</c-> <c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R2</c-><c- o>>></c->
  <c- k>constexpr</c-> <c- n>ranges</c-><c- o>::</c-><c- n>swap_ranges_result</c-><c- o>&lt;</c-><c- n>borrowed_iterator_t</c-><c- o>&lt;</c-><c- n>R1</c-><c- o>></c-><c- p>,</c-> <c- n>borrowed_iterator_t</c-><c- o>&lt;</c-><c- n>R2</c-><c- o>>></c->
    <c- n>ranges</c-><c- o>::</c-><c- n>swap_ranges</c-><c- p>(</c-><c- n>R1</c-><c- o>&amp;&amp;</c-> <c- n>r1</c-><c- p>,</c-> <c- n>R2</c-><c- o>&amp;&amp;</c-> <c- n>r2</c-><c- p>);</c->
</pre><p>1. Let: </p><ul><li data-md><p><code class="highlight"><c- n>last2</c-></code> be <code class="highlight"><c- n>first2</c-> <c- o>+</c-> <c- p>(</c-><c- n>last1</c-> <c- o>-</c-> <c- n>first1</c-><c- p>)</c-></code> for the overloads with no parameter named <code class="highlight"><c- n>last2</c-></code>;</p> </li><li data-md><p><em>M</em> be <code class="highlight"><c- n>min</c-><c- p>(</c-><c- n>last1</c-> <c- o>-</c-> <c- n>first1</c-><c- p>,</c-> <c- n>last2</c-> <c- o>-</c-> <c- n>first2</c-><c- p>)</c-></code>.</p> </li></ul> <p>2. <i>Preconditions:</i> The two ranges <code class="highlight"><c- p>[</c-><c- n>first1</c-><c- p>,</c-> <c- n>last1</c-><c- p>)</c-></code> and <code class="highlight"><c- p>[</c-><c- n>first2</c-><c- p>,</c-> <c- n>last2</c-><c- p>)</c-></code> do not overlap.
For the overloads in namespace <code class="highlight"><c- n>std</c-></code>, <code class="highlight"><c- o>*</c-><c- p>(</c-><c- n>first1</c-> <c- o>+</c-> <c- n>n</c-><c- p>)</c-></code> is swappable with ([swappable.requirements]) <code class="highlight"><c- o>*</c-><c- p>(</c-><c- n>first2</c-> <c- o>+</c-> <c- n>n</c-><c- p>)</c-></code> <ins>for all <code class="highlight"><c- n>n</c-></code> in the range <code class="highlight"><c- p>[</c-><c- mi>0</c-><c- p>,</c-> <c- n>M</c-><c- p>)</c-></code></ins>. </p><p>3. <i>Effects:</i> For each non-negative integer <em>n</em> &lt; <em>M</em> <del>performs</del> : </p><ul><li data-md><del><code class="highlight"><c- n>swap</c-><c- p>(</c-><c- o>*</c-><c- p>(</c-><c- n>first1</c-> <c- o>+</c-> <c- n>n</c-><c- p>),</c-> <c- o>*</c-><c- p>(</c-><c- n>first2</c-> <c- o>+</c-> <c- n>n</c-><c- p>))</c-></code></del> <ins>exchanges the values of <code class="highlight"><c- o>*</c-><c- p>(</c-><c- n>first1</c-> <c- o>+</c-> <c- n>n</c-><c- p>)</c-></code> and <code class="highlight"><c- o>*</c-><c- p>(</c-><c- n>first2</c-> <c- o>+</c-> <c- n>n</c-><c- p>)</c-></code></ins> for the overloads in namespace <code class="highlight"><c- n>std</c-></code>; </li><li data-md><ins>performs</ins> <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>iter_swap</c-><c- p>(</c-><c- n>first1</c-> <c- o>+</c-> <c- n>n</c-><c- p>,</c-> <c- n>first2</c-> <c- o>+</c-> <c- n>n</c-><c- p>)</c-></code> for the overloads in namespace <code class="highlight"><c- n>ranges</c-></code>. </li></ul> <p>4. <i>Returns:</i> </p><ul><li data-md><p><code class="highlight"><c- n>last2</c-></code> for the overloads in namespace <code class="highlight"><c- n>std</c-></code>.</p> </li><li data-md><p><code class="highlight"><c- p>{</c-><c- n>first1</c-> <c- o>+</c-> <c- n>M</c-><c- p>,</c-> <c- n>first2</c-> <c- o>+</c-> <c- n>M</c-><c- p>}</c-></code> for the overloads in namespace <code class="highlight"><c- n>ranges</c-></code>.</p> </li></ul> <p>5. <i>Complexity:</i> Exactly <em>M</em> swaps. </p><pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>ForwardIterator1</c-><c- p>,</c-> <c- k>class</c-> <c- nc>ForwardIterator2</c-><c- o>></c->
  <c- k>constexpr</c-> <c- b>void</c-> <c- n>iter_swap</c-><c- p>(</c-><c- n>ForwardIterator1</c-> <c- n>a</c-><c- p>,</c-> <c- n>ForwardIterator2</c-> <c- n>b</c-><c- p>);</c->
</pre><p>6. <i>Preconditions:</i> <code class="highlight"><c- n>a</c-></code> and <code class="highlight"><c- n>b</c-></code> are dereferenceable. <code class="highlight"><c- o>*</c-><c- n>a</c-></code> is swappable with ([swappable.requirements]) <code class="highlight"><c- o>*</c-><c- n>b</c-></code>. </p><p>7. <i>Effects:</i> As if by <code class="highlight"><c- n>swap</c-><c- p>(</c-><c- o>*</c-><c- n>a</c-><c- p>,</c-> <c- o>*</c-><c- n>b</c-><c- p>)</c-></code>. </p></small>
   </blockquote>
   <h3 class="heading settled" data-level="5.5" id="wording-utility.swap"><span class="secno">5.5. </span><span class="content">[utility.swap] (unchanged)</span><a class="self-link" href="#wording-utility.swap"></a></h3>
   <p><a href="https://eel.is/c++draft/utility.swap">[utility.swap]</a> does not seem to require any changes:</p>
   <p><small></small></p>
   <blockquote>
    <p></p>
    <small> <pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- o>></c->
  <c- k>constexpr</c-> <c- b>void</c-> <c- n>swap</c-><c- p>(</c-><c- n>T</c-><c- o>&amp;</c-> <c- n>a</c-><c- p>,</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>b</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>(</c-><i><c- n>see</c-> <c- n>below</c-></i><c- p>);</c->
</pre><p>1. <i>Constraints:</i> <code class="highlight"><c- n>is_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_move_assignable_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code>. </p><p>2. <i>Preconditions:</i> Type <code class="highlight"><c- n>T</c-></code> meets the <em>Cpp17MoveConstructible</em> (Table 31) and <em>Cpp17MoveAssignable</em> (Table 33) requirements. </p><p>3. <i>Effects:</i> Exchanges values stored in two locations. </p><p>4. <i>Remarks:</i> The exception specification is equivalent to: <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-> <c- o>&amp;&amp;</c-> <c- n>is_nothrow_move_assignable_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> </p><pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- p>,</c-> <c- b>size_t</c-> <c- n>N</c-><c- o>></c->
  <c- k>constexpr</c-> <c- b>void</c-> <c- n>swap</c-><c- p>(</c-><c- n>T</c-> <c- p>(</c-><c- o>&amp;</c-><c- n>a</c-><c- p>)[</c-><c- n>N</c-><c- p>],</c-> <c- n>T</c-> <c- p>(</c-><c- o>&amp;</c-><c- n>b</c-><c- p>)[</c-><c- n>N</c-><c- p>])</c-> <c- k>noexcept</c-><c- p>(</c-><c- n>is_nothrow_swappable_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>);</c->
</pre><p>5. <i>Constraints:</i> <code class="highlight"><c- n>is_swappable_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code>. </p><p>6. <i>Preconditions:</i> <code class="highlight"><c- n>a</c-><c- p>[</c-><c- n>i</c-><c- p>]</c-></code> is swappable with ([swappable.requirements]) <code class="highlight"><c- n>b</c-><c- p>[</c-><c- n>i</c-><c- p>]</c-></code> for all <code class="highlight"><c- n>i</c-></code> in the range <code class="highlight"><c- p>[</c-><c- mi>0</c-><c- p>,</c-> <c- n>N</c-><c- p>)</c-></code>. </p><p>7. <i>Effects:</i> As if by <code class="highlight"><c- n>swap_ranges</c-><c- p>(</c-><c- n>a</c-><c- p>,</c-> <c- n>a</c-> <c- o>+</c-> <c- n>N</c-><c- p>,</c-> <c- n>b</c-><c- p>)</c-></code>. </p></small>
   </blockquote>
   <h3 class="heading settled" data-level="5.6" id="wording-iterator.cust.swap"><span class="secno">5.6. </span><span class="content">[iterator.cust.swap] (unchanged)</span><a class="self-link" href="#wording-iterator.cust.swap"></a></h3>
   <p class="note" role="note"><span class="marker">Note:</span> Trivial types may ignore the first bullet below, because even if a user-defined ADL <code class="highlight"><c- n>iter_swap</c-></code> is
available, it must "exchange the values denoted by <code class="highlight"><c- n>E1</c-></code> and <code class="highlight"><c- n>E2</c-></code>" — that is, it must not be observably different
from an ordinary (possibly trivial) swap. The second and third bullets explicitly describe ways of performing
an ordinary (possibly trivial) swap by hand; for any P1144 trivially relocatable type, these are guaranteed to
be tantamount to swapping the bytes. Therefore vendors can already optimize <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>iter_swap</c-></code> today,
without any change in this section’s wording.</p>
   <p><a href="https://eel.is/c++draft/iterator.cust.swap">[iterator.cust.swap]</a> does not seem to require any changes:</p>
   <p><small></small></p>
   <blockquote>
    <p></p>
    <small> <p>1. The name <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>iter_swap</c-></code> denotes a customization point object ([customization.point.object]) that exchanges the values ([concept.swappable]) denoted by its arguments. </p><p>2. Let <code class="highlight"><i><c- n>iter</c-><c- o>-</c-><c- n>exchange</c-><c- o>-</c-><c- n>move</c-></i></code> be the exposition-only function template: </p><pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>X</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Y</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>iter_value_t</c-><c- o>&lt;</c-><c- n>X</c-><c- o>></c-> <i><c- n>iter</c-><c- o>-</c-><c- n>exchange</c-><c- o>-</c-><c- n>move</c-></i><c- p>(</c-><c- n>X</c-><c- o>&amp;&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- n>Y</c-><c- o>&amp;&amp;</c-> <c- n>y</c-><c- p>)</c->
    <c- k>noexcept</c-><c- p>(</c-><c- k>noexcept</c-><c- p>(</c-><c- n>iter_value_t</c-><c- o>&lt;</c-><c- n>X</c-><c- o>></c-><c- p>(</c-><c- n>iter_move</c-><c- p>(</c-><c- n>x</c-><c- p>)))</c-> <c- o>&amp;&amp;</c->
             <c- k>noexcept</c-><c- p>(</c-><c- o>*</c-><c- n>x</c-> <c- o>=</c-> <c- n>iter_move</c-><c- p>(</c-><c- n>y</c-><c- p>)));</c->
</pre><p>3. <em>Effects:</em> Equivalent to: </p><pre class="highlight"><c- n>iter_value_t</c-><c- o>&lt;</c-><c- n>X</c-><c- o>></c-> <c- n>old_value</c-><c- p>(</c-><c- n>iter_move</c-><c- p>(</c-><c- n>x</c-><c- p>));</c->
<c- o>*</c-><c- n>x</c-> <c- o>=</c-> <c- n>iter_move</c-><c- p>(</c-><c- n>y</c-><c- p>);</c->
<c- k>return</c-> <c- n>old_value</c-><c- p>;</c->
</pre><p>4. The expression <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>iter_swap</c-><c- p>(</c-><c- n>E1</c-><c- p>,</c-> <c- n>E2</c-><c- p>)</c-></code> for subexpressions <code class="highlight"><c- n>E1</c-></code> and <code class="highlight"><c- n>E2</c-></code> is expression-equivalent to: </p><ul><li data-md><p><code class="highlight"><c- p>(</c-><c- b>void</c-><c- p>)</c-><c- n>iter_swap</c-><c- p>(</c-><c- n>E1</c-><c- p>,</c-> <c- n>E2</c-><c- p>)</c-></code>, if either <code class="highlight"><c- n>E1</c-></code> or <code class="highlight"><c- n>E2</c-></code> has class or enumeration type and <code class="highlight"><c- n>iter_swap</c-><c- p>(</c-><c- n>E1</c-><c- p>,</c-> <c- n>E2</c-><c- p>)</c-></code> is a well-formed expression
    with overload resolution performed in a context that includes the declaration</p> <pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>I1</c-><c- p>,</c-> <c- k>class</c-> <c- nc>I2</c-><c- o>></c->
  <c- b>void</c-> <c- n>iter_swap</c-><c- p>(</c-><c- n>I1</c-><c- p>,</c-> <c- n>I2</c-><c- p>)</c-> <c- o>=</c-> <c- k>delete</c-><c- p>;</c->
</pre><p>and does not include a declaration of <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>iter_swap</c-></code>. If the function selected by overload resolution
    does not exchange the values denoted by <code class="highlight"><c- n>E1</c-></code> and <code class="highlight"><c- n>E2</c-></code>, the program is ill-formed, no diagnostic required.
    [<i>Note:</i> This precludes calling unconstrained <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>iter_swap</c-></code>. When the deleted overload is viable,
    program-defined overloads need to be more specialized ([temp.func.order]) to be selected. <i>—end note</i>]</p> </li><li data-md><p>Otherwise, if the types of <code class="highlight"><c- n>E1</c-></code> and <code class="highlight"><c- n>E2</c-></code> each model <code class="highlight"><c- n>indirectly_readable</c-></code>, and if the reference types of <code class="highlight"><c- n>E1</c-></code> and <code class="highlight"><c- n>E2</c-></code> model <code class="highlight"><c- n>swappable_with</c-></code> ([concept.swappable]), then <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>swap</c-><c- p>(</c-><c- o>*</c-><c- n>E1</c-><c- p>,</c-> <c- o>*</c-><c- n>E2</c-><c- p>)</c-></code>.</p> </li><li data-md><p>Otherwise, if the types <code class="highlight"><c- n>T1</c-></code> and <code class="highlight"><c- n>T2</c-></code> of <code class="highlight"><c- n>E1</c-></code> and <code class="highlight"><c- n>E2</c-></code> model <code class="highlight"><c- n>indirectly_movable_storable</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>T2</c-><c- o>></c-></code> and <code class="highlight"><c- n>indirectly_movable_storable</c-><c- o>&lt;</c-><c- n>T2</c-><c- p>,</c-> <c- n>T1</c-><c- o>></c-></code>,
    then <code class="highlight"><c- p>(</c-><c- b>void</c-><c- p>)(</c-><c- o>*</c-><c- n>E1</c-> <c- o>=</c-> <i><c- n>iter</c-><c- o>-</c-><c- n>exchange</c-><c- o>-</c-><c- n>move</c-></i><c- p>(</c-><c- n>E2</c-><c- p>,</c-> <c- n>E1</c-><c- p>))</c-></code>, except that <code class="highlight"><c- n>E1</c-></code> is evaluated only once.</p> </li><li data-md><p>Otherwise, <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>iter_swap</c-><c- p>(</c-><c- n>E1</c-><c- p>,</c-> <c- n>E2</c-><c- p>)</c-></code> is ill-formed.
    [<i>Note:</i> This case can result in substitution failure when <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>iter_swap</c-><c- p>(</c-><c- n>E1</c-><c- p>,</c-> <c- n>E2</c-><c- p>)</c-></code> appears
    in the immediate context of a template instantiation. <i>—end note</i>]</p> </li></ul> </small>
   </blockquote>
  </main>
<script>
(function() {
  "use strict";
  var collapseSidebarText = '<span aria-hidden="true">←</span> '
                          + '<span>Collapse Sidebar</span>';
  var expandSidebarText   = '<span aria-hidden="true">→</span> '
                          + '<span>Pop Out Sidebar</span>';
  var tocJumpText         = '<span aria-hidden="true">↑</span> '
                          + '<span>Jump to Table of Contents</span>';

  var sidebarMedia = window.matchMedia('screen and (min-width: 78em)');
  var autoToggle   = function(e){ toggleSidebar(e.matches) };
  if(sidebarMedia.addListener) {
    sidebarMedia.addListener(autoToggle);
  }

  function toggleSidebar(on) {
    if (on == undefined) {
      on = !document.body.classList.contains('toc-sidebar');
    }

    /* Don’t scroll to compensate for the ToC if we’re above it already. */
    var headY = 0;
    var head = document.querySelector('.head');
    if (head) {
      // terrible approx of "top of ToC"
      headY += head.offsetTop + head.offsetHeight;
    }
    var skipScroll = window.scrollY < headY;

    var toggle = document.getElementById('toc-toggle');
    var tocNav = document.getElementById('toc');
    if (on) {
      var tocHeight = tocNav.offsetHeight;
      document.body.classList.add('toc-sidebar');
      document.body.classList.remove('toc-inline');
      toggle.innerHTML = collapseSidebarText;
      if (!skipScroll) {
        window.scrollBy(0, 0 - tocHeight);
      }
      tocNav.focus();
      sidebarMedia.addListener(autoToggle); // auto-collapse when out of room
    }
    else {
      document.body.classList.add('toc-inline');
      document.body.classList.remove('toc-sidebar');
      toggle.innerHTML = expandSidebarText;
      if (!skipScroll) {
        window.scrollBy(0, tocNav.offsetHeight);
      }
      if (toggle.matches(':hover')) {
        /* Unfocus button when not using keyboard navigation,
           because I don’t know where else to send the focus. */
        toggle.blur();
      }
    }
  }

  function createSidebarToggle() {
    /* Create the sidebar toggle in JS; it shouldn’t exist when JS is off. */
    var toggle = document.createElement('a');
      /* This should probably be a button, but appearance isn’t standards-track.*/
    toggle.id = 'toc-toggle';
    toggle.class = 'toc-toggle';
    toggle.href = '#toc';
    toggle.innerHTML = collapseSidebarText;

    sidebarMedia.addListener(autoToggle);
    var toggler = function(e) {
      e.preventDefault();
      sidebarMedia.removeListener(autoToggle); // persist explicit off states
      toggleSidebar();
      return false;
    }
    toggle.addEventListener('click', toggler, false);


    /* Get <nav id=toc-nav>, or make it if we don’t have one. */
    var tocNav = document.getElementById('toc-nav');
    if (!tocNav) {
      tocNav = document.createElement('p');
      tocNav.id = 'toc-nav';
      /* Prepend for better keyboard navigation */
      document.body.insertBefore(tocNav, document.body.firstChild);
    }
    /* While we’re at it, make sure we have a Jump to Toc link. */
    var tocJump = document.getElementById('toc-jump');
    if (!tocJump) {
      tocJump = document.createElement('a');
      tocJump.id = 'toc-jump';
      tocJump.href = '#toc';
      tocJump.innerHTML = tocJumpText;
      tocNav.appendChild(tocJump);
    }

    tocNav.appendChild(toggle);
  }

  var toc = document.getElementById('toc');
  if (toc) {
    createSidebarToggle();
    toggleSidebar(sidebarMedia.matches);

    /* If the sidebar has been manually opened and is currently overlaying the text
       (window too small for the MQ to add the margin to body),
       then auto-close the sidebar once you click on something in there. */
    toc.addEventListener('click', function(e) {
      if(e.target.tagName.toLowerCase() == "a" && document.body.classList.contains('toc-sidebar') && !sidebarMedia.matches) {
        toggleSidebar(false);
      }
    }, false);
  }
  else {
    console.warn("Can’t find Table of Contents. Please use <nav id='toc'> around the ToC.");
  }

  /* Wrap tables in case they overflow */
  var tables = document.querySelectorAll(':not(.overlarge) > table.data, :not(.overlarge) > table.index');
  var numTables = tables.length;
  for (var i = 0; i < numTables; i++) {
    var table = tables[i];
    var wrapper = document.createElement('div');
    wrapper.className = 'overlarge';
    table.parentNode.insertBefore(wrapper, table);
    wrapper.appendChild(table);
  }

})();
</script>
  <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-p1144">[P1144]
   <dd>Arthur O'Dwyer. <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p1144r9.html"><cite>std::is_trivially_relocatable</cite></a>. October 2023. URL: <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p1144r9.html">https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p1144r9.html</a>
   <dt id="biblio-p2785">[P2785]
   <dd>Sébastien Bini; Ed Catmur. <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2785r3.html"><cite>Relocating prvalues</cite></a>. June 2023. URL: <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2785r3.html">https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2785r3.html</a>
   <dt id="biblio-p2786">[P2786]
   <dd>Mungo Gill; Alisdair Meredith. <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2786r3.pdf"><cite>Trivial relocatability for C++26</cite></a>. October 2023. URL: <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2786r3.pdf">https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2786r3.pdf</a>
   <dt id="biblio-p2839">[P2839]
   <dd>Brian Bi; Joshua Berne. <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2839r0.html"><cite>Non-trivial relocation via a new owning reference type</cite></a>. May 2023. URL: <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2839r0.html">https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2839r0.html</a>
   <dt id="biblio-p2959">[P2959]
   <dd>Alisdair Meredith. <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2959r0.html"><cite>Relocation within containers</cite></a>. October 2023. URL: <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2959r0.html">https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2959r0.html</a>
   <dt id="biblio-p2967">[P2967]
   <dd>Alisdair Meredith. <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2967r0.pdf"><cite>Relocation has a library interface</cite></a>. October 2023. URL: <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2967r0.pdf">https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2967r0.pdf</a>
  </dl>