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  <title>P2248R8: Enabling list-initialization for algorithms</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 */
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		font-family: sans-serif;
		widows: 2;
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		word-wrap: break-word;
		overflow-wrap: break-word;
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		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%;
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	div.head h2 { margin-bottom: 1.5em;}

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

	.head .logo {
		float: right;
		margin: 0.4rem 0 0.2rem .4rem;
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	.head img[src*="logos/W3C"] {
		display: block;
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		border: solid var(--logo-bg);
		border-width: .65rem .7rem .6rem;
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		background: #1a5e9a;
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		color: white;
		color: var(--logo-text);
		font-weight: bold;
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	.head a:hover > img[src*="logos/W3C"],
	.head a:focus > img[src*="logos/W3C"] {
		opacity: .8;
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	.head a:active > img[src*="logos/W3C"] {
		background: #c00;
		background: var(--logo-active-bg);
		border-color: #c00;
		border-color: var(--logo-active-bg);
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	/* 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;
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			margin: 0;
			min-width: 1.33em;
			border-top-right-radius: 2rem;
			box-shadow: 0 0 2px;
			font-size: 1.5em;
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		#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);
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		#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;
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	/* Hide main scroller when only the ToC is visible anyway */
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		body.toc-sidebar {
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	}

	/* 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 d765c696b, updated Fri Mar 8 15:58:52 2024 -0800" name="generator">
  <link href="https://isocpp.org/favicon.ico" rel="icon">
  <meta content="dark light" name="color-scheme">
<style>
ins  {background-color: #CCFFCC; text-decoration: underline;}
del  {background-color: #FFCACA; text-decoration: line-through;}
</style>
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 <body class="h-entry">
  <div class="head">
   <p data-fill-with="logo"></p>
   <h1 class="p-name no-ref" id="title">P2248R8<br>Enabling list-initialization for algorithms</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="2024-03-20">2024-03-20</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:giuseppe.dangelo@kdab.com">Giuseppe D'Angelo</a>
     <dt>Audience:
     <dd>LWG, LEWG, SG6, SG9
     <dt>Project:
     <dd>ISO/IEC 14882 Programming Languages — C++, ISO/IEC JTC1/SC22/WG21
    </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 propose to default some template type parameters in certain
Standard Library function templates, so that these functions become
callable using list-initialization. These functions are
algorithmic related functions, available in <code class="highlight"><c- o>&lt;</c-><c- n>algorithm</c-><c- o>></c-></code> or in standard containers' headers.</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="#tonytables"><span class="secno">2</span> <span class="content">Tony Tables</span></a>
    <li><a href="#motivation"><span class="secno">3</span> <span class="content">Motivation and Scope</span></a>
    <li><a href="#impact"><span class="secno">4</span> <span class="content">Impact On The Standard</span></a>
    <li>
     <a href="#designdecisions"><span class="secno">5</span> <span class="content">Design Decisions</span></a>
     <ol class="toc">
      <li>
       <a href="#rationale"><span class="secno">5.1</span> <span class="content">What is the rationale for the default chosen in each case?</span></a>
       <ol class="toc">
        <li><a href="##ccerationale"><span class="secno">5.1.1</span> <span class="content">Consistent Container Erasure</span></a>
        <li><a href="###outputalgorithmsrationale"><span class="secno">5.1.2</span> <span class="content">Algorithms with an output iterator/range (where <code class="highlight"><c- n>T</c-></code> belongs to that output)</span></a>
        <li><a href="#inputalgorithmsrationale"><span class="secno">5.1.3</span> <span class="content">Algorithms with a (mutable) input iterator/range (where <code class="highlight"><c- n>T</c-></code> belongs to the input)</span></a>
        <li><a href="#replace_copy"><span class="secno">5.1.4</span> <span class="content">The problem of establishing a default for <code class="highlight"><c- n>replace_copy</c-></code></span></a>
       </ol>
      <li><a href="#numericalgorithms"><span class="secno">5.2</span> <span class="content">Numeric algorithms</span></a>
      <li><a href="#apicompatibility"><span class="secno">5.3</span> <span class="content">Is this API compatible?</span></a>
      <li>
       <a href="#abicompatibility"><span class="secno">5.4</span> <span class="content">Is this ABI compatible?</span></a>
       <ol class="toc">
        <li><a href="#changes-to-consistent-container-erasure-and-non-range-based-algorithms"><span class="secno">5.4.1</span> <span class="content">Changes to consistent container erasure and non-range-based algorithms</span></a>
        <li><a href="#changes-to-range-based-algorithms"><span class="secno">5.4.2</span> <span class="content">Changes to range-based algorithms</span></a>
       </ol>
      <li><a href="#ranges"><span class="secno">5.5</span> <span class="content">Range-based algorithms</span></a>
      <li><a href="#userspecifiedtemplateparameters"><span class="secno">5.6</span> <span class="content">What about user-specified template parameters?</span></a>
      <li><a href="#templateparametersreordering"><span class="secno">5.7</span> <span class="content">Is the Standard Library allowed to reorder deducible template parameters of algorithms?</span></a>
      <li><a href="#outputiteratorsvoid"><span class="secno">5.8</span> <span class="content">What about output iterators, whose <code class="highlight"><c- n>value_type</c-></code> may be <code class="highlight"><c- b>void</c-></code>?</span></a>
      <li>
       <a href="#projection"><span class="secno">5.9</span> <span class="content">The need of a custom projection type transformation</span></a>
       <ol class="toc">
        <li><a href="#projectionapi"><span class="secno">5.9.1</span> <span class="content">Providing the projected value as an API</span></a>
       </ol>
     </ol>
    <li><a href="#implementationexperience"><span class="secno">6</span> <span class="content">Implementation experience</span></a>
    <li>
     <a href="#technicalspecifications"><span class="secno">7</span> <span class="content">Technical Specifications</span></a>
     <ol class="toc">
      <li><a href="#feature-testing-macro"><span class="secno">7.1</span> <span class="content">Feature testing macro</span></a>
      <li><a href="#consistent-container-erasure"><span class="secno">7.2</span> <span class="content">Consistent Container Erasure</span></a>
      <li><a href="#iterators"><span class="secno">7.3</span> <span class="content">Iterators</span></a>
      <li>
       <a href="#algorithms"><span class="secno">7.4</span> <span class="content">Algorithms</span></a>
       <ol class="toc">
        <li><a href="#algfind"><span class="secno">7.4.1</span> <span class="content">[alg.find]</span></a>
        <li><a href="#algcount"><span class="secno">7.4.2</span> <span class="content">[alg.count]</span></a>
        <li><a href="#algsearch"><span class="secno">7.4.3</span> <span class="content">[alg.search]</span></a>
        <li><a href="#algreplace"><span class="secno">7.4.4</span> <span class="content">[alg.replace]</span></a>
        <li><a href="#algfill"><span class="secno">7.4.5</span> <span class="content">[alg.fill]</span></a>
        <li><a href="#algremove"><span class="secno">7.4.6</span> <span class="content">[alg.remove]</span></a>
        <li><a href="#algbinarysearch"><span class="secno">7.4.7</span> <span class="content">[alg.binary.search]</span></a>
        <li><a href="#algfold"><span class="secno">7.4.8</span> <span class="content">[alg.fold]</span></a>
        <li><a href="#algcontains"><span class="secno">7.4.9</span> <span class="content">[alg.contains]</span></a>
       </ol>
     </ol>
    <li><a href="#acknowledgements"><span class="secno">8</span> <span class="content">Acknowledgements</span></a>
    <li>
     <a href="#references"><span class="secno"></span> <span class="content">References</span></a>
     <ol class="toc">
      <li><a href="#informative"><span class="secno"></span> <span class="content">Informative References</span></a>
     </ol>
   </ol>
  </nav>
  <main>
   <h2 class="heading settled" data-level="1" id="changelog"><span class="secno">1. </span><span class="content">Changelog</span><a class="self-link" href="#changelog"></a></h2>
   <ul>
    <li data-md>
     <p>R8</p>
     <ul>
      <li data-md>
       <p>Wording-only changes after LWG review:</p>
       <ul>
        <li data-md>
         <p>Rebase on top of the latest Standard draft.</p>
        <li data-md>
         <p>Incorporate the changes to <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>fold</c-></code> and <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>contains</c-></code> (the respective papers have been merged after R7).</p>
        <li data-md>
         <p>Fix a typo in the specification of <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>count</c-></code> (missing comma).</p>
        <li data-md>
         <p>Fix the reference to the exposition-only alias template <code class="highlight"><c- n>indirect</c-><c- o>-</c-><c- n>value</c-><c- o>-</c-><c- n>t</c-></code>.</p>
       </ul>
     </ul>
    <li data-md>
     <p>R7</p>
     <ul>
      <li data-md>
       <p>New revision incorporating the feedback from LEWG in Kona; see <a href="#templateparametersreordering">§ 5.7 Is the Standard Library allowed to reorder deducible template parameters of algorithms?</a>.</p>
      <li data-md>
       <p>Rebased the wording on top of the latest C++ Standard draft.</p>
      <li data-md>
       <p>Added freestanding comment to <code class="highlight"><c- n>projected_value_t</c-></code>.</p>
      <li data-md>
       <p>Fixed typos in the proposed wording.</p>
     </ul>
    <li data-md>
     <p>R6</p>
     <ul>
      <li data-md>
       <p>Removed the numeric algorithms from the present proposal (see <a href="#numericalgorithms">§ 5.2 Numeric algorithms</a>).</p>
     </ul>
    <li data-md>
     <p>R5</p>
     <ul>
      <li data-md>
       <p>New revision incorporating the feedback after a LEWG telecon.</p>
      <li data-md>
       <p><code class="highlight"><c- n>projected_value</c-></code> has been given a new, simpler formulation; and renamed to <code class="highlight"><c- n>projected_value_t</c-></code>.</p>
      <li data-md>
       <p>Discussed the interactions of <code class="highlight"><c- n>projected_value_t</c-></code> with <a data-link-type="biblio" href="#biblio-p2609r0" title="Relaxing Ranges Just A Smidge">[P2609R0]</a> (see <a href="#projectionapi">§ 5.9.1 Providing the projected value as an API</a>).</p>
      <li data-md>
       <p>Extended the proposal to also cover <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>fold</c-></code> (<a data-link-type="biblio" href="#biblio-p2322r6" title="ranges::fold">[P2322R6]</a>) and <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>contains</c-></code> (<a data-link-type="biblio" href="#biblio-p2302r4" title="std::ranges::contains">[P2302R4]</a>), should they get approved and merged.</p>
      <li data-md>
       <p>Added a reference to the implementation experience in HPX.</p>
     </ul>
    <li data-md>
     <p>R4</p>
     <ul>
      <li data-md>
       <p>Dropped the proposed default from the non-range version of <code class="highlight"><c- n>replace_copy</c-></code>, elaborating on the rationale (see <a href="#replace_copy">§ 5.1.4 The problem of establishing a default for replace_copy</a>).</p>
      <li data-md>
       <p>Fixed minor misspellings.</p>
      <li data-md>
       <p>Clarified the wording for some design decisions regarding the numeric algorithms (no design has actually changed).</p>
     </ul>
    <li data-md>
     <p>R3</p>
     <ul>
      <li data-md>
       <p>Fixed the default for the range version of <code class="highlight"><c- n>replace_copy_if</c-></code>. Thanks to Casey Carter for spotting it.</p>
      <li data-md>
       <p>Discussed the problem with projections in range-based algorithms.</p>
     </ul>
    <li data-md>
     <p>R2</p>
     <ul>
      <li data-md>
       <p>Elaborated on the rationale.</p>
      <li data-md>
       <p>Elaborated on [algorithms.requirements] and on <a data-link-type="biblio" href="#biblio-sd-8" title="SD-8: Standard Library Compatibility">[SD-8]</a>.</p>
      <li data-md>
       <p>Elaborated on defaulting value types for algorithms that use output iterators.</p>
      <li data-md>
       <p>Rebased on the top of the latest Standard.</p>
      <li data-md>
       <p>Added a link to a prototype implementation.</p>
      <li data-md>
       <p>Fixed the defaults for the <code class="highlight"><c- o>*</c-><c- n>_scan</c-></code> numeric algorithms.</p>
     </ul>
    <li data-md>
     <p>R1</p>
     <ul>
      <li data-md>
       <p>Clarified some possible sources of ABI incompatibility, which were (guiltly) not discussed in R0.</p>
      <li data-md>
       <p>Added a reference and some discussion related to <a data-link-type="biblio" href="#biblio-p1997r1" title="Relaxing Restrictions on Arrays">[P1997R1]</a>.</p>
      <li data-md>
       <p>Added a reference to [algorithms.requirements].</p>
      <li data-md>
       <p>Fixed misspellings / formatting.</p>
     </ul>
    <li data-md>
     <p>R0</p>
     <ul>
      <li data-md>
       <p>First submission</p>
     </ul>
   </ul>
   <h2 class="heading settled" data-level="2" id="tonytables"><span class="secno">2. </span><span class="content">Tony Tables</span><a class="self-link" href="#tonytables"></a></h2>
   <table>
    <thead>
     <tr>
      <th>Before
      <th>After
    <tbody>
     <tr>
      <td>
<pre class="highlight"><c- k>struct</c-> <c- nc>point</c-> <c- p>{</c-> <c- b>int</c-> <c- n>x</c-><c- p>;</c-> <c- b>int</c-> <c- n>y</c-><c- p>;</c-> <c- p>};</c->

<c- n>std</c-><c- o>::</c-><c- n>vector</c-><c- o>&lt;</c-><c- n>point</c-><c- o>></c-> <c- n>v</c-><c- p>;</c->

<c- n>v</c-><c- p>.</c-><c- n>push_back</c-><c- p>({</c-><c- mi>3</c-><c- p>,</c-> <c- mi>4</c-><c- p>});</c-> <c- c1>// No need to specify the "point" type here...</c->

<c- c1>// ... but must spell out the type here:</c->
<c- c1>// an initializer list in algorithms is not able to deduce the type</c->
<c- n>std</c-><c- o>::</c-><c- n>find</c-><c- p>(</c-><c- n>v</c-><c- p>.</c-><c- n>begin</c-><c- p>(),</c-> <c- n>v</c-><c- p>.</c-><c- n>end</c-><c- p>(),</c-> <u><c- n>point</c-><c- p>{</c-><c- mi>3</c-><c- p>,</c-> <c- mi>4</c-><c- p>}</c-></u><c- p>);</c->
<c- n>std</c-><c- o>::</c-><c- n>lower_bound</c-><c- p>(</c-><c- n>v</c-><c- p>.</c-><c- n>begin</c-><c- p>(),</c-> <c- n>v</c-><c- p>.</c-><c- n>end</c-><c- p>(),</c-> <u><c- n>point</c-><c- p>{</c-><c- mi>3</c-><c- p>,</c-> <c- mi>4</c-><c- p>}</c-></u><c- p>);</c->
<c- n>std</c-><c- o>::</c-><c- n>search_n</c-><c- p>(</c-><c- n>v</c-><c- p>.</c-><c- n>begin</c-><c- p>(),</c-> <c- n>v</c-><c- p>.</c-><c- n>end</c-><c- p>(),</c-> <c- mi>10</c-><c- p>,</c-> <u><c- n>point</c-><c- p>{</c-><c- mi>3</c-><c- p>,</c-> <c- mi>4</c-><c- p>}</c-></u><c- p>);</c->
<c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>fill</c-><c- p>(</c-><c- n>v</c-><c- p>,</c-> <u><c- n>point</c-><c- p>{</c-><c- mi>3</c-><c- p>,</c-> <c- mi>4</c-><c- p>}</c-></u><c- p>);</c->
<c- n>erase</c-><c- p>(</c-><c- n>v</c-><c- p>,</c-> <u><c- n>point</c-><c- p>{</c-><c- mi>3</c-><c- p>,</c-> <c- mi>4</c-><c- p>}</c-></u><c- p>);</c->
</pre>
      <td>
<pre class="highlight"><c- k>struct</c-> <c- nc>point</c-> <c- p>{</c-> <c- b>int</c-> <c- n>x</c-><c- p>;</c-> <c- b>int</c-> <c- n>y</c-><c- p>;</c-> <c- p>};</c->

<c- n>std</c-><c- o>::</c-><c- n>vector</c-><c- o>&lt;</c-><c- n>point</c-><c- o>></c-> <c- n>v</c-><c- p>;</c->

<c- n>v</c-><c- p>.</c-><c- n>push_back</c-><c- p>({</c-><c- mi>3</c-><c- p>,</c-> <c- mi>4</c-><c- p>});</c->

<c- c1>// With the proposed changes: can use initializer lists,</c->
<c- c1>// the type gets deduced from the iterators/ranges/containers</c->
<c- n>std</c-><c- o>::</c-><c- n>find</c-><c- p>(</c-><c- n>v</c-><c- p>.</c-><c- n>begin</c-><c- p>(),</c-> <c- n>v</c-><c- p>.</c-><c- n>end</c-><c- p>(),</c-> <u><c- p>{</c-><c- mi>3</c-><c- p>,</c-> <c- mi>4</c-><c- p>}</c-></u><c- p>);</c->
<c- n>std</c-><c- o>::</c-><c- n>lower_bound</c-><c- p>(</c-><c- n>v</c-><c- p>.</c-><c- n>begin</c-><c- p>(),</c-> <c- n>v</c-><c- p>.</c-><c- n>end</c-><c- p>(),</c-> <u><c- p>{</c-><c- mi>3</c-><c- p>,</c-> <c- mi>4</c-><c- p>}</c-></u><c- p>);</c->
<c- n>std</c-><c- o>::</c-><c- n>search_n</c-><c- p>(</c-><c- n>v</c-><c- p>.</c-><c- n>begin</c-><c- p>(),</c-> <c- n>v</c-><c- p>.</c-><c- n>end</c-><c- p>(),</c-> <c- mi>10</c-><c- p>,</c-> <u><c- p>{</c-><c- mi>3</c-><c- p>,</c-> <c- mi>4</c-><c- p>}</c-></u><c- p>);</c->
<c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>fill</c-><c- p>(</c-><c- n>v</c-><c- p>,</c-> <u><c- p>{</c-><c- mi>3</c-><c- p>,</c-> <c- mi>4</c-><c- p>}</c-></u><c- p>);</c->
<c- n>erase</c-><c- p>(</c-><c- n>v</c-><c- p>,</c-> <u><c- p>{</c-><c- mi>3</c-><c- p>,</c-> <c- mi>4</c-><c- p>}</c-></u><c- p>);</c->
</pre>
   </table>
   <h2 class="heading settled" data-level="3" id="motivation"><span class="secno">3. </span><span class="content">Motivation and Scope</span><a class="self-link" href="#motivation"></a></h2>
   <p>List-initialization ([dcl.init.list]) has been introduced in C++11. When
an initializer list is used as a function argument, overload resolution
works in a specific way to find a suitable overload, possibly
constructing a temporary object of the argument’s type (see
[over.ics.list]).</p>
   <p>This language feature allows to write code like this:</p>
<pre class="highlight"><c- b>void</c-> <c- nf>f</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>complex</c-><c- o>&lt;</c-><c- b>double</c-><c- o>></c-><c- p>);</c->
<c- n>f</c-><c- p>({</c-><c- mf>1.23</c-><c- p>,</c-> <c- mf>4.56</c-><c- p>});</c-> <c- c1>// OK</c->
</pre>
   <p>In case of function templates, the deduction rules do not allow
deduction in the general case, because a type cannot be determined
([temp.deduct.call]). It is however allowed to use an initalizer list
in case the corresponding template type parameter has a default:</p>
<pre class="highlight"><c- k>template</c-> <c- o>&lt;</c-><c- k>typename</c-> <c- nc>T</c-><c- o>></c-> <c- b>void</c-> <c- n>g</c-><c- p>(</c-><c- n>T</c-><c- p>);</c->
<c- n>g</c-><c- p>({</c-><c- mi>1</c-><c- p>,</c-> <c- mi>2</c-><c- p>});</c->     <c- c1>// ERROR: cannot deduce T</c->


<c- k>template</c-> <c- o>&lt;</c-><c- k>typename</c-> <c- nc>T</c-> <c- o>=</c-> <c- n>std</c-><c- o>::</c-><c- n>complex</c-><c- o>&lt;</c-><c- b>double</c-><c- o>>></c-> <c- b>void</c-> <c- n>h</c-><c- p>(</c-><c- n>T</c-><c- p>);</c->
<c- n>h</c-><c- p>({</c-><c- mf>1.0</c-><c- p>,</c-> <c- mf>2.0</c-><c- p>});</c-> <c- c1>// OK, the default is used for deducing T</c->
</pre>
   <p>Default template type parameters have a somehow poor adoption in the
Standard Library. They are used for instance in <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>exchange</c-></code>:</p>
<pre class="highlight"><c- k>namespace</c-> <c- nn>std</c-> <c- p>{</c->
  <c- c1>// [utility.exchange]</c->
  <c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- p>,</c-> <c- k>class</c-> <c- nc>U</c-> <c- o>=</c-> <c- n>T</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>T</c-> <c- n>exchange</c-><c- p>(</c-><c- n>T</c-><c- o>&amp;</c-> <c- n>obj</c-><c- p>,</c-> <c- n>U</c-><c- o>&amp;&amp;</c-> <c- n>new_val</c-><c- p>);</c->
<c- p>}</c->

<c- c1>// thanks to U defaulted to T, we can write this:</c->
<c- n>std</c-><c- o>::</c-><c- n>complex</c-><c- o>&lt;</c-><c- b>double</c-><c- o>></c-> <c- n>old_val</c-><c- p>;</c->
<c- k>auto</c-> <c- n>new_val</c-> <c- o>=</c-> <c- n>std</c-><c- o>::</c-><c- n>exchange</c-><c- p>(</c-><c- n>old_val</c-><c- p>,</c-> <c- p>{</c-><c- mf>3.0</c-><c- p>,</c-> <c- mf>4.0</c-><c- p>});</c-> <c- c1>// OK</c->

<c- c1>// old_vec is moved onto new_vec, and reset to a default-constructed state</c->
<c- n>std</c-><c- o>::</c-><c- n>vector</c-><c- o>&lt;</c-><c- b>int</c-><c- o>></c-> <c- n>old_vec</c-><c- p>;</c->
<c- k>auto</c-> <c- n>new_vec</c-> <c- o>=</c-> <c- n>std</c-><c- o>::</c-><c- n>exchange</c-><c- p>(</c-><c- n>old_vec</c-><c- p>,</c-> <c- p>{});</c-> <c- c1>// OK</c->
</pre>
   <p>Unfortunately, they are not used in a number of other places,
such as some standard algorithms, although reasonable defaults could
still be determined based on other available template parameters.</p>
   <p>Let’s consider C++20’s <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>erase</c-></code> for <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>vector</c-></code>:</p>
<pre class="highlight"><c- k>namespace</c-> <c- nn>std</c-> <c- p>{</c->
  <c- c1>// [vector.erasure]</c->
  <c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Allocator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>U</c-><c- o>></c->
  <c- k>constexpr</c-> <c- k>typename</c-> <c- nc>vector</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>Allocator</c-><c- o>>::</c-><c- n>size_type</c->
  <c- n>erase</c-><c- p>(</c-><c- n>vector</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>Allocator</c-><c- o>>&amp;</c-> <c- n>c</c-><c- p>,</c-> <c- k>const</c-> <c- n>U</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>);</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>complex</c-><c- o>&lt;</c-><c- b>double</c-><c- o>>></c-> <c- n>numbers</c-><c- p>;</c->
<c- n>numbers</c-><c- p>.</c-><c- n>push_back</c-><c- p>({</c-><c- mf>1.0</c-><c- p>,</c-> <c- mf>2.0</c-><c- p>});</c-> <c- c1>// OK</c->
<c- n>erase</c-><c- p>(</c-><c- n>numbers</c-><c- p>,</c-> <c- p>{</c-><c- mf>1.0</c-><c- p>,</c-> <c- mf>2.0</c-><c- p>});</c->    <c- c1>// ERROR: cannot deduce U</c->
</pre>
   <p>Since <code class="highlight"><c- n>U</c-></code> does not have a default, one cannot use list initialization
for the <code class="highlight"><c- n>value</c-></code> parameter (see the examples in the <a href="#tonytables">§ 2 Tony Tables</a> above). Instead, <code class="highlight"><c- n>U</c-></code> could be reasonably defaulted to <code class="highlight"><c- n>T</c-></code> in <code class="highlight"><c- n>erase</c-></code>’s
template argument list (just like <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>exchange</c-></code>) and therefore
enabling the above syntax. This is one of the changes we are proposing.</p>
   <p>Similarly, an algorithm like <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>find</c-></code> is also lacking a default:</p>
<pre class="highlight"><c- k>namespace</c-> <c- nn>std</c-> <c- p>{</c->
  <c- c1>// [alg.find]</c->
  <c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>InputIterator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>InputIterator</c->
  <c- n>find</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>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>);</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>complex</c-><c- o>&lt;</c-><c- b>double</c-><c- o>>></c-> <c- n>numbers</c-><c- p>;</c->
<c- n>numbers</c-><c- p>.</c-><c- n>push_back</c-><c- p>({</c-><c- mf>1.0</c-><c- p>,</c-> <c- mf>2.0</c-><c- p>});</c->                       <c- c1>// OK</c->
<c- n>std</c-><c- o>::</c-><c- n>find</c-><c- p>(</c-><c- n>vector</c-><c- p>.</c-><c- n>begin</c-><c- p>(),</c-> <c- n>vector</c-><c- p>.</c-><c- n>end</c-><c- p>(),</c-> <c- p>{</c-><c- mf>1.0</c-><c- p>,</c-> <c- mf>2.0</c-><c- p>});</c-> <c- c1>// ERROR</c->
</pre>
   <p>In this case <code class="highlight"><c- n>T</c-></code> could be reasonably defaulted to be the value type of
the input iterator, that is, <code class="highlight"><c- k>typename</c-> <c- nc>std</c-><c- o>::</c-><c- n>iterator_traits</c-><c- o>&lt;</c-><c- n>InputIterator</c-><c- o>>::</c-><c- n>value_type</c-></code>. We are also proposing
this change.</p>
   <div class="note" role="note">
    <p>In a nutshell: we are proposing to add a default template type
parameter to the "algorithmic" function templates in the Standard
Library:</p>
    <ol>
     <li data-md>
      <p>which have a "value"-like function argument; and</p>
     <li data-md>
      <p>for which a reasonable default type can be inferred from the other
template type parameters.</p>
    </ol>
    <p>This enables users to call these functions by using list-initialization
for the "value"-like arguments.</p>
   </div>
   <h2 class="heading settled" data-level="4" id="impact"><span class="secno">4. </span><span class="content">Impact On The Standard</span><a class="self-link" href="#impact"></a></h2>
   <p>The proposed changes only affect existing Standard Library function templates.
The impact is mostly positive: syntax that was ill-formed before becomes
well-formed. There is a chance of incompatibility w.r.t. user code, but <a data-link-type="biblio" href="#biblio-sd-8" title="SD-8: Standard Library Compatibility">[SD-8]</a> allows the kind of changes we are proposing.</p>
   <p>This proposal does not depend on any other library extensions.</p>
   <p>This proposal does not require any changes in the core language.</p>
   <p>The first part of <a data-link-type="biblio" href="#biblio-p2218r0" title="More flexible optional::value_or()">[P2218R0]</a> is related to this proposal. <a data-link-type="biblio" href="#biblio-p2218r0" title="More flexible optional::value_or()">[P2218R0]</a> proposes to default the template type parameter of <code class="highlight"><c- n>optional</c-><c- o>::</c-><c- n>value_or</c-></code>. We are not proposing the same, as we are limiting
the scope of this paper to algorithms; we can’t help but notice however
that the underlying rationale is exactly the same (enabling
list-initialization for a "value" parameter).</p>
   <p><a data-link-type="biblio" href="#biblio-p1997r1" title="Relaxing Restrictions on Arrays">[P1997R1]</a> proposes some changes to the core language in order to make array
types copiable, assignable, etc. We are not proposing any changes to the
language; however it’s interesting to note that, if <a data-link-type="biblio" href="#biblio-p1997r1" title="Relaxing Restrictions on Arrays">[P1997R1]</a> is adopted,
then using arrays as value types in containers and algorithms may become more
widespread. (Right now, array types are usable in containers/algorithms in
extremely limited ways.) The present proposal would then make it possible to
use list-initialization in order to create arrays as the arguments of
algorithmic-like functions, for instance like this:</p>
<pre class="highlight"><c- c1>// in principle, possible under P1997R1</c->
<c- n>std</c-><c- o>::</c-><c- n>vector</c-><c- o>&lt;</c-><c- b>int</c-><c- p>[</c-><c- mi>2</c-><c- p>]</c-><c- o>></c-> <c- n>v</c-><c- p>(</c-><c- mi>42</c-><c- p>);</c->
<c- n>v</c-><c- p>.</c-><c- n>push_back</c-><c- p>({</c-><c- mi>1</c-><c- p>,</c-> <c- mi>2</c-><c- p>});</c->

<c- c1>// in principle, possible under P1997R1 + this proposal</c->
<c- c1>// (T defaults to int[2], second parameter is deduced as const int(&amp;)[2],</c->
<c- c1>// then aggregate initialization is selected)</c->
<c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>fill</c-><c- p>(</c-><c- n>v</c-><c- p>,</c-> <c- p>{</c-><c- mi>123</c-><c- p>,</c-> <c- mi>456</c-><c- p>});</c->
</pre>
   <p><a data-link-type="biblio" href="#biblio-p2609r0" title="Relaxing Ranges Just A Smidge">[P2609R0]</a> proposes an alias template (<code class="highlight"><c- n>indirect_value_t</c-></code>) which is
extremely similar to the <code class="highlight"><c- n>projected_value_t</c-></code> alias proposed by this
paper. <code class="highlight"><c- n>projected_value_t</c-></code> could, in fact, be entirely reformulated in
terms of <code class="highlight"><c- n>indirect_value_t</c-></code> (cf. the discussion in <a href="#projectionapi">§ 5.9.1 Providing the projected value as an API</a>).</p>
   <h2 class="heading settled" data-level="5" id="designdecisions"><span class="secno">5. </span><span class="content">Design Decisions</span><a class="self-link" href="#designdecisions"></a></h2>
   <h3 class="heading settled" data-level="5.1" id="rationale"><span class="secno">5.1. </span><span class="content">What is the rationale for the default chosen in each case?</span><a class="self-link" href="#rationale"></a></h3>
   <p>We have tried to keep the choice of the default as much straightforward as
possible, by following this set of rules/guidelines.</p>
   <p>In the following, <code class="highlight"><c- n>T</c-></code> is the template type parameter for the value-like
parameter of each function.</p>
   <h4 class="heading settled" data-level="5.1.1" id="#ccerationale"><span class="secno">5.1.1. </span><span class="content">Consistent Container Erasure</span><a class="self-link" href="#%23ccerationale"></a></h4>
   <p>These would simply default <code class="highlight"><c- n>T</c-></code> to the "value type" of the container.
We are proposing to change all these algorithms (for <code class="highlight"><c- n>basic_string</c-></code>, <code class="highlight"><c- n>deque</c-></code>, <code class="highlight"><c- n>forward_list</c-></code>, <code class="highlight"><c- n>list</c-></code>, and <code class="highlight"><c- n>vector</c-></code>).</p>
   <h4 class="heading settled" data-level="5.1.2" id="##outputalgorithmsrationale"><span class="secno">5.1.2. </span><span class="content">Algorithms with an output iterator/range (where <code class="highlight"><c- n>T</c-></code> belongs to that output)</span><a class="self-link" href="#%23%23outputalgorithmsrationale"></a></h4>
   <p>For those we are proposing to use the <code class="highlight"><c- n>value_type</c-></code> of the output iterators/range.
(This may be <code class="highlight"><c- b>void</c-></code>; see <a href="#outputiteratorsvoid">§ 5.8 What about output iterators, whose value_type may be void?</a>). The rationale is that the
output iterator is going to give us the type which is going to be ultimately
stored into it, and therefore that’s the type to default to.</p>
   <p>The algorithms in this category that we are proposing to change are:</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>fill_n</c-></code></p>
    <li data-md>
     <p><code class="highlight"><c- n>replace_copy</c-></code> (see <a href="#replace_copy">§ 5.1.4 The problem of establishing a default for replace_copy</a>)</p>
    <li data-md>
     <p><code class="highlight"><c- n>replace_copy_if</c-></code></p>
   </ul>
   <h4 class="heading settled" data-level="5.1.3" id="inputalgorithmsrationale"><span class="secno">5.1.3. </span><span class="content">Algorithms with a (mutable) input iterator/range (where <code class="highlight"><c- n>T</c-></code> belongs to the input)</span><a class="self-link" href="#inputalgorithmsrationale"></a></h4>
   <p>Similarly, we’re proposing to default the value-like type to the <code class="highlight"><c- n>value_type</c-></code> of the input iterator/range, eventually after projection (in the case of
range-based algorithms); see the discussion in <a href="#projection">§ 5.9 The need of a custom projection type transformation</a>.</p>
   <p>The algorithms in this category that we are proposing to change are:</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>find</c-></code></p>
    <li data-md>
     <p><code class="highlight"><c- n>count</c-></code></p>
    <li data-md>
     <p><code class="highlight"><c- n>search_n</c-></code></p>
    <li data-md>
     <p><code class="highlight"><c- n>replace</c-></code></p>
    <li data-md>
     <p><code class="highlight"><c- n>replace_if</c-></code></p>
    <li data-md>
     <p><code class="highlight"><c- n>replace_copy</c-></code> (see <a href="#replace_copy">§ 5.1.4 The problem of establishing a default for replace_copy</a>)</p>
    <li data-md>
     <p><code class="highlight"><c- n>fill</c-></code></p>
    <li data-md>
     <p><code class="highlight"><c- n>remove</c-></code></p>
    <li data-md>
     <p><code class="highlight"><c- n>remove_copy</c-></code></p>
    <li data-md>
     <p><code class="highlight"><c- n>lower_bound</c-></code></p>
    <li data-md>
     <p><code class="highlight"><c- n>upper_bound</c-></code></p>
    <li data-md>
     <p><code class="highlight"><c- n>equal_range</c-></code></p>
    <li data-md>
     <p><code class="highlight"><c- n>binary_search</c-></code></p>
   </ul>
   <h4 class="heading settled" data-level="5.1.4" id="replace_copy"><span class="secno">5.1.4. </span><span class="content">The problem of establishing a default for <code class="highlight"><c- n>replace_copy</c-></code></span><a class="self-link" href="#replace_copy"></a></h4>
   <p>The non-range version of <code class="highlight"><c- n>replace_copy</c-></code> has this signature in [algorithm.syn]:</p>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>InputIterator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>OutputIterator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>OutputIterator</c-> <c- n>replace_copy</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- n>OutputIterator</c-> <c- n>result</c-><c- p>,</c->
                                        <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>old_value</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>new_value</c-><c- p>);</c->
</pre>
   <p>The issue with this signature is that there is only <strong>one</strong> template
type parameter for both the old value and the new value. (This is
probably an historical mistake; changing <code class="highlight"><c- n>replace_copy</c-></code> to have
two distinct template type parameters for the old value and the new
value is out of scope for the present proposal.)</p>
   <p>Now, if we were to pick a default for <code class="highlight"><c- n>T</c-></code>, we could choose to default
it to either the input iterator’s value type, or to the output
iterator’s value type. Unfortunately both choices could lead to confusion
and/or surprising behavior for end-users, who might expect the
parameter type to be defaulted to the "other" value type, and thus
accidentally introduce bugs.</p>
   <p>Consider this example, from a discussion on the LEWG reflector:</p>
<pre class="highlight"><c- n>std</c-><c- o>::</c-><c- n>vector</c-><c- o>&lt;</c-><c- n>std</c-><c- o>::</c-><c- n>pair</c-><c- o>&lt;</c-><c- b>int</c-><c- p>,</c-> <c- b>int</c-><c- o>>></c-> <c- n>intpairs</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>pair</c-><c- o>&lt;</c-><c- b>float</c-><c- p>,</c-> <c- b>float</c-><c- o>>></c-> <c- n>floatpairs</c-><c- p>;</c->

<c- n>std</c-><c- o>::</c-><c- n>replace_copy</c-><c- p>(</c-><c- n>intpairs</c-><c- p>.</c-><c- n>begin</c-><c- p>(),</c-> <c- n>intpairs</c-><c- p>.</c-><c- n>end</c-><c- p>(),</c->
                  <c- n>floatpairs</c-><c- p>.</c-><c- n>begin</c-><c- p>(),</c->
                  <c- p>{</c-> <c- mi>1</c-><c- p>,</c-> <c- mi>2</c-> <c- p>},</c->
                  <c- p>{</c-> <c- mf>3.14</c-><c- p>,</c-> <c- mf>3.14</c-> <c- p>});</c-> <c- c1>// &lt;-</c->
</pre>
   <p>If <code class="highlight"><c- n>T</c-></code> is defaulted to the <em>input</em>'s value type, then the last
parameter is actually a <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>pair</c-><c- o>&lt;</c-><c- b>int</c-><c- p>,</c-> <c- b>int</c-><c- o>></c-></code> equal to <code class="highlight"><c- p>{</c-><c- mi>3</c-><c- p>,</c-> <c- mi>3</c-><c- p>}</c-></code>; the
example has some (possibly unexpected) hidden data loss.</p>
   <p>If <code class="highlight"><c- n>T</c-></code> is instead defaulted to the <em>output</em>'s value type, one can build
a very similar example:</p>
<pre class="highlight"><c- n>std</c-><c- o>::</c-><c- n>replace_copy</c-><c- p>(</c-><c- n>floatpairs</c-><c- p>.</c-><c- n>begin</c-><c- p>(),</c-> <c- n>floatpairs</c-><c- p>.</c-><c- n>end</c-><c- p>(),</c->
                  <c- n>intpairs</c-><c- p>.</c-><c- n>begin</c-><c- p>(),</c->
                  <c- p>{</c-> <c- mf>3.14</c-><c- p>,</c-> <c- mf>3.14</c-> <c- p>},</c-> <c- c1>// &lt;-</c->
                  <c- p>{</c-> <c- mi>1</c-><c- p>,</c-> <c- mi>2</c-> <c- p>});</c->

</pre>
   <p>Now the fourth parameter will be converted to <code class="highlight"><c- p>{</c-><c- mi>3</c-><c- p>,</c-> <c- mi>3</c-><c- p>}</c-></code>, and again
possibly change the program semantics in an unexpected way.</p>
   <p>In conclusion: given no choice is <em>strongly</em> better than the other, and
given that ultimately the problem is due to an API flaw of <code class="highlight"><c- n>replace_copy</c-></code>, in R4 we are <strong>not</strong> proposing any change to the
non-range version.</p>
   <p>The range version of <code class="highlight"><c- n>replace_copy</c-></code> does not suffer from this issue,
because it features two different template type parameters, and
therefore allowing for two different defaults (the old value belongs to
the input range, the new value belongs to the output range). We
are proposing to add the defaults to that version, chosen according to
the above criteria.</p>
   <h3 class="heading settled" data-level="5.2" id="numericalgorithms"><span class="secno">5.2. </span><span class="content">Numeric algorithms</span><a class="self-link" href="#numericalgorithms"></a></h3>
   <p>Starting from the R6 revision of this paper, we are <strong>not</strong> proposing to
change the numeric algorithms (in <code class="highlight"><c- o>&lt;</c-><c- n>numeric</c-><c- o>></c-></code>).</p>
   <p>Although such algorithms also have a value-like parameter (usually used
a "starting point"), there does not seem to be consensus for
this change: a LEWG telecon poll on 2022-08-02 had results 1/6/1/5/1.</p>
   <p>Furthermore, additional discussion is needed in order to determine the
correct default, which may not necessarily be the <code class="highlight"><c- n>value_type</c-></code> of the
iterators.</p>
   <p>For these reasons, we are going to remove the numeric algorithms from
the present proposal, and submit a separate one to address them
specifically.</p>
   <h3 class="heading settled" data-level="5.3" id="apicompatibility"><span class="secno">5.3. </span><span class="content">Is this API compatible?</span><a class="self-link" href="#apicompatibility"></a></h3>
   <p>We are fairly certain that the proposed changes keep API compatibility.</p>
   <p>Technically speaking, defaulting a template type parameter of a
function template is a detectable change. Here’s an example (many
thanks to of Arthur O’Dwyer, who provided a much simpler one than ours):</p>
<pre class="highlight line-numbered"><span class="line-no" data-line="1"></span><span class="line"><c- k>template</c-> <c- o>&lt;</c-><c- k>typename</c-> <c- nc>A</c-><c- p>,</c-> <c- k>typename</c-> <c- nc>B</c-> <c- d>/* = A */</c-><c- o>></c-> <c- b>int</c-> <c- n>f</c-><c- p>(</c-><c- n>A</c-><c- p>,</c-> <c- n>B</c-><c- p>)</c-> <c- p>{</c-> <c- k>return</c-> <c- mi>1</c-><c- p>;</c-> <c- p>}</c-></span><span class="line-no" data-line="2"></span><span class="line"></span><span class="line-no" data-line="3"></span><span class="line"><c- b>int</c-> <c- n>f</c-><c- p>(</c-><c- b>int</c-><c- p>,</c-> <c- b>int</c-> <c- o>*</c-><c- p>)</c-> <c- p>{</c-> <c- k>return</c-> <c- mi>2</c-><c- p>;</c-> <c- p>}</c-></span><span class="line-no" data-line="4"></span><span class="line"></span><span class="line-no" data-line="5"></span><span class="line"><c- b>int</c-> <c- n>x</c-> <c- o>=</c-> <c- n>f</c-><c- p>(</c-><c- mi>0</c-><c- p>,</c-> <c- p>{</c-><c- mi>0</c-><c- p>});</c-></span></pre>
   <p>In this code <code class="highlight"><c- n>x</c-></code> is equal to 2 (there is only one candidate). If we
change line 1 so that <code class="highlight"><c- n>B</c-></code> is defaulted to <code class="highlight"><c- n>A</c-></code> (removing the comment
marks), then that function template is able to provide a better
candidate and <code class="highlight"><c- n>x</c-></code> will be 1 instead.</p>
   <p>We do not think this is actually a meaningful problem. For this to
affect client code, such code must be performing a function call that
somehow is including a Standard Library function during its overload
resolution, and then selecting some other function as the best
candidate. If that’s the case, any change in the Standard Library (such
as adding an overload) could affect the overload resolution and select
a different candidate.</p>
   <p>In a similar way, one can detect the presence of a defaulted template
parameter via SFINAE. If we take a "prototype" version of an algorithmic
function from the Standard Library that accepts two iterators and a "value":</p>
<pre class="highlight"><c- k>template</c-> <c- o>&lt;</c-><c- k>typename</c-> <c- nc>I</c-><c- p>,</c-> <c- k>typename</c-> <c- nc>T</c-><c- o>></c->
<c- n>I</c-> <c- n>algorithm</c-><c- p>(</c-><c- n>I</c-><c- p>,</c-> <c- n>I</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-> <c- o>&amp;</c-><c- p>);</c->
</pre>
   <p>then a call such as <code class="highlight"><c- n>algorithm</c-><c- p>(</c-><c- o>~~~</c-><c- p>,</c-> <c- o>~~~</c-><c- p>,</c-> <c- p>{})</c-></code> will fail to deduce <code class="highlight"><c- n>T</c-></code>, as the
corresponding function parameter constitutes a non-deduced context
([temp.deduct.type]/5.6). On the other hand, if we add a default to its
value-like template type parameter (like this paper is proposing):</p>
<pre class="highlight"><c- k>template</c-> <c- o>&lt;</c-><c- k>typename</c-> <c- nc>I</c-><c- p>,</c-> <c- k>typename</c-> <c- nc>T</c-> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>I</c-><c- o>>::</c-><c- n>value_type</c-><c- o>></c->
<c- n>I</c-> <c- n>algorithm</c-><c- p>(</c-><c- n>I</c-><c- p>,</c-> <c- n>I</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-> <c- o>&amp;</c-><c- p>);</c->
</pre>
   <p>then we are going to <em>allow</em> deduction for the corresponding function parameter,
and the call before may become well-formed.</p>
   <p>In principle, this will mean that code using SFINAE or other similar techniques
may change behavior. We think that this is extremely unlikely to be happening
in practice; if such code exists, it’s certainly a mistake, as it would always
currently be failing deduction (given the current specification of the Standard
Library algorithms).</p>
   <p>In conclusion, although an API break is possible in principle, it’s extremely
unlikely to be happening in practice. What’s more, the kind of proposed changes
fall under what the Standard Library is allowed to do. <a data-link-type="biblio" href="#biblio-sd-8" title="SD-8: Standard Library Compatibility">[SD-8]</a> in fact gives
us the explicit permission to default template parameters for function
templates in the Standard Library:</p>
   <blockquote>
    <p>Primarily, the standard reserves the right to:</p>
    <p>[...]</p>
    <ul>
     <li data-md>
      <p>Add new default arguments to functions and templates</p>
    </ul>
   </blockquote>
   <p>Based on this document, users are already not supposed to rely on the absence
of such defaults.</p>
   <h3 class="heading settled" data-level="5.4" id="abicompatibility"><span class="secno">5.4. </span><span class="content">Is this ABI compatible?</span><a class="self-link" href="#abicompatibility"></a></h3>
   <p>This proposal deals with two kind of changes to function templates.</p>
   <h4 class="heading settled" data-level="5.4.1" id="changes-to-consistent-container-erasure-and-non-range-based-algorithms"><span class="secno">5.4.1. </span><span class="content">Changes to consistent container erasure and non-range-based algorithms</span><a class="self-link" href="#changes-to-consistent-container-erasure-and-non-range-based-algorithms"></a></h4>
   <p>Here we are simply proposing to default a template type parameter in the
template parameter list of the related functions. This is entirely ABI
compatibile (we’re dealing with <em>function</em> templates, and not class
templates).</p>
   <h4 class="heading settled" data-level="5.4.2" id="changes-to-range-based-algorithms"><span class="secno">5.4.2. </span><span class="content">Changes to range-based algorithms</span><a class="self-link" href="#changes-to-range-based-algorithms"></a></h4>
   <p>These changes require reordering the template argument list (see the discussion
in <a href="#ranges">§ 5.5 Range-based algorithms</a>). This is unfortunately not 100% ABI
compatibile, as the instantiations of these functions would change their
mangling.</p>
   <p>With the reorderings proposed, we feel it’s very unlikely that this
incompatibility would cause a problem in practice. A user would have to call
range-based algorithm using the same type for the template parameters that got
reordered. For instance, for <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>remove</c-></code>, one would need to use the
same type as the projection type and for the value to remove (see <a href="#algremove">§ 7.4.6 [alg.remove]</a>) in order to get a clash.</p>
   <p>In the absence of such a type clash, then the problem would be averted: old
code would keep using the old mangled name, and code compiled against the new
version would use the new name. (The final binary may end up with multiple
copies of the instantiated function, under different symbols.)</p>
   <p>There would still be the chance of an ABI break for user code using explicit
template instantiations of one of these functions. The TU defining the
instantiation would then be incompatible with any other TU that uses a
different version of these functions (and merely declares the instantation).</p>
   <p>We are not sure that user code is actually allowed to use explicit
instantiations of Standard Library functions. Such a usage seems to violate the <a data-link-type="biblio" href="#biblio-sd-8" title="SD-8: Standard Library Compatibility">[SD-8]</a> directives, specifically the right of the Standard Library to:</p>
   <blockquote>
    <ul>
     <li data-md>
      <p>Make changes to existing interfaces in a fashion that will be backward
compatible, if those interfaces are solely used to instantiate types and invoke
functions. Implementation details (the primary name of a type, the
implementation details for a function callable) may not be depended upon.</p>
      <p>For example, we may change implementation details for standard function
templates so that those become callable function objects. If user code only
invokes that callable, the behavior is unchanged.</p>
    </ul>
   </blockquote>
   <p>Cf. also the discussion in the <a href="#userspecifiedtemplateparameters">§ 5.6 What about user-specified template parameters?</a> section.</p>
   <h3 class="heading settled" data-level="5.5" id="ranges"><span class="secno">5.5. </span><span class="content">Range-based algorithms</span><a class="self-link" href="#ranges"></a></h3>
   <p>The current specification in the Standard for range-based algorithms does not
allow for a "straightforward" defaulting, like the non-range-based variants.</p>
   <p><code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>find</c-></code> has this synopsis in [algorithm.syn]:</p>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- n>input_iterator</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- p>,</c-> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><c- o>></c->
  <c- k>requires</c-> <c- n>indirect_binary_predicate</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>equal_to</c-><c- p>,</c-> <c- n>projected</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>*></c->
  <c- k>constexpr</c-> <c- n>I</c-> <c- n>find</c-><c- p>(</c-><c- n>I</c-> <c- n>first</c-><c- p>,</c-> <c- n>S</c-> <c- n>last</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->

<c- k>template</c-><c- o>&lt;</c-><c- n>input_range</c-> <c- n>R</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><c- o>></c->
  <c- k>requires</c-> <c- n>indirect_binary_predicate</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>equal_to</c-><c- p>,</c->
                                     <c- n>projected</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>*></c->
  <c- k>constexpr</c-> <c- n>borrowed_iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c->
    <c- n>find</c-><c- p>(</c-><c- n>R</c-><c- o>&amp;&amp;</c-> <c- n>r</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->
</pre>
   <p>Both declarations do not allow for <code class="highlight"><c- n>T</c-></code> to be defaulted given the
ordering of template type parameters. <code class="highlight"><c- n>T</c-></code> should be defaulted to
something like <code class="highlight"><c- k>typename</c-> <c- nc>projected</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>>::</c-><c- n>value_type</c-></code> in the first
version, and to <code class="highlight"><c- k>typename</c-> <c- nc>projected</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>>::</c-><c- n>value_type</c-></code> in the second version. (Technically, neither; see the discussion in <a href="#projection">§ 5.9 The need of a custom projection type transformation</a>). This is not possible: the template parameter <code class="highlight"><c- n>Proj</c-></code> appears <em>after</em> <code class="highlight"><c- n>T</c-></code> in the template parameter list.</p>
   <p>In order to fix this, we need to reorder the template parameters.</p>
   <p>Some other algorithms need a slightly more elaborate change.
Let’s consider <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>fill</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- n>output_iterator</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>T</c-><c- o>&amp;></c-> <c- n>O</c-><c- p>,</c-> <c- n>sentinel_for</c-><c- o>&lt;</c-><c- n>O</c-><c- o>></c-> <c- n>S</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>O</c-> <c- n>fill</c-><c- p>(</c-><c- n>O</c-> <c- n>first</c-><c- p>,</c-> <c- n>S</c-> <c- n>last</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>);</c->

<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- p>,</c-> <c- n>output_range</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>T</c-><c- o>&amp;></c-> <c- n>R</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>borrowed_iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-> <c- n>fill</c-><c- p>(</c-><c- n>R</c-><c- o>&amp;&amp;</c-> <c- n>r</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>);</c->
</pre>
   <p>Here the output iterator <code class="highlight"><c- n>O</c-></code> is defined in terms of <code class="highlight"><c- n>T</c-></code>, making it
impossible to default <code class="highlight"><c- n>T</c-></code> in terms of <code class="highlight"><c- n>O</c-></code> instead. The proposed
solution in this case is reorder the template parameter list and move
the constraint out of it, in a <code class="highlight"><c- k>requires</c-></code> clause. This will keep the
pre-existing semantics while allowing <code class="highlight"><c- n>T</c-></code> to be defaulted.</p>
   <p>To summarize, the changes that we are proposing to the range-based algorithms go
in this direction: they move template parameters and/or constraints in order to
be able to give a meaningful default type to the "value"-like function
parameters.</p>
   <p>We believe that <a data-link-type="biblio" href="#biblio-sd-8" title="SD-8: Standard Library Compatibility">[SD-8]</a> allows us to do so under the interpretation that the
exact spelling or ordering of template type arguments and constraints is part
of the "implementation details" that users cannot depend upon. There will be no
changes for users who simply <em>call</em> these functions, letting the template
arguments to be deduced.</p>
   <h3 class="heading settled" data-level="5.6" id="userspecifiedtemplateparameters"><span class="secno">5.6. </span><span class="content">What about user-specified template parameters?</span><a class="self-link" href="#userspecifiedtemplateparameters"></a></h3>
   <p>For the non-algorithmic changes (that is, the ones to consistent container
erasure), we are not changing the order nor the meaning of the template
parameters. User code that is calling such functions specifying the template
type parameters explicitly is therefore not going to be affected.</p>
   <p>For the algorithms, users are already <em>not allowed</em> to rely on the number and
the order of deducible template parameters. [algorithms.requirements] / 15
says:</p>
   <blockquote>
     The number and order of deducible template parameters for algorithm
declarations are unspecified, except where explicitly stated otherwise. 
    <p>[Note 3: Consequently, an implementation can reject calls that specify an
explicit template argument list. — end note]</p>
   </blockquote>
   <p>Therefore, we do have the freedom not only of defaulting them, but also
of reordering them when necessary.</p>
   <p>Please note, however, that in spite of this paragraph in the Standard and of
the SD-8 rules, the kind of changes we are proposing may be ABI incompatible.
See <a href="#abicompatibility">§ 5.4 Is this ABI compatible?</a> for a discussion.</p>
   <h3 class="heading settled" data-level="5.7" id="templateparametersreordering"><span class="secno">5.7. </span><span class="content">Is the Standard Library allowed to reorder deducible template parameters of algorithms?</span><a class="self-link" href="#templateparametersreordering"></a></h3>
   <p>During the LEWG review of R6 of this paper in Kona a doubt has been raised
regarding whether or not the Standard Library is allowed to reorder deducible
template parameters. This reordering is necessary for range-based algorithms,
as explained in <a href="#ranges">§ 5.5 Range-based algorithms</a>.</p>
   <p><a data-link-type="biblio" href="#biblio-sd-8" title="SD-8: Standard Library Compatibility">[SD-8]</a> does not explicitly state whether such a reordering is admissibile or
not. Nonetheless, we argue that we have the freedom of doing so, for at least
two reasons.</p>
   <p>The first reason (discussed in <a href="#userspecifiedtemplateparameters">§ 5.6 What about user-specified template parameters?</a>) is that
users are already not allowed to rely on the order or the number of deducible
template parameters for algorithms. This is stated in [algorithms.requirements]
/ 15:</p>
   <blockquote>
     The number and order of deducible template parameters for algorithm
declarations are unspecified, except where explicitly stated otherwise. 
    <p>[Note 3: Consequently, an implementation can reject calls that specify an
explicit template argument list. — end note]</p>
   </blockquote>
   <p>None of the algorithms that we propose to modify offers guarantees regarding
the number and the order of their parameters; portable code can therefore make
no assumptions in this regard.</p>
   <p>The second reason (discussed in <a href="#abicompatibility">§ 5.4 Is this ABI compatible?</a> and <a href="#ranges">§ 5.5 Range-based algorithms</a>) is that <a data-link-type="biblio" href="#biblio-sd-8" title="SD-8: Standard Library Compatibility">[SD-8]</a> states:</p>
   <blockquote>
    <ul>
     <li data-md>
      <p>Make changes to existing interfaces in a fashion that will be backward
compatible, if those interfaces are solely used to instantiate types and invoke
functions. Implementation details (the primary name of a type, the
implementation details for a function callable) may not be depended upon.</p>
      <p>For example, we may change implementation details for standard function
templates so that those become callable function objects. If user code only
invokes that callable, the behavior is unchanged.</p>
    </ul>
   </blockquote>
   <p>We believe that the precise order and number of deducible template parameters
for algorithms belong to the "implementation details". We are not proposing any
behavioral change for code that simply calls an algorithmic function.</p>
   <h3 class="heading settled" data-level="5.8" id="outputiteratorsvoid"><span class="secno">5.8. </span><span class="content">What about output iterators, whose <code class="highlight"><c- n>value_type</c-></code> may be <code class="highlight"><c- b>void</c-></code>?</span><a class="self-link" href="#outputiteratorsvoid"></a></h3>
   <p>In this case, the changes proposed by this paper would not bring any effect;
an user would still not be able to call an algorithm using an initializer list
without also specifying the type to deduce.</p>
   <h3 class="heading settled" data-level="5.9" id="projection"><span class="secno">5.9. </span><span class="content">The need of a custom projection type transformation</span><a class="self-link" href="#projection"></a></h3>
   <p>Many range-based algorithms feature a projection function. Let’s use <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>find</c-></code> again as an example:</p>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- n>input_range</c-> <c- n>R</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><c- o>></c->
  <c- k>requires</c-> <c- n>indirect_binary_predicate</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>equal_to</c-><c- p>,</c->
                                     <c- n>projected</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>*></c->
  <c- k>constexpr</c-> <c- n>borrowed_iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c->
    <c- n>find</c-><c- p>(</c-><c- n>R</c-><c- o>&amp;&amp;</c-> <c- n>r</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->
</pre>
   <p>For these algorithms <code class="highlight"><c- n>T</c-></code> should not be defaulted to the <code class="highlight"><c- n>range_value_t</c-></code> of the input range, but rather to the type obtained after applying
the projection:</p>
<pre class="highlight"><c- k>struct</c-> <c- nc>point</c-> <c- p>{</c-> <c- b>int</c-> <c- n>x</c-><c- p>;</c-> <c- b>int</c-> <c- n>y</c-><c- p>;</c-> <c- p>};</c->

<c- k>struct</c-> <c- nc>tagged_point</c->
<c- p>{</c-> <c- n>std</c-><c- o>::</c-><c- n>string</c-> <c- n>tag</c-><c- p>;</c-> <c- n>point</c-> <c- n>p</c-><c- p>;</c-> <c- p>};</c->

<c- n>std</c-><c- o>::</c-><c- n>vector</c-><c- o>&lt;</c-><c- n>tagged_point</c-><c- o>></c-> <c- n>v</c-><c- p>;</c->

<c- k>auto</c-> <c- n>i</c-> <c- o>=</c-> <c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>find</c-><c- p>(</c-><c- n>v</c-><c- p>,</c->
                           <c- p>{</c-><c- mi>1</c-><c- p>,</c-> <c- mi>2</c-><c- p>},</c-> <c- c1>// should be a point because of the projection</c->
                           <c- o>&amp;</c-><c- n>tagged_point</c-><c- o>::</c-><c- n>p</c-><c- p>);</c->
</pre>
   <p>One could therefore conclude that the correct default for <code class="highlight"><c- n>find</c-></code>’s <code class="highlight"><c- n>T</c-></code> template parameter should be <code class="highlight"><c- k>typename</c-> <c- nc>std</c-><c- o>::</c-><c- n>projected</c-><c- o>&lt;</c-><c- n>std</c-><c- o>::</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>>::</c-><c- n>value_type</c-></code>.</p>
   <p>Unfortunately, as discussed by <a data-link-type="biblio" href="#biblio-p2322r6" title="ranges::fold">[P2322R6]</a>, this does not work in all
cases; ranges yielding proxy iterators would end up using the wrong
type as default.</p>
   <p>If <code class="highlight"><c- n>Proj</c-></code> is <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>identity</c-></code> (the common case), and the range is e.g. <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>vector</c-><c- o>&lt;</c-><c- b>bool</c-><c- o>></c-></code>, then <code class="highlight"><c- n>T</c-></code> would <em>not</em> be defaulted to <code class="highlight"><c- b>bool</c-></code> as one
would expect, rather to <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>vector</c-><c- o>&lt;</c-><c- b>bool</c-><c- o>>::</c-><c- n>reference</c-></code>. This type is
not copy-list constructible from <code class="highlight"><c- b>bool</c-></code>, and therefore would make this
code ill-formed:</p>
<pre class="highlight"><c- n>std</c-><c- o>::</c-><c- n>vector</c-><c- o>&lt;</c-><c- b>bool</c-><c- o>></c-> <c- n>v</c-><c- p>;</c->
<c- k>auto</c-> <c- n>i</c-> <c- o>=</c-> <c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>find</c-><c- p>(</c-><c- n>v</c-><c- p>,</c-> <c- p>{</c->true<c- p>});</c-> <c- c1>// ERROR</c->
</pre>
   <p>Another example (again brought forward by <a data-link-type="biblio" href="#biblio-p2322r6" title="ranges::fold">[P2322R6]</a>) is the case of
of <code class="highlight"><c- n>views</c-><c- o>::</c-><c- n>zip</c-></code>. A <code class="highlight"><c- n>zip</c-></code> over a range of <code class="highlight"><c- n>X</c-></code> uses a <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>tuple</c-><c- o>&lt;</c-><c- n>X</c-><c- o>&amp;></c-></code> as
its <code class="highlight"><c- n>range_reference_t</c-></code> type, and therefore <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>tuple</c-><c- o>&lt;</c-><c- n>X</c-><c- o>&amp;></c-></code> would be
the type obtained by the projection (again when using <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>identity</c-></code>).
This type is not useful at all as a default for <code class="highlight"><c- n>T</c-></code>, as one cannot
initialize such a tuple with, say, a prvalue <code class="highlight"><c- n>X</c-></code> in a list
initialization:</p>
<pre class="highlight"><c- n>std</c-><c- o>::</c-><c- n>vector</c-><c- o>&lt;</c-><c- b>int</c-><c- o>></c-> <c- n>v1</c-><c- p>,</c-> <c- n>v2</c-><c- p>;</c->
<c- k>auto</c-> <c- n>i</c-> <c- o>=</c-> <c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>find</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>views</c-><c- o>::</c-><c- n>zip</c-><c- p>(</c-><c- n>v1</c-><c- p>,</c-> <c- n>v2</c-><c- p>),</c-> <c- p>{</c-><c- mi>3</c-><c- p>,</c-> <c- mi>4</c-><c- p>});</c-> <c- c1>// ERROR</c->
</pre>
   <p>The problem here is that <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>projected</c-></code> is meant to be used to
constrain an algorithm based on the semantic operations that an
algorithm needs to perform in its implementation. These
operations are (normally) performed using projected references -- that
is, invoking the projection on the range’s <code class="highlight"><c- n>range_reference_t</c-></code>.</p>
   <p>The default for a value-like parameter does not however need reference
semantics -- it needs value semantics, projecting a range’s <em>value
type</em>. Specifically, projecting <code class="highlight"><c- n>range_value_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-> <c- o>&amp;</c-></code>, as that’s what’s
required from projections (and enforced by the <code class="highlight"><c- n>indirectly_regular_unary_invocable</c-></code> concept). While for most
"ordinary" ranges this would be the same as projecting the range’s
reference type, this would be different from ranges yielding proxy
iterators.</p>
   <p>In short, the correct default for <code class="highlight"><c- n>T</c-></code> given a range <code class="highlight"><c- n>R</c-></code> and a
projection <code class="highlight"><c- n>Proj</c-></code> should be:</p>
   <p><code class="highlight"><c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- n>invoke_result_t</c-><c- o>&lt;</c-><c- n>Proj</c-><c- o>&amp;</c-><c- p>,</c-> <c- n>range_value_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>>&amp;>></c-></code></p>
   <p>With this, the default for a <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>vector</c-><c- o>&lt;</c-><c- b>bool</c-><c- o>></c-></code> range would indeed be <code class="highlight"><c- b>bool</c-></code>; and the default for a <code class="highlight"><c- n>zip</c-></code> view over a range of <code class="highlight"><c- n>X</c-></code> would be <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>tuple</c-><c- o>&lt;</c-><c- n>X</c-><c- o>></c-></code> -- again assuming using <code class="highlight"><c- n>identity</c-></code> as projection, i.e.
the common case.</p>
   <p>Technically speaking, in the general case, an projection may return
different types when invoked with a <code class="highlight"><c- n>range_value_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>>&amp;</c-></code> instead of a <code class="highlight"><c- n>range_reference_t</c-></code>. This projection:</p>
<pre class="highlight"><c- k>struct</c-> <c- nc>evil_projection</c-> <c- p>{</c->
    <c- b>int</c-> <c- nf>operator</c-><c- p>()(</c-><c- k>const</c-> <c- b>bool</c-> <c- o>&amp;</c-><c- p>)</c-> <c- k>const</c-><c- p>;</c->
    <c- b>double</c-> <c- nf>operator</c-><c- p>()(</c-><c- b>bool</c-> <c- o>&amp;&amp;</c-><c- p>)</c-> <c- k>const</c-><c- p>;</c->
<c- p>};</c->
</pre>
   <p>used with a <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>vector</c-><c- o>&lt;</c-><c- b>bool</c-><c- o>></c-></code> range yields <code class="highlight"><c- b>int</c-></code> when projecting
lvalue references to range values (i.e. <code class="highlight"><c- b>bool</c-> <c- o>&amp;</c-></code>), and <code class="highlight"><c- b>double</c-></code> when
projecting range references (i.e. <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>vector</c-><c- o>&lt;</c-><c- b>bool</c-><c- o>>::</c-><c- n>reference</c-></code>).
While legal, such kind of projections has very dubious value, and we do
not believe they should constitute a problem in practice.
(They would just be used to determine the default type for <code class="highlight"><c- n>T</c-></code>; and
such default type would still be subjected to the other constraints
of the algorithms.)</p>
   <h4 class="heading settled" data-level="5.9.1" id="projectionapi"><span class="secno">5.9.1. </span><span class="content">Providing the projected value as an API</span><a class="self-link" href="#projectionapi"></a></h4>
   <p>While we could put the above solution to the projected value as an
exposition-only type transformation, we are actually proposing to
modify <code class="highlight"><c- o>&lt;</c-><c- n>iterator</c-><c- o>></c-></code> in order to provide this facility to end-users, so
that they can use it as well -- for instance, if they also want to
default the value-like parameters of their own algorithms following the
"lead" of the Standard Library itself.</p>
   <p>To this end, we are proposing to add a <code class="highlight"><c- n>projected_value_t</c-></code> alias
template. This alias exposes the type transformation described above;
it’s the logical counterpart of <code class="highlight"><c- k>typename</c-> <c- nc>projected</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>>::</c-><c- n>value_type</c-></code>,
obtained using <code class="highlight"><c- n>iter_value_t</c-><c- o>&lt;</c-><c- n>I</c-><c- o>>&amp;</c-></code> instead of <code class="highlight"><c- n>iter_reference_t</c-><c- o>&lt;</c-><c- n>I</c-><c- o>></c-></code>:</p>
<pre class="highlight"><c- c1>// Same as above, just using an indirectly_readable I rather than a range R</c->
<c- k>template</c-><c- o>&lt;</c-><c- n>indirectly_</c->­<c- n>readable</c-> <c- n>I</c-><c- p>,</c-> <c- n>indirectly_</c->­<c- n>regular_</c->­<c- n>unary_</c->­<c- n>invocable</c-><c- o>&lt;</c-><c- n>I</c-><c- o>></c-> <c- n>Proj</c-><c- o>></c->
  <c- k>using</c-> <c- n>projected_value_t</c-> <c- o>=</c-> <c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- n>invoke_result_t</c-><c- o>&lt;</c-><c- n>Proj</c-><c- o>&amp;</c-><c- p>,</c-> <c- n>iter_value_t</c-><c- o>&lt;</c-><c- n>I</c-><c- o>>&amp;>></c-><c- p>;</c->
</pre>
   <p>This allows us to reformulate the default for <code class="highlight"><c- n>T</c-></code> as:</p>
   <p><code class="highlight"><c- n>projected_value_t</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-></code></p>
   <p>which is the form found in the proposed wording.</p>
   <p><a data-link-type="biblio" href="#biblio-p2609r0" title="Relaxing Ranges Just A Smidge">[P2609R0]</a> proposes an alias template extremely similar to <code class="highlight"><c- n>projected_value_t</c-></code>, called <code class="highlight"><c- n>indirect_value_t</c-></code>. The latter is a
generalization of the former. In principle, following <a data-link-type="biblio" href="#biblio-p2609r0" title="Relaxing Ranges Just A Smidge">[P2609R0]</a>'s
adoption, <code class="highlight"><c- n>projected_value_t</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-></code> could be reformulated as <code class="highlight"><c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- n>indirect_value_t</c-><c- o>&lt;</c-><c- n>projected</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>>>></c-></code>, with absolutely
no change in semantics.</p>
   <h2 class="heading settled" data-level="6" id="implementationexperience"><span class="secno">6. </span><span class="content">Implementation experience</span><a class="self-link" href="#implementationexperience"></a></h2>
   <p>A working prototype of the changes proposed by this paper,
done on top of GCC 11, is available in this <a data-link-type="biblio" href="#biblio-p2248-gcc" title="P2248 prototype implementation">GCC branch</a> on
GitHub.</p>
   <p>The <a data-link-type="biblio" href="#biblio-p2248-hpx" title="Implementation of P2248 in HPX">HPX</a> library has also implemented changes along the
lines of the ones proposed by this paper.</p>
   <h2 class="heading settled" data-level="7" id="technicalspecifications"><span class="secno">7. </span><span class="content">Technical Specifications</span><a class="self-link" href="#technicalspecifications"></a></h2>
   <p>All the proposed changes are relative to <a data-link-type="biblio" href="#biblio-n4971" title="Working Draft, Standard for Programming Language C++">[N4971]</a>.</p>
   <h3 class="heading settled" data-level="7.1" id="feature-testing-macro"><span class="secno">7.1. </span><span class="content">Feature testing macro</span><a class="self-link" href="#feature-testing-macro"></a></h3>
   <p>Add to the list in [version.syn]:</p>
<pre class="highlight"><ins><c- cp>#define __cpp_lib_default_template_type_for_algorithm_values YYYYMML  </c-><c- c1>// also in</c->
    <c- c1>// &lt;algorithm>, &lt;ranges>,</c->
    <c- c1>// &lt;string>, &lt;deque>, &lt;list>, &lt;forward_list>, &lt;vector></c-></ins>
</pre>
   <p>with the value specified as usual (year and month of adoption).</p>
   <h3 class="heading settled" data-level="7.2" id="consistent-container-erasure"><span class="secno">7.2. </span><span class="content">Consistent Container Erasure</span><a class="self-link" href="#consistent-container-erasure"></a></h3>
   <p>Modify [string.syn] and [string.erasure]:</p>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>charT</c-><c- p>,</c-> <c- k>class</c-> <c- nc>traits</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Allocator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>U</c-><ins> <c- o>=</c-> <c- n>charT</c-></ins><c- o>></c->
  <c- k>constexpr</c-> <c- k>typename</c-> <c- nc>basic_string</c-><c- o>&lt;</c-><c- n>charT</c-><c- p>,</c-> <c- n>traits</c-><c- p>,</c-> <c- n>Allocator</c-><c- o>>::</c-><c- n>size_type</c->
    <c- n>erase</c-><c- p>(</c-><c- n>basic_string</c-><c- o>&lt;</c-><c- n>charT</c-><c- p>,</c-> <c- n>traits</c-><c- p>,</c-> <c- n>Allocator</c-><c- o>>&amp;</c-> <c- n>c</c-><c- p>,</c-> <c- k>const</c-> <c- n>U</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>);</c->
</pre>
   <p>Modify [deque.syn] and [deque.erasure]:</p>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Allocator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>U</c-><ins> <c- o>=</c-> <c- n>T</c-></ins><c- o>></c->
  <c- k>typename</c-> <c- nc>deque</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>Allocator</c-><c- o>>::</c-><c- n>size_type</c->
    <c- n>erase</c-><c- p>(</c-><c- n>deque</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>Allocator</c-><c- o>>&amp;</c-> <c- n>c</c-><c- p>,</c-> <c- k>const</c-> <c- n>U</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>);</c->
</pre>
   <p>Modify [forwardlist.syn] and [forward.list.erasure]:</p>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Allocator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>U</c-><ins> <c- o>=</c-> <c- n>T</c-></ins><c- o>></c->
  <c- k>typename</c-> <c- nc>forward_list</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>Allocator</c-><c- o>>::</c-><c- n>size_type</c->
    <c- n>erase</c-><c- p>(</c-><c- n>forward_list</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>Allocator</c-><c- o>>&amp;</c-> <c- n>c</c-><c- p>,</c-> <c- k>const</c-> <c- n>U</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>);</c->
</pre>
   <p>Modify [list.syn] and [list.erasure]:</p>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Allocator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>U</c-><ins> <c- o>=</c-> <c- n>T</c-></ins><c- o>></c->
  <c- k>typename</c-> <c- nc>list</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>Allocator</c-><c- o>>::</c-><c- n>size_type</c->
    <c- n>erase</c-><c- p>(</c-><c- n>list</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>Allocator</c-><c- o>>&amp;</c-> <c- n>c</c-><c- p>,</c-> <c- k>const</c-> <c- n>U</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>);</c->
</pre>
   <p>Modify [vector.syn] and [vector.erasure]:</p>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Allocator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>U</c-><ins> <c- o>=</c-> <c- n>T</c-></ins><c- o>></c->
  <c- k>constexpr</c-> <c- k>typename</c-> <c- nc>vector</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>Allocator</c-><c- o>>::</c-><c- n>size_type</c->
    <c- n>erase</c-><c- p>(</c-><c- n>vector</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>Allocator</c-><c- o>>&amp;</c-> <c- n>c</c-><c- p>,</c-> <c- k>const</c-> <c- n>U</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>);</c->
</pre>
   <h3 class="heading settled" data-level="7.3" id="iterators"><span class="secno">7.3. </span><span class="content">Iterators</span><a class="self-link" href="#iterators"></a></h3>
   <p>Modify the <code class="highlight"><c- o>&lt;</c-><c- n>iterator</c-><c- o>></c-></code> header synopsis ([iterator.synopsis]):</p>
<pre class="highlight"><c- c1>// [projected], projected</c->
<c- k>template</c-><c- o>&lt;</c-><c- n>indirectly_</c->­<c- n>readable</c-> <c- n>I</c-><c- p>,</c-> <c- n>indirectly_</c->­<c- n>regular_</c->­<c- n>unary_</c->­<c- n>invocable</c-><c- o>&lt;</c-><c- n>I</c-><c- o>></c-> <c- n>Proj</c-><c- o>></c->
  <c- k>struct</c-> <c- nc>projected</c-><c- p>;</c-> <c- c1>// freestanding</c->

<c- k>template</c-><c- o>&lt;</c-><c- n>weakly_</c->­<c- n>incrementable</c-> <c- n>I</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Proj</c-><c- o>></c->
  <c- k>struct</c-> <c- nc>incrementable_traits</c-><c- o>&lt;</c-><c- n>projected</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>>></c-><c- p>;</c-> <c- c1>// freestanding</c->

<ins>
<c- k>template</c-><c- o>&lt;</c-><c- n>indirectly_</c->­<c- n>readable</c-> <c- n>I</c-><c- p>,</c-> <c- n>indirectly_</c->­<c- n>regular_</c->­<c- n>unary_</c->­<c- n>invocable</c-><c- o>&lt;</c-><c- n>I</c-><c- o>></c-> <c- n>Proj</c-><c- o>></c->
  <c- k>using</c-> <c- n>projected_value_t</c-> <c- o>=</c-> <c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- n>invoke_result_t</c-><c- o>&lt;</c-><c- n>Proj</c-><c- o>&amp;</c-><c- p>,</c-> <c- n>iter_value_t</c-><c- o>&lt;</c-><c- n>I</c-><c- o>>&amp;>></c-><c- p>;</c-> <c- c1>// freestanding</c->
</ins>
</pre>
   <p><strong>Note to LWG / to the editor</strong>: this specification of <code class="highlight"><c- n>projected_value_t</c-></code> could be changed to a completely equivalent one using the exposition-only
alias template <code class="highlight"><c- n>indirect</c-><c- o>-</c-><c- n>value</c-><c- o>-</c-><c- n>t</c-></code>. Please see the
discussion in <a href="#projectionapi">§ 5.9.1 Providing the projected value as an API</a>.</p>
   <h3 class="heading settled" data-level="7.4" id="algorithms"><span class="secno">7.4. </span><span class="content">Algorithms</span><a class="self-link" href="#algorithms"></a></h3>
   <p>Modify both the <code class="highlight"><c- o>&lt;</c-><c- n>algorithm</c-><c- o>></c-></code> synopsis ([algorithm.syn])
as well as the algorithm signatures in each and every referenced
section:</p>
   <h4 class="heading settled" data-level="7.4.1" id="algfind"><span class="secno">7.4.1. </span><span class="content">[alg.find]</span><a class="self-link" href="#algfind"></a></h4>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>InputIterator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>InputIterator</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- o>></c->
  <c- k>constexpr</c-> <c- n>InputIterator</c-> <c- n>find</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>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</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- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>ForwardIterator</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- o>></c->
  <c- n>ForwardIterator</c-> <c- n>find</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>last</c-><c- p>,</c->
                       <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>);</c->
</pre>
<pre class="highlight"><c- k>namespace</c-> <c- nn>ranges</c-> <c- p>{</c->
  <c- k>template</c-><c- o>&lt;</c-><c- n>input_iterator</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- p>,</c-><del> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-></del> <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><ins><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-> <c- o>=</c-> <c- n>projected_value_t</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-></ins><c- o>></c->
    <c- k>requires</c-> <c- n>indirect_binary_predicate</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>equal_to</c-><c- p>,</c-> <c- n>projected</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>*></c->
    <c- k>constexpr</c-> <c- n>I</c-> <c- n>find</c-><c- p>(</c-><c- n>I</c-> <c- n>first</c-><c- p>,</c-> <c- n>S</c-> <c- n>last</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->
  <c- k>template</c-><c- o>&lt;</c-><c- n>input_range</c-> <c- n>R</c-><c- p>,</c-><del> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-></del> <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><ins><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-> <c- o>=</c-> <c- n>projected_value_t</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-></ins><c- o>></c->
    <c- k>requires</c-> <c- n>indirect_binary_predicate</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>equal_to</c-><c- p>,</c->
                                       <c- n>projected</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>*></c->
    <c- k>constexpr</c-> <c- n>borrowed_iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c->
      <c- n>find</c-><c- p>(</c-><c- n>R</c-><c- o>&amp;&amp;</c-> <c- n>r</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->
<c- p>}</c->
</pre>
   <h4 class="heading settled" data-level="7.4.2" id="algcount"><span class="secno">7.4.2. </span><span class="content">[alg.count]</span><a class="self-link" href="#algcount"></a></h4>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>InputIterator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>InputIterator</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- o>></c->
  <c- k>constexpr</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>InputIterator</c-><c- o>>::</c-><c- n>difference_type</c->
    <c- n>count</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>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</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- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>ForwardIterator</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- o>></c->
  <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>ForwardIterator</c-><c- o>>::</c-><c- n>difference_type</c->
    <c- n>count</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>last</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>);</c->
</pre>
<pre class="highlight"><c- k>namespace</c-> <c- nn>ranges</c-> <c- p>{</c->
  <c- k>template</c-><c- o>&lt;</c-><c- n>input_iterator</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- p>,</c-><del> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-></del> <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><ins><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-> <c- o>=</c-> <c- n>projected_value_t</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-></ins><c- o>></c->
    <c- k>requires</c-> <c- n>indirect_binary_predicate</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>equal_to</c-><c- p>,</c-> <c- n>projected</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>*></c->
    <c- k>constexpr</c-> <c- n>iter_difference_t</c-><c- o>&lt;</c-><c- n>I</c-><c- o>></c->
      <c- n>count</c-><c- p>(</c-><c- n>I</c-> <c- n>first</c-><c- p>,</c-> <c- n>S</c-> <c- n>last</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->
  <c- k>template</c-><c- o>&lt;</c-><c- n>input_range</c-> <c- n>R</c-><c- p>,</c-><del> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-></del> <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><ins><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-> <c- o>=</c-> <c- n>projected_value_t</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-></ins><c- o>></c->
    <c- k>requires</c-> <c- n>indirect_binary_predicate</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>equal_to</c-><c- p>,</c->
                                        <c- n>projected</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>*></c->
    <c- k>constexpr</c-> <c- n>range_difference_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c->
      <c- n>count</c-><c- p>(</c-><c- n>R</c-><c- o>&amp;&amp;</c-> <c- n>r</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->
<c- p>}</c->
</pre>
   <h4 class="heading settled" data-level="7.4.3" id="algsearch"><span class="secno">7.4.3. </span><span class="content">[alg.search]</span><a class="self-link" href="#algsearch"></a></h4>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>ForwardIterator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Size</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>ForwardIterator</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- o>></c->
  <c- k>constexpr</c-> <c- n>ForwardIterator</c->
    <c- n>search_n</c-><c- p>(</c-><c- n>ForwardIterator</c-> <c- n>first</c-><c- p>,</c-> <c- n>ForwardIterator</c-> <c- n>last</c-><c- p>,</c->
             <c- n>Size</c-> <c- n>count</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>);</c->
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>ForwardIterator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Size</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>ForwardIterator</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- p>,</c-> <c- k>class</c-> <c- nc>BinaryPredicate</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>ForwardIterator</c->
    <c- n>search_n</c-><c- p>(</c-><c- n>ForwardIterator</c-> <c- n>first</c-><c- p>,</c-> <c- n>ForwardIterator</c-> <c- n>last</c-><c- p>,</c->
             <c- n>Size</c-> <c- n>count</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>BinaryPredicate</c-> <c- n>pred</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- p>,</c-> <c- k>class</c-> <c- nc>Size</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>ForwardIterator</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- o>></c->
  <c- n>ForwardIterator</c->
    <c- n>search_n</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>last</c-><c- p>,</c->
             <c- n>Size</c-> <c- n>count</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</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- p>,</c-> <c- k>class</c-> <c- nc>Size</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>ForwardIterator</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- p>,</c->
         <c- k>class</c-> <c- nc>BinaryPredicate</c-><c- o>></c->
  <c- n>ForwardIterator</c->
    <c- n>search_n</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>last</c-><c- p>,</c->
             <c- n>Size</c-> <c- n>count</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c->
             <c- n>BinaryPredicate</c-> <c- n>pred</c-><c- p>);</c->
</pre>
<pre class="highlight"><c- k>namespace</c-> <c- nn>ranges</c-> <c- p>{</c->
  <c- k>template</c-><c- o>&lt;</c-><c- n>forward_iterator</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- p>,</c-><del> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-></del>
           <c- k>class</c-> <c- nc>Pred</c-> <c- o>=</c-> <c- n>ranges</c-><c- o>::</c-><c- n>equal_to</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><ins><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-> <c- o>=</c-> <c- n>projected_value_t</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-></ins><c- o>></c->
    <c- k>requires</c-> <c- n>indirectly_comparable</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>*</c-><c- p>,</c-> <c- n>Pred</c-><c- p>,</c-> <c- n>Proj</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>search_n</c-><c- p>(</c-><c- n>I</c-> <c- n>first</c-><c- p>,</c-> <c- n>S</c-> <c- n>last</c-><c- p>,</c-> <c- n>iter_difference_t</c-><c- o>&lt;</c-><c- n>I</c-><c- o>></c-> <c- n>count</c-><c- p>,</c->
               <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Pred</c-> <c- n>pred</c-> <c- o>=</c-> <c- p>{},</c-> <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->
  <c- k>template</c-><c- o>&lt;</c-><c- n>forward_range</c-> <c- n>R</c-><c- p>,</c-><del> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-></del> <c- k>class</c-> <c- nc>Pred</c-> <c- o>=</c-> <c- n>ranges</c-><c- o>::</c-><c- n>equal_to</c-><c- p>,</c->
           <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><ins><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-> <c- o>=</c-> <c- n>projected_value_t</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-></ins><c- o>></c->
    <c- k>requires</c-> <c- n>indirectly_comparable</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>*</c-><c- p>,</c-> <c- n>Pred</c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c->
    <c- k>constexpr</c-> <c- n>borrowed_subrange_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c->
      <c- n>search_n</c-><c- p>(</c-><c- n>R</c-><c- o>&amp;&amp;</c-> <c- n>r</c-><c- p>,</c-> <c- n>range_difference_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-> <c- n>count</c-><c- p>,</c->
               <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Pred</c-> <c- n>pred</c-> <c- o>=</c-> <c- p>{},</c-> <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->
<c- p>}</c->
</pre>
   <h4 class="heading settled" data-level="7.4.4" id="algreplace"><span class="secno">7.4.4. </span><span class="content">[alg.replace]</span><a class="self-link" href="#algreplace"></a></h4>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>ForwardIterator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>ForwardIterator</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- o>></c->
  <c- k>constexpr</c-> <c- b>void</c-> <c- n>replace</c-><c- p>(</c-><c- n>ForwardIterator</c-> <c- n>first</c-><c- p>,</c-> <c- n>ForwardIterator</c-> <c- n>last</c-><c- p>,</c->
                         <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>old_value</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>new_value</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- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>ForwardIterator</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- o>></c->
  <c- b>void</c-> <c- n>replace</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>last</c-><c- p>,</c->
               <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>old_value</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>new_value</c-><c- p>);</c->
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>ForwardIterator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Predicate</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>ForwardIterator</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- o>></c->
  <c- k>constexpr</c-> <c- b>void</c-> <c- n>replace_if</c-><c- p>(</c-><c- n>ForwardIterator</c-> <c- n>first</c-><c- p>,</c-> <c- n>ForwardIterator</c-> <c- n>last</c-><c- p>,</c->
                            <c- n>Predicate</c-> <c- n>pred</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>new_value</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- p>,</c-> <c- k>class</c-> <c- nc>Predicate</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>ForwardIterator</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- o>></c->
  <c- b>void</c-> <c- n>replace_if</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>last</c-><c- p>,</c->
                  <c- n>Predicate</c-> <c- n>pred</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>new_value</c-><c- p>);</c->

</pre>
<pre class="highlight"><c- k>namespace</c-> <c- nn>ranges</c-> <c- p>{</c->
  <c- k>template</c-><c- o>&lt;</c-><c- n>input_iterator</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- p>,</c-><del> <c- k>class</c-> <c- nc>T1</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T2</c-><c- p>,</c-></del> <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><ins><c- p>,</c-> <c- k>class</c-> <c- nc>T1</c-> <c- o>=</c-> <c- n>projected_value_t</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-><c- p>,</c-> <c- k>class</c-> <c- nc>T2</c-> <c- o>=</c-> <c- n>T1</c-></ins><c- o>></c->
    <c- k>requires</c-> <c- n>indirectly_writable</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- k>const</c-> <c- n>T2</c-><c- o>&amp;></c-> <c- o>&amp;&amp;</c->
             <c- n>indirect_binary_predicate</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>equal_to</c-><c- p>,</c-> <c- n>projected</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>T1</c-><c- o>*></c->
    <c- k>constexpr</c-> <c- n>I</c->
      <c- n>replace</c-><c- p>(</c-><c- n>I</c-> <c- n>first</c-><c- p>,</c-> <c- n>S</c-> <c- n>last</c-><c- p>,</c-> <c- k>const</c-> <c- n>T1</c-><c- o>&amp;</c-> <c- n>old_value</c-><c- p>,</c-> <c- k>const</c-> <c- n>T2</c-><c- o>&amp;</c-> <c- n>new_value</c-><c- p>,</c-> <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->
  <c- k>template</c-><c- o>&lt;</c-><c- n>input_range</c-> <c- n>R</c-><c- p>,</c-><del> <c- k>class</c-> <c- nc>T1</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T2</c-><c- p>,</c-></del> <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><ins><c- p>,</c-> <c- k>class</c-> <c- nc>T1</c-> <c- o>=</c-> <c- n>projected_value_t</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-><c- p>,</c-> <c- k>class</c-> <c- nc>T2</c-> <c- o>=</c-> <c- n>T1</c-></ins><c- o>></c->
    <c- k>requires</c-> <c- n>indirectly_writable</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>T2</c-><c- o>&amp;></c-> <c- o>&amp;&amp;</c->
             <c- n>indirect_binary_predicate</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>equal_to</c-><c- p>,</c->
                                       <c- n>projected</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>T1</c-><c- o>*></c->
    <c- k>constexpr</c-> <c- n>borrowed_iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c->
      <c- n>replace</c-><c- p>(</c-><c- n>R</c-><c- o>&amp;&amp;</c-> <c- n>r</c-><c- p>,</c-> <c- k>const</c-> <c- n>T1</c-><c- o>&amp;</c-> <c- n>old_value</c-><c- p>,</c-> <c- k>const</c-> <c- n>T2</c-><c- o>&amp;</c-> <c- n>new_value</c-><c- p>,</c-> <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->
  <c- k>template</c-><c- o>&lt;</c-><c- n>input_iterator</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- p>,</c-><del> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-></del> <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><c- p>,</c-><ins> <c- k>class</c-> <c- nc>T</c-> <c- o>=</c-> <c- n>projected_value_t</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-><c- p>,</c-></ins>
           <c- n>indirect_unary_predicate</c-><c- o>&lt;</c-><c- n>projected</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>>></c-> <c- n>Pred</c-><c- o>></c->
    <c- k>requires</c-> <c- n>indirectly_writable</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;></c->
    <c- k>constexpr</c-> <c- n>I</c-> <c- n>replace_if</c-><c- p>(</c-><c- n>I</c-> <c- n>first</c-><c- p>,</c-> <c- n>S</c-> <c- n>last</c-><c- p>,</c-> <c- n>Pred</c-> <c- n>pred</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>new_value</c-><c- p>,</c-> <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->
  <c- k>template</c-><c- o>&lt;</c-><c- n>input_range</c-> <c- n>R</c-><c- p>,</c-><del> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-></del> <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><c- p>,</c-><ins> <c- k>class</c-> <c- nc>T</c-> <c- o>=</c-> <c- n>projected_value_t</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-><c- p>,</c-></ins>
           <c- n>indirect_unary_predicate</c-><c- o>&lt;</c-><c- n>projected</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>>></c-> <c- n>Pred</c-><c- o>></c->
    <c- k>requires</c-> <c- n>indirectly_writable</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;></c->
    <c- k>constexpr</c-> <c- n>borrowed_iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c->
      <c- n>replace_if</c-><c- p>(</c-><c- n>R</c-><c- o>&amp;&amp;</c-> <c- n>r</c-><c- p>,</c-> <c- n>Pred</c-> <c- n>pred</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>new_value</c-><c- p>,</c-> <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->
<c- p>}</c->
</pre>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>InputIterator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>OutputIterator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Predicate</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>OutputIterator</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- o>></c->
  <c- k>constexpr</c-> <c- n>OutputIterator</c-> <c- n>replace_copy_if</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- n>OutputIterator</c-> <c- n>result</c-><c- p>,</c->
                                           <c- n>Predicate</c-> <c- n>pred</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>new_value</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- p>,</c->
         <c- k>class</c-> <c- nc>Predicate</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>ForwardIterator2</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- o>></c->
  <c- n>ForwardIterator2</c-> <c- n>replace_copy_if</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>first</c-><c- p>,</c-> <c- n>ForwardIterator1</c-> <c- n>last</c-><c- p>,</c->
                                   <c- n>ForwardIterator2</c-> <c- n>result</c-><c- p>,</c->
                                   <c- n>Predicate</c-> <c- n>pred</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>new_value</c-><c- p>);</c->
</pre>
<pre class="highlight"><c- k>namespace</c-> <c- nn>ranges</c-> <c- p>{</c->
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>I</c-><c- p>,</c-> <c- k>class</c-> <c- nc>O</c-><c- o>></c->
  <c- k>using</c-> <c- n>replace_copy_result</c-> <c- o>=</c-> <c- n>in_out_result</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>O</c-><c- o>></c-><c- p>;</c->

<del><c- k>template</c-><c- o>&lt;</c-><c- n>input_iterator</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- p>,</c-> <c- k>class</c-> <c- nc>T1</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T2</c-><c- p>,</c->
         <c- n>output_iterator</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>T2</c-><c- o>&amp;></c-> <c- n>O</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><c- o>></c-></del>
<ins><c- k>template</c-><c- o>&lt;</c-><c- n>input_iterator</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- p>,</c-> <c- k>class</c-> <c- nc>O</c-><c- p>,</c->
         <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T1</c-> <c- o>=</c-> <c- n>projected_value_t</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-><c- p>,</c-> <c- k>class</c-> <c- nc>T2</c-> <c- o>=</c-> <c- n>iter_value_t</c-><c- o>&lt;</c-><c- n>O</c-><c- o>>></c-></ins>
  <c- k>requires</c-> <c- n>indirectly_copyable</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>O</c-><c- o>></c-> <c- o>&amp;&amp;</c->
           <c- n>indirect_binary_predicate</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>equal_to</c-><c- p>,</c-> <c- n>projected</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>T1</c-><c- o>*></c-><ins> <c- o>&amp;&amp;</c->
           <c- n>output_iterator</c-><c- o>&lt;</c-><c- n>O</c-><c- p>,</c-> <c- k>const</c-> <c- n>T2</c-><c- o>&amp;></c-></ins>
  <c- k>constexpr</c-> <c- n>replace_copy_result</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>O</c-><c- o>></c->
    <c- n>replace_copy</c-><c- p>(</c-><c- n>I</c-> <c- n>first</c-><c- p>,</c-> <c- n>S</c-> <c- n>last</c-><c- p>,</c-> <c- n>O</c-> <c- n>result</c-><c- p>,</c-> <c- k>const</c-> <c- n>T1</c-><c- o>&amp;</c-> <c- n>old_value</c-><c- p>,</c-> <c- k>const</c-> <c- n>T2</c-><c- o>&amp;</c-> <c- n>new_value</c-><c- p>,</c->
                 <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->
<del><c- k>template</c-><c- o>&lt;</c-><c- n>input_range</c-> <c- n>R</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T1</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T2</c-><c- p>,</c-> <c- n>output_iterator</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>T2</c-><c- o>&amp;></c-> <c- n>O</c-><c- p>,</c->
         <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><c- o>></c-></del>
<ins><c- k>template</c-><c- o>&lt;</c-><c- n>input_range</c-> <c- n>R</c-><c- p>,</c-> <c- k>class</c-> <c- nc>O</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><c- p>,</c->
         <c- k>class</c-> <c- nc>T1</c-> <c- o>=</c-> <c- n>projected_value_t</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-><c- p>,</c-> <c- k>class</c-> <c- nc>T2</c-> <c- o>=</c-> <c- n>iter_value_t</c-><c- o>&lt;</c-><c- n>O</c-><c- o>>></c-></ins>
  <c- k>requires</c-> <c- n>indirectly_copyable</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>O</c-><c- o>></c-> <c- o>&amp;&amp;</c->
           <c- n>indirect_binary_predicate</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>equal_to</c-><c- p>,</c->
                                     <c- n>projected</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>T1</c-><c- o>*></c-><ins> <c- o>&amp;&amp;</c->
           <c- n>output_iterator</c-><c- o>&lt;</c-><c- n>O</c-><c- p>,</c-> <c- k>const</c-> <c- n>T2</c-><c- o>&amp;></c-></ins>
  <c- k>constexpr</c-> <c- n>replace_copy_result</c-><c- o>&lt;</c-><c- n>borrowed_iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>O</c-><c- o>></c->
    <c- n>replace_copy</c-><c- p>(</c-><c- n>R</c-><c- o>&amp;&amp;</c-> <c- n>r</c-><c- p>,</c-> <c- n>O</c-> <c- n>result</c-><c- p>,</c-> <c- k>const</c-> <c- n>T1</c-><c- o>&amp;</c-> <c- n>old_value</c-><c- p>,</c-> <c- k>const</c-> <c- n>T2</c-><c- o>&amp;</c-> <c- n>new_value</c-><c- p>,</c->
                 <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->

<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>I</c-><c- p>,</c-> <c- k>class</c-> <c- nc>O</c-><c- o>></c->
  <c- k>using</c-> <c- n>replace_copy_if_result</c-> <c- o>=</c-> <c- n>in_out_result</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>O</c-><c- o>></c-><c- p>;</c->

<c- k>template</c-><c- o>&lt;</c-><c- n>input_iterator</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- p>,</c-><del> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-> <c- n>output_iterator</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>T</c-><c- o>&amp;></c-> <c- n>O</c-><c- p>,</c-></del><ins><c- k>class</c-> <c- nc>O</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-> <c- o>=</c-> <c- n>iter_value_t</c-><c- o>&lt;</c-><c- n>O</c-><c- o>></c-><c- p>,</c-></ins>
         <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><c- p>,</c-> <c- n>indirect_unary_predicate</c-><c- o>&lt;</c-><c- n>projected</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>>></c-> <c- n>Pred</c-><c- o>></c->
  <c- k>requires</c-> <c- n>indirectly_copyable</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>O</c-><c- o>></c-><ins> <c- o>&amp;&amp;</c-> <c- n>output_iterator</c-><c- o>&lt;</c-><c- n>O</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;></c-></ins>
  <c- k>constexpr</c-> <c- n>replace_copy_if_result</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>O</c-><c- o>></c->
    <c- n>replace_copy_if</c-><c- p>(</c-><c- n>I</c-> <c- n>first</c-><c- p>,</c-> <c- n>S</c-> <c- n>last</c-><c- p>,</c-> <c- n>O</c-> <c- n>result</c-><c- p>,</c-> <c- n>Pred</c-> <c- n>pred</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>new_value</c-><c- p>,</c->
                    <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->
<c- k>template</c-><c- o>&lt;</c-><c- n>input_range</c-> <c- n>R</c-><c- p>,</c-><del> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-> <c- n>output_iterator</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>T</c-><c- o>&amp;></c-> <c- n>O</c-><c- p>,</c-></del><ins><c- k>class</c-> <c- nc>O</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-> <c- o>=</c-> <c- n>iter_value_t</c-><c- o>&lt;</c-><c- n>O</c-><c- o>></c-><c- p>,</c-></ins> <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><c- p>,</c->
         <c- n>indirect_unary_predicate</c-><c- o>&lt;</c-><c- n>projected</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>>></c-> <c- n>Pred</c-><c- o>></c->
  <c- k>requires</c-> <c- n>indirectly_copyable</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>O</c-><c- o>></c-><ins> <c- o>&amp;&amp;</c-> <c- n>output_iterator</c-><c- o>&lt;</c-><c- n>O</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;></c-></ins>
  <c- k>constexpr</c-> <c- n>replace_copy_if_result</c-><c- o>&lt;</c-><c- n>borrowed_iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>O</c-><c- o>></c->
    <c- n>replace_copy_if</c-><c- p>(</c-><c- n>R</c-><c- o>&amp;&amp;</c-> <c- n>r</c-><c- p>,</c-> <c- n>O</c-> <c- n>result</c-><c- p>,</c-> <c- n>Pred</c-> <c- n>pred</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>new_value</c-><c- p>,</c->
                    <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->
<c- p>}</c->
</pre>
   <h4 class="heading settled" data-level="7.4.5" id="algfill"><span class="secno">7.4.5. </span><span class="content">[alg.fill]</span><a class="self-link" href="#algfill"></a></h4>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>ForwardIterator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>ForwardIterator</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- o>></c->
  <c- k>constexpr</c-> <c- b>void</c-> <c- n>fill</c-><c- p>(</c-><c- n>ForwardIterator</c-> <c- n>first</c-><c- p>,</c-> <c- n>ForwardIterator</c-> <c- n>last</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</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- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>ForwardIterator</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- o>></c->
  <c- b>void</c-> <c- n>fill</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>last</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>);</c->
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>OutputIterator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Size</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>OutputIterator</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- o>></c->
  <c- k>constexpr</c-> <c- n>OutputIterator</c-> <c- n>fill_n</c-><c- p>(</c-><c- n>OutputIterator</c-> <c- n>first</c-><c- p>,</c-> <c- n>Size</c-> <c- n>n</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</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- p>,</c->
         <c- k>class</c-> <c- nc>Size</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>ForwardIterator</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- o>></c->
  <c- n>ForwardIterator</c-> <c- n>fill_n</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>Size</c-> <c- n>n</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>);</c->
</pre>
<pre class="highlight"><c- k>namespace</c-> <c- nn>ranges</c-> <c- p>{</c->
<del>  <c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- p>,</c-> <c- n>output_iterator</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>T</c-><c- o>&amp;></c-> <c- n>O</c-><c- p>,</c-> <c- n>sentinel_for</c-><c- o>&lt;</c-><c- n>O</c-><c- o>></c-> <c- n>S</c-><c- o>></c-></del>
<ins>  <c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>O</c-><c- p>,</c-> <c- n>sentinel_for</c-><c- o>&lt;</c-><c- n>O</c-><c- o>></c-> <c- n>S</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-> <c- o>=</c-> <c- n>iter_value_t</c-><c- o>&lt;</c-><c- n>O</c-><c- o>>></c->
    <c- k>requires</c-> <c- n>output_iterator</c-><c- o>&lt;</c-><c- n>O</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;></c-></ins>
    <c- k>constexpr</c-> <c- n>O</c-> <c- n>fill</c-><c- p>(</c-><c- n>O</c-> <c- n>first</c-><c- p>,</c-> <c- n>S</c-> <c- n>last</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>);</c->
<del>  <c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- p>,</c-> <c- n>output_range</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>T</c-><c- o>&amp;></c-> <c- n>R</c-><c- o>></c-></del>
<ins>  <c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>R</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-> <c- o>=</c-> <c- n>range_value_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>>></c->
    <c- k>requires</c-> <c- n>output_range</c-><c- o>&lt;</c-><c- n>R</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;></c-></ins>
    <c- k>constexpr</c-> <c- n>borrowed_iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-> <c- n>fill</c-><c- p>(</c-><c- n>R</c-><c- o>&amp;&amp;</c-> <c- n>r</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>);</c->
<del>  <c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- p>,</c-> <c- n>output_iterator</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>T</c-><c- o>&amp;></c-> <c- n>O</c-><c- o>></c-></del>
<ins>  <c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>O</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-> <c- o>=</c-> <c- n>iter_value_t</c-><c- o>&lt;</c-><c- n>O</c-><c- o>>></c->
    <c- k>requires</c-> <c- n>output_iterator</c-><c- o>&lt;</c-><c- n>O</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;></c-></ins>
    <c- k>constexpr</c-> <c- n>O</c-> <c- n>fill_n</c-><c- p>(</c-><c- n>O</c-> <c- n>first</c-><c- p>,</c-> <c- n>iter_difference_t</c-><c- o>&lt;</c-><c- n>O</c-><c- o>></c-> <c- n>n</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>);</c->
<c- p>}</c->
</pre>
   <h4 class="heading settled" data-level="7.4.6" id="algremove"><span class="secno">7.4.6. </span><span class="content">[alg.remove]</span><a class="self-link" href="#algremove"></a></h4>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>ForwardIterator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>ForwardIterator</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- o>></c->
  <c- k>constexpr</c-> <c- n>ForwardIterator</c-> <c- n>remove</c-><c- p>(</c-><c- n>ForwardIterator</c-> <c- n>first</c-><c- p>,</c-> <c- n>ForwardIterator</c-> <c- n>last</c-><c- p>,</c->
                                   <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</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- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>ForwardIterator</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- o>></c->
  <c- n>ForwardIterator</c-> <c- n>remove</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>last</c-><c- p>,</c->
                         <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>);</c->
</pre>
<pre class="highlight"><c- k>namespace</c-> <c- nn>ranges</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- p>,</c-><del> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-></del> <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><ins><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-> <c- o>=</c-> <c- n>projected_value_t</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-></ins><c- o>></c->
    <c- k>requires</c-> <c- n>indirect_binary_predicate</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>equal_to</c-><c- p>,</c-> <c- n>projected</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>T</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>remove</c-><c- p>(</c-><c- n>I</c-> <c- n>first</c-><c- p>,</c-> <c- n>S</c-> <c- n>last</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->
  <c- k>template</c-><c- o>&lt;</c-><c- n>forward_range</c-> <c- n>R</c-><c- p>,</c-><del> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-></del> <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><ins><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-> <c- o>=</c-> <c- n>projected_value_t</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-></ins><c- o>></c->
    <c- k>requires</c-> <c- n>permutable</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>>></c-> <c- o>&amp;&amp;</c->
             <c- n>indirect_binary_predicate</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>equal_to</c-><c- p>,</c->
                                       <c- n>projected</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>*></c->
    <c- k>constexpr</c-> <c- n>borrowed_subrange_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c->
      <c- n>remove</c-><c- p>(</c-><c- n>R</c-><c- o>&amp;&amp;</c-> <c- n>r</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->
<c- p>}</c->
</pre>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>InputIterator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>OutputIterator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>InputIterator</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- o>></c->
  <c- k>constexpr</c-> <c- n>OutputIterator</c->
    <c- n>remove_copy</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- n>OutputIterator</c-> <c- n>result</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</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- p>,</c->
         <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>ForwardIterator1</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- o>></c->
  <c- n>ForwardIterator2</c->
    <c- n>remove_copy</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>first</c-><c- p>,</c-> <c- n>ForwardIterator1</c-> <c- n>last</c-><c- p>,</c->
                <c- n>ForwardIterator2</c-> <c- n>result</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>);</c->
</pre>
<pre class="highlight"><c- k>namespace</c-> <c- nn>ranges</c-> <c- p>{</c->
  <c- k>template</c-><c- o>&lt;</c-><c- n>input_iterator</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- p>,</c-> <c- n>weakly_incrementable</c-> <c- n>O</c-><c- p>,</c-><del> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-></del>
           <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><ins><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-> <c- o>=</c-> <c- n>projected_value_t</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-></ins><c- o>></c->
    <c- k>requires</c-> <c- n>indirectly_copyable</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>O</c-><c- o>></c-> <c- o>&amp;&amp;</c->
             <c- n>indirect_binary_predicate</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>equal_to</c-><c- p>,</c-> <c- n>projected</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>*></c->
    <c- k>constexpr</c-> <c- n>remove_copy_result</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>O</c-><c- o>></c->
      <c- n>remove_copy</c-><c- p>(</c-><c- n>I</c-> <c- n>first</c-><c- p>,</c-> <c- n>S</c-> <c- n>last</c-><c- p>,</c-> <c- n>O</c-> <c- n>result</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->
  <c- k>template</c-><c- o>&lt;</c-><c- n>input_range</c-> <c- n>R</c-><c- p>,</c-> <c- n>weakly_incrementable</c-> <c- n>O</c-><c- p>,</c-><del> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-></del> <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><ins><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-> <c- o>=</c-> <c- n>projected_value_t</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-></ins><c- o>></c->
    <c- k>requires</c-> <c- n>indirectly_copyable</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>O</c-><c- o>></c-> <c- o>&amp;&amp;</c->
             <c- n>indirect_binary_predicate</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>equal_to</c-><c- p>,</c->
                                       <c- n>projected</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>*></c->
    <c- k>constexpr</c-> <c- n>remove_copy_result</c-><c- o>&lt;</c-><c- n>borrowed_iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>O</c-><c- o>></c->
      <c- n>remove_copy</c-><c- p>(</c-><c- n>R</c-><c- o>&amp;&amp;</c-> <c- n>r</c-><c- p>,</c-> <c- n>O</c-> <c- n>result</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->
<c- p>}</c->
</pre>
   <h4 class="heading settled" data-level="7.4.7" id="algbinarysearch"><span class="secno">7.4.7. </span><span class="content">[alg.binary.search]</span><a class="self-link" href="#algbinarysearch"></a></h4>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>ForwardIterator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>ForwardIterator</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- o>></c->
  <c- k>constexpr</c-> <c- n>ForwardIterator</c->
    <c- n>lower_bound</c-><c- p>(</c-><c- n>ForwardIterator</c-> <c- n>first</c-><c- p>,</c-> <c- n>ForwardIterator</c-> <c- n>last</c-><c- p>,</c->
                <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>);</c->
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>ForwardIterator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>ForwardIterator</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- p>,</c-> <c- k>class</c-> <c- nc>Compare</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>ForwardIterator</c->
    <c- n>lower_bound</c-><c- p>(</c-><c- n>ForwardIterator</c-> <c- n>first</c-><c- p>,</c-> <c- n>ForwardIterator</c-> <c- n>last</c-><c- p>,</c->
                <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Compare</c-> <c- n>comp</c-><c- p>);</c->
</pre>
<pre class="highlight"><c- k>namespace</c-> <c- nn>ranges</c-> <c- p>{</c->
  <c- k>template</c-><c- o>&lt;</c-><c- n>forward_iterator</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- p>,</c-><del> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-></del> <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><ins><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-> <c- o>=</c-> <c- n>projected_value_t</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-></ins><c- p>,</c->
           <c- n>indirect_strict_weak_order</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>T</c-><c- o>*</c-><c- p>,</c-> <c- n>projected</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>>></c-> <c- n>Comp</c-> <c- o>=</c-> <c- n>ranges</c-><c- o>::</c-><c- n>less</c-><c- o>></c->
    <c- k>constexpr</c-> <c- n>I</c-> <c- n>lower_bound</c-><c- p>(</c-><c- n>I</c-> <c- n>first</c-><c- p>,</c-> <c- n>S</c-> <c- n>last</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Comp</c-> <c- n>comp</c-> <c- o>=</c-> <c- p>{},</c->
                            <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->
  <c- k>template</c-><c- o>&lt;</c-><c- n>forward_range</c-> <c- n>R</c-><c- p>,</c-><del> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-></del> <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><ins><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-> <c- o>=</c-> <c- n>projected_value_t</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-></ins><c- p>,</c->
           <c- n>indirect_strict_weak_order</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>T</c-><c- o>*</c-><c- p>,</c-> <c- n>projected</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>>></c-> <c- n>Comp</c-> <c- o>=</c->
             <c- n>ranges</c-><c- o>::</c-><c- n>less</c-><c- o>></c->
    <c- k>constexpr</c-> <c- n>borrowed_iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c->
      <c- n>lower_bound</c-><c- p>(</c-><c- n>R</c-><c- o>&amp;&amp;</c-> <c- n>r</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Comp</c-> <c- n>comp</c-> <c- o>=</c-> <c- p>{},</c-> <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->
<c- p>}</c->
</pre>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>ForwardIterator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>ForwardIterator</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- o>></c->
  <c- k>constexpr</c-> <c- n>ForwardIterator</c->
    <c- n>upper_bound</c-><c- p>(</c-><c- n>ForwardIterator</c-> <c- n>first</c-><c- p>,</c-> <c- n>ForwardIterator</c-> <c- n>last</c-><c- p>,</c->
                <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>);</c->
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>ForwardIterator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>ForwardIterator</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- p>,</c-> <c- k>class</c-> <c- nc>Compare</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>ForwardIterator</c->
    <c- n>upper_bound</c-><c- p>(</c-><c- n>ForwardIterator</c-> <c- n>first</c-><c- p>,</c-> <c- n>ForwardIterator</c-> <c- n>last</c-><c- p>,</c->
                <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Compare</c-> <c- n>comp</c-><c- p>);</c->
</pre>
<pre class="highlight"><c- k>namespace</c-> <c- nn>ranges</c-> <c- p>{</c->
  <c- k>template</c-><c- o>&lt;</c-><c- n>forward_iterator</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- p>,</c-><del> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-></del> <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><ins><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-> <c- o>=</c-> <c- n>projected_value_t</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-></ins><c- p>,</c->
           <c- n>indirect_strict_weak_order</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>T</c-><c- o>*</c-><c- p>,</c-> <c- n>projected</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>>></c-> <c- n>Comp</c-> <c- o>=</c-> <c- n>ranges</c-><c- o>::</c-><c- n>less</c-><c- o>></c->
    <c- k>constexpr</c-> <c- n>I</c-> <c- n>upper_bound</c-><c- p>(</c-><c- n>I</c-> <c- n>first</c-><c- p>,</c-> <c- n>S</c-> <c- n>last</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Comp</c-> <c- n>comp</c-> <c- o>=</c-> <c- p>{},</c-> <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->
  <c- k>template</c-><c- o>&lt;</c-><c- n>forward_range</c-> <c- n>R</c-><c- p>,</c-><del> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-></del> <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><ins><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-> <c- o>=</c-> <c- n>projected_value_t</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-></ins><c- p>,</c->
           <c- n>indirect_strict_weak_order</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>T</c-><c- o>*</c-><c- p>,</c-> <c- n>projected</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>>></c-> <c- n>Comp</c-> <c- o>=</c->
             <c- n>ranges</c-><c- o>::</c-><c- n>less</c-><c- o>></c->
    <c- k>constexpr</c-> <c- n>borrowed_iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c->
      <c- n>upper_bound</c-><c- p>(</c-><c- n>R</c-><c- o>&amp;&amp;</c-> <c- n>r</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Comp</c-> <c- n>comp</c-> <c- o>=</c-> <c- p>{},</c-> <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->
<c- p>}</c->
</pre>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>ForwardIterator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>ForwardIterator</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- o>></c->
  <c- k>constexpr</c-> <c- n>pair</c-><c- o>&lt;</c-><c- n>ForwardIterator</c-><c- p>,</c-> <c- n>ForwardIterator</c-><c- o>></c->
    <c- n>equal_range</c-><c- p>(</c-><c- n>ForwardIterator</c-> <c- n>first</c-><c- p>,</c-> <c- n>ForwardIterator</c-> <c- n>last</c-><c- p>,</c->
                <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>);</c->
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>ForwardIterator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>ForwardIterator</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- p>,</c-> <c- k>class</c-> <c- nc>Compare</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>pair</c-><c- o>&lt;</c-><c- n>ForwardIterator</c-><c- p>,</c-> <c- n>ForwardIterator</c-><c- o>></c->
    <c- n>equal_range</c-><c- p>(</c-><c- n>ForwardIterator</c-> <c- n>first</c-><c- p>,</c-> <c- n>ForwardIterator</c-> <c- n>last</c-><c- p>,</c->
                <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Compare</c-> <c- n>comp</c-><c- p>);</c->
</pre>
<pre class="highlight"><c- k>namespace</c-> <c- nn>ranges</c-> <c- p>{</c->
  <c- k>template</c-><c- o>&lt;</c-><c- n>forward_iterator</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- p>,</c-><del> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-></del> <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><ins><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-> <c- o>=</c-> <c- n>projected_value_t</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-></ins><c- p>,</c->
           <c- n>indirect_strict_weak_order</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>T</c-><c- o>*</c-><c- p>,</c-> <c- n>projected</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>>></c-> <c- n>Comp</c-> <c- o>=</c-> <c- n>ranges</c-><c- o>::</c-><c- n>less</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>equal_range</c-><c- p>(</c-><c- n>I</c-> <c- n>first</c-><c- p>,</c-> <c- n>S</c-> <c- n>last</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Comp</c-> <c- n>comp</c-> <c- o>=</c-> <c- p>{},</c-> <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->
  <c- k>template</c-><c- o>&lt;</c-><c- n>forward_range</c-> <c- n>R</c-><c- p>,</c-><del> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-></del> <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><ins><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-> <c- o>=</c-> <c- n>projected_value_t</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-></ins><c- p>,</c->
           <c- n>indirect_strict_weak_order</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>T</c-><c- o>*</c-><c- p>,</c-> <c- n>projected</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>>></c-> <c- n>Comp</c-> <c- o>=</c->
             <c- n>ranges</c-><c- o>::</c-><c- n>less</c-><c- o>></c->
    <c- k>constexpr</c-> <c- n>borrowed_subrange_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c->
      <c- n>equal_range</c-><c- p>(</c-><c- n>R</c-><c- o>&amp;&amp;</c-> <c- n>r</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Comp</c-> <c- n>comp</c-> <c- o>=</c-> <c- p>{},</c-> <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->
<c- p>}</c->
</pre>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>ForwardIterator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>ForwardIterator</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- o>></c->
  <c- k>constexpr</c-> <c- b>bool</c->
    <c- n>binary_search</c-><c- p>(</c-><c- n>ForwardIterator</c-> <c- n>first</c-><c- p>,</c-> <c- n>ForwardIterator</c-> <c- n>last</c-><c- p>,</c->
                  <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>);</c->
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>ForwardIterator</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- k>typename</c-> <c- nc>iterator_traits</c-><c- o>&lt;</c-><c- n>ForwardIterator</c-><c- o>>::</c-><c- n>value_type</c-></ins><c- p>,</c-> <c- k>class</c-> <c- nc>Compare</c-><c- o>></c->
  <c- k>constexpr</c-> <c- b>bool</c->
    <c- n>binary_search</c-><c- p>(</c-><c- n>ForwardIterator</c-> <c- n>first</c-><c- p>,</c-> <c- n>ForwardIterator</c-> <c- n>last</c-><c- p>,</c->
                  <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Compare</c-> <c- n>comp</c-><c- p>);</c->
</pre>
<pre class="highlight"><c- k>namespace</c-> <c- nn>ranges</c-> <c- p>{</c->
  <c- k>template</c-><c- o>&lt;</c-><c- n>forward_iterator</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- p>,</c-><del> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-></del> <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><ins><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-> <c- o>=</c-> <c- n>projected_value_t</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-></ins><c- p>,</c->
           <c- n>indirect_strict_weak_order</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>T</c-><c- o>*</c-><c- p>,</c-> <c- n>projected</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>>></c-> <c- n>Comp</c-> <c- o>=</c-> <c- n>ranges</c-><c- o>::</c-><c- n>less</c-><c- o>></c->
    <c- k>constexpr</c-> <c- b>bool</c-> <c- n>binary_search</c-><c- p>(</c-><c- n>I</c-> <c- n>first</c-><c- p>,</c-> <c- n>S</c-> <c- n>last</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Comp</c-> <c- n>comp</c-> <c- o>=</c-> <c- p>{},</c->
                                 <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->
  <c- k>template</c-><c- o>&lt;</c-><c- n>forward_range</c-> <c- n>R</c-><c- p>,</c-><del> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-></del> <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><ins><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-> <c- o>=</c-> <c- n>projected_value_t</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-></ins><c- p>,</c->
           <c- n>indirect_strict_weak_order</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>T</c-><c- o>*</c-><c- p>,</c-> <c- n>projected</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>>></c-> <c- n>Comp</c-> <c- o>=</c->
             <c- n>ranges</c-><c- o>::</c-><c- n>less</c-><c- o>></c->
    <c- k>constexpr</c-> <c- b>bool</c-> <c- n>binary_search</c-><c- p>(</c-><c- n>R</c-><c- o>&amp;&amp;</c-> <c- n>r</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Comp</c-> <c- n>comp</c-> <c- o>=</c-> <c- p>{},</c->
                                 <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->
<c- p>}</c->
</pre>
   <h4 class="heading settled" data-level="7.4.8" id="algfold"><span class="secno">7.4.8. </span><span class="content">[alg.fold]</span><a class="self-link" href="#algfold"></a></h4>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- n>input_iterator</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- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- n>iter_value_t</c-><c- o>&lt;</c-><c- n>I</c-><c- o>></c-></ins><c- p>,</c-> <i><c- n>indirectly</c-><c- o>-</c-><c- n>binary</c-><c- o>-</c-><c- n>left</c-><c- o>-</c-><c- n>foldable</c-></i><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>I</c-><c- o>></c-> <c- n>F</c-><c- o>></c->
  <c- k>constexpr</c-> <c- k>auto</c-> <c- n>ranges</c-><c- o>::</c-><c- n>fold_left</c-><c- p>(</c-><c- n>I</c-> <c- n>first</c-><c- p>,</c-> <c- n>S</c-> <c- n>last</c-><c- p>,</c-> <c- n>T</c-> <c- n>init</c-><c- p>,</c-> <c- n>F</c-> <c- n>f</c-><c- p>);</c->

<c- k>template</c-><c- o>&lt;</c-><c- n>input_range</c-> <c- n>R</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- n>range_value_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-></ins><c- p>,</c-> <i><c- n>indirectly</c-><c- o>-</c-><c- n>binary</c-><c- o>-</c-><c- n>left</c-><c- o>-</c-><c- n>foldable</c-></i><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>>></c-> <c- n>F</c-><c- o>></c->
  <c- k>constexpr</c-> <c- k>auto</c-> <c- n>ranges</c-><c- o>::</c-><c- n>fold_left</c-><c- p>(</c-><c- n>R</c-><c- o>&amp;&amp;</c-> <c- n>r</c-><c- p>,</c-> <c- n>T</c-> <c- n>init</c-><c- p>,</c-> <c- n>F</c-> <c- n>f</c-><c- p>);</c->
</pre>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- n>bidirectional_iterator</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- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- n>iter_value_t</c-><c- o>&lt;</c-><c- n>I</c-><c- o>></c-></ins><c- p>,</c->
         <c- n>indirectly</c-><c- o>-</c-><c- n>binary</c-><c- o>-</c-><c- n>right</c-><c- o>-</c-><c- n>foldable</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>I</c-><c- o>></c-> <c- n>F</c-><c- o>></c->
  <c- k>constexpr</c-> <c- k>auto</c-> <c- n>ranges</c-><c- o>::</c-><c- n>fold_right</c-><c- p>(</c-><c- n>I</c-> <c- n>first</c-><c- p>,</c-> <c- n>S</c-> <c- n>last</c-><c- p>,</c-> <c- n>T</c-> <c- n>init</c-><c- p>,</c-> <c- n>F</c-> <c- n>f</c-><c- p>);</c->
<c- k>template</c-><c- o>&lt;</c-><c- n>bidirectional_range</c-> <c- n>R</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- n>range_value_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-></ins><c- p>,</c->
         <c- n>indirectly</c-><c- o>-</c-><c- n>binary</c-><c- o>-</c-><c- n>right</c-><c- o>-</c-><c- n>foldable</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>>></c-> <c- n>F</c-><c- o>></c->
  <c- k>constexpr</c-> <c- k>auto</c-> <c- n>ranges</c-><c- o>::</c-><c- n>fold_right</c-><c- p>(</c-><c- n>R</c-><c- o>&amp;&amp;</c-> <c- n>r</c-><c- p>,</c-> <c- n>T</c-> <c- n>init</c-><c- p>,</c-> <c- n>F</c-> <c- n>f</c-><c- p>);</c->
</pre>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- n>input_iterator</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- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- n>iter_value_t</c-><c- o>&lt;</c-><c- n>I</c-><c- o>></c-></ins><c- p>,</c->
         <i><c- n>indirectly</c-><c- o>-</c-><c- n>binary</c-><c- o>-</c-><c- n>left</c-><c- o>-</c-><c- n>foldable</c-></i><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>I</c-><c- o>></c-> <c- n>F</c-><c- o>></c->
  <c- k>constexpr</c-> <i><c- n>see</c-> <c- n>below</c-></i> <c- n>ranges</c-><c- o>::</c-><c- n>fold_left_with_iter</c-><c- p>(</c-><c- n>I</c-> <c- n>first</c-><c- p>,</c-> <c- n>S</c-> <c- n>last</c-><c- p>,</c-> <c- n>T</c-> <c- n>init</c-><c- p>,</c-> <c- n>F</c-> <c- n>f</c-><c- p>);</c->
<c- k>template</c-><c- o>&lt;</c-><c- n>input_range</c-> <c- n>R</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><ins> <c- o>=</c-> <c- n>range_value_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-></ins><c- p>,</c-> <i><c- n>indirectly</c-><c- o>-</c-><c- n>binary</c-><c- o>-</c-><c- n>left</c-><c- o>-</c-><c- n>foldable</c-></i><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>>></c-> <c- n>F</c-><c- o>></c->
  <c- k>constexpr</c-> <i><c- n>see</c-> <c- n>below</c-></i> <c- n>ranges</c-><c- o>::</c-><c- n>fold_left_with_iter</c-><c- p>(</c-><c- n>R</c-><c- o>&amp;&amp;</c-> <c- n>r</c-><c- p>,</c-> <c- n>T</c-> <c- n>init</c-><c- p>,</c-> <c- n>F</c-> <c- n>f</c-><c- p>);</c->
</pre>
   <h4 class="heading settled" data-level="7.4.9" id="algcontains"><span class="secno">7.4.9. </span><span class="content">[alg.contains]</span><a class="self-link" href="#algcontains"></a></h4>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- n>input_</c->­<c- n>iterator</c-> <c- n>I</c-><c- p>,</c-> <c- n>sentinel_</c->­<c- k>for</c-><c- o>&lt;</c-><c- n>I</c-><c- o>></c-> <c- n>S</c-><c- p>,</c-><del> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-></del> <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><ins><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-> <c- o>=</c-> <c- n>projected_value_t</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-></ins><c- o>></c->
  <c- k>requires</c-> <c- n>indirect_</c->­<c- n>binary_</c->­<c- n>predicate</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>equal_to</c-><c- p>,</c-> <c- n>projected</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>*></c->
  <c- k>constexpr</c-> <c- b>bool</c-> <c- n>contains</c-><c- p>(</c-><c- n>I</c-> <c- n>first</c-><c- p>,</c-> <c- n>S</c-> <c- n>last</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->

<c- k>template</c-><c- o>&lt;</c-><c- n>input_</c->­<c- n>range</c-> <c- n>R</c-><c- p>,</c-><del> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-></del> <c- k>class</c-> <c- nc>Proj</c-> <c- o>=</c-> <c- n>identity</c-><ins><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-> <c- o>=</c-> <c- n>projected_value_t</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-></ins><c- o>></c->
  <c- k>requires</c-> <c- n>indirect_</c->­<c- n>binary_</c->­<c- n>predicate</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>equal_to</c-><c- p>,</c-> <c- n>projected</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Proj</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>*></c->
  <c- k>constexpr</c-> <c- b>bool</c-> <c- n>contains</c-><c- p>(</c-><c- n>R</c-><c- o>&amp;&amp;</c-> <c- n>r</c-><c- p>,</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>,</c-> <c- n>Proj</c-> <c- n>proj</c-> <c- o>=</c-> <c- p>{});</c->
</pre>
   <h2 class="heading settled" data-level="8" id="acknowledgements"><span class="secno">8. </span><span class="content">Acknowledgements</span><a class="self-link" href="#acknowledgements"></a></h2>
   <p>Thanks to KDAB for supporting this work.</p>
   <p>Special thanks to Stephan T. Lavavej for confirming that the omission
of a default argument from the <code class="highlight"><c- n>erase</c-><c- p>()</c-></code> functions was not a deliberate
design choice of the consistent container erasure proposal. Thanks to
Arthur O’Dwyer for the insightful discussions. Thanks to Will Wray for
the discussions regarding supporting array types and the mentions of
related paper work. Thanks to Michał Dominiak for pointing out the
possible ABI issues but still encouraging to bring the paper forward.
Thanks to Tim Song for raising the problem of establishing the default
type in the presence of projections, and to Barry Revzin for the
excellent analysis in <a data-link-type="biblio" href="#biblio-p2322r6" title="ranges::fold">[P2322R6]</a>.</p>
   <p>All remaining errors are ours and ours only.</p>
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  <h2 class="no-num no-ref heading settled" id="references"><span class="content">References</span><a class="self-link" href="#references"></a></h2>
  <h3 class="no-num no-ref heading settled" id="informative"><span class="content">Informative References</span><a class="self-link" href="#informative"></a></h3>
  <dl>
   <dt id="biblio-n4971">[N4971]
   <dd>Thomas Köppe. <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/n4971.pdf"><cite>Working Draft, Standard for Programming Language C++</cite></a>. URL: <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/n4971.pdf">https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/n4971.pdf</a>
   <dt id="biblio-p1997r1">[P1997R1]
   <dd>Krystian Stasiowski; Theodoric Stier. <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/p1997r1.pdf"><cite>Relaxing Restrictions on Arrays</cite></a>. URL: <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/p1997r1.pdf">http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/p1997r1.pdf</a>
   <dt id="biblio-p2218r0">[P2218R0]
   <dd>Marc Mutz. <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/p2218r0.pdf"><cite>More flexible optional::value_or()</cite></a>. URL: <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/p2218r0.pdf">http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/p2218r0.pdf</a>
   <dt id="biblio-p2248-gcc">[P2248-GCC]
   <dd>Giuseppe D'Angelo. <a href="https://github.com/dangelog/gcc/tree/std-proposals"><cite>P2248 prototype implementation</cite></a>. URL: <a href="https://github.com/dangelog/gcc/tree/std-proposals">https://github.com/dangelog/gcc/tree/std-proposals</a>
   <dt id="biblio-p2248-hpx">[P2248-HPX]
   <dd><a href="https://github.com/STEllAR-GROUP/hpx/pull/5675"><cite>Implementation of P2248 in HPX</cite></a>. URL: <a href="https://github.com/STEllAR-GROUP/hpx/pull/5675">https://github.com/STEllAR-GROUP/hpx/pull/5675</a>
   <dt id="biblio-p2302r4">[P2302R4]
   <dd>Christopher Di Bella. <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2302r4.html"><cite>std::ranges::contains</cite></a>. URL: <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2302r4.html">https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2302r4.html</a>
   <dt id="biblio-p2322r6">[P2322R6]
   <dd>Barry Revzin. <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2322r6.html"><cite>ranges::fold</cite></a>. URL: <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2322r6.html">https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2322r6.html</a>
   <dt id="biblio-p2609r0">[P2609R0]
   <dd>John Eivind Helset. <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2609r0.html"><cite>Relaxing Ranges Just A Smidge</cite></a>. URL: <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2609r0.html">https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2609r0.html</a>
   <dt id="biblio-sd-8">[SD-8]
   <dd>Titus Winter. <a href="https://isocpp.org/std/standing-documents/sd-8-standard-library-compatibility"><cite>SD-8: Standard Library Compatibility</cite></a>. URL: <a href="https://isocpp.org/std/standing-documents/sd-8-standard-library-compatibility">https://isocpp.org/std/standing-documents/sd-8-standard-library-compatibility</a>
  </dl>