<!doctype html><html lang="en">
 <head>
  <meta content="text/html; charset=utf-8" http-equiv="Content-Type">
  <meta content="width=device-width, initial-scale=1, shrink-to-fit=no" name="viewport">
  <title>p1040R1: std::embed</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
 *
 * 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)
 *   - .assertion  for assertions                    (div, p, span)
 *   - .advisement for loud normative statements     (div, p, strong)
 *   - .annoying-warning for spec obsoletion notices (div, aside, details)
 *
 * 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
 *
 * 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)
 *
 ******************************************************************************/

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

	body {
		counter-reset: example figure issue;

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

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

		/* Colors */
		color: black;
		background: white top left fixed no-repeat;
		background-size: 25px auto;
	}


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

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

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

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

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

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

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

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

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

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

	/* 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: 2;
			bottom: 0; left: 0;
			margin: 0;
			min-width: 1.33em;
			border-top-right-radius: 2rem;
			box-shadow: 0 0 2px;
			font-size: 1.5em;
			color: black;
		}
		#toc-nav > a {
			display: block;
			white-space: nowrap;

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

			background: white;
			box-shadow: 0 0 2px;
			border: none;
			border-top-right-radius: 1.33em;
			background: white;
		}
		#toc-nav > #toc-jump {
			padding-bottom: 2em;
			margin-bottom: -1.9em;
		}

		#toc-nav > a:hover,
		#toc-nav > a:focus {
			background: #f8f8f8;
		}
		#toc-nav > a:not(:hover):not(:focus) {
			color: #707070;
		}

		/* 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-toggle-inline {
			vertical-align: 0.05em;
			font-size: 80%;
			color: gray;
			color: hsla(203,20%,40%,.7);
			border-style: none;
			background: transparent;
			position: relative;
		}
		#toc-toggle-inline:hover:not(:active),
		#toc-toggle-inline:focus:not(:active) {
			text-shadow: 1px 1px silver;
			top: -1px;
			left: -1px;
		}

		#toc-nav :active {
			color: #C00;
		}
	}

/** 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);
			background: inherit;
			background-color: #f7f8f9;
			z-index: 1;
			box-shadow: -.1em 0 .25em rgba(0,0,0,.1) 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);
		}
		body.toc-sidebar #toc-jump:not(:focus) {
			width: 0;
			height: 0;
			padding: 0;
			position: absolute;
			overflow: hidden;
		}
	}
	/* Hide main scroller when only the ToC is visible anyway */
	@media screen and (max-width: 28em) {
		body.toc-sidebar {
			overflow: hidden;
		}
	}

	/* Sidebar with its own space */
	@media screen and (min-width: 78em) {
		body:not(.toc-inline) #toc {
			position: fixed;
			top: 0; bottom: 0;
			left: 0;
			width: 23.5em;
			overflow: auto;
			padding: 0 1em;
			padding-left: 42px;
			padding-left: calc(1em + 26px);
			background: inherit;
			background-color: #f7f8f9;
			z-index: 1;
			box-shadow: -.1em 0 .25em rgba(0,0,0,.1) 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);
		}

		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;
		background: transparent;
	}

	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,
	#subtitle {
		/* #subtitle 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) > hr {
		font-size: 1.5em;
		text-align: center;
		margin: 1em auto;
		height: auto;
		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;
	}

	/* Put nice boxes around each algorithm. */
	[data-algorithm]:not(.heading) {
	  padding: .5em;
	  border: thin solid #ddd; 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: medium;
	}
	dfn var {
		font-style: normal;
	}

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

	del { color: red;  text-decoration: line-through; }
	ins { color: #080; text-decoration: underline;    }

/** 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;
		page-break-inside: avoid;
		hyphens: none;
		text-transform: none;
	}
	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;
		text-decoration: none;
		border-bottom: 1px solid #707070;
		/* Need a bit of extending for it to look okay */
		padding: 0 1px 0;
		margin: 0 -1px 0;
	}
	a:visited {
		border-bottom-color: #BBB;
	}

	/* Use distinguishing colors when user is interacting with the link */
	a[href]:focus,
	a[href]:hover {
		background: #f8f8f8;
		background: rgba(75%, 75%, 75%, .25);
		border-bottom-width: 3px;
		margin-bottom: -2px;
	}
	a[href]:active {
		color: #C00;
		border-color: #C00;
	}

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

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

	img {
		border-style: none;
	}

	/* 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;
	}
	.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 {
		padding: .5em;
		border: .5em;
		border-left-style: solid;
		page-break-inside: avoid;
	}
	span.issue, span.note {
		padding: .1em .5em .15em;
		border-right-style: solid;
	}

	.issue,
	.note,
	.example,
	.advisement,
	.assertion,
	blockquote {
		margin: 1em auto;
	}
	.note  > p:first-child,
	.issue > p:first-child,
	blockquote > :first-child {
		margin-top: 0;
	}
	blockquote > :last-child {
		margin-bottom: 0;
	}

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

	blockquote {
		border-color: silver;
	}

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

	.issue {
		border-color: #E05252;
		background: #FBE9E9;
		counter-increment: issue;
		overflow: auto;
	}
	.issue::before, .issue > .marker {
		text-transform: uppercase;
		color: #AE1E1E;
		padding-right: 1em;
		text-transform: uppercase;
	}
	/* 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;
		background: #FCFAEE;
		counter-increment: example;
		overflow: auto;
		clear: both;
	}
	.example::before, .example > .marker {
		text-transform: uppercase;
		color: #827017;
		min-width: 7.5em;
		display: block;
	}
	/* 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;
		background: #E9FBE9;
		overflow: auto;
	}

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

	details.note > summary {
		display: block;
		color: hsl(120, 70%, 30%);
	}
	details.note[open] > summary {
		border-bottom: 1px silver solid;
	}

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

	.assertion {
		border-color: #AAA;
		background: #EEE;
	}

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

	.advisement {
		border-color: orange;
		border-style: none solid;
		background: #FFEECC;
	}
	strong.advisement {
		display: block;
		text-align: center;
	}
	.advisement > .marker {
		color: #B35F00;
	}

/** 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: #fdd;
		color: red;
		font-weight: bold;
		padding: .75em 1em;
		border: thick red;
		border-style: solid;
		border-radius: 1em;
	}
	.annoying-warning :last-child {
		margin-bottom: 0;
	}

@media not print {
	details.annoying-warning[open] {
		position: fixed;
		left: 1em;
		right: 1em;
		bottom: 1em;
		z-index: 1000;
	}
}

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

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

	.def {
		padding: .5em 1em;
		background: #DEF;
		margin: 1.2em 0;
		border-left: 0.5em solid #8CCBF2;
	}

/******************************************************************************/
/*                                    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;
	}

	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-top-style: solid;
	}

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

	table.data  thead,
	table.index thead,
	table.data  tbody,
	table.index tbody {
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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">p1040R1<br>std::embed</h1>
   <h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Published Proposal, <time class="dt-updated" datetime="2018-06-06">6 June 2018</time></span></h2>
   <div data-fill-with="spec-metadata">
    <dl>
     <dt>Author:
     <dd>
      <dd class="editor p-author h-card vcard"><span class="p-name fn">JeanHeyd Meneide</span>
     <dt>Audience:
     <dd>EWG, LEWG
     <dt>Project:
     <dd>ISO JTC1/SC22/WG21: Programming Language C++
     <dt>Current Source:
     <dd><a href="https://github.com/ThePhD/embed/blob/master/papers/source/d1040.bs">github.com/ThePhD/embed/blob/master/papers/source/d1040.bs</a>
     <dt>Current:
     <dd><a href="https://rawgit.com/ThePhD/embed/master/papers/d1040.html">https://rawgit.com/ThePhD/embed/master/papers/d1040.html</a>
     <dt>Implementation:
     <dd><a href="https://github.com/ThePhD/embed-implementation">https://github.com/ThePhD/embed-implementation</a>
    </dl>
   </div>
   <div data-fill-with="warning"></div>
   <hr title="Separator for header">
  </div>
  <div class="p-summary" data-fill-with="abstract">
   <h2 class="no-num no-toc no-ref heading settled" id="abstract"><span class="content">Abstract</span></h2>
   <blockquote>
    <p>I’m very keen on std::embed. I’ve been hand-embedding data in executables for NEARLY FORTY YEARS now. — <cite>Guy "Hatcat" Davidson, June 15, 2018</cite></p>
   </blockquote>
  </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">Revision History</span></a>
     <ol class="toc">
      <li><a href="#changelog-r1"><span class="secno">1.1</span> <span class="content">Revision 1</span></a>
      <li><a href="#changelog-r0"><span class="secno">1.2</span> <span class="content">Revision 0</span></a>
     </ol>
    <li><a href="#motivation"><span class="secno">2</span> <span class="content">Motivation</span></a>
    <li><a href="#scope"><span class="secno">3</span> <span class="content">Scope and Impact</span></a>
    <li>
     <a href="#design"><span class="secno">4</span> <span class="content">Design Decisions</span></a>
     <ol class="toc">
      <li>
       <a href="#design-practice"><span class="secno">4.1</span> <span class="content">Current Practice</span></a>
       <ol class="toc">
        <li><a href="#design-practice-manual"><span class="secno">4.1.1</span> <span class="content">Manual Work</span></a>
        <li><a href="#design-practice-tools"><span class="secno">4.1.2</span> <span class="content">Processing Tools</span></a>
        <li><a href="#design-practice-vendor"><span class="secno">4.1.3</span> <span class="content"><code class="highlight"><span class="n">ld</span></code>, resource files, and other vendor-specific link-time tools</span></a>
        <li><a href="#design.practice.incbin"><span class="secno">4.1.4</span> <span class="content">The <code class="highlight"><span class="n">incbin</span></code> tool</span></a>
       </ol>
      <li>
       <a href="#design-prior"><span class="secno">4.2</span> <span class="content">Prior Art</span></a>
       <ol class="toc">
        <li><a href="#design-prior-literal"><span class="secno">4.2.1</span> <span class="content">Literal-Based, constexpr</span></a>
        <li><a href="#design-prior-null"><span class="secno">4.2.2</span> <span class="content">Literal-Based, Null Terminated (?)</span></a>
        <li><a href="#design-prior-encoding"><span class="secno">4.2.3</span> <span class="content">Encoding</span></a>
       </ol>
      <li>
       <a href="#design-goals"><span class="secno">4.3</span> <span class="content">Design Goals</span></a>
       <ol class="toc">
        <li><a href="#design-goals-impldefn"><span class="secno">4.3.1</span> <span class="content">Implementation Defined</span></a>
        <li><a href="#design-goals-binary"><span class="secno">4.3.2</span> <span class="content">Binary Only</span></a>
        <li><a href="#design-goals-null"><span class="secno">4.3.3</span> <span class="content">Opt-in and Optional Null Termination</span></a>
        <li><a href="#design-goals-align"><span class="secno">4.3.4</span> <span class="content">Opt-in Alignment</span></a>
        <li><a href="#design-goals-options"><span class="secno">4.3.5</span> <span class="content">Options</span></a>
        <li><a href="#design-goals-constexpr"><span class="secno">4.3.6</span> <span class="content">Constexpr Compatibility</span></a>
        <li><a href="#design-goals-macro"><span class="secno">4.3.7</span> <span class="content">Feature Macro</span></a>
       </ol>
     </ol>
    <li>
     <a href="#help"><span class="secno">5</span> <span class="content">Help Requested</span></a>
     <ol class="toc">
      <li><a href="#help-represent"><span class="secno">5.1</span> <span class="content">Feeling Underrepresented?</span></a>
      <li>
       <a href="#help-bikshed"><span class="secno">5.2</span> <span class="content">Bikeshedding</span></a>
       <ol class="toc">
        <li><a href="#help-bikeshed-alternative"><span class="secno">5.2.1</span> <span class="content">Alternative Names</span></a>
        <li><a href="#help-bikeshed-open"><span class="secno">5.2.2</span> <span class="content">Open Questions</span></a>
        <li><a href="#help-bikeshed-answered"><span class="secno">5.2.3</span> <span class="content">Answered Questions</span></a>
       </ol>
     </ol>
    <li><a href="#synopsis"><span class="secno">6</span> <span class="content">Header Overview</span></a>
    <li><a href="#future"><span class="secno">7</span> <span class="content">Future Direction</span></a>
    <li>
     <a href="#appendix"><span class="secno">8</span> <span class="content">Appendix</span></a>
     <ol class="toc">
      <li>
       <a href="#appendix-sadness"><span class="secno">8.1</span> <span class="content">Sadness</span></a>
       <ol class="toc">
        <li><a href="#appendix-tools"><span class="secno">8.1.1</span> <span class="content">Pre-Processing Tools Sadness</span></a>
        <li><a href="#appendix-mongo"><span class="secno">8.1.2</span> <span class="content"><code class="highlight"><span class="n">python</span></code> Sadness</span></a>
        <li><a href="#appendix-ld"><span class="secno">8.1.3</span> <span class="content"><code class="highlight"><span class="n">ld</span></code> Sadness</span></a>
       </ol>
     </ol>
    <li><a href="#acknowledgements"><span class="secno">9</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>
   <p>Accessing external resources at compile-time and making them available to the language and user.</p>
   <p>This paper introduces a function <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">embed</span></code> in the <code class="highlight"><span class="o">&lt;</span><span class="n">embed</span><span class="o">></span></code> header for pulling resources at compile-time into a program and optionally guaranteeing that they are stored in the resulting program in an implementation-defined manner.</p>
   <h2 class="heading settled" data-level="1" id="changelog"><span class="secno">1. </span><span class="content">Revision History</span><a class="self-link" href="#changelog"></a></h2>
   <h3 class="heading settled" data-level="1.1" id="changelog-r1"><span class="secno">1.1. </span><span class="content">Revision 1</span><a class="self-link" href="#changelog-r1"></a></h3>
   <p>Create future directions section, follow up on Library Evolution Working Group comments.</p>
   <p>Change <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">embed_options</span><span class="o">::</span><span class="n">null_terminated</span></code> to <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">embed_options</span><span class="o">::</span><span class="n">null_terminate</span></code>.</p>
   <p>Add more code demonstrating the old way and motivating examples.</p>
   <p>Incorporate LEWG feedback, particularly alignment requirements illuminated by Odin Holmes and Niall Douglass. Add a feature macro on top of having <code class="highlight"><span class="n">__has_include</span><span class="p">(</span> <span class="o">&lt;</span><span class="n">embed</span><span class="o">></span> <span class="p">)</span></code>.</p>
   <h3 class="heading settled" data-level="1.2" id="changelog-r0"><span class="secno">1.2. </span><span class="content">Revision 0</span><a class="self-link" href="#changelog-r0"></a></h3>
   <p>Initial release.</p>
   <h2 class="heading settled" data-level="2" id="motivation"><span class="secno">2. </span><span class="content">Motivation</span><a class="self-link" href="#motivation"></a></h2>
   <p>Every C and C++ programmer -- at some point -- attempts to <code class="highlight"><span class="cp">#include</span></code> large chunks of non-C++ data into their code. Of course, <code class="highlight"><span class="cp">#include</span></code> expects the format of the data to be source code, and thusly the program fails with spectacular lexer errors. Thusly, many different tools and practices were adapted to handle this, as far back as 1995 with the <code class="highlight"><span class="n">xxd</span></code> tool. Many industries need such functionality, including (but hardly limited to):</p>
   <ul>
    <li data-md="">
     <p>Financial Development</p>
     <ul>
      <li data-md="">
       <p>representing coefficients and numeric constants for performance-critical algorithms;</p>
     </ul>
    <li data-md="">
     <p>Game Development</p>
     <ul>
      <li data-md="">
       <p>assets that do not change at runtime, such as icons, fixed textures and other data</p>
      <li data-md="">
       <p>Shader and scripting code;</p>
     </ul>
    <li data-md="">
     <p>Embedded Development</p>
     <ul>
      <li data-md="">
       <p>storing large chunks of binary, such as firmware, in a well-compressed format</p>
      <li data-md="">
       <p>placing data in memory on chips and systems that do not have an operating system or file system;</p>
     </ul>
    <li data-md="">
     <p>Application Development</p>
     <ul>
      <li data-md="">
       <p>compressed binary blobs representing data</p>
      <li data-md="">
       <p>non-C++ script code that is not changed at runtime; and</p>
     </ul>
    <li data-md="">
     <p>Server Development</p>
     <ul>
      <li data-md="">
       <p>configuration parameters which are known at build-time and are baked in to set limits and give compile-time information to tweak performance under certain loads</p>
      <li data-md="">
       <p>SSL/TLS Certificates hard-coded into your executable (requiring a rebuild and potential authorization before deploying new certificates).</p>
     </ul>
   </ul>
   <p>In the pursuit of this goal, these tools have proven to have inadequacies and contribute poorly to the C++ development cycle as it continues to scale up for larger and better low-end devices and high-performance machines, bogging developers down with menial build tasks and trying to cover-up disappointing differences between platforms.</p>
   <p>MongoDB has been kind enough to share some of their code <a href="#appendix-mongo">below</a>. Other companies have had their example code anonymized or simply not included directly out of shame for the things they need to do to support their workflows. The author thanks MongoDB for their courage and their support for <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">embed</span></code>.</p>
   <p>The request for some form of <code class="highlight"><span class="cp">#include</span>_string</code> or similar dates back quite a long time, with one of the oldest stack overflow questions asked-and-answered about it dating back nearly 10 years. Predating even that is a plethora of mailing list posts and forum posts asking how to get script code and other things that are not likely to change into the binary.</p>
   <p>This paper proposes <code class="highlight"><span class="o">&lt;</span><span class="n">embed</span><span class="o">></span></code> to make this process much more efficient, portable, and streamlined. Here’s an example of the ideal:</p>
<pre class="highlight"><span class="cp">#include</span> &lt;embed><span class="cp"></span>
<span class="cp"></span>
<span class="kt">int</span> <span class="nf">main</span> <span class="p">(</span><span class="kt">int</span><span class="p">,</span> <span class="kt">char</span><span class="o">*</span><span class="p">[])</span> <span class="p">{</span>
  <span class="k">constexpr</span> <span class="n">std</span><span class="o">::</span><span class="n">span</span><span class="o">&lt;</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">byte</span><span class="o">></span> <span class="n">fxaa_binary</span> <span class="o">=</span> <span class="n">std</span><span class="o">::</span><span class="n">embed</span><span class="p">(</span> <span class="s">"fxaa.spirv"</span> <span class="p">);</span>
	
  <span class="c1">// assert this is a SPIRV file, compile-time  </span>
<span class="c1"></span>  <span class="k">static_assert</span><span class="p">(</span> <span class="n">fxaa_binary</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="o">==</span> <span class="mh">0x03</span> <span class="o">&amp;&amp;</span> <span class="n">fxaa_binary</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span> <span class="o">==</span> <span class="mh">0x02</span>
    <span class="o">&amp;&amp;</span> <span class="n">fxaa_binary</span><span class="p">[</span><span class="mi">2</span><span class="p">]</span> <span class="o">==</span> <span class="mh">0x23</span> <span class="o">&amp;&amp;</span> <span class="n">fxaa_binary</span><span class="p">[</span><span class="mi">3</span><span class="p">]</span> <span class="o">==</span> <span class="mh">0x07</span>
    <span class="p">,</span> <span class="s">"given wrong SPIRV data, check rebuild or check the binaries!"</span> <span class="p">)</span>

  <span class="k">auto</span> <span class="n">context</span> <span class="o">=</span> <span class="n">make_vulkan_context</span><span class="p">();</span>

  <span class="c1">// data kept around and made available for binary</span>
<span class="c1"></span>  <span class="c1">// to use at runtime</span>
<span class="c1"></span>  <span class="k">auto</span> <span class="n">fxaa_shader</span> <span class="o">=</span> <span class="n">make_shader</span><span class="p">(</span> <span class="n">context</span><span class="p">,</span> <span class="n">fxaa_binary</span> <span class="p">);</span>

  <span class="k">for</span> <span class="p">(;;)</span> <span class="p">{</span>
    <span class="c1">// ...</span>
<span class="c1"></span>    <span class="c1">// and we’re off!</span>
<span class="c1"></span>    <span class="c1">// ...</span>
<span class="c1"></span>  <span class="p">}</span>

  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
<span class="p">}</span>
</pre>
   <h2 class="heading settled" data-level="3" id="scope"><span class="secno">3. </span><span class="content">Scope and Impact</span><a class="self-link" href="#scope"></a></h2>
   <p><code class="highlight"><span class="k">constexpr</span> <span class="n">span</span><span class="o">&lt;</span><span class="k">const</span> <span class="n">byte</span><span class="o">></span> <span class="n">embed</span><span class="p">(</span> <span class="n">string_view</span> <span class="n">resource_identifier</span><span class="p">,</span> <span class="kt">size_t</span> <span class="n">alignment</span> <span class="o">=</span> <span class="k">alignof</span><span class="p">(</span><span class="n">byte</span><span class="p">),</span> <span class="n">embed_options</span> <span class="n">options</span> <span class="o">=</span> <span class="n">embed_options</span><span class="o">::</span><span class="n">none</span> <span class="p">)</span></code> is an extension to the language proposed entirely as a library construct. The goal is to have it implemented with compiler intrinsics, builtins, or other suitable mechanisms. It does not affect the language. The proposed header to expose this functionality is <code class="highlight"><span class="o">&lt;</span><span class="n">embed</span><span class="o">></span></code>, making the feature entirely-opt-in. It is preprocessor-testable using <code class="highlight"><span class="n">__has_include</span><span class="p">(</span> <span class="o">&lt;</span><span class="n">embed</span><span class="o">></span> <span class="p">)</span></code>, and also exposes a feature macro when included called <code class="highlight"><span class="n">__cpp_lib_embed</span></code>.</p>
   <h2 class="heading settled" data-level="4" id="design"><span class="secno">4. </span><span class="content">Design Decisions</span><a class="self-link" href="#design"></a></h2>
   <p><code class="highlight"><span class="o">&lt;</span><span class="n">embed</span><span class="o">></span></code> avoids using the preprocessor or defining new string literal syntax like its predecessors, preferring the use of a free function in the <code class="highlight"><span class="n">std</span></code> namespace and some associated utility flags. <code class="highlight"><span class="o">&lt;</span><span class="n">embed</span><span class="o">></span></code>'s design is derived heavily from community feedback plus the rejection of the prior art up to this point, as well as the community needs demonstrated by existing practice and their pit falls.</p>
   <h3 class="heading settled" data-level="4.1" id="design-practice"><span class="secno">4.1. </span><span class="content">Current Practice</span><a class="self-link" href="#design-practice"></a></h3>
   <p>Here, we examine current practice, their benefits, and their pitfalls. There are a few cross-platform (and not-so-cross-platform) paths for getting data into an executable.</p>
   <h4 class="heading settled" data-level="4.1.1" id="design-practice-manual"><span class="secno">4.1.1. </span><span class="content">Manual Work</span><a class="self-link" href="#design-practice-manual"></a></h4>
   <p>Many developers also hand-wrap their files in (raw) string literals, or similar to massage their data -- binary or not -- into a conforming representation that can be parsed at source code:</p>
   <ol start="0">
    <li data-md="">
     <p>Have a file <code class="highlight"><span class="n">data</span><span class="p">.</span><span class="n">json</span></code> with some data, for example:</p>
   </ol>
<pre class="highlight"><span class="p">{</span> <span class="s">"Hello"</span><span class="o">:</span> <span class="s">"World!"</span> <span class="p">}</span></pre>
   <ol>
    <li data-md="">
     <p>Mangle that file with raw string literals, and save it as <code class="highlight"><span class="n">raw_include_data</span><span class="p">.</span><span class="n">h</span></code>:</p>
   </ol>
<pre class="highlight">R<span class="s">"</span>json(<span class="s">{ "Hello": "World!" }</span>)json<span class="s">"</span></pre>
   <ol start="2">
    <li data-md="">
     <p>Include it into a variable, optionally made <code class="highlight"><span class="k">constexpr</span></code>, and use it in the program:</p>
   </ol>
<pre class="highlight"><span class="cp">#include</span> &lt;iostream><span class="cp"></span>
<span class="cp">#include</span> &lt;string_view><span class="cp"></span>
<span class="cp"></span>
<span class="kt">int</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
  <span class="k">constexpr</span> <span class="n">std</span><span class="o">::</span><span class="n">string_view</span> <span class="n">json_view</span> <span class="o">=</span>
<span class="cp">#include</span> "raw_include_data.h"<span class="cp"></span>
<span class="cp"></span>    <span class="p">;</span>
		
  <span class="c1">// { "Hello": "World!" }</span>
<span class="c1"></span>  <span class="n">std</span><span class="o">::</span><span class="n">cout</span> <span class="o">&lt;&lt;</span> <span class="n">json_view</span> <span class="o">&lt;&lt;</span> <span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span>
  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
<span class="p">}</span>
</pre>
   <p>This happens often in the case of people who have not yet taken the "add a build step" mantra to heart. The biggest problem is that the above C++-ready source file is no longer valid in as its original representation, meaning the file as-is cannot be passed to any validation tools, schema checkers, or otherwise. This hurts the portability and interop story of C++ with other tools and languages.</p>
   <p>Furthermore, if the string literal is too big vendors such as VC++ will hard error <a data-link-type="biblio" href="#biblio-nonius-visual-c-error">the build (example from Nonius, benchmarking framework)</a>.</p>
   <h4 class="heading settled" data-level="4.1.2" id="design-practice-tools"><span class="secno">4.1.2. </span><span class="content">Processing Tools</span><a class="self-link" href="#design-practice-tools"></a></h4>
   <p>Other developers use pre-processors for data that can’t be easily hacked into a C++ source-code appropriate state (e.g., binary). The most popular one is <code class="highlight"><span class="n">xxd</span> <span class="o">-</span><span class="n">i</span> <span class="n">my_data</span><span class="p">.</span><span class="n">bin</span></code>, which outputs an array in a file which developers then include. This is problematic because it turns binary data in C++ source. In many cases, this results in a larger file due to having to restructure the data to fit grammar requirements. It also results in needing an extra build step, which throws any programmer immediately at the mercy of build tools and project management. An example and further analysis can be found in the <a href="#appendix-tools">§8.1.1 Pre-Processing Tools Sadness</a> and the <a href="#appendix-mongo">§8.1.2 python Sadness</a> section.</p>
   <h4 class="heading settled" data-level="4.1.3" id="design-practice-vendor"><span class="secno">4.1.3. </span><span class="content"><code class="highlight"><span class="n">ld</span></code>, resource files, and other vendor-specific link-time tools</span><a class="self-link" href="#design-practice-vendor"></a></h4>
   <p>Resource files and other "link time" or post-processing measures have one benefit over the previous method: they are fast to perform in terms of compilation time. A example can be seen in the <a href="#appendix-ld">§8.1.3 ld Sadness</a> section.</p>
   <h4 class="heading settled" data-level="4.1.4" id="design.practice.incbin"><span class="secno">4.1.4. </span><span class="content">The <code class="highlight"><span class="n">incbin</span></code> tool</span><a class="self-link" href="#design.practice.incbin"></a></h4>
   <p>There is a tool called <a data-link-type="biblio" href="#biblio-incbin">[incbin]</a> which is a 3rd party attempt at pulling files in at "assembly time". Its approach is incredibly similar to <code class="highlight"><span class="n">ld</span></code>, with the caveat that files must be shipped with their binary. It unfortnately falls prey to the same problems of cross-platform woes when dealing with VC++, requiring additional pre-processing to work out in full.</p>
   <h3 class="heading settled" data-level="4.2" id="design-prior"><span class="secno">4.2. </span><span class="content">Prior Art</span><a class="self-link" href="#design-prior"></a></h3>
   <p>There has been a lot of discussion over the years in many arenas, from Stack Overflow to mailing lists to meetings with the Committee itself. The latest advancements that had been brought to WG21’s attention was <a data-link-type="biblio" href="#biblio-p0373r0">p0373r0 - File String Literals</a>. It proposed the syntax <code class="highlight"><span class="n">F</span><span class="s">"my_file.txt"</span></code> and <code class="highlight"><span class="n">bF</span><span class="s">"my_file.txt"</span></code>, with a few other amenities, to load files at compilation time. The following is an analysis of the previous proposal.</p>
   <h4 class="heading settled" data-level="4.2.1" id="design-prior-literal"><span class="secno">4.2.1. </span><span class="content">Literal-Based, constexpr</span><a class="self-link" href="#design-prior-literal"></a></h4>
   <p>A user could reasonably assign (or want to assign) the resulting array to a <code class="highlight"><span class="k">constexpr</span></code> variable as its expected to be handled like most other string literals. This allowed some degree of compile-time reflection. It is entirely helpful that such file contents be assigned to constexpr: e.g., string literals of JSON being loaded at compile time to be parsed by Ben Deane and Jason Turner in their CppCon 2017 talk, <a data-link-type="biblio" href="#biblio-constexpr-all-the-things">constexpr All The Things</a>.</p>
   <h4 class="heading settled" data-level="4.2.2" id="design-prior-null"><span class="secno">4.2.2. </span><span class="content">Literal-Based, Null Terminated (?)</span><a class="self-link" href="#design-prior-null"></a></h4>
   <p>It is unclear whether the resulting array of characters or bytes was to be null terminated. The usage and expression imply that it will be, due to its string-like appearance. However, is adding an additional null terminator fitting for desired usage? From the existing tools and practice (e.g., <code class="highlight"><span class="n">xxd</span> <span class="o">-</span><span class="n">i</span></code> or linking a data-dumped object file), the answer is no: but the syntax <code class="highlight"><span class="n">bF</span><span class="s">"hello.txt"</span></code> makes the answer seem like a "yes". This is confusing: the user should be given an explicit choice.</p>
   <h4 class="heading settled" data-level="4.2.3" id="design-prior-encoding"><span class="secno">4.2.3. </span><span class="content">Encoding</span><a class="self-link" href="#design-prior-encoding"></a></h4>
   <p>Because the proposal used a string literal, several questions came up as to the actual encoding of the returned information. The author gave both <code class="highlight"><span class="n">bF</span><span class="s">"my_file.txt"</span></code> and <code class="highlight"><span class="n">F</span><span class="s">"my_file.txt"</span></code> to separate binary versus string-based arrays of returns. Not only did this conflate issues with expectations in the previous section, it also became a heavily contested discussion on both the mailing list group discussion of the original proposal and in the paper itself. This is likely one of the biggest pitfalls between separating "binary" data from "string" data: imbuing an object with string-like properties at translation time provide for all the same hairy questions around source/execution character set and the contents of a literal.</p>
   <h3 class="heading settled" data-level="4.3" id="design-goals"><span class="secno">4.3. </span><span class="content">Design Goals</span><a class="self-link" href="#design-goals"></a></h3>
   <p>Because of the aforementioned reasons, it seems more prudent to take a "compiler intrinsic"/"magic function" approach. The function takes the form:</p>
<pre class="highlight"><span class="k">constexpr</span> <span class="n">span</span><span class="o">&lt;</span><span class="k">const</span> <span class="n">byte</span><span class="o">></span> <span class="n">embed</span><span class="p">(</span> 
  <span class="n">string_view</span> <span class="n">resource_identifier</span><span class="p">,</span> 
  <span class="kt">size_t</span> <span class="n">alignment</span> <span class="o">=</span> <span class="k">alignof</span><span class="p">(</span><span class="n">byte</span><span class="p">),</span>
  <span class="n">embed_options</span> <span class="n">options</span> <span class="o">=</span> <span class="n">embed_options</span><span class="o">::</span><span class="n">none</span>
<span class="p">);</span>
</pre>
   <p><code class="highlight"><span class="n">resource_identifier</span></code> is a <code class="highlight"><span class="n">string_view</span></code> processed in an implementation-defined manner to find and pull resources into C++. The most obvious source will be the file system, with the intention of having this evaluated at compile-time. We do not attempt to restrict the <code class="highlight"><span class="n">string_view</span></code> to a specific subset: whatever the implementation accepts (typically expected to be a relative or absolute file path, but can be other identification scheme), the implementation should use.</p>
   <p><code class="highlight"><span class="n">alignment</span></code> is the desired alignment memory alignment in <code class="highlight"><span class="kt">size_t</span></code> of the resource loaded into memory and represented by the returned span. This is critical for applications which require memory to sit at certain offsets in (virtual) memory.</p>
   <p><code class="highlight"><span class="n">options</span></code> is a <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">embed_options</span></code> enumeration used as a set of flags to add some basic control behaviors to the</p>
   <h4 class="heading settled" data-level="4.3.1" id="design-goals-impldefn"><span class="secno">4.3.1. </span><span class="content">Implementation Defined</span><a class="self-link" href="#design-goals-impldefn"></a></h4>
   <p>Calls such as <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">embed</span><span class="p">(</span> <span class="s">"my_file.txt"</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="n">std</span><span class="o">::</span><span class="n">embed_options</span><span class="o">::</span><span class="n">null_terminate</span> <span class="p">);</span></code>, <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">embed</span><span class="p">(</span> <span class="s">"data.dll"</span> <span class="p">);</span></code>, and <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">embed</span><span class="p">(</span> <span class="s">"vertices.bin"</span> <span class="p">);</span></code> are meant to be evaluated in a <code class="highlight"><span class="k">constexpr</span></code> context (with "core constant expressions" only), where the behavior is implementation-defined. The function has unspecified behavior when evaluated in a non-constexpr context (with the expectation that the implementation will provide a failing diagnostic in these cases). This is similar to how include paths work, albeit <code class="highlight"><span class="cp">#include</span></code> interacts with the programmer through the preprocessor. There is, however, precedent for specifying library features that are implemented only through compile-time compiler intrinsics (<code class="highlight"><span class="n">type_traits</span></code>, <code class="highlight"><span class="n">source_location</span></code>, and similar utilities).</p>
   <p>Core -- for other proposals such as <a data-link-type="biblio" href="#biblio-p0466r1">p0466r1 - Layout-compatibility and Pointer-interconvertibility Traits </a> -- indicated their preference in using a <code class="highlight"><span class="k">constexpr</span></code> magic function implemented by intrinsic in the standard library over some form of <code class="highlight"><span class="k">template</span> <span class="o">&lt;</span><span class="k">auto</span> <span class="n">X</span><span class="o">></span> <span class="n">thing</span> <span class="p">{</span> <span class="cm">/* implementation specified */</span> <span class="n">value</span><span class="p">;</span> <span class="p">};</span></code> construct. However, it is important to note that <a data-link-type="biblio" href="#biblio-p0466r1">[p0466r1]</a> proposes type traits, where as this has entirely different functionality, and so its reception and opinions may be different.</p>
   <p>As <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">embed</span></code> is meant to exist at compile-time only, it may be prudent to rely on <a data-link-type="biblio" href="#biblio-p1073r0">p1073r0 - constexpr! functions</a>. However, these are only design decisions to more clearly express the intent of the paper. This paper does not explicitly rely on <a data-link-type="biblio" href="#biblio-p1073r0">[p1073r0]</a> at this time.</p>
   <h4 class="heading settled" data-level="4.3.2" id="design-goals-binary"><span class="secno">4.3.2. </span><span class="content">Binary Only</span><a class="self-link" href="#design-goals-binary"></a></h4>
   <p>Creating two separate forms or options for loading data that is meant to be a "string" always fuels controversy and debate about what the resulting contents should be. The problem is sidestepped entirely by demanding that the resource loaded by <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">embed</span></code> represents the bytes exactly as they come from the resource, modulo any options passed to <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">embed</span></code>. This prevents encoding confusion, conversion issues, and other pitfalls related to trying to match the user’s idea of "string" data or non-binary formats. Data is received exactly as it is from the resource as defined by the implementation, whether it is a supposed text file or otherwise. <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">embed</span><span class="p">(</span> <span class="s">"my_text_file.txt"</span> <span class="p">)</span></code> and <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">embed</span><span class="p">(</span> <span class="s">"my_binary_file.bin"</span> <span class="p">)</span></code> behave exactly the same concerning their treatment of the resource.</p>
   <h4 class="heading settled" data-level="4.3.3" id="design-goals-null"><span class="secno">4.3.3. </span><span class="content">Opt-in and Optional Null Termination</span><a class="self-link" href="#design-goals-null"></a></h4>
   <p>With the Binary Only stipulation, some users will feel left out as there are many system calls, source processing APIs, and other interfaces which require a null terminated sequence similar to a string. Therefore, one of the options of <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">embed_options</span></code> is <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">embed_options</span><span class="o">::</span><span class="n">null_terminate</span></code>. If this option is specified, then the data returned is null terminated, even if the resource itself exists but is empty:</p>
<pre class="highlight"><span class="cp">#include</span> &lt;embed><span class="cp"></span>
<span class="cp"></span>
<span class="kt">int</span> <span class="nf">main</span> <span class="p">()</span> <span class="p">{</span>
  <span class="k">constexpr</span> <span class="n">std</span><span class="o">::</span><span class="n">span</span><span class="o">&lt;</span><span class="k">const</span> <span class="kt">char</span><span class="o">></span> <span class="n">data</span> <span class="o">=</span> 
    <span class="n">std</span><span class="o">::</span><span class="n">embed</span><span class="o">&lt;</span><span class="kt">char</span><span class="o">></span><span class="p">(</span> <span class="s">"my_file.txt"</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="n">std</span><span class="o">::</span><span class="n">embed_options</span><span class="o">::</span><span class="n">null_terminate</span> <span class="p">);</span>
  <span class="k">static_assert</span><span class="p">(</span> <span class="n">data</span><span class="p">[</span><span class="n">data</span><span class="p">.</span><span class="n">size</span><span class="p">()]</span> <span class="o">==</span> <span class="sc">'\0'</span> <span class="p">);</span>
  <span class="c1">// use as desired, potentially with system calls and graphics APIs...</span>
<span class="c1"></span>  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
<span class="p">}</span>
</pre>
   <h4 class="heading settled" data-level="4.3.4" id="design-goals-align"><span class="secno">4.3.4. </span><span class="content">Opt-in Alignment</span><a class="self-link" href="#design-goals-align"></a></h4>
   <p>It is important that the data that is loaded respect the alignment of the target (abstract) machine. This is why we present an integer argument to handle such a thing as the last argument to embed:</p>
<pre class="highlight"><span class="cp">#include</span> &lt;embed><span class="cp"></span>
<span class="cp"></span>
<span class="k">alignas</span><span class="p">(</span><span class="mi">16</span><span class="p">)</span> <span class="k">struct</span> <span class="n">vec4</span> <span class="p">{</span>
  <span class="kt">float</span> <span class="n">elements</span><span class="p">[</span><span class="mi">4</span><span class="p">];</span>
<span class="p">};</span>

<span class="kt">int</span> <span class="nf">main</span> <span class="p">()</span> <span class="p">{</span>
  <span class="k">constexpr</span> <span class="k">auto</span> <span class="n">vec_data</span> <span class="o">=</span> <span class="n">std</span><span class="o">::</span><span class="n">embed</span><span class="p">(</span> <span class="s">"my_floats.bin"</span><span class="p">,</span> <span class="k">alignof</span><span class="p">(</span><span class="n">vec4</span><span class="p">)</span> <span class="p">);</span>
  <span class="c1">// use as desired, with the start of the resource’s data</span>
<span class="c1"></span>  <span class="c1">// properly aligned in the returned span&lt;const byte></span>
<span class="c1"></span>  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
<span class="p">}</span>
</pre>
   <h4 class="heading settled" data-level="4.3.5" id="design-goals-options"><span class="secno">4.3.5. </span><span class="content">Options</span><a class="self-link" href="#design-goals-options"></a></h4>
   <p>Similar to the above, <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">embed</span></code>'s base behavior can be extended using options. This allows for simple needs that come up in the future or that are missed due to oversight to be corrected for. Currently, the only option flag is for <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">embed_options</span><span class="o">::</span><span class="n">null_terminate</span></code>, but there might be future flags that do things like e.g. force the data to be baked into a specific section of the binary. Having such flags be standardized means that compiler vendors would have to agree about said flags and their specification before shipping: this is <em>not the place for vendors to place their own implementation-specific flags</em> (the goal is to reduce fragmentation, not encourage it).</p>
   <h4 class="heading settled" data-level="4.3.6" id="design-goals-constexpr"><span class="secno">4.3.6. </span><span class="content">Constexpr Compatibility</span><a class="self-link" href="#design-goals-constexpr"></a></h4>
   <p>The entire implementation must be usable in a <code class="highlight"><span class="k">constexpr</span></code> context. It is not just for the purposes of processing the data at compile time, but because it matches existing implementations that store strings and huge array literals into a variable via <code class="highlight"><span class="cp">#include</span></code>. These variables can be <code class="highlight"><span class="k">constexpr</span></code>: to not have a constexpr implementation is to leave many of the programmers who utilize this behavior out in the cold, and change their expectations.</p>
   <h4 class="heading settled" data-level="4.3.7" id="design-goals-macro"><span class="secno">4.3.7. </span><span class="content">Feature Macro</span><a class="self-link" href="#design-goals-macro"></a></h4>
   <p>The desired feature macro for <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">embed</span></code> is <code class="highlight"><span class="n">__cpp_lib_embed</span></code>.</p>
   <h2 class="heading settled" data-level="5" id="help"><span class="secno">5. </span><span class="content">Help Requested</span><a class="self-link" href="#help"></a></h2>
   <p>The author of this proposal is extremely new to writing standardese. While the author has read other papers and consumed the standard, there is a definite need for help and any guidance and direction is certainly welcome. The author expects that this paper may undergo several revisions and undertake quite a few moments of "bikeshedding".</p>
   <h3 class="heading settled" data-level="5.1" id="help-represent"><span class="secno">5.1. </span><span class="content">Feeling Underrepresented?</span><a class="self-link" href="#help-represent"></a></h3>
   <p>The author has consulted dozens of C++ users in each of the Text Processing, Video Game, Financial, Server, Embedded and Desktop Application development subspaces. The author has also queried the opinions of Academia. The author feels this paper adequately covers many use cases, existing practice and prior art. If there is a use case or a problem not being adequately addressed by this proposal, the author encourages anyone and everyone to reach out to have their voice heard.</p>
   <h3 class="heading settled" data-level="5.2" id="help-bikshed"><span class="secno">5.2. </span><span class="content">Bikeshedding</span><a class="self-link" href="#help-bikshed"></a></h3>
   <h4 class="heading settled" data-level="5.2.1" id="help-bikeshed-alternative"><span class="secno">5.2.1. </span><span class="content">Alternative Names</span><a class="self-link" href="#help-bikeshed-alternative"></a></h4>
   <p>Some people feel that <code class="highlight"><span class="n">embed</span></code> is not a good name for this function. Therefore, here are some alternative names contribute by the community, in order of very good to very terrible:</p>
   <ul>
    <li data-md="">
     <p><code class="highlight"><span class="n">embed</span></code></p>
    <li data-md="">
     <p><code class="highlight"><span class="n">embed_resource</span></code></p>
    <li data-md="">
     <p><code class="highlight"><span class="n">slurp</span></code></p>
    <li data-md="">
     <p><code class="highlight"><span class="n">constexpr_read</span></code></p>
    <li data-md="">
     <p><code class="highlight"><span class="n">static_read</span></code></p>
    <li data-md="">
     <p><code class="highlight"><span class="n">static_resource</span></code></p>
    <li data-md="">
     <p><code class="highlight"><span class="n">static_include</span></code></p>
    <li data-md="">
     <p><code class="highlight"><span class="n">cfsread</span></code></p>
   </ul>
   <h4 class="heading settled" data-level="5.2.2" id="help-bikeshed-open"><span class="secno">5.2.2. </span><span class="content">Open Questions</span><a class="self-link" href="#help-bikeshed-open"></a></h4>
   <ol>
    <li data-md="">
     <p>Is a magic library function in a header the most desirable? Other proposals for other avenies have fallen flat and not garnered enough support, but the discussion around previous features has only indicated distate, never a definitive preference for where to go. This is the most important question to be answered as soon as possible.</p>
   </ol>
   <h4 class="heading settled" data-level="5.2.3" id="help-bikeshed-answered"><span class="secno">5.2.3. </span><span class="content">Answered Questions</span><a class="self-link" href="#help-bikeshed-answered"></a></h4>
   <blockquote>
    <p>Is <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o">&lt;</span><span class="n">std</span><span class="o">::</span><span class="n">byte</span><span class="o">></span></code> in <code class="highlight"><span class="k">constexpr</span></code> format better as a return value (i.e., do we depend on Louis Dionne, Roger Orr, and Daveed Vandevoorde’s work in <a data-link-type="biblio" href="#biblio-p0784r3">[p0784r3]</a>, <a data-link-type="biblio" href="#biblio-p1002r0">[p1002r0]</a>, <a data-link-type="biblio" href="#biblio-p1004r0">[p1004r0]</a> and <a data-link-type="biblio" href="#biblio-p1023r0">[p1023r0]</a>)?</p>
   </blockquote>
   <p>No, but can be persuaded otherwise. Do not want to lock this feature down as a dependency to these other papers in-flight.</p>
   <blockquote>
    <p>Is it desireable to make <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">embed</span></code> templated so it can return other kinds of views / types at constexpr time, which does not yet have a concept of a constexpr <code class="highlight"><span class="k">reinterpret_cast</span></code> or <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">bless</span></code> + <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">launder</span></code>?</p>
   </blockquote>
   <p>Yes.</p>
   <blockquote>
    <p>Should <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">embedded</span></code> (<a data-link-type="biblio" href="#biblio-p1040r0">std::embed revision 0</a>) just be replaced with <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">span</span></code>?</p>
   </blockquote>
   <p>Yes. <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">span</span></code> covers all of the use cases here, is <code class="highlight"><span class="k">constexpr</span></code>, and makes the most sense. <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">array</span><span class="o">&lt;</span><span class="k">const</span> <span class="n">byte</span><span class="p">,</span> <span class="n">N</span><span class="o">></span></code> cannot be returned because <code class="highlight"><span class="n">N</span></code> cannot be named until it is deduced by the actual value being returned. It is a poor interface to force the user to always <code class="highlight"><span class="k">decltype</span></code> the return. (LEWG confirmed.)</p>
   <blockquote>
    <p>Should the return <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">span</span></code> be const-qualified, as in <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">span</span><span class="o">&lt;</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">byte</span><span class="o">></span></code>?</p>
   </blockquote>
   <p>Yes. (LEWG confirmed.)</p>
   <blockquote>
    <p>What is the lookup scheme for files and other resources?</p>
   </blockquote>
   <p>Implementation defined. We expect compilers to expose an option similar to <code class="highlight"><span class="o">--</span><span class="n">embed</span><span class="o">-</span><span class="n">paths</span><span class="o">=</span><span class="p">...</span></code>, <code class="highlight"><span class="o">/</span><span class="nl">EMBEDPATH</span><span class="p">:...</span></code>, or whatever tickles the implementer’s fancy. (LEWG confirmed.)</p>
   <blockquote>
    <p>Pulling in large data files on every compile might be expensive?</p>
   </blockquote>
   <p>We fully expect implementations to employ techniques already in use for compilation dependency tracking to ensure this is not a frequent problem past the first compilation.</p>
   <blockquote>
    <p>Is this more suitable for WG14 (the standards C committee) rather than WG21 (the standards C++ committee)?</p>
   </blockquote>
   <p>The author does not think that the C standards committee will be the best place for some feature of this variety at this time. All of the typical solutions that would work in C were rejected previously (preprocessor or special literal). Indication has shown that the C standards committee might be able to support this idea and come up with a better design than WG21 or provide more fine-grained mechanisms for it, but there is no evidence that they are either interested or have the time. (Raised in LEWG, confirmed in general post-LEWG discussion.)</p>
   <h2 class="heading settled" data-level="6" id="synopsis"><span class="secno">6. </span><span class="content">Header Overview</span><a class="self-link" href="#synopsis"></a></h2>
   <p><code class="highlight"><span class="o">&lt;</span><span class="n">embed</span><span class="o">></span></code> Overview</p>
<pre class="highlight"><span class="k">namespace</span> <span class="n">std</span> <span class="p">{</span>
  <span class="k">enum</span> <span class="k">class</span> <span class="nc">embed_options</span> <span class="p">{</span>
    <span class="n">none</span> <span class="o">=</span> <span class="mi">0</span><span class="p">,</span>
    <span class="n">null_terminate</span> <span class="o">=</span> <span class="mi">1</span>
  <span class="p">};</span>

  <span class="c1">// bit-flag manipulations</span>
<span class="c1"></span>  <span class="k">constexpr</span> <span class="n">embed_options</span> <span class="k">operator</span><span class="o">|</span> <span class="p">(</span><span class="n">embed_options</span> <span class="n">left</span><span class="p">,</span> <span class="n">embed_options</span> <span class="n">right</span><span class="p">);</span>
  <span class="k">constexpr</span> <span class="n">embed_options</span> <span class="k">operator</span><span class="o">&amp;</span> <span class="p">(</span><span class="n">embed_options</span> <span class="n">left</span><span class="p">,</span> <span class="n">embed_options</span> <span class="n">right</span><span class="p">);</span>
  <span class="k">constexpr</span> <span class="n">embed_options</span> <span class="k">operator</span><span class="o">^</span> <span class="p">(</span><span class="n">embed_options</span> <span class="n">left</span><span class="p">,</span> <span class="n">embed_options</span> <span class="n">right</span><span class="p">);</span>
  <span class="k">constexpr</span> <span class="n">embed_options</span><span class="o">&amp;</span> <span class="k">operator</span><span class="o">|=</span> <span class="p">(</span><span class="n">embed_options</span><span class="o">&amp;</span> <span class="n">left</span><span class="p">,</span> <span class="n">embed_options</span> <span class="n">right</span><span class="p">);</span>
  <span class="k">constexpr</span> <span class="n">embed_options</span><span class="o">&amp;</span> <span class="k">operator</span><span class="o">&amp;=</span> <span class="p">(</span><span class="n">embed_options</span><span class="o">&amp;</span> <span class="n">left</span><span class="p">,</span> <span class="n">embed_options</span> <span class="n">right</span><span class="p">);</span>
  <span class="k">constexpr</span> <span class="n">embed_options</span><span class="o">&amp;</span> <span class="k">operator</span><span class="o">^=</span> <span class="p">(</span><span class="n">embed_options</span><span class="o">&amp;</span> <span class="n">left</span><span class="p">,</span> <span class="n">embed_options</span> <span class="n">right</span><span class="p">);</span>
<span class="p">}</span> <span class="c1">// namespace std</span>
</pre>
   <ol>
    <li data-md="">
     <p><code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">embed_options</span></code> is the enumeration that specifies additional transformations that the implementation should do to modify the data made available through <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">embedded</span></code>.</p>
    <li data-md="">
     <p>The operators are provided for ease of use to combine and otherwise modify flags, now and into the future.</p>
   </ol>
<pre class="highlight"><span class="cp">#include</span> &lt;string_view> // for std::string_view<span class="cp"></span>
<span class="cp">#include</span> &lt;span> // for std::span<span class="cp"></span>
<span class="cp">#include</span> &lt;cstddef> // for std::byte, std::size_t<span class="cp"></span>
<span class="cp"></span>
<span class="k">namespace</span> <span class="n">std</span> <span class="p">{</span>
  <span class="k">constexpr</span> <span class="n">span</span><span class="o">&lt;</span><span class="k">const</span> <span class="n">byte</span><span class="o">></span> <span class="n">embed</span><span class="p">(</span> 
    <span class="n">string_view</span> <span class="n">resource_identifier</span><span class="p">,</span> 
    <span class="kt">size_t</span> <span class="n">alignment</span> <span class="o">=</span> <span class="k">alignof</span><span class="p">(</span><span class="n">byte</span><span class="p">),</span> 
    <span class="n">embed_options</span> <span class="n">options</span> <span class="o">=</span> <span class="n">embed_options</span><span class="o">::</span><span class="n">none</span>
  <span class="p">);</span>
<span class="p">}</span> <span class="c1">// namespace std</span>
</pre>
   <ol>
    <li data-md="">
     <p>The implementation defines what strings it accepts for <code class="highlight"><span class="n">resource_identifier</span></code>. [Note— It is the hope that compiler vendors will provide a mechanism similar to include paths for finding things on the local filesystem. — End Note]</p>
    <li data-md="">
     <p>If the function succeeds, then the bytes visible are aligned to the boundary specified by the</p>
    <li data-md="">
     <p>If this function is called at runtime, then the behavior is unspecified. [Note— A valid implementation can declare a runtime usage ill-formed and provide a diagnostic. — End Note]</p>
   </ol>
   <h2 class="heading settled" data-level="7" id="future"><span class="secno">7. </span><span class="content">Future Direction</span><a class="self-link" href="#future"></a></h2>
   <p>Many developers in all spaces are concerned that <code class="highlight"><span class="k">constexpr</span></code> does not allow <code class="highlight"><span class="k">reinterpret_cast</span></code> to be used. This means that the bytes cannot be viewed -- at <code class="highlight"><span class="k">constexpr</span></code> time -- as more complex entities. There are 2 directions to solve this problem. This paper proposes neither of the fixes at this time.</p>
   <p>The first is to word a <code class="highlight"><span class="n">bit_cast</span></code>, <code class="highlight"><span class="k">reinterpret_cast</span></code>, and/or <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">bless</span></code> that can work on this memory at constexpr time. The second is to use a more blunt hammer and simply template <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">embed</span></code>, specifying it as follows:</p>
<pre class="highlight"><span class="k">template</span> <span class="o">&lt;</span><span class="k">typename</span> <span class="n">T</span> <span class="o">=</span> <span class="n">std</span><span class="o">::</span><span class="n">byte</span><span class="o">></span> 
<span class="k">constexpr</span> <span class="n">span</span><span class="o">&lt;</span><span class="k">const</span> <span class="n">T</span><span class="o">></span> <span class="n">embed</span><span class="p">(</span> 
  <span class="n">string_view</span> <span class="n">resource_identifier</span><span class="p">,</span> 
  <span class="kt">size_t</span> <span class="n">alignment</span> <span class="o">=</span> <span class="k">alignof</span><span class="p">(</span><span class="n">T</span><span class="p">),</span> 
  <span class="n">embed_options</span> <span class="n">options</span> <span class="o">=</span> <span class="n">embed_options</span><span class="o">::</span><span class="n">none</span> 
<span class="p">);</span>
</pre>
   <p>This would supply the data and view it as a type <code class="highlight"><span class="n">T</span></code>. However, this brings up questions of destructors and similar for when the data goes away. It also gets in the way of caching. Is it possible for an implementation to cache the retrieved storage based solely on <code class="highlight"><span class="n">resource_identifier</span></code> since a destructor could run over the data? If destructors or constructors are run based on type <code class="highlight"><span class="n">T</span></code> then the data cannot be the same between template instantions even with the same <code class="highlight"><span class="n">resource_identifier</span></code>.</p>
   <p>A way to help with this would be to <code class="highlight"><span class="k">static_assert</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">is_trivial</span><span class="o">&lt;</span><span class="n">T</span><span class="o">></span><span class="p">)</span></code>, to not have to worry about such problems. The good news is that such a templated transformation can be applied to <code class="highlight"><span class="n">std</span><span class="o">::</span><span class="n">embed</span></code> at a later date with no API breakage, provided the templated arguments are defaulted.</p>
   <p>We do not propose any of these future directions at this time.</p>
   <h2 class="heading settled" data-level="8" id="appendix"><span class="secno">8. </span><span class="content">Appendix</span><a class="self-link" href="#appendix"></a></h2>
   <h3 class="heading settled" data-level="8.1" id="appendix-sadness"><span class="secno">8.1. </span><span class="content">Sadness</span><a class="self-link" href="#appendix-sadness"></a></h3>
   <p>Other techniques used include pre-processing data, link-time based tooling, and assembly-time runtime loading. They are detailed below, for a complete picture of today’s sad landscape of options.</p>
   <h4 class="heading settled" data-level="8.1.1" id="appendix-tools"><span class="secno">8.1.1. </span><span class="content">Pre-Processing Tools Sadness</span><a class="self-link" href="#appendix-tools"></a></h4>
   <ol>
    <li data-md="">
     <p>Run the tool over the data (<code class="highlight"><span class="n">xxd</span> <span class="o">-</span><span class="n">i</span> <span class="n">xxd_data</span><span class="p">.</span><span class="n">bin</span> <span class="o">></span> <span class="n">xxd_data</span><span class="p">.</span><span class="n">h</span></code>) to obtain the generated file (<code class="highlight"><span class="n">xxd_data</span><span class="p">.</span><span class="n">h</span></code>):</p>
   </ol>
<pre class="highlight"><span class="kt">unsigned</span> <span class="kt">char</span> <span class="n">xxd_data_bin</span><span class="p">[]</span> <span class="o">=</span> <span class="p">{</span>
  <span class="mh">0x48</span><span class="p">,</span> <span class="mh">0x65</span><span class="p">,</span> <span class="mh">0x6c</span><span class="p">,</span> <span class="mh">0x6c</span><span class="p">,</span> <span class="mh">0x6f</span><span class="p">,</span> <span class="mh">0x2c</span><span class="p">,</span> <span class="mh">0x20</span><span class="p">,</span> <span class="mh">0x57</span><span class="p">,</span> <span class="mh">0x6f</span><span class="p">,</span> <span class="mh">0x72</span><span class="p">,</span> <span class="mh">0x6c</span><span class="p">,</span> <span class="mh">0x64</span><span class="p">,</span>
  <span class="mh">0x0a</span>
<span class="p">};</span>
<span class="kt">unsigned</span> <span class="kt">int</span> <span class="n">xxd_data_bin_len</span> <span class="o">=</span> <span class="mi">13</span><span class="p">;</span>
</pre>
   <ol start="2">
    <li data-md="">
     <p>Compile <code class="highlight"><span class="n">main</span><span class="p">.</span><span class="n">cpp</span></code>:</p>
   </ol>
<pre class="highlight"><span class="cp">#include</span> &lt;iostream><span class="cp"></span>
<span class="cp">#include</span> &lt;string_view><span class="cp"></span>
<span class="cp"></span>
<span class="c1">// prefix as constexpr,</span>
<span class="c1">// even if it generates some warnings in g++/clang++</span>
<span class="c1"></span><span class="k">constexpr</span>
<span class="cp">#include</span> "xxd_data.h"<span class="cp"></span>
<span class="cp"></span><span class="p">;</span>

<span class="k">template</span> <span class="o">&lt;</span><span class="k">typename</span> <span class="n">T</span><span class="p">,</span> <span class="n">std</span><span class="o">::</span><span class="kt">size_t</span> <span class="n">N</span><span class="o">></span>
<span class="k">constexpr</span> <span class="n">std</span><span class="o">::</span><span class="kt">size_t</span> <span class="n">array_size</span><span class="p">(</span><span class="k">const</span> <span class="n">T</span> <span class="p">(</span><span class="o">&amp;</span><span class="p">)[</span><span class="n">N</span><span class="p">])</span> <span class="p">{</span>
    <span class="k">return</span> <span class="n">N</span><span class="p">;</span>
<span class="p">}</span>

<span class="kt">int</span> <span class="n">main</span><span class="p">()</span> <span class="p">{</span>
    <span class="k">static_assert</span><span class="p">(</span><span class="n">xxd_data_bin</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="o">==</span> <span class="sc">'H'</span><span class="p">);</span>
    <span class="k">static_assert</span><span class="p">(</span><span class="n">array_size</span><span class="p">(</span><span class="n">xxd_data_bin</span><span class="p">)</span> <span class="o">==</span> <span class="mi">13</span><span class="p">);</span>

    <span class="n">std</span><span class="o">::</span><span class="n">string_view</span> <span class="n">data_view</span><span class="p">(</span>
        <span class="k">reinterpret_cast</span><span class="o">&lt;</span><span class="k">const</span> <span class="kt">char</span><span class="o">*></span><span class="p">(</span><span class="n">xxd_data_bin</span><span class="p">),</span>
        <span class="n">array_size</span><span class="p">(</span><span class="n">xxd_data_bin</span><span class="p">));</span>
    <span class="n">std</span><span class="o">::</span><span class="n">cout</span> <span class="o">&lt;&lt;</span> <span class="n">data_view</span> <span class="o">&lt;&lt;</span> <span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span> <span class="c1">// Hello, World!</span>
<span class="c1"></span>    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
<span class="p">}</span>
</pre>
   <p>Others still use python or other small scripting languages as part of their build process, outputting data in the exact C++ format that they require.</p>
   <p>There are problems with the <code class="highlight"><span class="n">xxd</span> <span class="o">-</span><span class="n">i</span></code> or similar tool-based approach. Lexing and Parsing data-as-source-code adds an enormous overhead to actually reading and making that data available.</p>
   <p>Binary data as C(++) arrays provide the overhead of having to comma-delimit every single byte present, it also requires that the compiler verify every entry in that array is a valid literal or entry according to the C++ language.</p>
   <p>This scales poorly with larger files, and build times suffer for any non-trivial binary file, especially when it scales into Megabytes in size (e.g., firmware and similar).</p>
   <h4 class="heading settled" data-level="8.1.2" id="appendix-mongo"><span class="secno">8.1.2. </span><span class="content"><code class="highlight"><span class="n">python</span></code> Sadness</span><a class="self-link" href="#appendix-mongo"></a></h4>
   <p>Other companies are forced to create their own ad-hoc tools to embed data and files into their C++ code. MongoDB uses a <a href="https://github.com/mongodb/mongo/blob/master/site_scons/site_tools/jstoh.py">custom python script</a>, just to get their data into C++:</p>
<pre class="highlight"><span class="n">import</span> <span class="n">os</span>
<span class="n">import</span> <span class="n">sys</span>

<span class="n">def</span> <span class="nf">jsToHeader</span><span class="p">(</span><span class="n">target</span><span class="p">,</span> <span class="n">source</span><span class="p">)</span><span class="o">:</span>
    <span class="n">outFile</span> <span class="o">=</span> <span class="n">target</span>
    <span class="n">h</span> <span class="o">=</span> <span class="p">[</span>
        '#<span class="n">include</span> <span class="s">"mongo/base/string_data.h"</span>'<span class="p">,</span>
        '#<span class="n">include</span> <span class="s">"mongo/scripting/engine.h"</span>'<span class="p">,</span>
        '<span class="k">namespace</span> <span class="n">mongo</span> <span class="p">{</span>'<span class="p">,</span>
        '<span class="k">namespace</span> <span class="n">JSFiles</span><span class="p">{</span>'<span class="p">,</span>
    <span class="p">]</span>
    <span class="n">def</span> <span class="n">lineToChars</span><span class="p">(</span><span class="n">s</span><span class="p">)</span><span class="o">:</span>
        <span class="k">return</span> <span class="sc">','</span><span class="p">.</span><span class="n">join</span><span class="p">(</span><span class="n">str</span><span class="p">(</span><span class="n">ord</span><span class="p">(</span><span class="n">c</span><span class="p">))</span> <span class="k">for</span> <span class="n">c</span> <span class="n">in</span> <span class="p">(</span><span class="n">s</span><span class="p">.</span><span class="n">rstrip</span><span class="p">()</span> <span class="o">+</span> <span class="sc">'\n'</span><span class="p">))</span> <span class="o">+</span> <span class="sc">','</span>
    <span class="k">for</span> <span class="n">s</span> <span class="n">in</span> <span class="nl">source</span><span class="p">:</span>
        <span class="n">filename</span> <span class="o">=</span> <span class="n">str</span><span class="p">(</span><span class="n">s</span><span class="p">)</span>
        <span class="n">objname</span> <span class="o">=</span> <span class="n">os</span><span class="p">.</span><span class="n">path</span><span class="p">.</span><span class="n">split</span><span class="p">(</span><span class="n">filename</span><span class="p">)[</span><span class="mi">1</span><span class="p">].</span><span class="n">split</span><span class="p">(</span><span class="sc">'.'</span><span class="p">)[</span><span class="mi">0</span><span class="p">]</span>
        <span class="n">stringname</span> <span class="o">=</span> '<span class="n">_jscode_raw_</span>' <span class="o">+</span> <span class="n">objname</span>

        <span class="n">h</span><span class="p">.</span><span class="n">append</span><span class="p">(</span>'<span class="k">constexpr</span> <span class="kt">char</span> ' <span class="o">+</span> <span class="n">stringname</span> <span class="o">+</span> <span class="s">"[] = {"</span><span class="p">)</span>

        <span class="n">with</span> <span class="n">open</span><span class="p">(</span><span class="n">filename</span><span class="p">,</span> <span class="sc">'r'</span><span class="p">)</span> <span class="n">as</span> <span class="nl">f</span><span class="p">:</span>
            <span class="k">for</span> <span class="n">line</span> <span class="n">in</span> <span class="nl">f</span><span class="p">:</span>
                <span class="n">h</span><span class="p">.</span><span class="n">append</span><span class="p">(</span><span class="n">lineToChars</span><span class="p">(</span><span class="n">line</span><span class="p">))</span>

        <span class="n">h</span><span class="p">.</span><span class="n">append</span><span class="p">(</span><span class="s">"0};"</span><span class="p">)</span>
        <span class="cp"># symbols aren’t exported w/o this</span>
<span class="cp"></span>        <span class="n">h</span><span class="p">.</span><span class="n">append</span><span class="p">(</span>'<span class="k">extern</span> <span class="k">const</span> <span class="n">JSFile</span> <span class="o">%</span><span class="n">s</span><span class="p">;</span>' <span class="o">%</span> <span class="n">objname</span><span class="p">)</span>
        <span class="n">h</span><span class="p">.</span><span class="n">append</span><span class="p">(</span>'<span class="k">const</span> <span class="n">JSFile</span> <span class="o">%</span><span class="n">s</span> <span class="o">=</span> <span class="p">{</span> <span class="s">"%s"</span><span class="p">,</span> <span class="n">StringData</span><span class="p">(</span><span class="o">%</span><span class="n">s</span><span class="p">,</span> <span class="k">sizeof</span><span class="p">(</span><span class="o">%</span><span class="n">s</span><span class="p">)</span> <span class="o">-</span> <span class="mi">1</span><span class="p">)</span> <span class="p">};</span>' <span class="o">%</span>
                 <span class="p">(</span><span class="n">objname</span><span class="p">,</span> <span class="n">filename</span><span class="p">.</span><span class="n">replace</span><span class="p">(</span><span class="sc">'\\'</span><span class="p">,</span> <span class="sc">'/'</span><span class="p">),</span> <span class="n">stringname</span><span class="p">,</span> <span class="n">stringname</span><span class="p">))</span>

    <span class="n">h</span><span class="p">.</span><span class="n">append</span><span class="p">(</span><span class="s">"} // namespace JSFiles"</span><span class="p">)</span>
    <span class="n">h</span><span class="p">.</span><span class="n">append</span><span class="p">(</span><span class="s">"} // namespace mongo"</span><span class="p">)</span>
    <span class="n">h</span><span class="p">.</span><span class="n">append</span><span class="p">(</span><span class="s">""</span><span class="p">)</span>

    <span class="n">text</span> <span class="o">=</span> <span class="sc">'\n'</span><span class="p">.</span><span class="n">join</span><span class="p">(</span><span class="n">h</span><span class="p">)</span>

    <span class="n">with</span> <span class="n">open</span><span class="p">(</span><span class="n">outFile</span><span class="p">,</span> '<span class="n">wb</span>'<span class="p">)</span> <span class="n">as</span> <span class="nl">out</span><span class="p">:</span>
        <span class="k">try</span><span class="o">:</span>
            <span class="n">out</span><span class="p">.</span><span class="n">write</span><span class="p">(</span><span class="n">text</span><span class="p">)</span>
        <span class="nl">finally</span><span class="p">:</span>
            <span class="n">out</span><span class="p">.</span><span class="n">close</span><span class="p">()</span>


<span class="k">if</span> <span class="n">__name__</span> <span class="o">==</span> <span class="s">"__main__"</span><span class="o">:</span>
    <span class="k">if</span> <span class="n">len</span><span class="p">(</span><span class="n">sys</span><span class="p">.</span><span class="n">argv</span><span class="p">)</span> <span class="o">&lt;</span> <span class="mi">3</span><span class="o">:</span>
        <span class="n">print</span> <span class="s">"Must specify [target] [source] "</span>
        <span class="n">sys</span><span class="p">.</span><span class="n">exit</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
    <span class="n">jsToHeader</span><span class="p">(</span><span class="n">sys</span><span class="p">.</span><span class="n">argv</span><span class="p">[</span><span class="mi">1</span><span class="p">],</span> <span class="n">sys</span><span class="p">.</span><span class="n">argv</span><span class="p">[</span><span class="mi">2</span><span class="o">:</span><span class="p">])</span>
</pre>
   <p>MongoDB were brave enough to share their code with me and make public the things they have to do: other companies have shared many similar concerns, but do not have the same bravery. We thank MongoDB for sharing.</p>
   <h4 class="heading settled" data-level="8.1.3" id="appendix-ld"><span class="secno">8.1.3. </span><span class="content"><code class="highlight"><span class="n">ld</span></code> Sadness</span><a class="self-link" href="#appendix-ld"></a></h4>
   <p>A full, compilable example (except on Visual C++):</p>
   <ol start="0">
    <li data-md="">
     <p>Have a file ld_data.bin with the contents <code class="highlight"><span class="n">Hello</span><span class="p">,</span> <span class="n">World</span><span class="o">!</span></code>.</p>
    <li data-md="">
     <p>Run <code class="highlight"><span class="n">ld</span> <span class="o">-</span><span class="n">r</span> <span class="n">binary</span> <span class="o">-</span><span class="n">o</span> <span class="n">ld_data</span><span class="p">.</span><span class="n">o</span> <span class="n">ld_data</span><span class="p">.</span><span class="n">bin</span></code>.</p>
    <li data-md="">
     <p>Compile the following <code class="highlight"><span class="n">main</span><span class="p">.</span><span class="n">cpp</span></code> with <code class="highlight"><span class="n">c</span><span class="o">++</span> <span class="o">-</span><span class="n">std</span><span class="o">=</span><span class="n">c</span><span class="o">++</span><span class="mi">17</span> <span class="n">ld_data</span><span class="p">.</span><span class="n">o</span> <span class="n">main</span><span class="p">.</span><span class="n">cpp</span></code>:</p>
   </ol>
<pre class="highlight"><span class="cp">#include</span> &lt;iostream><span class="cp"></span>
<span class="cp">#include</span> &lt;string_view><span class="cp"></span>
<span class="cp"></span>
<span class="cp">#ifdef __APPLE__</span>
<span class="cp">#include</span> &lt;mach-o/getsect.h><span class="cp"></span>
<span class="cp"></span>
<span class="cp">#define DECLARE_LD(NAME) extern const unsigned char _section$__DATA__##NAME[];</span>
<span class="cp">#define LD_NAME(NAME) _section$__DATA__##NAME</span>
<span class="cp">#define LD_SIZE(NAME) (getsectbyname("__DATA", "__" #NAME)->size)</span>
<span class="cp"></span>
<span class="cp">#elif (defined __MINGW32__) </span><span class="cm">/* mingw */</span><span class="cp"></span>
<span class="cp"></span>
<span class="cp">#define DECLARE_LD(NAME)                                 \</span>
<span class="cp">  extern const unsigned char binary_##NAME##_start[]; \</span>
<span class="cp">  extern const unsigned char binary_##NAME##_end[];</span>
<span class="cp">#define LD_NAME(NAME) binary_##NAME##_start</span>
<span class="cp">#define LD_SIZE(NAME) ((binary_##NAME##_end) - (binary_##NAME##_start))</span>
<span class="cp"></span>
<span class="cp">#else </span><span class="cm">/* gnu/linux ld */</span><span class="cp"></span>
<span class="cp"></span>
<span class="cp">#define DECLARE_LD(NAME)                                  \</span>
<span class="cp">  extern const unsigned char _binary_##NAME##_start[]; \</span>
<span class="cp">  extern const unsigned char _binary_##NAME##_end[];</span>
<span class="cp">#define LD_NAME(NAME) _binary_##NAME##_start</span>
<span class="cp">#define LD_SIZE(NAME) ((_binary_##NAME##_end) - (_binary_##NAME##_start))</span>
<span class="cp">#endif</span>
<span class="cp"></span>
<span class="n">DECLARE_LD</span><span class="p">(</span><span class="n">ld_data_bin</span><span class="p">);</span>

<span class="kt">int</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
  <span class="c1">// impossible</span>
<span class="c1"></span>  <span class="c1">//static_assert(xxd_data_bin[0] == 'H');</span>
<span class="c1"></span>  <span class="n">std</span><span class="o">::</span><span class="n">string_view</span> <span class="n">data_view</span><span class="p">(</span>
    <span class="k">reinterpret_cast</span><span class="o">&lt;</span><span class="k">const</span> <span class="kt">char</span><span class="o">*></span><span class="p">(</span><span class="n">LD_NAME</span><span class="p">(</span><span class="n">ld_data_bin</span><span class="p">)),</span> 
    <span class="n">LD_SIZE</span><span class="p">(</span><span class="n">ld_data_bin</span><span class="p">)</span>
  <span class="p">);</span>
  <span class="n">std</span><span class="o">::</span><span class="n">cout</span> <span class="o">&lt;&lt;</span> <span class="n">data_view</span> <span class="o">&lt;&lt;</span> <span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span> <span class="c1">// Hello, World!</span>
<span class="c1"></span>  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
<span class="p">}</span>
</pre>
   <p>This scales a little bit better in terms of raw compilation time but is shockingly OS, vendor and platform specific in ways that novice developers would be able to handle fully. The macros are required to erase differences, lest subtle differences in name will destroy one’s ability to use these macros effectively. We ommitted the code for handling VC++ resource files because it is excessively verbose than what is present here.</p>
   <p>N.B.: Because these declarations are <code class="highlight"><span class="k">extern</span></code>, the values in the array cannot be accessed at compilation/translation-time.</p>
   <h2 class="heading settled" data-level="9" id="acknowledgements"><span class="secno">9. </span><span class="content">Acknowledgements</span><a class="self-link" href="#acknowledgements"></a></h2>
   <p>A big thank you to Andrew Tomazos for replying to the author’s e-mails about the prior art. Thank you to Arthur O’Dwyer for providing the author with incredible insight into the Committee’s previous process for how they interpreted the Prior Art.</p>
   <p>A special thank you to Agustín Bergé for encouraging the author to talk to the creator of the Prior Art and getting started on this. Thank you to Tom Honermann for direction and insight on how to write a paper and apply for a proposal.</p>
   <p>Thank you to Arvid Gerstmann for helping the author understand and use the link-time tools.</p>
   <p>Thank you to Tony Van Eerd for valuable advice in improving the main text of this paper.</p>
   <p>Thank you to Lilly (Cpplang Slack, @lillypad) for the valuable bikeshed and hole-poking in original designs, alongside Ben Craig who very thoroughly explained his woes when trying to embed large firmware images into a C++ program for deployment into production.</p>
   <p>For all this hard work, it is the author’s hope to carry this into C++. It would be the author’s distinct honor to make development cycles easier and better with the programming language we work in and love. ♥</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>
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   <dd>Ben Deane; Jason Turner. <a href="https://www.youtube.com/watch?v=PJwd4JLYJJY">constexpr All The Things: CppCon 2017</a>. September 25th, 2017. URL: <a href="https://www.youtube.com/watch?v=PJwd4JLYJJY">https://www.youtube.com/watch?v=PJwd4JLYJJY</a>
   <dt id="biblio-incbin">[INCBIN]
   <dd>Dale Weiler (graphitemaster). <a href="https://github.com/graphitemaster/incbin">incbin: load files at 'assembly' time</a>. URL: <a href="https://github.com/graphitemaster/incbin">https://github.com/graphitemaster/incbin</a>
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   <dt id="biblio-p0373r0">[P0373R0]
   <dd>Andrew Tomazos. <a href="https://wg21.link/p0373r0">Proposal of File Literals</a>. 21 May 2016. URL: <a href="https://wg21.link/p0373r0">https://wg21.link/p0373r0</a>
   <dt id="biblio-p0466r1">[P0466R1]
   <dd>Lisa Lippincott. <a href="https://wg21.link/p0466r1">Layout-compatibility and Pointer-interconvertibility Traits</a>. URL: <a href="https://wg21.link/p0466r1">https://wg21.link/p0466r1</a>
   <dt id="biblio-p0784r3">[P0784R3]
   <dd>Louis Dionne; et al. <a href="https://wg21.link/p0784r3">More constexpr containers</a>. May 4th, 2018. P. URL: <a href="https://wg21.link/p0784r3">https://wg21.link/p0784r3</a>
   <dt id="biblio-p1002r0">[P1002R0]
   <dd>Louis Dionne. <a href="https://wg21.link/p1002r0">try-catch blocks in constexpr functions</a>. May 5th, 2018. P. URL: <a href="https://wg21.link/p1002r0">https://wg21.link/p1002r0</a>
   <dt id="biblio-p1004r0">[P1004R0]
   <dd>Louis Dionne; Daveed Vandevoorde. <a href="https://wg21.link/p1004r0">Making std::vector constexpr</a>. May 5th, 2018. P. URL: <a href="https://wg21.link/p1004r0">https://wg21.link/p1004r0</a>
   <dt id="biblio-p1023r0">[P1023R0]
   <dd>Roger Orr. <a href="https://wg21.link/p1023r0">constexpr comparison operators for std::array</a>. May 5th, 2018. P. URL: <a href="https://wg21.link/p1023r0">https://wg21.link/p1023r0</a>
   <dt id="biblio-p1040r0">[P1040R0]
   <dd>JeanHeyd Meneide. <a href="https://wg21.link/p1040r0">std::embed</a>. May 5th, 2018. P. URL: <a href="https://wg21.link/p1040r0">https://wg21.link/p1040r0</a>
   <dt id="biblio-p1073r0">[P1073R0]
   <dd>Richard Smith; Andrew Sutton; Daveed Vandevoorde. <a href="https://wg21.link/p1073r0">constexpr! functions</a>. May 5th, 2018. P. URL: <a href="https://wg21.link/p1073r0">https://wg21.link/p1073r0</a>
  </dl>