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  <title>P1873R0: &lt;code>remove.dots.in.module.names&lt;/code></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,
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/******************************************************************************/
/*                                  Indices                                   */
/******************************************************************************/


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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">P1873R0<br><code class="highlight"><c- n>remove</c-><c- p>.</c-><c- n>dots</c-><c- p>.</c-><c- n>in</c-><c- p>.</c-><c- n>module</c-><c- p>.</c-><c- n>names</c-></code></h1>
   <h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Published Proposal, <time class="dt-updated" datetime="2019-09-17">2019-09-17</time></span></h2>
   <div data-fill-with="spec-metadata">
    <dl>
     <dt>This version:
     <dd><a class="u-url" href="http://wg21.link/D1873">http://wg21.link/D1873</a>
     <dt>Author:
     <dd>
      <dd class="editor p-author h-card vcard"><a class="p-name fn u-email email" href="mailto:michael_spencer@apple.com">Michael Spencer</a> (<span class="p-org org">Apple</span>)
     <dt>Audience:
     <dd>EWG, SG2
     <dt>Project:
     <dd>ISO/IEC JTC1/SC22/WG21 14882: Programming Language — C++
    </dl>
   </div>
   <div data-fill-with="warning"></div>
   <hr title="Separator for header">
  </div>
  <div class="p-summary" data-fill-with="abstract">
   <h2 class="no-num no-toc no-ref heading settled" id="abstract"><span class="content">Abstract</span></h2>
   <p><code class="highlight"><c- p>.</c-></code>s in module names exist in support of submodules, which

          we don’t have.  We should remove them for now, as they are likely to
          cause confusion and may prevent us from getting the submodules we want
          in the future.</p>
  </div>
  <nav data-fill-with="table-of-contents" id="toc">
   <h2 class="no-num no-toc no-ref" id="contents">Table of Contents</h2>
   <ol class="toc" role="directory">
    <li><a href="#semantics"><span class="secno">1</span> <span class="content">Current Semantics</span></a>
    <li>
     <a href="#current-use"><span class="secno">2</span> <span class="content">Current Use</span></a>
     <ol class="toc">
      <li><a href="#implied-structure"><span class="secno">2.1</span> <span class="content">Implied Structure</span></a>
      <li><a href="#fs-mapping"><span class="secno">2.2</span> <span class="content">Filesystem Mapping</span></a>
     </ol>
    <li><a href="#history"><span class="secno">3</span> <span class="content">History</span></a>
    <li>
     <a href="#problems"><span class="secno">4</span> <span class="content">Problems</span></a>
     <ol class="toc">
      <li><a href="#confusion"><span class="secno">4.1</span> <span class="content">User Confusion</span></a>
      <li><a href="#future"><span class="secno">4.2</span> <span class="content">Walling off the future</span></a>
     </ol>
    <li>
     <a href="#possible-semantics"><span class="secno">5</span> <span class="content">Possible Semantics</span></a>
     <ol class="toc">
      <li><a href="#other-languages"><span class="secno">5.1</span> <span class="content">Other Languages</span></a>
     </ol>
    <li><a href="#tradeoffs"><span class="secno">6</span> <span class="content">Design Tradeoffs</span></a>
    <li>
     <a href="#wording"><span class="secno">7</span> <span class="content">Wording</span></a>
     <ol class="toc">
      <li><a href="#module-unit"><span class="secno">7.1</span> <span class="content">[module.unit]</span></a>
     </ol>
    <li>
     <a href="#references"><span class="secno"></span> <span class="content">References</span></a>
     <ol class="toc">
      <li><a href="#informative"><span class="secno"></span> <span class="content">Informative References</span></a>
     </ol>
   </ol>
  </nav>
  <main>
   <h2 class="heading settled" data-level="1" id="semantics"><span class="secno">1. </span><span class="content">Current Semantics</span><a class="self-link" href="#semantics"></a></h2>
   <p><code class="highlight"><c- p>.</c-></code>s in module names currently have no semantics. There is no relation defined
by the standard between <code class="highlight"><c- n>hello</c-><c- p>.</c-><c- n>leftpad</c-></code> and <code class="highlight"><c- n>hello</c-><c- p>.</c-><c- n>rightpad</c-></code> or <code class="highlight"><c- n>hello</c-></code>. The
only meaning they have is the implied hierarchy that developers read into them.</p>
   <h2 class="heading settled" data-level="2" id="current-use"><span class="secno">2. </span><span class="content">Current Use</span><a class="self-link" href="#current-use"></a></h2>
   <p>There are two current uses of <code class="highlight"><c- p>.</c-></code>s in module names that I am aware of.</p>
   <h3 class="heading settled" data-level="2.1" id="implied-structure"><span class="secno">2.1. </span><span class="content">Implied Structure</span><a class="self-link" href="#implied-structure"></a></h3>
   <p>The first is to communicate with developers by implying some structure and relationship between module names with
a common prefix. The general approach is that a module <code class="highlight"><c- n>m</c-></code> should <code class="highlight"><c- k>export</c-> <c- n>import</c-></code> all modules with names that start with <code class="highlight"><c- n>m</c-><c- p>.</c-></code>.  For example:</p>
<pre class="highlight"><c- k>export</c-> <c- n>module</c-> <c- n>std</c-><c- p>;</c->
<c- k>export</c-> <c- n>import</c-> <c- n>std</c-><c- p>.</c-><c- n>vector</c-><c- p>;</c->
<c- k>export</c-> <c- n>import</c-> <c- n>std</c-><c- p>.</c-><c- n>algorithm</c-><c- p>;</c->
<c- p>...</c->
</pre>
   <h3 class="heading settled" data-level="2.2" id="fs-mapping"><span class="secno">2.2. </span><span class="content">Filesystem Mapping</span><a class="self-link" href="#fs-mapping"></a></h3>
   <p>The second is for mapping module names to filesystem paths.  Here <code class="highlight"><c- p>.</c-></code> is used
as a proxy for <code class="highlight"><c- o>/</c-></code>. For example, <code class="highlight"><c- n>a</c-><c- p>.</c-><c- n>b</c-><c- p>.</c-><c- n>c</c-></code> could map to <code class="highlight"><c- n>a</c-><c- o>/</c-><c- n>b</c-><c- o>/</c-><c- n>c</c-><c- p>.</c-><c- n>cppm</c-></code>.</p>
   <h2 class="heading settled" data-level="3" id="history"><span class="secno">3. </span><span class="content">History</span><a class="self-link" href="#history"></a></h2>
   <p>Modules have had a long history in C++ dating back to at least 2004. Every paper
until recently had an idea for something similar to submodules. It’s useful to
explore this history to see which directions we may want to go in the future.</p>
   <p>First let’s start with Daveed Vandevoorde’s 2004 paper: <a data-link-type="biblio" href="#biblio-n1736">[N1736]</a></p>
   <p>In this paper submodules are known as module partitions.  These are different from the module partitions we have today in that they are externally visible.  The syntax started as <code class="highlight"><c- k>namespace</c-> <c- o>&lt;&lt;</c-> <c- n>std</c-><c- p>[</c-><c- s>"vector"</c-><c- p>];</c-></code>, but in 2007 moved to <code class="highlight"><c- n>import</c-> <c- n>std</c-><c- p>.</c-><c- n>vector</c-><c- p>;</c-></code> . In this model, partitions export a subset of names from their parent module.  Additionally, non-exported names from a partition are visible to any other partition of the same module.  Note that this proposal also supports <code class="highlight"><c- o>::</c-></code> in module names.  It has no semantic meaning, and is for the purpose of allowing module names to match the namespace they define.</p>
   <p>Next let’s look at Doug Gregor’s <a href="http://wiki.edg.com/pub/Wg21bristol/SG2/SG2_Modules.pdf">2013 SG2 presentation</a>, which also had submodules.</p>
   <p>This was a description of clang modules and additional syntax.  In this model a module exports all of its submodules as defined in a module map.  Today submodules are used in clang for two primary purposes.  The first is to restrict which names are visible when importing a submodule to those in the submodule.  The second is to allow interdependencies between submodules without causing a cycle.  Clang compiles a single module together along with all of its submodules as a single translation unit, and keeps track of which names are visible from which submodules.</p>
   <p>Next is Microsoft’s 2014 modules proposal, which also had submodules as part of the design: <a data-link-type="biblio" href="#biblio-n4214">[N4214]</a></p>
   <p>Section 4.1.1 Module Names and Filenames</p>
   <blockquote>
    <p>We propose a hierarchical naming scheme for the namespace of module-name
in support of submodules</p>
   </blockquote>
   <p>Section 4.5 Submodules</p>
   <blockquote>
    <p>A submodule can serve as cluster of translation units sharing implementation detail information (within a module) that is not meant to be accessible to outside
consumers of the parent module.</p>
   </blockquote>
   <p>The design was intended to allow control of visibility of names in submodules.  This functionality never made it into the wording.  The design didn’t go into enough detail about how it would be implemented to determine if adding this functionality would be a breaking change.</p>
   <p>Next we have Google’s ATOM proposal: <a data-link-type="biblio" href="#biblio-p0947r1">[P0947r1]</a></p>
   <p>This proposal adds the module partitions we have today, but keeps <code class="highlight"><c- p>.</c-></code> in module names.  A key part of module partitions is that the partition name is not visible outside of the module in which they are defined.</p>
   <h2 class="heading settled" data-level="4" id="problems"><span class="secno">4. </span><span class="content">Problems</span><a class="self-link" href="#problems"></a></h2>
   <p>There are two main issues with keeping the <code class="highlight"><c- p>.</c-></code> in module names.</p>
   <h3 class="heading settled" data-level="4.1" id="confusion"><span class="secno">4.1. </span><span class="content">User Confusion</span><a class="self-link" href="#confusion"></a></h3>
   <p>In C++ the <code class="highlight"><em><c- n>identifier</c-></em><c- p>.</c-><em><c- n>identifier</c-></em></code> syntax is used by every developer. It has very specific
semantic meanings, but even at the highest level it always establishes some form
of hierarchy. We’ve already seen people be confused about C++ modules having no
hierarchy, and even today a search for subpackages in Java leads to questions
and answers centered on this confusion.</p>
   <p>Developers will use <code class="highlight"><c- p>.</c-></code> to communicate something to their users, but will they
communicate the same thing? We will end up with different behaviors in different
libraries, which will cause additional confusion.</p>
   <h3 class="heading settled" data-level="4.2" id="future"><span class="secno">4.2. </span><span class="content">Walling off the future</span><a class="self-link" href="#future"></a></h3>
   <p>By allowing <code class="highlight"><c- p>.</c-></code> in module names without semantics, we potentially prevent giving
them semantics in the future as it may be a breaking change.</p>
   <h2 class="heading settled" data-level="5" id="possible-semantics"><span class="secno">5. </span><span class="content">Possible Semantics</span><a class="self-link" href="#possible-semantics"></a></h2>
   <h3 class="heading settled" data-level="5.1" id="other-languages"><span class="secno">5.1. </span><span class="content">Other Languages</span><a class="self-link" href="#other-languages"></a></h3>
   <p>Java/Groovy: <code class="highlight"><c- p>.</c-></code> in package and module names only impacts where the classloader (basically the runtime dynamic linker) looks up <code class="highlight"><c- p>.</c-><c- k>class</c-></code> files (Java bytecode) on the filesystem (or in <code class="highlight"><c- p>.</c-><c- n>jar</c-></code>s).  They have no semantic meaning in the source code.</p>
   <p>Python: Modules cannot have <code class="highlight"><c- p>.</c-></code> in their names.  Instead <code class="highlight"><c- p>.</c-></code>s are used for packages and subpackages (which both contain modules).  Packages are determined by filesystem layout and directories are accessed using <code class="highlight"><c- p>.</c-></code>.  The syntax <code class="highlight"><c- n>import</c-> <c- n>package</c-><c- p>.</c-><c- o>*</c-></code> is controlled by the <code class="highlight"><c- n>__all__</c-></code> variable in the package’s <code class="highlight"><c- n>__init__</c-><c- p>.</c-><c- n>py</c-></code> and can select which, if any, modules from that package are imported.  Additionally, there are relative imports using <code class="highlight"><c- p>..</c-></code> which go up the package hierarchy.</p>
   <p>C#/VB.NET: No modules/packages, just namespaces.  Namespaces are separated by <code class="highlight"><c- p>.</c-></code> when referencing them, and are hierarchical.</p>
   <p>JavaScript: Modules don’t have names, they have paths represented by strings.  Paths can contain <code class="highlight"><c- p>.</c-></code>s and don’t mean anything special. <code class="highlight"><c- o>/</c-></code> is special as it is a directory separator.</p>
   <p>Objective-C{,++}: Uses clang modules.  Module names are separated by <code class="highlight"><c- p>.</c-></code> into submodules.  Submodules are used to control visibility of names and are hierarchical.</p>
   <p>Delphi/Object Pascal: Namespaces can have <code class="highlight"><c- p>.</c-></code>s in their names and there’s no hierarchy.</p>
   <p>Go: Package names cannot contain <code class="highlight"><c- p>.</c-></code>, no subpackages.</p>
   <p>Ruby: Modules in ruby are closer to namespaces, not really a modules system, and can’t contain <code class="highlight"><c- p>.</c-></code>s.  Ruby uses library names represented by strings for loading other code, these can also be absolute paths.</p>
   <p>Swift: Module names cannot contain <code class="highlight"><c- p>.</c-></code>s.  Can import Objective-C (clang) modules and submodules.</p>
   <p>MATLAB: Package names can’t contain <code class="highlight"><c- p>.</c-></code>s.  Subpackages are hierarchical and are accessed via <code class="highlight"><c- p>.</c-></code>.</p>
   <p>R: All identifiers can contain <code class="highlight"><c- p>.</c-></code>s. <code class="highlight"><c- o>::</c-></code> is used as the namespace separator.</p>
   <p>Perl: Uses <code class="highlight"><c- o>::</c-></code> and are translated to filesystem paths, can’t contain <code class="highlight"><c- p>.</c-></code>.</p>
   <p>Rust: No <code class="highlight"><c- p>.</c-></code> in module names. <code class="highlight"><c- o>::</c-></code> is used as a crate and file system separator.</p>
   <p>Of these only two have a <code class="highlight"><c- p>.</c-></code> symbol that means something in normal code but means nothing in a package/module name.  One is from the 80s and the other is from the 90s.  Additionally every reference I found for Java was either someone confused about what <code class="highlight"><c- p>.</c-></code> meant, or someone explaining what it meant to people who were confused. We shouldn’t follow Java’s example here.</p>
   <h2 class="heading settled" data-level="6" id="tradeoffs"><span class="secno">6. </span><span class="content">Design Tradeoffs</span><a class="self-link" href="#tradeoffs"></a></h2>
   <p>When choosing a syntax there is always a design tradeoff. In this case that
tradeoff has three major factors: utility, understandability, and extensibility.</p>
   <p>There are valid usecases for <code class="highlight"><c- p>.</c-></code>, as it does provide additonal ways for a module author to communicate to their
users a relationship between modules. We could have restricted identifiers to
just <a class="property" data-link-type="propdesc">a</a> and <a class="property" data-link-type="propdesc">b</a> and have equal semantic power, but we didn’t because that would
severely limit communication.</p>
   <p>We want new syntax to be understandable to existing and new C++ users. We
often do this by reusing or mimicking existing syntax when it is close enough
in semantics that we want that knowledge to carry over. We also choose different
syntaxes when we want to avoid conflating two different concepts.</p>
   <p>C++ cares about backwards compatibility, even in edge cases (due to Hyrum’s
law). When we choose a syntax we’re pretty much stuck with that syntax and have
great difficulty changing what it means. We should have a high bar for the
benefit we get from a syntax due to this.</p>
   <p>Given these tradeoffs, I think that for C++20 the risks to understandability and
extensibility far outweigh the utility gained by allowing <code class="highlight"><c- p>.</c-></code>s in module names.
Over the next few years we should get to know modules better and how they are
used and what changes we really want before closing this door.</p>
   <h2 class="heading settled" data-level="7" id="wording"><span class="secno">7. </span><span class="content">Wording</span><a class="self-link" href="#wording"></a></h2>
   <h3 class="heading settled" data-level="7.1" id="module-unit"><span class="secno">7.1. </span><span class="content">[module.unit]</span><a class="self-link" href="#module-unit"></a></h3>
   <blockquote>
<pre class="highlight"><em><c- n>module</c-><c- o>-</c-><c- nl>declaration</c-></em><c- p>:</c->
    <strong><c- n>export</c-></strong><sub><c- n>opt</c-></sub> <strong><c- n>module</c-></strong> <em><c- n>module</c-><c- o>-</c-><c- n>name</c-> <c- n>module</c-><c- o>-</c-><c- n>partition</c-><sub><c- n>opt</c-></sub> <c- n>attribute</c-><c- o>-</c-><c- n>specifier</c-><c- o>-</c-><c- n>seq</c-><sub><c- n>opt</c-></sub></em> <strong><c- p>;</c-></strong>
<em><c- n>module</c-><c- o>-</c-><c- nl>name</c-></em><c- p>:</c->
    <em><del><c- n>module</c-><c- o>-</c-><c- n>name</c-><c- o>-</c-><c- n>qualifier</c-><sub><c- n>opt</c-></sub> </del><c- n>identifier</c-></em>
<em><c- n>module</c-><c- o>-</c-><c- nl>partition</c-></em><c- p>:</c->
    <strong><c- o>:</c-></strong> <em><del><c- n>module</c-><c- o>-</c-><c- n>name</c-><c- o>-</c-><c- n>qualifier</c-><sub><c- n>opt</c-></sub> </del><c- n>identifier</c-></em>
<del><em><c- n>module</c-><c- o>-</c-><c- n>name</c-><c- o>-</c-><c- nl>qualifier</c-></em><c- p>:</c->
    <em><c- n>identifier</c-></em> <strong><c- p>.</c-></strong>
    <em><c- n>module</c-><c- o>-</c-><c- n>name</c-><c- o>-</c-><c- n>qualifier</c-> <c- n>identifier</c-></em> <strong><c- p>.</c-></strong></del>
</pre>
   </blockquote>
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  <h2 class="no-num no-ref heading settled" id="references"><span class="content">References</span><a class="self-link" href="#references"></a></h2>
  <h3 class="no-num no-ref heading settled" id="informative"><span class="content">Informative References</span><a class="self-link" href="#informative"></a></h3>
  <dl>
   <dt id="biblio-n1736">[N1736]
   <dd>Daveed Vandevoorde. <a href="https://wg21.link/n1736">Modules in C++ (Revision 1)</a>. 5 November 2004. URL: <a href="https://wg21.link/n1736">https://wg21.link/n1736</a>
   <dt id="biblio-n4214">[N4214]
   <dd>G. Dos Reis, M. Hall, G. Nishanov. <a href="https://wg21.link/n4214">A Module System for C++ (Revision 2)</a>. 13 October 2014. URL: <a href="https://wg21.link/n4214">https://wg21.link/n4214</a>
   <dt id="biblio-p0947r1">[P0947r1]
   <dd>Richard Smith. <a href="https://wg21.link/p0947r1">Another take on Modules</a>. 6 March 2018. URL: <a href="https://wg21.link/p0947r1">https://wg21.link/p0947r1</a>
  </dl>