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 <head>
  <meta content="text/html; charset=utf-8" http-equiv="Content-Type">
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  <title>P1275R0: Desert Sessions: Improving hostile environment interactions</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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*/

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


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

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/******************************************************************************/
/*                                    Legacy                                  */
/******************************************************************************/

	/* This rule is inherited from past style sheets. No idea what it's for. */
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/******************************************************************************/
/*                             Overflow Control                               */
/******************************************************************************/

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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">P1275R0<br>Desert Sessions: Improving hostile environment interactions</h1>
   <h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Published Proposal, <time class="dt-updated" datetime="2018-10-06">2018-10-06</time></span></h2>
   <div data-fill-with="spec-metadata">
    <dl>
     <dt>This version:
     <dd><a class="u-url" href="https://wg21.link/p1275r0">https://wg21.link/p1275r0</a>
     <dt>Author:
     <dd>
      <dd class="editor p-author h-card vcard"><a class="p-name fn u-url url" href="https://twitter.com/slurpsmadrips">Isabella Muerte</a>
     <dt>Audience:
     <dd>LEWG, SG15, SG16
     <dt>Project:
     <dd>ISO/IEC JTC1/SC22/WG21 14882: Programming Language — C++
     <dt>Current Render:
     <dd><a href="https://api.csswg.org/bikeshed/?force=1&amp;url=https://git.io/fxsCx">P1275R0</a>
     <dt>Current Source:
     <dd><a href="https://git.io/fxsWe">slurps-mad-rips/papers/proposals/desert-sessions.bs</a>
     <dt>Implementation:
     <dd><a href="https://git.io/fxGTH">slurps-mad-rips/sessions</a>
    </dl>
   </div>
   <div data-fill-with="warning"></div>
   <hr title="Separator for header">
  </div>
  <div class="p-summary" data-fill-with="abstract">
   <h2 class="no-num no-toc no-ref heading settled" id="abstract"><span class="content">Abstract</span></h2>
   <p>Working with environment variables and command line arguments is

painful, platform specific, and lacking a modern C++ touch.</p>
  </div>
  <nav data-fill-with="table-of-contents" id="toc">
   <h2 class="no-num no-toc no-ref" id="contents">Table of Contents</h2>
   <ol class="toc" role="directory">
    <li>
     <a href="#changelog"><span class="secno">1</span> <span class="content">Revision History</span></a>
     <ol class="toc">
      <li><a href="#r0"><span class="secno">1.1</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="#design"><span class="secno">3</span> <span class="content">Design</span></a>
     <ol class="toc">
      <li>
       <a href="#design-synopsis"><span class="secno">3.1</span> <span class="content">Synopsis</span></a>
       <ol class="toc">
        <li><a href="#design-synopsis-arguments"><span class="secno">3.1.1</span> <span class="content">Arguments</span></a>
        <li><a href="#design-synopsis-environment"><span class="secno">3.1.2</span> <span class="content">Environment</span></a>
       </ol>
     </ol>
   </ol>
  </nav>
  <main>
   <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="r0"><span class="secno">1.1. </span><span class="content">Revision 0</span><a class="self-link" href="#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>Environment variables are an important aspect of modern systems. Yet, as of
right now, C and C++ lack a standardized way to iterate through all current
environment variables. An interface to iterate, get, set, erase, and modify
environment variables, as well as providing familiar syntax found in other
programming languages is needed.</p>
   <p>Additionally, accessing command line arguments when <code class="highlight"><c- n>main</c-></code> is outside of
your control is currently not possible. Instead, objects must be initialized
inside of <code class="highlight"><c- n>main</c-></code>, or global variables must be initialized once <code class="highlight"><c- n>main</c-></code> has
started. Additionally, on Windows, the standard <code class="highlight"><c- b>char</c-><c- o>**</c-> <c- n>argv</c-></code> type is
deprecated for use in <code class="highlight"><c- n>main</c-></code>, and the only correct way to get the command line
arguments is to call platform specific functions or use <code class="highlight"><c- n>WinMain</c-></code> and <code class="highlight"><c- n>wmain</c-></code>,
both of which are non-standard entry points into the program. This is all such
a strange approach compared to most other languages, especially due to command
line arguments existing for the duration of a programs life. In languages such
as Python, Rust, Ruby, Haskell, and C#, getting the list of command line
arguments is just a function or member call away.</p>
   <p>This paper aims to rectify both of these problems, while providing a familiar
interface for users of <code class="highlight"><c- n>argv</c-></code> as well as providing an interaction with Ranges.</p>
   <h2 class="heading settled" data-level="3" id="design"><span class="secno">3. </span><span class="content">Design</span><a class="self-link" href="#design"></a></h2>
   <p>This paper proposes the addition of a new header, <code class="highlight"><c- o>&lt;</c-><c- n>session</c-><c- o>></c-></code>, for any and all
types or functions that affect the current program’s running session. To begin
with we add two types into this header: <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>arguments</c-></code> and <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>environment</c-></code>. Each one is a wrapper interface around the command line and
environment variables respectively.</p>
   <p><code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>arguments</c-></code> attempts to meet <em>most</em> of the Named Requirements found in <em>SequenceContainer</em>. However, because it is an immutable container (it can not
grow, shrink, delete or add its elements), its interface is effectively reduced
to that of a <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>vector</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-> <c- k>const</c-></code>. If mutation or modifications are desired,
it is recommended that one construct a <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>vector</c-></code> from the elements of <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>arguments</c-></code>. The elements found inside of <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>arguments</c-></code> is currently <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>string_view</c-></code>. Whether the contents of these <code class="highlight"><c- n>string_view</c-></code>s are bytes or
UTF-8 is intended to be implementation defined. The interface for <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>arguments</c-></code> will need to be revisited once SG16’s initial work is
released, as a unicode-only interface for arguments is desirable.</p>
   <p><code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>environment</c-></code> is a bit more complex. It can be seen as an associative
container, however it attempts to store no state unless absolutely needed.
Additionally, for ease of use, it provides three ranges interfaces:</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>environment</c-><c- p>.</c-><c- n>keys</c-><c- p>()</c-></code></p>
    <li data-md>
     <p><code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>environment</c-><c- p>.</c-><c- n>values</c-><c- p>()</c-></code></p>
    <li data-md>
     <p><code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>environment</c-></code></p>
   </ul>
   <p>Each of these ranges provides iteration over the keys, values, or the pair of
both. Additionally subscript gets and sets are possible as well:</p>
<pre class="language-cpp highlight"><c- k>auto</c-> <c- n>x</c-> <c- o>=</c-> <c- n>std</c-><c- o>::</c-><c- n>environment</c-><c- p>[</c-><c- s>"PATH"</c-><c- p>];</c->
</pre>
   <p>The following straw polls are requested regarding the interface for both <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>arguments</c-></code> and <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>environment</c-></code>:</p>
   <ul>
    <li data-md>
     <p>Should they be <code class="highlight"><c- k>static</c-> <c- kr>inline</c-></code> variables?</p>
    <li data-md>
     <p>Should they be templated on their argument values?</p>
    <li data-md>
     <p>Should they have (optionally template) aliases provided?</p>
    <li data-md>
     <p>Should they have shorter names available (<code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>args</c-></code>, <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>env</c-></code>)?</p>
   </ul>
   <p>Additionally, the plan is to provide two functions to easily iterate over a
"path list". On platforms where this matters, an implementation specific path
separator (e.g., <code class="highlight"><c- o>:</c-></code> on POSIX, <code class="highlight"><c- p>;</c-></code> on Windows) is used to separate multiple
values when storing file system paths in enviroment variables. These functions
create iterators that permit both the splitting of <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>string_view</c-></code> objects
into <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>filesystem</c-><c- o>::</c-><c- n>path</c-></code> objects, as well as joining <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>filesystem</c-><c- o>::</c-><c- n>path</c-></code> objects into a <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>string</c-></code> that can then be assigned
to an environment variable.</p>
   <p>Lastly, on platforms where arguments or environment variables cannot typically
be passed in or read from, attempting to iterate <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>arguments</c-></code> and <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>environment</c-></code> will yield an empty range, and attempting to index or
subscript into them will return empty <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>string_view</c-></code> objects.</p>
   <p class="note" role="note"><span>Note:</span> For security reasons we do not currently provide a cross platform way to
get the current executable or home directory.</p>
   <p>Wording has been witheld in this initial paper to see what interface changes
are necessary.</p>
   <h3 class="heading settled" data-level="3.1" id="design-synopsis"><span class="secno">3.1. </span><span class="content">Synopsis</span><a class="self-link" href="#design-synopsis"></a></h3>
   <p>The <code class="highlight"><c- o>&lt;</c-><c- n>session</c-><c- o>></c-></code> headers full specification is:</p>
<pre class="language-c++ highlight"><c- n>namespace</c-> <c- n>std</c-> <c- p>{</c->
    <c- n>class</c-> <c- n>arguments</c-><c- p>;</c->
    <c- n>class</c-> <c- n>environment</c-><c- p>;</c->

    <c- n>std</c-><c- o>::</c-><c- n>string</c-> <c- n>join_paths</c-> <c- p>(</c-><c- n>Iter</c-> <c- n>begin</c-><c- p>,</c-> <c- n>Iter</c-> <c- n>end</c-><c- p>);</c->
    <c- n>std</c-><c- o>::</c-><c- n>string</c-> <c- n>join_paths</c-> <c- p>(</c-><c- n>Range</c-><c- p>);</c->
<c- p>}</c->
</pre>
   <h4 class="heading settled" data-level="3.1.1" id="design-synopsis-arguments"><span class="secno">3.1.1. </span><span class="content">Arguments</span><a class="self-link" href="#design-synopsis-arguments"></a></h4>
   <p>The <code class="highlight"><c- n>arguments</c-></code> class represents a mostly sequence-like container. It can be
seen as a wrapper around <code class="highlight"><c- n>argv</c-></code>, while still being accessible from outside of <code class="highlight"><c- n>main</c-></code>. The object itself is immutable, and could technically be treated as a
singleton. Reading from <code class="highlight"><c- n>arguments</c-></code> is thread-safe, as is iterating over it.
The type it currently returns is <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>string_view</c-></code>, as this type can represent
both UTF-8 and raw bytes. While the wording is not yet complete in this initial
draft, it is intended that <code class="highlight"><c- n>arguments</c-></code> only permit bytes from the operating
system directly <em>or</em> UTF-8 only. Treating UTF-16 characters as bytes will not
be permitted. At some point in the future, this will have to change, or an
additional unicode-only <code class="highlight"><c- n>arguments</c-></code> class will have to be implemented.</p>
   <p>Additionally, it still provides access to the underlying <code class="highlight"><c- b>char</c-><c- o>**</c-> <c- n>argv</c-></code> and
length of <code class="highlight"><c- n>argc</c-></code> for backwards compatibility with APIs that still expect it as
such.</p>
<pre class="language-cpp highlight"><c- k>class</c-> <c- nc>arguments</c-> <c- p>{</c->
  <c- k>using</c-> <c- n>iterator</c-> <c- o>=</c-> <c- d>/* implementation-defined */</c->
  <c- k>using</c-> <c- n>reverse_iterator</c-> <c- o>=</c-> <c- n>reverse_iterator</c-><c- o>&lt;</c-><c- n>iterator</c-><c- o>></c-><c- p>;</c->
  <c- k>using</c-> <c- n>value_type</c-> <c- o>=</c-> <c- n>std</c-><c- o>::</c-><c- n>string_view</c-><c- p>;</c->
  <c- k>using</c-> <c- n>index_type</c-> <c- o>=</c-> <c- b>size_t</c-><c- p>;</c->
  <c- k>using</c-> <c- n>size_type</c-> <c- o>=</c-> <c- b>size_t</c-><c- p>;</c->

  <c- n>value_type</c-> <c- k>operator</c-> <c- p>[]</c-> <c- p>(</c-><c- n>index_type</c-><c- p>)</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->
  <c- n>value_type</c-> <c- nf>at</c-> <c- p>(</c-><c- n>index_type</c-><c- p>)</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>(</c->false<c- p>);</c->

  <c- p>[[</c-><c- n>nodiscard</c-><c- p>]]</c-> <c- b>bool</c-> <c- n>empty</c-> <c- p>()</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->
  <c- n>size_type</c-> <c- nf>size</c-> <c- p>()</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->

  <c- n>iterator</c-> <c- nf>cbegin</c-> <c- p>()</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->
  <c- n>iterator</c-> <c- nf>cend</c-> <c- p>()</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->

  <c- n>iterator</c-> <c- nf>begin</c-> <c- p>()</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->
  <c- n>iterator</c-> <c- nf>end</c-> <c- p>()</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->

  <c- n>reverse_iterator</c-> <c- nf>crbegin</c-> <c- p>()</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->
  <c- n>reverse_iterator</c-> <c- nf>crend</c-> <c- p>()</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->

  <c- n>reverse_iterator</c-> <c- nf>rbegin</c-> <c- p>()</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->
  <c- n>reverse_ierator</c-> <c- nf>rend</c-> <c- p>()</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->

  <c- p>[[</c-><c- n>nodiscard</c-><c- p>]]</c-> <c- b>char</c-><c- o>**</c-> <c- n>argv</c-> <c- p>()</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->
  <c- p>[[</c-><c- n>nodiscard</c-><c- p>]]</c-> <c- b>int</c-> <c- n>argc</c-> <c- p>()</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->
<c- p>};</c->
</pre>
   <h4 class="heading settled" data-level="3.1.2" id="design-synopsis-environment"><span class="secno">3.1.2. </span><span class="content">Environment</span><a class="self-link" href="#design-synopsis-environment"></a></h4>
   <p>The <code class="highlight"><c- n>environment</c-></code> mapping object is also <em>mostly</em> immutable itself. It does
support removing keys directly, although setting them directly is not
supported. However, the environment can be modified by operating on the <code class="highlight"><c- n>variable</c-></code> class it returns from <code class="highlight"><c- k>operator</c-> <c- p>[]</c-></code>. This type acts as a proxy
object and can be assigned to with nearly any string-like object. Additionally,
it can return an object that has a pair of iterators that permit range
operations to "split" on the path separator for a given environment variable.</p>
   <p>Some platform’s keys are case insensitive and for this reason, the <code class="highlight"><c- n>environment</c-></code> silently checks both upper and lower case keys for their
validity. This is safe to do as currently all platforms store their keys as
ASCII strings.</p>
   <p class="note" role="note"><span>Note:</span> Due to platform specific restrictions, environments can be iterated on
while also actively mutating them. However, the underlying iterator’s
environment will still iterate on the unmodified version of the environment.
After extensively looking at all operating systems available, it was confirmed
that they all behave in this same way.</p>
<pre class="language-cpp highlight"><c- k>class</c-> <c- nc>environment</c-> <c- p>{</c->
  <c- k>class</c-> <c- nc>variable</c-> <c- p>{</c->
    <c- k>operator</c-> <c- n>std</c-><c- o>::</c-><c- n>string_view</c-> <c- p>()</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->
    <c- n>variable</c-><c- o>&amp;</c-> <c- k>operator</c-> <c- o>=</c-> <c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>string_view</c-><c- p>);</c->
    <c- n>std</c-><c- o>::</c-><c- n>string_view</c-> <c- n>key</c-> <c- p>()</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->
    <c- d>/* implementation-defined */</c-> <c- n>split</c-> <c- p>()</c-> <c- k>const</c-><c- p>;</c->
  <c- p>};</c->

  <c- k>using</c-> <c- n>value_range</c-> <c- o>=</c-> <c- d>/* implementation-defined */</c->
  <c- k>using</c-> <c- n>key_range</c-> <c- o>=</c-> <c- d>/* implementation-defined */</c->
  <c- k>using</c-> <c- n>iterator</c-> <c- o>=</c-> <c- d>/* implementation-defined */</c->
  <c- k>using</c-> <c- n>value_type</c-> <c- o>=</c-> <c- n>variable</c-><c- p>;</c->

  <c- k>template</c-> <c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- o>></c->
  <c- n>value_type</c-> <c- k>operator</c-> <c- p>[]</c-> <c- p>(</c-><c- n>T</c-> <c- k>const</c-><c- o>&amp;</c-><c- p>)</c-> <c- k>const</c-><c- p>;</c-> <c- c1>// see below</c->

  <c- n>value_type</c-> <c- k>operator</c-> <c- p>[]</c-> <c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>string</c-> <c- k>const</c-><c- o>&amp;</c-><c- p>)</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->
  <c- n>value_type</c-> <c- k>operator</c-> <c- p>[]</c-> <c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>string_view</c-><c- p>)</c-> <c- k>const</c-><c- p>;</c->
  <c- n>value_type</c-> <c- k>operator</c-> <c- p>[]</c-> <c- p>(</c-><c- b>char</c-> <c- k>const</c-><c- o>*</c-><c- p>)</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->

  <c- k>template</c-> <c- o>&lt;</c-><c- k>class</c-> <c- nc>K</c-><c- o>></c->
  <c- n>iterator</c-> <c- n>find</c-> <c- p>(</c-><c- n>K</c-> <c- k>const</c-><c- o>&amp;</c-><c- p>)</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->

  <c- b>bool</c-> <c- nf>contains</c-> <c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>string_view</c-><c- p>)</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->

  <c- n>iterator</c-> <c- nf>cbegin</c-> <c- p>()</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->
  <c- n>iterator</c-> <c- nf>cend</c-> <c- p>()</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->

  <c- n>iterator</c-> <c- nf>begin</c-> <c- p>()</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->
  <c- n>iterator</c-> <c- nf>end</c-> <c- p>()</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->

  <c- n>size_type</c-> <c- nf>size</c-> <c- p>()</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->
  <c- b>bool</c-> <c- nf>empty</c-> <c- p>()</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->

  <c- n>value_range</c-> <c- nf>values</c-> <c- p>()</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->
  <c- n>key_range</c-> <c- nf>keys</c-> <c- p>()</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->

  <c- k>template</c-> <c- o>&lt;</c-><c- k>class</c-> <c- nc>K</c-><c- o>></c->
  <c- b>void</c-> <c- n>erase</c-> <c- p>(</c-><c- n>K</c-> <c- k>const</c-><c- o>&amp;</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
<c- p>};</c->
</pre>
   <p>All member functions that take a <code class="highlight"><c- n>T</c-> <c- k>const</c-><c- o>&amp;</c-></code> follow the same rules regarding <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>string</c-></code>'s 10th and 11th constructors regarding <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>string_view</c-></code> conversion.</p>
   <p>In the case of <code class="highlight"><c- n>environment</c-><c- o>::</c-><c- n>find</c-></code>, this function follows the same rules of <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>map</c-><c- o>::</c-><c- n>find</c-></code> as though it’s <code class="highlight"><c- n>Compare</c-><c- o>::</c-><c- n>is_transparent</c-></code> were valid.</p>
   <p class="note" role="note"><span>Note:</span> <code class="highlight"><c- n>environment</c-></code> does not have a <code class="highlight"><c- n>Compare</c-></code> template member, but can act as
though it has one, since it works almost exclusively on strings.</p>
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