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feature/st
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@@ -2,22 +2,21 @@
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||||
<html lang="en">
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||||
<head>
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||||
<meta charset="UTF-8">
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||||
<!--[if IE]><meta http-equiv="X-UA-Compatible" content="IE=edge"><![endif]-->
|
||||
<meta http-equiv="X-UA-Compatible" content="IE=edge">
|
||||
<meta name="viewport" content="width=device-width, initial-scale=1.0">
|
||||
<meta name="generator" content="Asciidoctor 1.5.7">
|
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<meta name="generator" content="Asciidoctor 2.0.9">
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||||
<meta name="author" content="Peter Dimov">
|
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<title>Boost.Variant2: A never valueless variant type</title>
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||||
<link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Open+Sans:300,300italic,400,400italic,600,600italic%7CNoto+Serif:400,400italic,700,700italic%7CDroid+Sans+Mono:400,700">
|
||||
<style>
|
||||
/* Asciidoctor default stylesheet | MIT License | http://asciidoctor.org */
|
||||
/* Uncomment @import statement below to use as custom stylesheet */
|
||||
/* Asciidoctor default stylesheet | MIT License | https://asciidoctor.org */
|
||||
/* Uncomment @import statement to use as custom stylesheet */
|
||||
/*@import "https://fonts.googleapis.com/css?family=Open+Sans:300,300italic,400,400italic,600,600italic%7CNoto+Serif:400,400italic,700,700italic%7CDroid+Sans+Mono:400,700";*/
|
||||
article,aside,details,figcaption,figure,footer,header,hgroup,main,nav,section,summary{display:block}
|
||||
audio,canvas,video{display:inline-block}
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article,aside,details,figcaption,figure,footer,header,hgroup,main,nav,section{display:block}
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audio,video{display:inline-block}
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||||
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||||
script{display:none!important}
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html{font-family:sans-serif;-ms-text-size-adjust:100%;-webkit-text-size-adjust:100%}
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||||
a{background:transparent}
|
||||
a{background:none}
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a:focus{outline:thin dotted}
|
||||
a:active,a:hover{outline:0}
|
||||
h1{font-size:2em;margin:.67em 0}
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||||
@@ -70,7 +69,7 @@ select{width:100%}
|
||||
div,dl,dt,dd,ul,ol,li,h1,h2,h3,#toctitle,.sidebarblock>.content>.title,h4,h5,h6,pre,form,p,blockquote,th,td{margin:0;padding:0;direction:ltr}
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a{color:#2156a5;text-decoration:underline;line-height:inherit}
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a:hover,a:focus{color:#1d4b8f}
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a img{border:none}
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a img{border:0}
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p{font-family:inherit;font-weight:400;font-size:1em;line-height:1.6;margin-bottom:1.25em;text-rendering:optimizeLegibility}
|
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p aside{font-size:.875em;line-height:1.35;font-style:italic}
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h1,h2,h3,#toctitle,.sidebarblock>.content>.title,h4,h5,h6{font-family:"Open Sans","DejaVu Sans",sans-serif;font-weight:300;font-style:normal;color:#ba3925;text-rendering:optimizeLegibility;margin-top:1em;margin-bottom:.5em;line-height:1.0125em}
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@@ -80,7 +79,7 @@ h2{font-size:1.6875em}
|
||||
h3,#toctitle,.sidebarblock>.content>.title{font-size:1.375em}
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h4,h5{font-size:1.125em}
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h6{font-size:1em}
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hr{border:solid #ddddd8;border-width:1px 0 0;clear:both;margin:1.25em 0 1.1875em;height:0}
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em,i{font-style:italic;line-height:inherit}
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strong,b{font-weight:bold;line-height:inherit}
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small{font-size:60%;line-height:inherit}
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||||
@@ -111,20 +110,23 @@ table{background:#fff;margin-bottom:1.25em;border:solid 1px #dedede}
|
||||
table thead,table tfoot{background:#f7f8f7}
|
||||
table thead tr th,table thead tr td,table tfoot tr th,table tfoot tr td{padding:.5em .625em .625em;font-size:inherit;color:rgba(0,0,0,.8);text-align:left}
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||||
table tr th,table tr td{padding:.5625em .625em;font-size:inherit;color:rgba(0,0,0,.8)}
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||||
table tr.even,table tr.alt,table tr:nth-of-type(even){background:#f8f8f7}
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table tr.even,table tr.alt{background:#f8f8f7}
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table thead tr th,table tfoot tr th,table tbody tr td,table tr td,table tfoot tr td{display:table-cell;line-height:1.6}
|
||||
h1,h2,h3,#toctitle,.sidebarblock>.content>.title,h4,h5,h6{line-height:1.2;word-spacing:-.05em}
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||||
h1 strong,h2 strong,h3 strong,#toctitle strong,.sidebarblock>.content>.title strong,h4 strong,h5 strong,h6 strong{font-weight:400}
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||||
.clearfix::before,.clearfix::after,.float-group::before,.float-group::after{content:" ";display:table}
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.clearfix::after,.float-group::after{clear:both}
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*:not(pre)>code{font-size:.9375em;font-style:normal!important;letter-spacing:0;padding:.1em .5ex;word-spacing:-.15em;background-color:#f7f7f8;-webkit-border-radius:4px;border-radius:4px;line-height:1.45;text-rendering:optimizeSpeed;word-wrap:break-word}
|
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*:not(pre)>code.nobreak{word-wrap:normal}
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*:not(pre)>code.nowrap{white-space:nowrap}
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pre,pre>code{line-height:1.45;color:rgba(0,0,0,.9);font-family:"Droid Sans Mono","DejaVu Sans Mono",monospace;font-weight:400;text-rendering:optimizeSpeed}
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:not(pre):not([class^=L])>code{font-size:.9375em;font-style:normal!important;letter-spacing:0;padding:.1em .5ex;word-spacing:-.15em;background:#f7f7f8;-webkit-border-radius:4px;border-radius:4px;line-height:1.45;text-rendering:optimizeSpeed;word-wrap:break-word}
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:not(pre)>code.nobreak{word-wrap:normal}
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pre{color:rgba(0,0,0,.9);font-family:"Droid Sans Mono","DejaVu Sans Mono",monospace;line-height:1.45;text-rendering:optimizeSpeed}
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pre code,pre pre{color:inherit;font-size:inherit;line-height:inherit}
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pre>code{display:block}
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pre.nowrap,pre.nowrap pre{white-space:pre;word-wrap:normal}
|
||||
em em{font-style:normal}
|
||||
strong strong{font-weight:400}
|
||||
.keyseq{color:rgba(51,51,51,.8)}
|
||||
kbd{font-family:"Droid Sans Mono","DejaVu Sans Mono",monospace;display:inline-block;color:rgba(0,0,0,.8);font-size:.65em;line-height:1.45;background-color:#f7f7f7;border:1px solid #ccc;-webkit-border-radius:3px;border-radius:3px;-webkit-box-shadow:0 1px 0 rgba(0,0,0,.2),0 0 0 .1em white inset;box-shadow:0 1px 0 rgba(0,0,0,.2),0 0 0 .1em #fff inset;margin:0 .15em;padding:.2em .5em;vertical-align:middle;position:relative;top:-.1em;white-space:nowrap}
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kbd{font-family:"Droid Sans Mono","DejaVu Sans Mono",monospace;display:inline-block;color:rgba(0,0,0,.8);font-size:.65em;line-height:1.45;background:#f7f7f7;border:1px solid #ccc;-webkit-border-radius:3px;border-radius:3px;-webkit-box-shadow:0 1px 0 rgba(0,0,0,.2),0 0 0 .1em white inset;box-shadow:0 1px 0 rgba(0,0,0,.2),0 0 0 .1em #fff inset;margin:0 .15em;padding:.2em .5em;vertical-align:middle;position:relative;top:-.1em;white-space:nowrap}
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.keyseq kbd:first-child{margin-left:0}
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.keyseq kbd:last-child{margin-right:0}
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.menuseq,.menuref{color:#000}
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||||
@@ -142,9 +144,9 @@ p a>code:hover{color:rgba(0,0,0,.9)}
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||||
#content{margin-top:1.25em}
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#content::before{content:none}
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#header>h1:first-child{color:rgba(0,0,0,.85);margin-top:2.25rem;margin-bottom:0}
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#header>h1:first-child+#toc{margin-top:8px;border-top:1px solid #ddddd8}
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#header>h1:only-child,body.toc2 #header>h1:nth-last-child(2){border-bottom:1px solid #ddddd8;padding-bottom:8px}
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#header .details{border-bottom:1px solid #ddddd8;line-height:1.45;padding-top:.25em;padding-bottom:.25em;padding-left:.25em;color:rgba(0,0,0,.6);display:-ms-flexbox;display:-webkit-flex;display:flex;-ms-flex-flow:row wrap;-webkit-flex-flow:row wrap;flex-flow:row wrap}
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#header>h1:first-child+#toc{margin-top:8px;border-top:1px solid #dddddf}
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||||
#header>h1:only-child,body.toc2 #header>h1:nth-last-child(2){border-bottom:1px solid #dddddf;padding-bottom:8px}
|
||||
#header .details{border-bottom:1px solid #dddddf;line-height:1.45;padding-top:.25em;padding-bottom:.25em;padding-left:.25em;color:rgba(0,0,0,.6);display:-ms-flexbox;display:-webkit-flex;display:flex;-ms-flex-flow:row wrap;-webkit-flex-flow:row wrap;flex-flow:row wrap}
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#header .details span:first-child{margin-left:-.125em}
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#header .details span.email a{color:rgba(0,0,0,.85)}
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#header .details br{display:none}
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@@ -153,8 +155,8 @@ p a>code:hover{color:rgba(0,0,0,.9)}
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||||
#header .details br+span#revremark::before{content:"\00a0|\00a0"}
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||||
#header #revnumber{text-transform:capitalize}
|
||||
#header #revnumber::after{content:"\00a0"}
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#content>h1:first-child:not([class]){color:rgba(0,0,0,.85);border-bottom:1px solid #ddddd8;padding-bottom:8px;margin-top:0;padding-top:1rem;margin-bottom:1.25rem}
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#toc{border-bottom:1px solid #efefed;padding-bottom:.5em}
|
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#content>h1:first-child:not([class]){color:rgba(0,0,0,.85);border-bottom:1px solid #dddddf;padding-bottom:8px;margin-top:0;padding-top:1rem;margin-bottom:1.25rem}
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#toc{border-bottom:1px solid #e7e7e9;padding-bottom:.5em}
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#toc>ul{margin-left:.125em}
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#toc ul.sectlevel0>li>a{font-style:italic}
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#toc ul.sectlevel0 ul.sectlevel1{margin:.5em 0}
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@@ -165,13 +167,13 @@ p a>code:hover{color:rgba(0,0,0,.9)}
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#toctitle{color:#7a2518;font-size:1.2em}
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@media screen and (min-width:768px){#toctitle{font-size:1.375em}
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body.toc2{padding-left:15em;padding-right:0}
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#toc.toc2{margin-top:0!important;background-color:#f8f8f7;position:fixed;width:15em;left:0;top:0;border-right:1px solid #efefed;border-top-width:0!important;border-bottom-width:0!important;z-index:1000;padding:1.25em 1em;height:100%;overflow:auto}
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#toc.toc2{margin-top:0!important;background:#f8f8f7;position:fixed;width:15em;left:0;top:0;border-right:1px solid #e7e7e9;border-top-width:0!important;border-bottom-width:0!important;z-index:1000;padding:1.25em 1em;height:100%;overflow:auto}
|
||||
#toc.toc2 #toctitle{margin-top:0;margin-bottom:.8rem;font-size:1.2em}
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#toc.toc2>ul{font-size:.9em;margin-bottom:0}
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#toc.toc2 ul ul{margin-left:0;padding-left:1em}
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#toc.toc2 ul.sectlevel0 ul.sectlevel1{padding-left:0;margin-top:.5em;margin-bottom:.5em}
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body.toc2.toc-right{padding-left:0;padding-right:15em}
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body.toc2.toc-right #toc.toc2{border-right-width:0;border-left:1px solid #efefed;left:auto;right:0}}
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body.toc2.toc-right #toc.toc2{border-right-width:0;border-left:1px solid #e7e7e9;left:auto;right:0}}
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#toc.toc2{width:20em}
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#toc.toc2 #toctitle{font-size:1.375em}
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@@ -181,69 +183,70 @@ body.toc2.toc-right{padding-left:0;padding-right:20em}}
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#content{margin-bottom:.625em}
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.sect1{padding-bottom:.625em}
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@media screen and (min-width:768px){#content{margin-bottom:1.25em}
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.sect1{padding-bottom:1.25em}}
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|
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|
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.audioblock,.imageblock,.literalblock,.listingblock,.stemblock,.videoblock{margin-bottom:1.25em}
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details,.audioblock,.imageblock,.literalblock,.listingblock,.stemblock,.videoblock{margin-bottom:1.25em}
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details>summary:first-of-type{cursor:pointer;display:list-item;outline:none;margin-bottom:.75em}
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table.tableblock #preamble>.sectionbody>.paragraph:first-of-type p{font-size:inherit}
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table.tableblock #preamble>.sectionbody>[class="paragraph"]:first-of-type p{font-size:inherit}
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.exampleblock>.content{border-style:solid;border-width:1px;border-color:#e6e6e6;margin-bottom:1.25em;padding:1.25em;background:#fff;-webkit-border-radius:4px;border-radius:4px}
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.exampleblock>.content>:first-child{margin-top:0}
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.exampleblock>.content>:last-child{margin-bottom:0}
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.sidebarblock{border-style:solid;border-width:1px;border-color:#e0e0dc;margin-bottom:1.25em;padding:1.25em;background:#f8f8f7;-webkit-border-radius:4px;border-radius:4px}
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.sidebarblock{border-style:solid;border-width:1px;border-color:#dbdbd6;margin-bottom:1.25em;padding:1.25em;background:#f3f3f2;-webkit-border-radius:4px;border-radius:4px}
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.sidebarblock>:first-child{margin-top:0}
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.sidebarblock>:last-child{margin-bottom:0}
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.sidebarblock>.content>.title{color:#7a2518;margin-top:0;text-align:center}
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.exampleblock>.content>:last-child>:last-child,.exampleblock>.content .olist>ol>li:last-child>:last-child,.exampleblock>.content .ulist>ul>li:last-child>:last-child,.exampleblock>.content .qlist>ol>li:last-child>:last-child,.sidebarblock>.content>:last-child>:last-child,.sidebarblock>.content .olist>ol>li:last-child>:last-child,.sidebarblock>.content .ulist>ul>li:last-child>:last-child,.sidebarblock>.content .qlist>ol>li:last-child>:last-child{margin-bottom:0}
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.literalblock pre,.listingblock pre:not(.highlight),.listingblock pre[class="highlight"],.listingblock pre[class^="highlight "],.listingblock pre.CodeRay,.listingblock pre.prettyprint{background:#f7f7f8}
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.sidebarblock .literalblock pre,.sidebarblock .listingblock pre:not(.highlight),.sidebarblock .listingblock pre[class="highlight"],.sidebarblock .listingblock pre[class^="highlight "],.sidebarblock .listingblock pre.CodeRay,.sidebarblock .listingblock pre.prettyprint{background:#f2f1f1}
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.literalblock pre,.literalblock pre[class],.listingblock pre,.listingblock pre[class]{-webkit-border-radius:4px;border-radius:4px;word-wrap:break-word;padding:1em;font-size:.8125em}
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.literalblock.output pre{color:#f7f7f8;background-color:rgba(0,0,0,.9)}
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.literalblock pre,.listingblock>.content>pre{-webkit-border-radius:4px;border-radius:4px;word-wrap:break-word;overflow-x:auto;padding:1em;font-size:.8125em}
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@@ -251,13 +254,17 @@ table.pyhltable .linenodiv{background:none!important;padding-right:0!important}
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table.grid-all>tfoot>tr>.tableblock{border-width:1px 1px 0 0}
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@@ -269,8 +276,7 @@ table.grid-all>tbody>tr:last-child>.tableblock,table.grid-all>thead:last-child>t
|
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table.frame-all{border-width:1px}
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table.frame-sides{border-width:0 1px}
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table.stripes-all tr,table.stripes-odd tr:nth-of-type(odd){background:#f8f8f7}
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table.stripes-none tr,table.stripes-odd tr:nth-of-type(even){background:none}
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table.stripes-all tr,table.stripes-odd tr:nth-of-type(odd),table.stripes-even tr:nth-of-type(even),table.stripes-hover tr:hover{background:#f8f8f7}
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th.halign-left,td.halign-left{text-align:left}
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th.halign-right,td.halign-right{text-align:right}
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th.halign-center,td.halign-center{text-align:center}
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@@ -282,7 +288,6 @@ tbody tr th{display:table-cell;line-height:1.6;background:#f7f8f7}
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tbody tr th,tbody tr th p,tfoot tr th,tfoot tr th p{color:rgba(0,0,0,.8);font-weight:bold}
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td>div.verse{white-space:pre}
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ol{margin-left:1.75em}
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ul li ol{margin-left:1.5em}
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dl dd{margin-left:1.125em}
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@@ -313,8 +318,8 @@ td.hdlist1{font-weight:bold;padding-bottom:1.25em}
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.imageblock.thumb,.imageblock.th{border-width:6px}
|
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.imageblock.thumb>.title,.imageblock.th>.title{padding:0 .125em}
|
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@@ -341,37 +346,37 @@ div.unbreakable{page-break-inside:avoid}
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||||
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|
||||
@@ -380,7 +385,7 @@ a span.icon>.fa{cursor:inherit}
|
||||
.admonitionblock td.icon .icon-warning::before{content:"\f071";color:#bf6900}
|
||||
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|
||||
.admonitionblock td.icon .icon-important::before{content:"\f06a";color:#bf0000}
|
||||
.conum[data-value]{display:inline-block;color:#fff!important;background-color:rgba(0,0,0,.8);-webkit-border-radius:100px;border-radius:100px;text-align:center;font-size:.75em;width:1.67em;height:1.67em;line-height:1.67em;font-family:"Open Sans","DejaVu Sans",sans-serif;font-style:normal;font-weight:bold}
|
||||
.conum[data-value]{display:inline-block;color:#fff!important;background:rgba(0,0,0,.8);-webkit-border-radius:100px;border-radius:100px;text-align:center;font-size:.75em;width:1.67em;height:1.67em;line-height:1.67em;font-family:"Open Sans","DejaVu Sans",sans-serif;font-style:normal;font-weight:bold}
|
||||
.conum[data-value] *{color:#fff!important}
|
||||
.conum[data-value]+b{display:none}
|
||||
.conum[data-value]::after{content:attr(data-value)}
|
||||
@@ -393,7 +398,7 @@ p strong,td.content strong,div.footnote strong{letter-spacing:-.005em}
|
||||
p,blockquote,dt,td.content,span.alt{font-size:1.0625rem}
|
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p{margin-bottom:1.25rem}
|
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|
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.exampleblock>.content{background-color:#fffef7;border-color:#e0e0dc;-webkit-box-shadow:0 1px 4px #e0e0dc;box-shadow:0 1px 4px #e0e0dc}
|
||||
.exampleblock>.content{background:#fffef7;border-color:#e0e0dc;-webkit-box-shadow:0 1px 4px #e0e0dc;box-shadow:0 1px 4px #e0e0dc}
|
||||
.print-only{display:none!important}
|
||||
@page{margin:1.25cm .75cm}
|
||||
@media print{*{-webkit-box-shadow:none!important;box-shadow:none!important;text-shadow:none!important}
|
||||
@@ -408,7 +413,7 @@ svg{max-width:100%}
|
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p,blockquote,dt,td.content{font-size:1em;orphans:3;widows:3}
|
||||
h2,h3,#toctitle,.sidebarblock>.content>.title{page-break-after:avoid}
|
||||
#toc,.sidebarblock,.exampleblock>.content{background:none!important}
|
||||
#toc{border-bottom:1px solid #ddddd8!important;padding-bottom:0!important}
|
||||
#toc{border-bottom:1px solid #dddddf!important;padding-bottom:0!important}
|
||||
body.book #header{text-align:center}
|
||||
body.book #header>h1:first-child{border:0!important;margin:2.5em 0 1em}
|
||||
body.book #header .details{border:0!important;display:block;padding:0!important}
|
||||
@@ -440,7 +445,16 @@ body.book #toc,body.book #preamble,body.book h1.sect0,body.book .sect1>h2{page-b
|
||||
<div id="toc" class="toc2">
|
||||
<div id="toctitle">Table of Contents</div>
|
||||
<ul class="sectlevel1">
|
||||
<li><a href="#overview">Overview</a></li>
|
||||
<li><a href="#overview">Overview</a>
|
||||
<ul class="sectlevel2">
|
||||
<li><a href="#overview_description">Description</a></li>
|
||||
<li><a href="#overview_usage_examples">Usage Examples</a></li>
|
||||
<li><a href="#overview_construction_and_assignment">Construction and Assignment</a></li>
|
||||
<li><a href="#overview_inspecting_the_value">Inspecting the Value</a></li>
|
||||
<li><a href="#overview_visitation">Visitation</a></li>
|
||||
<li><a href="#overview_default_construction">Default Construction</a></li>
|
||||
</ul>
|
||||
</li>
|
||||
<li><a href="#reference">Reference</a>
|
||||
<ul class="sectlevel2">
|
||||
<li><a href="#ref_boostvariant2variant_hpp"><boost/variant2/variant.hpp></a>
|
||||
@@ -478,56 +492,372 @@ body.book #toc,body.book #preamble,body.book h1.sect0,body.book .sect1>h2{page-b
|
||||
<div class="sect1">
|
||||
<h2 id="overview">Overview</h2>
|
||||
<div class="sectionbody">
|
||||
<div class="sect2">
|
||||
<h3 id="overview_description">Description</h3>
|
||||
<div class="paragraph">
|
||||
<p>This library implements a type-safe discriminated union (variant) type,
|
||||
<code>variant<T…​></code>, that almost conforms to the C++17 Standard’s
|
||||
<a href="http://en.cppreference.com/w/cpp/utility/variant"><code>std::variant<T…​></code></a>. The
|
||||
main differences between the two are:</p>
|
||||
</div>
|
||||
<div class="ulist">
|
||||
<ul>
|
||||
<li>
|
||||
<p><code>variant<T…​></code> does not have a valueless-by-exception state;</p>
|
||||
</li>
|
||||
<li>
|
||||
<p>A converting constructor from, e.g. <code>variant<int, float></code> to
|
||||
<code>variant<float, double, int></code> is provided as an extension;</p>
|
||||
</li>
|
||||
<li>
|
||||
<p>The reverse operation, going from <code>variant<float, double, int></code> to
|
||||
<code>variant<int, float></code> is provided as the member function <code>subset<U…​></code>.
|
||||
(This operation can throw if the current state of the variant cannot be
|
||||
represented.)</p>
|
||||
</li>
|
||||
<li>
|
||||
<p><code>variant<T…​></code> is not trivial when all contained types are trivial, as
|
||||
mandated by C++17.</p>
|
||||
</li>
|
||||
</ul>
|
||||
<p>This library implements a type-safe discriminated/tagged union type,
|
||||
<code>variant<T…​></code>, that is API-compatible with the C++17 Standard’s
|
||||
<a href="http://en.cppreference.com/w/cpp/utility/variant"><code>std::variant<T…​></code></a>.</p>
|
||||
</div>
|
||||
<div class="paragraph">
|
||||
<p>To avoid the valueless-by-exception state, this implementation falls
|
||||
back to using double storage unless</p>
|
||||
</div>
|
||||
<div class="ulist">
|
||||
<ul>
|
||||
<li>
|
||||
<p>one of the alternatives is the type <code>monostate</code>,</p>
|
||||
</li>
|
||||
<li>
|
||||
<p>one of the alternatives has a nonthrowing default constructor, or</p>
|
||||
</li>
|
||||
<li>
|
||||
<p>all the contained types are nothrow move constructible.</p>
|
||||
</li>
|
||||
</ul>
|
||||
<p>A <code>variant<T1, T2, …​, Tn></code> variable can hold a value of any of the
|
||||
types <code>T1</code>, <code>T2</code>, …​, <code>Tn</code>. For example,
|
||||
<code>variant<int64_t, double, std::string></code> can hold an <code>int64_t</code> value, a
|
||||
<code>double</code> value, or a <code>string</code> value.</p>
|
||||
</div>
|
||||
<div class="paragraph">
|
||||
<p>If the first two bullets don’t hold, but the third does, the variant uses
|
||||
single storage, but <code>emplace</code> constructs a temporary and moves it into place
|
||||
if the construction of the object can throw. In case this is undesirable, one
|
||||
can force <code>emplace</code> into always constructing in-place by adding <code>monostate</code> as
|
||||
one of the alternatives.</p>
|
||||
<p>Such a type is sometimes called a "tagged union", because it’s roughly
|
||||
equivalent to</p>
|
||||
</div>
|
||||
<div class="listingblock">
|
||||
<div class="content">
|
||||
<pre class="highlight"><code>struct V
|
||||
{
|
||||
enum tag { tag_int64_t, tag_double, tag_string };
|
||||
|
||||
tag tag_;
|
||||
|
||||
union
|
||||
{
|
||||
int64_t i_;
|
||||
double d_;
|
||||
std::string s_;
|
||||
};
|
||||
};</code></pre>
|
||||
</div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="sect2">
|
||||
<h3 id="overview_usage_examples">Usage Examples</h3>
|
||||
<div class="paragraph">
|
||||
<p>Variants can be used to represent dynamically-typed values. A configuration
|
||||
file of the form</p>
|
||||
</div>
|
||||
<div class="listingblock">
|
||||
<div class="content">
|
||||
<pre class="highlight"><code>server.host=test.example.com
|
||||
server.port=9174
|
||||
cache.max_load=0.7</code></pre>
|
||||
</div>
|
||||
</div>
|
||||
<div class="paragraph">
|
||||
<p>can be represented as <code>std::map<std::string, variant<int64_t, double,
|
||||
std::string>></code>.</p>
|
||||
</div>
|
||||
<div class="paragraph">
|
||||
<p>Variants can also represent polymorphism. To take a classic example, a
|
||||
polymorphic collection of shapes:</p>
|
||||
</div>
|
||||
<div class="listingblock">
|
||||
<div class="content">
|
||||
<pre class="highlight"><code>#define _USE_MATH_DEFINES
|
||||
#include <iostream>
|
||||
#include <vector>
|
||||
#include <memory>
|
||||
#include <cmath>
|
||||
|
||||
class Shape
|
||||
{
|
||||
public:
|
||||
|
||||
virtual ~Shape() = default;
|
||||
virtual double area() const = 0;
|
||||
};
|
||||
|
||||
class Rectangle: public Shape
|
||||
{
|
||||
private:
|
||||
|
||||
double width_, height_;
|
||||
|
||||
public:
|
||||
|
||||
Rectangle( double width, double height ):
|
||||
width_( width ), height_( height ) {}
|
||||
|
||||
virtual double area() const { return width_ * height_; }
|
||||
};
|
||||
|
||||
class Circle: public Shape
|
||||
{
|
||||
private:
|
||||
|
||||
double radius_;
|
||||
|
||||
public:
|
||||
|
||||
explicit Circle( double radius ): radius_( radius ) {}
|
||||
virtual double area() const { return M_PI * radius_ * radius_; }
|
||||
};
|
||||
|
||||
double total_area( std::vector<std::unique_ptr<Shape>> const & v )
|
||||
{
|
||||
double s = 0.0;
|
||||
|
||||
for( auto const& p: v )
|
||||
{
|
||||
s += p->area();
|
||||
}
|
||||
|
||||
return s;
|
||||
}
|
||||
|
||||
int main()
|
||||
{
|
||||
std::vector<std::unique_ptr<Shape>> v;
|
||||
|
||||
v.push_back( std::unique_ptr<Shape>( new Circle( 1.0 ) ) );
|
||||
v.push_back( std::unique_ptr<Shape>( new Rectangle( 2.0, 3.0 ) ) );
|
||||
|
||||
std::cout << "Total area: " << total_area( v ) << std::endl;
|
||||
}</code></pre>
|
||||
</div>
|
||||
</div>
|
||||
<div class="paragraph">
|
||||
<p>can instead be represented as a collection of <code>variant<Rectangle, Circle></code>
|
||||
values. This requires the possible <code>Shape</code> types be known in advance, as is
|
||||
often the case. In return, we no longer need virtual functions, or to allocate
|
||||
the values on the heap with <code>new Rectangle</code> and <code>new Circle</code>:</p>
|
||||
</div>
|
||||
<div class="listingblock">
|
||||
<div class="content">
|
||||
<pre class="highlight"><code>#define _USE_MATH_DEFINES
|
||||
#include <iostream>
|
||||
#include <vector>
|
||||
#include <cmath>
|
||||
|
||||
#include <boost/variant2/variant.hpp>
|
||||
using namespace boost::variant2;
|
||||
|
||||
struct Rectangle
|
||||
{
|
||||
double width_, height_;
|
||||
double area() const { return width_ * height_; }
|
||||
};
|
||||
|
||||
struct Circle
|
||||
{
|
||||
double radius_;
|
||||
double area() const { return M_PI * radius_ * radius_; }
|
||||
};
|
||||
|
||||
double total_area( std::vector<variant<Rectangle, Circle>> const & v )
|
||||
{
|
||||
double s = 0.0;
|
||||
|
||||
for( auto const& x: v )
|
||||
{
|
||||
s += visit( []( auto const& y ){ return y.area(); }, x );
|
||||
}
|
||||
|
||||
return s;
|
||||
}
|
||||
|
||||
int main()
|
||||
{
|
||||
std::vector<variant<Rectangle, Circle>> v;
|
||||
|
||||
v.push_back( Circle{ 1.0 } );
|
||||
v.push_back( Rectangle{ 2.0, 3.0 } );
|
||||
|
||||
std::cout << "Total area: " << total_area( v ) << std::endl;
|
||||
}</code></pre>
|
||||
</div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="sect2">
|
||||
<h3 id="overview_construction_and_assignment">Construction and Assignment</h3>
|
||||
<div class="paragraph">
|
||||
<p>If we look at the</p>
|
||||
</div>
|
||||
<div class="listingblock">
|
||||
<div class="content">
|
||||
<pre class="highlight"><code> v.push_back( Circle{ 1.0 } );</code></pre>
|
||||
</div>
|
||||
</div>
|
||||
<div class="paragraph">
|
||||
<p>line, we can deduce that <code>variant<Rectangle, Circle></code> can be (implicitly)
|
||||
constructed from <code>Circle</code> (and <code>Rectangle</code>), and indeed it can. It can also
|
||||
be assigned a <code>Circle</code> or a <code>Rectangle</code>:</p>
|
||||
</div>
|
||||
<div class="listingblock">
|
||||
<div class="content">
|
||||
<pre class="highlight"><code>variant<Rectangle, Circle> v = Circle{ 1.0 }; // v holds Circle
|
||||
v = Rectangle{ 2.0, 3.0 }; // v now holds Rectangle</code></pre>
|
||||
</div>
|
||||
</div>
|
||||
<div class="paragraph">
|
||||
<p>If we try to construct <code>variant<int, float></code> from something that is neither
|
||||
<code>int</code> nor <code>float</code>, say, <code>(short)1</code>, the behavior is "as if" the <code>variant</code> has
|
||||
declared two constructors,</p>
|
||||
</div>
|
||||
<div class="listingblock">
|
||||
<div class="content">
|
||||
<pre class="highlight"><code>variant::variant(int x);
|
||||
variant::variant(float x);</code></pre>
|
||||
</div>
|
||||
</div>
|
||||
<div class="paragraph">
|
||||
<p>and the standard overload resolution rules are used to pick the one that will
|
||||
be used. So <code>variant<int, float>((short)1)</code> will hold an <code>int</code>.</p>
|
||||
</div>
|
||||
</div>
|
||||
<div class="sect2">
|
||||
<h3 id="overview_inspecting_the_value">Inspecting the Value</h3>
|
||||
<div class="paragraph">
|
||||
<p>Putting values into a <code>variant</code> is easy, but taking them out is necessarily a
|
||||
bit more convoluted. It’s not possible for <code>variant<int, float></code> to define a
|
||||
member function <code>get() const</code>, because such a function will need its return
|
||||
type fixed at compile time, and whether the correct return type is <code>int</code> or
|
||||
<code>float</code> will only become known at run time.</p>
|
||||
</div>
|
||||
<div class="paragraph">
|
||||
<p>There are a few ways around that. First, there is the accessor member function</p>
|
||||
</div>
|
||||
<div class="listingblock">
|
||||
<div class="content">
|
||||
<pre class="highlight"><code>std::size_t variant::index() const noexcept;</code></pre>
|
||||
</div>
|
||||
</div>
|
||||
<div class="paragraph">
|
||||
<p>that returns the zero-based index of the current type. For <code>variant<int,
|
||||
float></code>, it will return <code>0</code> for <code>int</code> and <code>1</code> for <code>float</code>.</p>
|
||||
</div>
|
||||
<div class="paragraph">
|
||||
<p>Once we have the index, we can use the free function <code>get<N></code> to obtain the
|
||||
value. Since we’re passing the type index to <code>get</code>, it knows what to return.
|
||||
<code>get<0>(v)</code> will return <code>int</code>, and <code>get<1>(v)</code> will return <code>float</code>:</p>
|
||||
</div>
|
||||
<div class="listingblock">
|
||||
<div class="content">
|
||||
<pre class="highlight"><code>void f( variant<int, float> const& v )
|
||||
{
|
||||
switch( v.index() )
|
||||
{
|
||||
case 0:
|
||||
|
||||
// use get<0>(v)
|
||||
break;
|
||||
|
||||
case 1:
|
||||
|
||||
// use get<1>(v)
|
||||
break;
|
||||
|
||||
default:
|
||||
|
||||
assert(false); // never happens
|
||||
}
|
||||
}</code></pre>
|
||||
</div>
|
||||
</div>
|
||||
<div class="paragraph">
|
||||
<p>If we call <code>get<0>(v)</code>, and <code>v.index()</code> is not currently <code>0</code>, an exception
|
||||
(of type <code>bad_variant_access</code>) will be thrown.</p>
|
||||
</div>
|
||||
<div class="paragraph">
|
||||
<p>An alternative approach is to use <code>get<int>(v)</code> or <code>get<float>(v)</code>. This
|
||||
works similarly.</p>
|
||||
</div>
|
||||
<div class="paragraph">
|
||||
<p>Another alternative that avoids the possibility of <code>bad_variant_access</code> is
|
||||
to use <code>get_if</code>. Instead of a reference to the contained value, it returns
|
||||
a pointer to it, returning <code>nullptr</code> to indicate type mismatch. <code>get_if</code>
|
||||
takes a pointer to the <code>variant</code>, so in our example we’ll use something along
|
||||
the following lines:</p>
|
||||
</div>
|
||||
<div class="listingblock">
|
||||
<div class="content">
|
||||
<pre class="highlight"><code>void f( variant<int, float> const& v )
|
||||
{
|
||||
if( int const * p = get_if<int>(&v) )
|
||||
{
|
||||
// use *p
|
||||
}
|
||||
else if( float const * p = get_if<float>(&v) )
|
||||
{
|
||||
// use *p
|
||||
}
|
||||
else
|
||||
{
|
||||
assert(false); // never happens
|
||||
}
|
||||
}</code></pre>
|
||||
</div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="sect2">
|
||||
<h3 id="overview_visitation">Visitation</h3>
|
||||
<div class="paragraph">
|
||||
<p>Last but not least, there’s <code>visit</code>. <code>visit(f, v)</code> calls the a function object
|
||||
<code>f</code> with the value contained in the <code>variant</code> <code>v</code> and returns the result. When
|
||||
<code>v</code> is <code>variant<int, float></code>, it will call <code>f</code> with either an <code>int</code> or a
|
||||
<code>float</code>. The function object must be prepared to accept both.</p>
|
||||
</div>
|
||||
<div class="paragraph">
|
||||
<p>In practice, this can be achieved by having the function take a type that can
|
||||
be passed either <code>int</code> or <code>float</code>, such as <code>double</code>:</p>
|
||||
</div>
|
||||
<div class="listingblock">
|
||||
<div class="content">
|
||||
<pre class="highlight"><code>double f( double x ) { return x; }
|
||||
|
||||
double g( variant<int, float> const& v )
|
||||
{
|
||||
return visit( f, v );
|
||||
}</code></pre>
|
||||
</div>
|
||||
</div>
|
||||
<div class="paragraph">
|
||||
<p>By using a function object with an overloaded <code>operator()</code>:</p>
|
||||
</div>
|
||||
<div class="listingblock">
|
||||
<div class="content">
|
||||
<pre class="highlight"><code>struct F
|
||||
{
|
||||
void operator()(int x) const { /* use x */ }
|
||||
void operator()(float x) const { /* use x */ }
|
||||
};
|
||||
|
||||
void g( variant<int, float> const& v )
|
||||
{
|
||||
visit( F(), v );
|
||||
}</code></pre>
|
||||
</div>
|
||||
</div>
|
||||
<div class="paragraph">
|
||||
<p>Or by using a polymorphic lambda, as we did in our <code>Circle</code>/<code>Rectangle</code>
|
||||
example:</p>
|
||||
</div>
|
||||
<div class="listingblock">
|
||||
<div class="content">
|
||||
<pre class="highlight"><code>void g( variant<int, float> const& v )
|
||||
{
|
||||
visit( [&]( auto const& x ){ std::cout << x << std::endl; }, v );
|
||||
}</code></pre>
|
||||
</div>
|
||||
</div>
|
||||
<div class="paragraph">
|
||||
<p><code>visit</code> can also take more than one <code>variant</code>. <code>visit(f, v1, v2)</code> calls
|
||||
<code>f(x1, x2)</code>, where <code>x1</code> is the value contained in <code>v1</code> and <code>x2</code> is the value
|
||||
in <code>v2</code>.</p>
|
||||
</div>
|
||||
</div>
|
||||
<div class="sect2">
|
||||
<h3 id="overview_default_construction">Default Construction</h3>
|
||||
<div class="paragraph">
|
||||
<p>The default constructor of <code>variant</code> value-initializes the first type in
|
||||
the list. <code>variant<int, float>{}</code> holds <code>0</code> (of type <code>int</code>), and
|
||||
<code>variant<float, int>{}</code> holds <code>0.0f</code>.</p>
|
||||
</div>
|
||||
<div class="paragraph">
|
||||
<p>This is usually the desired behavior. However, in cases such as
|
||||
<code>variant<std::mutex, std::recursive_mutex></code>, one might legitimately wish to
|
||||
avoid constructing a <code>std::mutex</code> by default. A provided type, <code>monostate</code>,
|
||||
can be used as the first type in those scenarios. <code>variant<monostate,
|
||||
std::mutex, std::recursive_mutex></code> will default-construct a <code>monostate</code>,
|
||||
which is basically a no-op, as <code>monostate</code> is effectively an empty <code>struct</code>.</p>
|
||||
</div>
|
||||
</div>
|
||||
</div>
|
||||
</div>
|
||||
@@ -1107,8 +1437,7 @@ there is exactly one occurrence of <code>U</code> in <code>T…​</code
|
||||
<div class="listingblock">
|
||||
<div class="content">
|
||||
<pre class="highlight"><code>constexpr variant& operator=( const variant& r )
|
||||
noexcept( mp_all<std::is_nothrow_copy_constructible<T>...,
|
||||
std::is_nothrow_copy_assignable<T>...>::value );</code></pre>
|
||||
noexcept( mp_all<std::is_nothrow_copy_constructible<T>...>::value );</code></pre>
|
||||
</div>
|
||||
</div>
|
||||
<div class="ulist none">
|
||||
@@ -1122,17 +1451,7 @@ there is exactly one occurrence of <code>U</code> in <code>T…​</code
|
||||
<dl>
|
||||
<dt class="hdlist1">Effects: </dt>
|
||||
<dd>
|
||||
<div class="ulist">
|
||||
<ul>
|
||||
<li>
|
||||
<p>If <code>index() == j</code>, assigns the value contained in <code>r</code> to the value
|
||||
contained in <code>*this</code>.</p>
|
||||
</li>
|
||||
<li>
|
||||
<p>Otherwise, equivalent to <code>emplace<j>(get<j>(r))</code>.</p>
|
||||
</li>
|
||||
</ul>
|
||||
</div>
|
||||
<p><code>emplace<j>(get<j>(r))</code>.</p>
|
||||
</dd>
|
||||
<dt class="hdlist1">Returns: </dt>
|
||||
<dd>
|
||||
@@ -1156,8 +1475,7 @@ contained in <code>*this</code>.</p>
|
||||
<div class="listingblock">
|
||||
<div class="content">
|
||||
<pre class="highlight"><code>constexpr variant& operator=( variant&& r )
|
||||
noexcept( mp_all<std::is_nothrow_move_constructible<T>...,
|
||||
std::is_nothrow_move_assignable<T>...>::value );</code></pre>
|
||||
noexcept( mp_all<std::is_nothrow_move_constructible<T>...>::value );</code></pre>
|
||||
</div>
|
||||
</div>
|
||||
<div class="ulist none">
|
||||
@@ -1171,17 +1489,7 @@ contained in <code>*this</code>.</p>
|
||||
<dl>
|
||||
<dt class="hdlist1">Effects: </dt>
|
||||
<dd>
|
||||
<div class="ulist">
|
||||
<ul>
|
||||
<li>
|
||||
<p>If <code>index() == j</code>, assigns the value contained in <code>std::move(r)</code> to the
|
||||
value contained in <code>*this</code>.</p>
|
||||
</li>
|
||||
<li>
|
||||
<p>Otherwise, equivalent to <code>emplace<j>(get<j>(std::move(r)))</code>.</p>
|
||||
</li>
|
||||
</ul>
|
||||
</div>
|
||||
<p><code>emplace<j>(get<j>(std::move(r)))</code>.</p>
|
||||
</dd>
|
||||
<dt class="hdlist1">Returns: </dt>
|
||||
<dd>
|
||||
@@ -1222,17 +1530,7 @@ alternative <code>Tj</code> which is the type of the contained value after const
|
||||
<dl>
|
||||
<dt class="hdlist1">Effects: </dt>
|
||||
<dd>
|
||||
<div class="ulist">
|
||||
<ul>
|
||||
<li>
|
||||
<p>If <code>index() == j</code>, assigns <code>std::forward<U>(u)</code> to the value contained in
|
||||
<code>*this</code>.</p>
|
||||
</li>
|
||||
<li>
|
||||
<p>Otherwise, equivalent to <code>emplace<j>(std::forward<U>(u))</code>.</p>
|
||||
</li>
|
||||
</ul>
|
||||
</div>
|
||||
<p><code>emplace<j>(std::forward<U>(u))</code>.</p>
|
||||
</dd>
|
||||
<dt class="hdlist1">Returns: </dt>
|
||||
<dd>
|
||||
@@ -1244,8 +1542,7 @@ alternative <code>Tj</code> which is the type of the contained value after const
|
||||
</dd>
|
||||
<dt class="hdlist1">Remarks: </dt>
|
||||
<dd>
|
||||
<p>The expression inside <code>noexcept</code> is <code>std::is_nothrow_constructible_v<Tj, U>
|
||||
&& std::is_nothrow_assignable_v<Tj&, U></code>.
|
||||
<p>The expression inside <code>noexcept</code> is <code>std::is_nothrow_constructible_v<Tj, U&&></code>.
|
||||
This operator does not participate in overload resolution unless</p>
|
||||
<div class="ulist">
|
||||
<ul>
|
||||
@@ -1253,7 +1550,7 @@ This operator does not participate in overload resolution unless</p>
|
||||
<p><code>std::is_same_v<std::remove_cvref_t<T>, variant></code> is <code>false</code>,</p>
|
||||
</li>
|
||||
<li>
|
||||
<p><code>std::is_constructible_v<Tj, U> && std::is_assignable_v<Tj&, U></code> is
|
||||
<p><code>std::is_constructible_v<Tj, U&&> && std::is_assignable_v<Tj&, U&&></code> is
|
||||
<code>true</code>, and</p>
|
||||
</li>
|
||||
<li>
|
||||
@@ -1293,7 +1590,7 @@ above-mentioned set of imaginary functions) is well-formed.</p>
|
||||
<dt class="hdlist1">Remarks: </dt>
|
||||
<dd>
|
||||
<p>This function shall not participate in overload resolution unless
|
||||
<code>std::is_constructible_v<U, A…​></code> is <code>true</code> and <code>U</code> occurs exactly once
|
||||
<code>std::is_constructible_v<U, A&&…​></code> is <code>true</code> and <code>U</code> occurs exactly once
|
||||
in <code>T…​</code>.</p>
|
||||
</dd>
|
||||
</dl>
|
||||
@@ -1323,7 +1620,7 @@ in <code>T…​</code>.</p>
|
||||
<dt class="hdlist1">Remarks: </dt>
|
||||
<dd>
|
||||
<p>This function shall not participate in overload resolution unless
|
||||
<code>std::is_constructible_v<U, std::initializer_list<V>&, A…​></code> is <code>true</code>
|
||||
<code>std::is_constructible_v<U, std::initializer_list<V>&, A&&…​></code> is <code>true</code>
|
||||
and <code>U</code> occurs exactly once in <code>T…​</code>.</p>
|
||||
</dd>
|
||||
</dl>
|
||||
@@ -1346,7 +1643,7 @@ and <code>U</code> occurs exactly once in <code>T…​</code>.</p>
|
||||
<dl>
|
||||
<dt class="hdlist1">Requires: </dt>
|
||||
<dd>
|
||||
<p><code>I < sizeof(T…​)</code>.</p>
|
||||
<p><code>I < sizeof…​(T)</code>.</p>
|
||||
</dd>
|
||||
<dt class="hdlist1">Effects: </dt>
|
||||
<dd>
|
||||
@@ -1361,10 +1658,18 @@ value as if using the expression <code>Ti(std::forward<A>(a)…​
|
||||
<dd>
|
||||
<p>A reference to the new contained value.</p>
|
||||
</dd>
|
||||
<dt class="hdlist1">Throws: </dt>
|
||||
<dd>
|
||||
<p>Nothing unless the initialization of the new contained value throws.</p>
|
||||
</dd>
|
||||
<dt class="hdlist1">Exception Safety: </dt>
|
||||
<dd>
|
||||
<p>Strong. On exception, the contained value is unchanged.</p>
|
||||
</dd>
|
||||
<dt class="hdlist1">Remarks: </dt>
|
||||
<dd>
|
||||
<p>This function shall not participate in overload resolution unless
|
||||
<code>std::is_constructible_v<Ti, A…​></code> is <code>true</code>.</p>
|
||||
<code>std::is_constructible_v<Ti, A&&…​></code> is <code>true</code>.</p>
|
||||
</dd>
|
||||
</dl>
|
||||
</div>
|
||||
@@ -1386,7 +1691,7 @@ value as if using the expression <code>Ti(std::forward<A>(a)…​
|
||||
<dl>
|
||||
<dt class="hdlist1">Requires: </dt>
|
||||
<dd>
|
||||
<p><code>I < sizeof(T…​)</code>.</p>
|
||||
<p><code>I < sizeof…​(T)</code>.</p>
|
||||
</dd>
|
||||
<dt class="hdlist1">Effects: </dt>
|
||||
<dd>
|
||||
@@ -1401,10 +1706,18 @@ value as if using the expression <code>Ti(il, std::forward<A>(a)…
|
||||
<dd>
|
||||
<p>A reference to the new contained value.</p>
|
||||
</dd>
|
||||
<dt class="hdlist1">Throws: </dt>
|
||||
<dd>
|
||||
<p>Nothing unless the initialization of the new contained value throws.</p>
|
||||
</dd>
|
||||
<dt class="hdlist1">Exception Safety: </dt>
|
||||
<dd>
|
||||
<p>Strong. On exception, the contained value is unchanged.</p>
|
||||
</dd>
|
||||
<dt class="hdlist1">Remarks: </dt>
|
||||
<dd>
|
||||
<p>This function shall not participate in overload resolution unless
|
||||
<code>std::is_constructible_v<Ti, std::initializer_list<V>&, A…​></code> is <code>true</code>.</p>
|
||||
<code>std::is_constructible_v<Ti, std::initializer_list<V>&, A&&…​></code> is <code>true</code>.</p>
|
||||
</dd>
|
||||
</dl>
|
||||
</div>
|
||||
@@ -1431,6 +1744,18 @@ value as if using the expression <code>Ti(il, std::forward<A>(a)…
|
||||
</dd>
|
||||
</dl>
|
||||
</div>
|
||||
<div class="admonitionblock note">
|
||||
<table>
|
||||
<tr>
|
||||
<td class="icon">
|
||||
<div class="title">Note</div>
|
||||
</td>
|
||||
<td class="content">
|
||||
This function is provided purely for compatibility with <code>std::variant</code>.
|
||||
</td>
|
||||
</tr>
|
||||
</table>
|
||||
</div>
|
||||
</li>
|
||||
</ul>
|
||||
</div>
|
||||
@@ -2141,12 +2466,13 @@ the <a href="http://www.boost.org/LICENSE_1_0.txt">Boost Software License, Versi
|
||||
</div>
|
||||
<div id="footer">
|
||||
<div id="footer-text">
|
||||
Last updated 2019-02-22 19:16:54 GTBST
|
||||
Last updated 2019-05-12 00:15:41 +0300
|
||||
</div>
|
||||
</div>
|
||||
<style>
|
||||
|
||||
*:not(pre)>code { background: none; color: #600000; }
|
||||
:not(pre):not([class^=L])>code { background: none; color: #600000; }
|
||||
|
||||
</style>
|
||||
</body>
|
||||
|
||||
@@ -1,5 +1,6 @@
|
||||
<style>
|
||||
|
||||
*:not(pre)>code { background: none; color: #600000; }
|
||||
:not(pre):not([class^=L])>code { background: none; color: #600000; }
|
||||
|
||||
</style>
|
||||
|
||||
@@ -1,5 +1,5 @@
|
||||
////
|
||||
Copyright 2018 Peter Dimov
|
||||
Copyright 2018, 2019 Peter Dimov
|
||||
|
||||
Distributed under the Boost Software License, Version 1.0.
|
||||
|
||||
@@ -9,32 +9,327 @@ http://www.boost.org/LICENSE_1_0.txt
|
||||
|
||||
[#overview]
|
||||
# Overview
|
||||
:idprefix:
|
||||
:idprefix: overview_
|
||||
|
||||
This library implements a type-safe discriminated union (variant) type,
|
||||
`variant<T...>`, that almost conforms to the {cpp}17 Standard's
|
||||
http://en.cppreference.com/w/cpp/utility/variant[`std::variant<T...>`]. The
|
||||
main differences between the two are:
|
||||
## Description
|
||||
|
||||
* `variant<T...>` does not have a valueless-by-exception state;
|
||||
* A converting constructor from, e.g. `variant<int, float>` to
|
||||
`variant<float, double, int>` is provided as an extension;
|
||||
* The reverse operation, going from `variant<float, double, int>` to
|
||||
`variant<int, float>` is provided as the member function `subset<U...>`.
|
||||
(This operation can throw if the current state of the variant cannot be
|
||||
represented.)
|
||||
* `variant<T...>` is not trivial when all contained types are trivial, as
|
||||
mandated by {cpp}17.
|
||||
This library implements a type-safe discriminated/tagged union type,
|
||||
`variant<T...>`, that is API-compatible with the {cpp}17 Standard's
|
||||
http://en.cppreference.com/w/cpp/utility/variant[`std::variant<T...>`].
|
||||
|
||||
To avoid the valueless-by-exception state, this implementation falls
|
||||
back to using double storage unless
|
||||
A `variant<T1, T2, ..., Tn>` variable can hold a value of any of the
|
||||
types `T1`, `T2`, ..., `Tn`. For example,
|
||||
`variant<int64_t, double, std::string>` can hold an `int64_t` value, a
|
||||
`double` value, or a `string` value.
|
||||
|
||||
* one of the alternatives is the type `monostate`,
|
||||
* one of the alternatives has a nonthrowing default constructor, or
|
||||
* all the contained types are nothrow move constructible.
|
||||
Such a type is sometimes called a "tagged union", because it's roughly
|
||||
equivalent to
|
||||
|
||||
If the first two bullets don't hold, but the third does, the variant uses
|
||||
single storage, but `emplace` constructs a temporary and moves it into place
|
||||
if the construction of the object can throw. In case this is undesirable, one
|
||||
can force `emplace` into always constructing in-place by adding `monostate` as
|
||||
one of the alternatives.
|
||||
```
|
||||
struct V
|
||||
{
|
||||
enum tag { tag_int64_t, tag_double, tag_string };
|
||||
|
||||
tag tag_;
|
||||
|
||||
union
|
||||
{
|
||||
int64_t i_;
|
||||
double d_;
|
||||
std::string s_;
|
||||
};
|
||||
};
|
||||
```
|
||||
|
||||
## Usage Examples
|
||||
|
||||
Variants can be used to represent dynamically-typed values. A configuration
|
||||
file of the form
|
||||
|
||||
```
|
||||
server.host=test.example.com
|
||||
server.port=9174
|
||||
cache.max_load=0.7
|
||||
```
|
||||
|
||||
can be represented as `std::map<std::string, variant<int64_t, double,
|
||||
std::string>>`.
|
||||
|
||||
Variants can also represent polymorphism. To take a classic example, a
|
||||
polymorphic collection of shapes:
|
||||
|
||||
```
|
||||
#define _USE_MATH_DEFINES
|
||||
#include <iostream>
|
||||
#include <vector>
|
||||
#include <memory>
|
||||
#include <cmath>
|
||||
|
||||
class Shape
|
||||
{
|
||||
public:
|
||||
|
||||
virtual ~Shape() = default;
|
||||
virtual double area() const = 0;
|
||||
};
|
||||
|
||||
class Rectangle: public Shape
|
||||
{
|
||||
private:
|
||||
|
||||
double width_, height_;
|
||||
|
||||
public:
|
||||
|
||||
Rectangle( double width, double height ):
|
||||
width_( width ), height_( height ) {}
|
||||
|
||||
virtual double area() const { return width_ * height_; }
|
||||
};
|
||||
|
||||
class Circle: public Shape
|
||||
{
|
||||
private:
|
||||
|
||||
double radius_;
|
||||
|
||||
public:
|
||||
|
||||
explicit Circle( double radius ): radius_( radius ) {}
|
||||
virtual double area() const { return M_PI * radius_ * radius_; }
|
||||
};
|
||||
|
||||
double total_area( std::vector<std::unique_ptr<Shape>> const & v )
|
||||
{
|
||||
double s = 0.0;
|
||||
|
||||
for( auto const& p: v )
|
||||
{
|
||||
s += p->area();
|
||||
}
|
||||
|
||||
return s;
|
||||
}
|
||||
|
||||
int main()
|
||||
{
|
||||
std::vector<std::unique_ptr<Shape>> v;
|
||||
|
||||
v.push_back( std::unique_ptr<Shape>( new Circle( 1.0 ) ) );
|
||||
v.push_back( std::unique_ptr<Shape>( new Rectangle( 2.0, 3.0 ) ) );
|
||||
|
||||
std::cout << "Total area: " << total_area( v ) << std::endl;
|
||||
}
|
||||
```
|
||||
|
||||
can instead be represented as a collection of `variant<Rectangle, Circle>`
|
||||
values. This requires the possible `Shape` types be known in advance, as is
|
||||
often the case. In return, we no longer need virtual functions, or to allocate
|
||||
the values on the heap with `new Rectangle` and `new Circle`:
|
||||
|
||||
```
|
||||
#define _USE_MATH_DEFINES
|
||||
#include <iostream>
|
||||
#include <vector>
|
||||
#include <cmath>
|
||||
|
||||
#include <boost/variant2/variant.hpp>
|
||||
using namespace boost::variant2;
|
||||
|
||||
struct Rectangle
|
||||
{
|
||||
double width_, height_;
|
||||
double area() const { return width_ * height_; }
|
||||
};
|
||||
|
||||
struct Circle
|
||||
{
|
||||
double radius_;
|
||||
double area() const { return M_PI * radius_ * radius_; }
|
||||
};
|
||||
|
||||
double total_area( std::vector<variant<Rectangle, Circle>> const & v )
|
||||
{
|
||||
double s = 0.0;
|
||||
|
||||
for( auto const& x: v )
|
||||
{
|
||||
s += visit( []( auto const& y ){ return y.area(); }, x );
|
||||
}
|
||||
|
||||
return s;
|
||||
}
|
||||
|
||||
int main()
|
||||
{
|
||||
std::vector<variant<Rectangle, Circle>> v;
|
||||
|
||||
v.push_back( Circle{ 1.0 } );
|
||||
v.push_back( Rectangle{ 2.0, 3.0 } );
|
||||
|
||||
std::cout << "Total area: " << total_area( v ) << std::endl;
|
||||
}
|
||||
```
|
||||
|
||||
## Construction and Assignment
|
||||
|
||||
If we look at the
|
||||
|
||||
```
|
||||
v.push_back( Circle{ 1.0 } );
|
||||
```
|
||||
|
||||
line, we can deduce that `variant<Rectangle, Circle>` can be (implicitly)
|
||||
constructed from `Circle` (and `Rectangle`), and indeed it can. It can also
|
||||
be assigned a `Circle` or a `Rectangle`:
|
||||
|
||||
```
|
||||
variant<Rectangle, Circle> v = Circle{ 1.0 }; // v holds Circle
|
||||
v = Rectangle{ 2.0, 3.0 }; // v now holds Rectangle
|
||||
```
|
||||
|
||||
If we try to construct `variant<int, float>` from something that is neither
|
||||
`int` nor `float`, say, `(short)1`, the behavior is "as if" the `variant` has
|
||||
declared two constructors,
|
||||
|
||||
```
|
||||
variant::variant(int x);
|
||||
variant::variant(float x);
|
||||
```
|
||||
|
||||
and the standard overload resolution rules are used to pick the one that will
|
||||
be used. So `variant<int, float>((short)1)` will hold an `int`.
|
||||
|
||||
## Inspecting the Value
|
||||
|
||||
Putting values into a `variant` is easy, but taking them out is necessarily a
|
||||
bit more convoluted. It's not possible for `variant<int, float>` to define a
|
||||
member function `get() const`, because such a function will need its return
|
||||
type fixed at compile time, and whether the correct return type is `int` or
|
||||
`float` will only become known at run time.
|
||||
|
||||
There are a few ways around that. First, there is the accessor member function
|
||||
|
||||
```
|
||||
std::size_t variant::index() const noexcept;
|
||||
```
|
||||
|
||||
that returns the zero-based index of the current type. For `variant<int,
|
||||
float>`, it will return `0` for `int` and `1` for `float`.
|
||||
|
||||
Once we have the index, we can use the free function `get<N>` to obtain the
|
||||
value. Since we're passing the type index to `get`, it knows what to return.
|
||||
`get<0>(v)` will return `int`, and `get<1>(v)` will return `float`:
|
||||
|
||||
```
|
||||
void f( variant<int, float> const& v )
|
||||
{
|
||||
switch( v.index() )
|
||||
{
|
||||
case 0:
|
||||
|
||||
// use get<0>(v)
|
||||
break;
|
||||
|
||||
case 1:
|
||||
|
||||
// use get<1>(v)
|
||||
break;
|
||||
|
||||
default:
|
||||
|
||||
assert(false); // never happens
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
If we call `get<0>(v)`, and `v.index()` is not currently `0`, an exception
|
||||
(of type `bad_variant_access`) will be thrown.
|
||||
|
||||
An alternative approach is to use `get<int>(v)` or `get<float>(v)`. This
|
||||
works similarly.
|
||||
|
||||
Another alternative that avoids the possibility of `bad_variant_access` is
|
||||
to use `get_if`. Instead of a reference to the contained value, it returns
|
||||
a pointer to it, returning `nullptr` to indicate type mismatch. `get_if`
|
||||
takes a pointer to the `variant`, so in our example we'll use something along
|
||||
the following lines:
|
||||
|
||||
```
|
||||
void f( variant<int, float> const& v )
|
||||
{
|
||||
if( int const * p = get_if<int>(&v) )
|
||||
{
|
||||
// use *p
|
||||
}
|
||||
else if( float const * p = get_if<float>(&v) )
|
||||
{
|
||||
// use *p
|
||||
}
|
||||
else
|
||||
{
|
||||
assert(false); // never happens
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
## Visitation
|
||||
|
||||
Last but not least, there's `visit`. `visit(f, v)` calls the a function object
|
||||
`f` with the value contained in the `variant` `v` and returns the result. When
|
||||
`v` is `variant<int, float>`, it will call `f` with either an `int` or a
|
||||
`float`. The function object must be prepared to accept both.
|
||||
|
||||
In practice, this can be achieved by having the function take a type that can
|
||||
be passed either `int` or `float`, such as `double`:
|
||||
|
||||
```
|
||||
double f( double x ) { return x; }
|
||||
|
||||
double g( variant<int, float> const& v )
|
||||
{
|
||||
return visit( f, v );
|
||||
}
|
||||
```
|
||||
|
||||
By using a function object with an overloaded `operator()`:
|
||||
|
||||
```
|
||||
struct F
|
||||
{
|
||||
void operator()(int x) const { /* use x */ }
|
||||
void operator()(float x) const { /* use x */ }
|
||||
};
|
||||
|
||||
void g( variant<int, float> const& v )
|
||||
{
|
||||
visit( F(), v );
|
||||
}
|
||||
```
|
||||
|
||||
Or by using a polymorphic lambda, as we did in our `Circle`/`Rectangle`
|
||||
example:
|
||||
|
||||
```
|
||||
void g( variant<int, float> const& v )
|
||||
{
|
||||
visit( [&]( auto const& x ){ std::cout << x << std::endl; }, v );
|
||||
}
|
||||
```
|
||||
|
||||
`visit` can also take more than one `variant`. `visit(f, v1, v2)` calls
|
||||
`f(x1, x2)`, where `x1` is the value contained in `v1` and `x2` is the value
|
||||
in `v2`.
|
||||
|
||||
## Default Construction
|
||||
|
||||
The default constructor of `variant` value-initializes the first type in
|
||||
the list. `variant<int, float>{}` holds `0` (of type `int`), and
|
||||
`variant<float, int>{}` holds `0.0f`.
|
||||
|
||||
This is usually the desired behavior. However, in cases such as
|
||||
`variant<std::mutex, std::recursive_mutex>`, one might legitimately wish to
|
||||
avoid constructing a `std::mutex` by default. A provided type, `monostate`,
|
||||
can be used as the first type in those scenarios. `variant<monostate,
|
||||
std::mutex, std::recursive_mutex>` will default-construct a `monostate`,
|
||||
which is basically a no-op, as `monostate` is effectively an empty `struct`.
|
||||
|
||||
@@ -383,24 +383,21 @@ Remarks: :: This function does not participate in overload resolution unless
|
||||
[none]
|
||||
* {blank}
|
||||
+
|
||||
Effects: :: Destroys the currently contained value.
|
||||
Effects: ::
|
||||
Destroys the currently contained value.
|
||||
|
||||
#### Assignment
|
||||
|
||||
```
|
||||
constexpr variant& operator=( const variant& r )
|
||||
noexcept( mp_all<std::is_nothrow_copy_constructible<T>...,
|
||||
std::is_nothrow_copy_assignable<T>...>::value );
|
||||
noexcept( mp_all<std::is_nothrow_copy_constructible<T>...>::value );
|
||||
```
|
||||
[none]
|
||||
* {blank}
|
||||
+
|
||||
Let `j` be `r.index()`.
|
||||
|
||||
Effects: ::
|
||||
- If `index() == j`, assigns the value contained in `r` to the value
|
||||
contained in `*this`.
|
||||
- Otherwise, equivalent to `emplace<j>(get<j>(r))`.
|
||||
Effects: :: `emplace<j>(get<j>(r))`.
|
||||
Returns: :: `*this`.
|
||||
Ensures: :: `index() == r.index()`.
|
||||
Remarks: :: This operator does not participate in overload resolution unless
|
||||
@@ -409,18 +406,14 @@ Remarks: :: This operator does not participate in overload resolution unless
|
||||
|
||||
```
|
||||
constexpr variant& operator=( variant&& r )
|
||||
noexcept( mp_all<std::is_nothrow_move_constructible<T>...,
|
||||
std::is_nothrow_move_assignable<T>...>::value );
|
||||
noexcept( mp_all<std::is_nothrow_move_constructible<T>...>::value );
|
||||
```
|
||||
[none]
|
||||
* {blank}
|
||||
+
|
||||
Let `j` be `r.index()`.
|
||||
|
||||
Effects: ::
|
||||
- If `index() == j`, assigns the value contained in `std::move(r)` to the
|
||||
value contained in `*this`.
|
||||
- Otherwise, equivalent to `emplace<j>(get<j>(std::move(r)))`.
|
||||
Effects: :: `emplace<j>(get<j>(std::move(r)))`.
|
||||
Returns: :: `*this`.
|
||||
Ensures: :: `index() == r.index()`.
|
||||
Remarks: :: This operator does not participate in overload resolution unless
|
||||
@@ -439,18 +432,14 @@ Let `Tj` be a type that is determined as follows: build an imaginary function
|
||||
overload resolution for the expression `FUN(std::forward<U>(u))` defines the
|
||||
alternative `Tj` which is the type of the contained value after construction.
|
||||
|
||||
Effects: ::
|
||||
- If `index() == j`, assigns `std::forward<U>(u)` to the value contained in
|
||||
`*this`.
|
||||
- Otherwise, equivalent to `emplace<j>(std::forward<U>(u))`.
|
||||
Effects: :: `emplace<j>(std::forward<U>(u))`.
|
||||
Returns: :: `*this`.
|
||||
Ensures: :: `index() == j`.
|
||||
Remarks: ::
|
||||
The expression inside `noexcept` is `std::is_nothrow_constructible_v<Tj, U>
|
||||
&& std::is_nothrow_assignable_v<Tj&, U>`.
|
||||
The expression inside `noexcept` is `std::is_nothrow_constructible_v<Tj, U&&>`.
|
||||
This operator does not participate in overload resolution unless
|
||||
- `std::is_same_v<std::remove_cvref_t<T>, variant>` is `false`,
|
||||
- `std::is_constructible_v<Tj, U> && std::is_assignable_v<Tj&, U>` is
|
||||
- `std::is_constructible_v<Tj, U&&> && std::is_assignable_v<Tj&, U&&>` is
|
||||
`true`, and
|
||||
- the expression `FUN(std::forward<U>(u))` (with `FUN` being the
|
||||
above-mentioned set of imaginary functions) is well-formed.
|
||||
@@ -469,7 +458,7 @@ Let `I` be the zero-based index of `U` in `T...`.
|
||||
Effects: :: Equivalent to: `return emplace<I>(std::forward<A>(a)...);`
|
||||
Remarks: ::
|
||||
This function shall not participate in overload resolution unless
|
||||
`std::is_constructible_v<U, A...>` is `true` and `U` occurs exactly once
|
||||
`std::is_constructible_v<U, A&&...>` is `true` and `U` occurs exactly once
|
||||
in `T...`.
|
||||
|
||||
```
|
||||
@@ -484,7 +473,7 @@ Let `I` be the zero-based index of `U` in `T...`.
|
||||
Effects: :: Equivalent to: `return emplace<I>(il, std::forward<A>(a)...);`
|
||||
Remarks: ::
|
||||
This function shall not participate in overload resolution unless
|
||||
`std::is_constructible_v<U, std::initializer_list<V>&, A...>` is `true`
|
||||
`std::is_constructible_v<U, std::initializer_list<V>&, A&&...>` is `true`
|
||||
and `U` occurs exactly once in `T...`.
|
||||
|
||||
|
||||
@@ -496,15 +485,18 @@ template<size_t I, class... A>
|
||||
[none]
|
||||
* {blank}
|
||||
+
|
||||
Requires: :: `I < sizeof(T...)`.
|
||||
Requires: :: `I < sizeof...(T)`.
|
||||
Effects: ::
|
||||
Destroys the currently contained value, then initializes a new contained
|
||||
value as if using the expression `Ti(std::forward<A>(a)...)`.
|
||||
Ensures: :: `index() == I`.
|
||||
Returns: :: A reference to the new contained value.
|
||||
Throws: ::
|
||||
Nothing unless the initialization of the new contained value throws.
|
||||
Exception Safety: :: Strong. On exception, the contained value is unchanged.
|
||||
Remarks: ::
|
||||
This function shall not participate in overload resolution unless
|
||||
`std::is_constructible_v<Ti, A...>` is `true`.
|
||||
`std::is_constructible_v<Ti, A&&...>` is `true`.
|
||||
|
||||
```
|
||||
template<size_t I, class V, class... A>
|
||||
@@ -514,15 +506,18 @@ template<size_t I, class V, class... A>
|
||||
[none]
|
||||
* {blank}
|
||||
+
|
||||
Requires: :: `I < sizeof(T...)`.
|
||||
Requires: :: `I < sizeof...(T)`.
|
||||
Effects: ::
|
||||
Destroys the currently contained value, then initializes a new contained
|
||||
value as if using the expression `Ti(il, std::forward<A>(a)...)`.
|
||||
Ensures: :: `index() == I`.
|
||||
Returns: :: A reference to the new contained value.
|
||||
Throws: ::
|
||||
Nothing unless the initialization of the new contained value throws.
|
||||
Exception Safety: :: Strong. On exception, the contained value is unchanged.
|
||||
Remarks: ::
|
||||
This function shall not participate in overload resolution unless
|
||||
`std::is_constructible_v<Ti, std::initializer_list<V>&, A...>` is `true`.
|
||||
`std::is_constructible_v<Ti, std::initializer_list<V>&, A&&...>` is `true`.
|
||||
|
||||
#### Value Status
|
||||
|
||||
@@ -534,13 +529,16 @@ constexpr bool valueless_by_exception() const noexcept;
|
||||
+
|
||||
Returns: :: `false`.
|
||||
|
||||
NOTE: This function is provided purely for compatibility with `std::variant`.
|
||||
|
||||
```
|
||||
constexpr size_t index() const noexcept;
|
||||
```
|
||||
[none]
|
||||
* {blank}
|
||||
+
|
||||
Returns: :: The zero-based index of the active alternative.
|
||||
Returns: ::
|
||||
The zero-based index of the active alternative.
|
||||
|
||||
#### Swap
|
||||
|
||||
@@ -828,7 +826,8 @@ template<class... T>
|
||||
[none]
|
||||
* {blank}
|
||||
+
|
||||
Returns: :: `w \<= v`.
|
||||
Returns: ::
|
||||
`w \<= v`.
|
||||
|
||||
### visit
|
||||
|
||||
@@ -851,7 +850,8 @@ template<class... T>
|
||||
[none]
|
||||
* {blank}
|
||||
+
|
||||
Effects: :: Equivalent to `v.swap(w)`.
|
||||
Effects: ::
|
||||
Equivalent to `v.swap(w)`.
|
||||
|
||||
### bad_variant_access
|
||||
|
||||
|
||||
@@ -1,259 +0,0 @@
|
||||
#ifndef BOOST_VARIANT2_OUTCOME_HPP_INCLUDED
|
||||
#define BOOST_VARIANT2_OUTCOME_HPP_INCLUDED
|
||||
|
||||
// Copyright 2017 Peter Dimov.
|
||||
//
|
||||
// Distributed under the Boost Software License, Version 1.0.
|
||||
//
|
||||
// See accompanying file LICENSE_1_0.txt or copy at
|
||||
// http://www.boost.org/LICENSE_1_0.txt
|
||||
|
||||
#ifndef BOOST_VARIANT2_VARIANT_HPP_INCLUDED
|
||||
#include <boost/variant2/variant.hpp>
|
||||
#endif
|
||||
#include <system_error>
|
||||
#include <exception>
|
||||
#include <type_traits>
|
||||
#include <cassert>
|
||||
|
||||
//
|
||||
|
||||
namespace boost
|
||||
{
|
||||
namespace variant2
|
||||
{
|
||||
|
||||
enum class outcome_errc
|
||||
{
|
||||
not_initialized
|
||||
};
|
||||
|
||||
class outcome_error_category: public std::error_category
|
||||
{
|
||||
public:
|
||||
|
||||
virtual const char * name() const noexcept
|
||||
{
|
||||
return "boost::variant2::outcome";
|
||||
}
|
||||
|
||||
virtual std::string message( int e ) const
|
||||
{
|
||||
switch( e )
|
||||
{
|
||||
case (int)outcome_errc::not_initialized:
|
||||
|
||||
return "outcome<> not initialized";
|
||||
|
||||
default:
|
||||
|
||||
return "unknown outcome<> error";
|
||||
}
|
||||
}
|
||||
|
||||
static outcome_error_category const & instance()
|
||||
{
|
||||
static outcome_error_category cat;
|
||||
return cat;
|
||||
}
|
||||
};
|
||||
|
||||
std::error_code make_error_code( outcome_errc e )
|
||||
{
|
||||
return std::error_code( static_cast<int>( e ), outcome_error_category::instance() );
|
||||
}
|
||||
|
||||
template<class T> class outcome
|
||||
{
|
||||
private:
|
||||
|
||||
variant<T, std::error_code, std::exception_ptr> v_;
|
||||
|
||||
public:
|
||||
|
||||
// constructors
|
||||
|
||||
constexpr outcome() noexcept: v_( make_error_code( outcome_errc::not_initialized ) )
|
||||
{
|
||||
}
|
||||
|
||||
constexpr outcome( T const& t ): v_( t )
|
||||
{
|
||||
}
|
||||
|
||||
constexpr outcome( T&& t ): v_( std::move(t) )
|
||||
{
|
||||
}
|
||||
|
||||
constexpr outcome( std::error_code const & ec ) noexcept: v_( ec )
|
||||
{
|
||||
}
|
||||
|
||||
constexpr outcome( std::exception_ptr const & ep ) noexcept: v_( ep )
|
||||
{
|
||||
}
|
||||
|
||||
// queries
|
||||
|
||||
constexpr bool has_value() const noexcept
|
||||
{
|
||||
return v_.index() == 0;
|
||||
}
|
||||
|
||||
constexpr bool has_error() const noexcept
|
||||
{
|
||||
return v_.index() == 1;
|
||||
}
|
||||
|
||||
constexpr bool has_exception() const noexcept
|
||||
{
|
||||
return v_.index() == 2;
|
||||
}
|
||||
|
||||
constexpr explicit operator bool() const noexcept
|
||||
{
|
||||
return v_.index() == 0;
|
||||
}
|
||||
|
||||
// checked value access
|
||||
|
||||
constexpr T& value() &
|
||||
{
|
||||
if( has_value() )
|
||||
{
|
||||
return *get_if<0>(&v_);
|
||||
}
|
||||
else
|
||||
{
|
||||
throw std::system_error( *get_if<1>(&v_) );
|
||||
}
|
||||
}
|
||||
|
||||
constexpr T const& value() const&
|
||||
{
|
||||
if( has_value() )
|
||||
{
|
||||
return *get_if<0>(&v_);
|
||||
}
|
||||
else
|
||||
{
|
||||
throw std::system_error( *get_if<1>(&v_) );
|
||||
}
|
||||
}
|
||||
|
||||
constexpr T&& value() &&
|
||||
{
|
||||
return std::move( value() );
|
||||
}
|
||||
|
||||
constexpr T const&& value() const&&
|
||||
{
|
||||
return std::move( value() );
|
||||
}
|
||||
|
||||
// unchecked value access
|
||||
|
||||
T* operator->() noexcept
|
||||
{
|
||||
return get_if<0>(&v_);
|
||||
}
|
||||
|
||||
T const* operator->() const noexcept
|
||||
{
|
||||
return get_if<0>(&v_);
|
||||
}
|
||||
|
||||
T& operator*() & noexcept
|
||||
{
|
||||
T* p = get_if<0>(&v_);
|
||||
|
||||
assert( p != 0 );
|
||||
|
||||
return *p;
|
||||
}
|
||||
|
||||
T const& operator*() const & noexcept
|
||||
{
|
||||
T const* p = get_if<0>(&v_);
|
||||
|
||||
assert( p != 0 );
|
||||
|
||||
return *p;
|
||||
}
|
||||
|
||||
T&& operator*() && noexcept
|
||||
{
|
||||
return std::move(**this);
|
||||
}
|
||||
|
||||
T const&& operator*() const && noexcept
|
||||
{
|
||||
return std::move(**this);
|
||||
}
|
||||
|
||||
// error access
|
||||
|
||||
/*constexpr*/ std::error_code error() const noexcept
|
||||
{
|
||||
if( has_error() )
|
||||
{
|
||||
return *get_if<1>(&v_);
|
||||
}
|
||||
else
|
||||
{
|
||||
return std::error_code();
|
||||
}
|
||||
}
|
||||
|
||||
// exception access
|
||||
|
||||
std::exception_ptr exception() const noexcept
|
||||
{
|
||||
if( has_exception() )
|
||||
{
|
||||
return *get_if<2>(&v_);
|
||||
}
|
||||
else if( has_value() )
|
||||
{
|
||||
return std::exception_ptr();
|
||||
}
|
||||
else
|
||||
{
|
||||
return std::make_exception_ptr( std::system_error( *get_if<1>(&v_) ) );
|
||||
}
|
||||
}
|
||||
|
||||
// setters
|
||||
|
||||
void set_value( T const& t ) noexcept( std::is_nothrow_copy_constructible<T>::value )
|
||||
{
|
||||
v_.emplace<0>( t );
|
||||
}
|
||||
|
||||
void set_value( T&& t ) noexcept( std::is_nothrow_move_constructible<T>::value )
|
||||
{
|
||||
v_.emplace<0>( std::move( t ) );
|
||||
}
|
||||
|
||||
void set_error( std::error_code const & e ) noexcept
|
||||
{
|
||||
v_.emplace<1>( e );
|
||||
}
|
||||
|
||||
void set_exception( std::exception_ptr const & x ) noexcept
|
||||
{
|
||||
v_.emplace<2>( x );
|
||||
}
|
||||
|
||||
// swap
|
||||
|
||||
void swap( outcome& r ) noexcept( noexcept( v_.swap( r.v_ ) ) )
|
||||
{
|
||||
v_.swap( r.v_ );
|
||||
}
|
||||
};
|
||||
|
||||
} // namespace variant2
|
||||
} // namespace boost
|
||||
|
||||
#endif // #ifndef BOOST_VARIANT2_OUTCOME_HPP_INCLUDED
|
||||
@@ -1,226 +0,0 @@
|
||||
#ifndef BOOST_VARIANT2_RESULT_HPP_INCLUDED
|
||||
#define BOOST_VARIANT2_RESULT_HPP_INCLUDED
|
||||
|
||||
// Copyright 2017 Peter Dimov.
|
||||
//
|
||||
// Distributed under the Boost Software License, Version 1.0.
|
||||
//
|
||||
// See accompanying file LICENSE_1_0.txt or copy at
|
||||
// http://www.boost.org/LICENSE_1_0.txt
|
||||
|
||||
#ifndef BOOST_VARIANT2_VARIANT_HPP_INCLUDED
|
||||
#include <boost/variant2/variant.hpp>
|
||||
#endif
|
||||
#include <system_error>
|
||||
#include <type_traits>
|
||||
#include <cassert>
|
||||
|
||||
//
|
||||
|
||||
namespace boost
|
||||
{
|
||||
namespace variant2
|
||||
{
|
||||
|
||||
enum class result_errc
|
||||
{
|
||||
not_initialized
|
||||
};
|
||||
|
||||
class result_error_category: public std::error_category
|
||||
{
|
||||
public:
|
||||
|
||||
virtual const char * name() const noexcept
|
||||
{
|
||||
return "boost::variant2::result";
|
||||
}
|
||||
|
||||
virtual std::string message( int e ) const
|
||||
{
|
||||
switch( e )
|
||||
{
|
||||
case (int)result_errc::not_initialized:
|
||||
|
||||
return "result<> not initialized";
|
||||
|
||||
default:
|
||||
|
||||
return "unknown result<> error";
|
||||
}
|
||||
}
|
||||
|
||||
static result_error_category const & instance()
|
||||
{
|
||||
static result_error_category cat;
|
||||
return cat;
|
||||
}
|
||||
};
|
||||
|
||||
std::error_code make_error_code( result_errc e )
|
||||
{
|
||||
return std::error_code( static_cast<int>( e ), result_error_category::instance() );
|
||||
}
|
||||
|
||||
template<class T> class result
|
||||
{
|
||||
private:
|
||||
|
||||
variant<T, std::error_code> v_;
|
||||
|
||||
public:
|
||||
|
||||
// constructors
|
||||
|
||||
constexpr result() noexcept: v_( make_error_code( result_errc::not_initialized ) )
|
||||
{
|
||||
}
|
||||
|
||||
constexpr result( T const& t ): v_( t )
|
||||
{
|
||||
}
|
||||
|
||||
constexpr result( T&& t ): v_( std::move(t) )
|
||||
{
|
||||
}
|
||||
|
||||
constexpr result( std::error_code const & ec ) noexcept: v_( ec )
|
||||
{
|
||||
}
|
||||
|
||||
// queries
|
||||
|
||||
constexpr bool has_value() const noexcept
|
||||
{
|
||||
return v_.index() == 0;
|
||||
}
|
||||
|
||||
constexpr bool has_error() const noexcept
|
||||
{
|
||||
return v_.index() == 1;
|
||||
}
|
||||
|
||||
constexpr explicit operator bool() const noexcept
|
||||
{
|
||||
return v_.index() == 0;
|
||||
}
|
||||
|
||||
// checked value access
|
||||
|
||||
constexpr T& value() &
|
||||
{
|
||||
if( has_value() )
|
||||
{
|
||||
return *get_if<0>(&v_);
|
||||
}
|
||||
else
|
||||
{
|
||||
throw std::system_error( *get_if<1>(&v_) );
|
||||
}
|
||||
}
|
||||
|
||||
constexpr T const& value() const&
|
||||
{
|
||||
if( has_value() )
|
||||
{
|
||||
return *get_if<0>(&v_);
|
||||
}
|
||||
else
|
||||
{
|
||||
throw std::system_error( *get_if<1>(&v_) );
|
||||
}
|
||||
}
|
||||
|
||||
constexpr T&& value() &&
|
||||
{
|
||||
return std::move( value() );
|
||||
}
|
||||
|
||||
constexpr T const&& value() const&&
|
||||
{
|
||||
return std::move( value() );
|
||||
}
|
||||
|
||||
// unchecked value access
|
||||
|
||||
T* operator->() noexcept
|
||||
{
|
||||
return get_if<0>(&v_);
|
||||
}
|
||||
|
||||
T const* operator->() const noexcept
|
||||
{
|
||||
return get_if<0>(&v_);
|
||||
}
|
||||
|
||||
T& operator*() & noexcept
|
||||
{
|
||||
T* p = get_if<0>(&v_);
|
||||
|
||||
assert( p != 0 );
|
||||
|
||||
return *p;
|
||||
}
|
||||
|
||||
T const& operator*() const & noexcept
|
||||
{
|
||||
T const* p = get_if<0>(&v_);
|
||||
|
||||
assert( p != 0 );
|
||||
|
||||
return *p;
|
||||
}
|
||||
|
||||
T&& operator*() && noexcept
|
||||
{
|
||||
return std::move(**this);
|
||||
}
|
||||
|
||||
T const&& operator*() const && noexcept
|
||||
{
|
||||
return std::move(**this);
|
||||
}
|
||||
|
||||
// error access
|
||||
|
||||
/*constexpr*/ std::error_code error() const noexcept
|
||||
{
|
||||
if( has_error() )
|
||||
{
|
||||
return *get_if<1>(&v_);
|
||||
}
|
||||
else
|
||||
{
|
||||
return std::error_code();
|
||||
}
|
||||
}
|
||||
|
||||
// setters
|
||||
|
||||
void set_value( T const& t ) noexcept( std::is_nothrow_copy_constructible<T>::value )
|
||||
{
|
||||
v_.emplace<0>( t );
|
||||
}
|
||||
|
||||
void set_value( T&& t ) noexcept( std::is_nothrow_move_constructible<T>::value )
|
||||
{
|
||||
v_.emplace<0>( std::move( t ) );
|
||||
}
|
||||
|
||||
void set_error( std::error_code const & e ) noexcept
|
||||
{
|
||||
v_.emplace<1>( e );
|
||||
}
|
||||
|
||||
// swap
|
||||
|
||||
void swap( result& r ) noexcept( noexcept( v_.swap( r.v_ ) ) )
|
||||
{
|
||||
v_.swap( r.v_ );
|
||||
}
|
||||
};
|
||||
|
||||
} // namespace variant2
|
||||
} // namespace boost
|
||||
|
||||
#endif // #ifndef BOOST_VARIANT2_RESULT_HPP_INCLUDED
|
||||
@@ -1,7 +1,7 @@
|
||||
#ifndef BOOST_VARIANT2_VARIANT_HPP_INCLUDED
|
||||
#define BOOST_VARIANT2_VARIANT_HPP_INCLUDED
|
||||
|
||||
// Copyright 2017, 2018 Peter Dimov.
|
||||
// Copyright 2017-2019 Peter Dimov.
|
||||
//
|
||||
// Distributed under the Boost Software License, Version 1.0.
|
||||
//
|
||||
@@ -266,6 +266,10 @@ template<std::size_t I, class... T> struct variant_alternative<I, variant<T...>>
|
||||
|
||||
#endif
|
||||
|
||||
// variant_npos
|
||||
|
||||
constexpr std::size_t variant_npos = ~static_cast<std::size_t>( 0 );
|
||||
|
||||
// holds_alternative
|
||||
|
||||
template<class U, class... T> constexpr bool holds_alternative( variant<T...> const& v ) noexcept
|
||||
@@ -286,7 +290,7 @@ template<std::size_t I, class... T> constexpr variant_alternative_t<I, variant<T
|
||||
{
|
||||
static_assert( I < sizeof...(T), "Index out of bounds" );
|
||||
|
||||
#if !BOOST_WORKAROUND(BOOST_MSVC, < 1920)
|
||||
#if !BOOST_WORKAROUND(BOOST_MSVC, < 1930)
|
||||
|
||||
return (void)( v.index() != I? throw bad_variant_access(): 0 ), std::move( v._get_impl( mp11::mp_size_t<I>() ) );
|
||||
|
||||
@@ -308,7 +312,7 @@ template<std::size_t I, class... T> constexpr variant_alternative_t<I, variant<T
|
||||
{
|
||||
static_assert( I < sizeof...(T), "Index out of bounds" );
|
||||
|
||||
#if !BOOST_WORKAROUND(BOOST_MSVC, < 1920)
|
||||
#if !BOOST_WORKAROUND(BOOST_MSVC, < 1930)
|
||||
|
||||
return (void)( v.index() != I? throw bad_variant_access(): 0 ), std::move( v._get_impl( mp11::mp_size_t<I>() ) );
|
||||
|
||||
@@ -368,7 +372,7 @@ template<class U, class... T> constexpr U&& get(variant<T...>&& v)
|
||||
|
||||
using I = mp11::mp_find<variant<T...>, U>;
|
||||
|
||||
#if !BOOST_WORKAROUND(BOOST_MSVC, < 1920)
|
||||
#if !BOOST_WORKAROUND(BOOST_MSVC, < 1930)
|
||||
|
||||
return (void)( v.index() != I::value? throw bad_variant_access(): 0 ), std::move( v._get_impl( I() ) );
|
||||
|
||||
@@ -395,7 +399,7 @@ template<class U, class... T> constexpr U const&& get(variant<T...> const&& v)
|
||||
|
||||
using I = mp11::mp_find<variant<T...>, U>;
|
||||
|
||||
#if !BOOST_WORKAROUND(BOOST_MSVC, < 1920)
|
||||
#if !BOOST_WORKAROUND(BOOST_MSVC, < 1930)
|
||||
|
||||
return (void)( v.index() != I::value? throw bad_variant_access(): 0 ), std::move( v._get_impl( I() ) );
|
||||
|
||||
@@ -574,7 +578,7 @@ template<class T1, class... T> struct overload<T1, T...>: overload<T...>
|
||||
mp11::mp_identity<T1> operator()(T1) const;
|
||||
};
|
||||
|
||||
#if BOOST_WORKAROUND( BOOST_MSVC, < 1920 )
|
||||
#if BOOST_WORKAROUND( BOOST_MSVC, < 1930 )
|
||||
|
||||
template<class U, class... T> using resolve_overload_type_ = decltype( overload<T...>()(std::declval<U>()) );
|
||||
|
||||
@@ -594,11 +598,8 @@ template<class U, class... T> using resolve_overload_index = mp11::mp_find<mp11:
|
||||
|
||||
// variant_base
|
||||
|
||||
template<class... T> using can_be_valueless = mp11::mp_any<std::is_same<T, monostate>..., std::is_nothrow_default_constructible<T>...>;
|
||||
template<class... T> using valueless_index = mp11::mp_if<mp11::mp_contains<mp11::mp_list<T...>, monostate>, mp11::mp_find<mp11::mp_list<T...>, monostate>, mp11::mp_find_if<mp11::mp_list<T...>, std::is_nothrow_default_constructible>>;
|
||||
|
||||
template<bool is_trivially_destructible, bool is_single_buffered, class... T> struct variant_base_impl; // trivially destructible, single buffered
|
||||
template<class... T> using variant_base = variant_base_impl<mp11::mp_all<std::is_trivially_destructible<T>...>::value, mp11::mp_any<mp11::mp_all<std::is_nothrow_move_constructible<T>...>, can_be_valueless<T...>>::value, T...>;
|
||||
template<bool is_trivially_destructible, bool is_single_buffered, class... T> struct variant_base_impl;
|
||||
template<class... T> using variant_base = variant_base_impl<mp11::mp_all<std::is_trivially_destructible<T>...>::value, mp11::mp_all<std::is_nothrow_move_constructible<T>...>::value, T...>;
|
||||
|
||||
struct none {};
|
||||
|
||||
@@ -645,58 +646,30 @@ template<class... T> struct variant_base_impl<true, true, T...>
|
||||
return st1_.get( mp11::mp_size_t<I+1>() );
|
||||
}
|
||||
|
||||
template<std::size_t J, class U, bool B, class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_true, mp11::mp_bool<B>, A&&... a )
|
||||
template<std::size_t J, class U, class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_true, A&&... a )
|
||||
{
|
||||
static_assert( std::is_nothrow_constructible<U, A&&...>::value, "Logic error: U must be nothrow constructible from A&&..." );
|
||||
|
||||
st1_.emplace( mp11::mp_size_t<J>(), std::forward<A>(a)... );
|
||||
ix_ = J;
|
||||
}
|
||||
|
||||
template<std::size_t J, class U, class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_false, mp11::mp_true, A&&... a )
|
||||
template<std::size_t J, class U, class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_false, A&&... a )
|
||||
{
|
||||
static_assert( std::is_nothrow_move_constructible<U>::value, "Logic error: U must be nothrow move constructible" );
|
||||
|
||||
U tmp( std::forward<A>(a)... );
|
||||
|
||||
st1_.emplace( mp11::mp_size_t<J>(), std::move(tmp) );
|
||||
ix_ = J;
|
||||
}
|
||||
|
||||
template<std::size_t J, class U, class... A> void emplace_impl( mp11::mp_false, mp11::mp_false, A&&... a )
|
||||
{
|
||||
if( can_be_valueless<T...>::value )
|
||||
{
|
||||
std::size_t const K = valueless_index<T...>::value;
|
||||
|
||||
assert( K < sizeof...(T) );
|
||||
|
||||
try
|
||||
{
|
||||
st1_.emplace( mp11::mp_size_t<J>(), std::forward<A>(a)... );
|
||||
ix_ = J;
|
||||
}
|
||||
catch( ... )
|
||||
{
|
||||
st1_.emplace( mp11::mp_size_t<K+1>() );
|
||||
ix_ = K+1;
|
||||
|
||||
throw;
|
||||
}
|
||||
}
|
||||
else
|
||||
{
|
||||
assert( std::is_nothrow_move_constructible<U>::value );
|
||||
|
||||
U tmp( std::forward<A>(a)... );
|
||||
|
||||
st1_.emplace( mp11::mp_size_t<J>(), std::move(tmp) );
|
||||
ix_ = J;
|
||||
}
|
||||
}
|
||||
|
||||
template<std::size_t I, class... A> BOOST_CXX14_CONSTEXPR void emplace( A&&... a )
|
||||
{
|
||||
std::size_t const J = I+1;
|
||||
using U = mp11::mp_at_c<variant<T...>, I>;
|
||||
|
||||
this->emplace_impl<J, U>( std::is_nothrow_constructible<U, A&&...>(), mp11::mp_all<detail::is_trivially_move_constructible<U>, detail::is_trivially_move_assignable<T>...>(), std::forward<A>(a)... );
|
||||
this->emplace_impl<J, U>( std::is_nothrow_constructible<U, A&&...>(), std::forward<A>(a)... );
|
||||
}
|
||||
};
|
||||
|
||||
@@ -841,45 +814,14 @@ template<class... T> struct variant_base_impl<false, true, T...>
|
||||
|
||||
using U = mp11::mp_at_c<variant<T...>, I>;
|
||||
|
||||
if( std::is_nothrow_constructible<U, A...>::value )
|
||||
{
|
||||
_destroy();
|
||||
static_assert( std::is_nothrow_move_constructible<U>::value, "Logic error: U must be nothrow move constructible" );
|
||||
|
||||
st1_.emplace( mp11::mp_size_t<J>(), std::forward<A>(a)... );
|
||||
ix_ = J;
|
||||
}
|
||||
else if( can_be_valueless<T...>::value )
|
||||
{
|
||||
std::size_t const K = valueless_index<T...>::value;
|
||||
U tmp( std::forward<A>(a)... );
|
||||
|
||||
assert( K < sizeof...(T) );
|
||||
_destroy();
|
||||
|
||||
_destroy();
|
||||
|
||||
try
|
||||
{
|
||||
st1_.emplace( mp11::mp_size_t<J>(), std::forward<A>(a)... );
|
||||
ix_ = J;
|
||||
}
|
||||
catch( ... )
|
||||
{
|
||||
st1_.emplace( mp11::mp_size_t<K+1>() );
|
||||
ix_ = K+1;
|
||||
|
||||
throw;
|
||||
}
|
||||
}
|
||||
else
|
||||
{
|
||||
assert( std::is_nothrow_move_constructible<U>::value );
|
||||
|
||||
U tmp( std::forward<A>(a)... );
|
||||
|
||||
_destroy();
|
||||
|
||||
st1_.emplace( mp11::mp_size_t<J>(), std::move(tmp) );
|
||||
ix_ = J;
|
||||
}
|
||||
st1_.emplace( mp11::mp_size_t<J>(), std::move(tmp) );
|
||||
ix_ = J;
|
||||
}
|
||||
};
|
||||
|
||||
@@ -1179,30 +1121,30 @@ public:
|
||||
class Ud = typename std::decay<U>::type,
|
||||
class E1 = typename std::enable_if< !std::is_same<Ud, variant>::value && !detail::is_in_place_index<Ud>::value && !detail::is_in_place_type<Ud>::value >::type,
|
||||
class V = detail::resolve_overload_type<U&&, T...>,
|
||||
class E2 = typename std::enable_if<std::is_constructible<V, U>::value>::type
|
||||
class E2 = typename std::enable_if<std::is_constructible<V, U&&>::value>::type
|
||||
>
|
||||
constexpr variant( U&& u )
|
||||
noexcept( std::is_nothrow_constructible<V, U>::value )
|
||||
noexcept( std::is_nothrow_constructible<V, U&&>::value )
|
||||
: variant_base( detail::resolve_overload_index<U&&, T...>(), std::forward<U>(u) )
|
||||
{
|
||||
}
|
||||
|
||||
template<class U, class... A, class I = mp11::mp_find<variant<T...>, U>, class E = typename std::enable_if<std::is_constructible<U, A...>::value>::type>
|
||||
template<class U, class... A, class I = mp11::mp_find<variant<T...>, U>, class E = typename std::enable_if<std::is_constructible<U, A&&...>::value>::type>
|
||||
constexpr explicit variant( in_place_type_t<U>, A&&... a ): variant_base( I(), std::forward<A>(a)... )
|
||||
{
|
||||
}
|
||||
|
||||
template<class U, class V, class... A, class I = mp11::mp_find<variant<T...>, U>, class E = typename std::enable_if<std::is_constructible<U, std::initializer_list<V>&, A...>::value>::type>
|
||||
template<class U, class V, class... A, class I = mp11::mp_find<variant<T...>, U>, class E = typename std::enable_if<std::is_constructible<U, std::initializer_list<V>&, A&&...>::value>::type>
|
||||
constexpr explicit variant( in_place_type_t<U>, std::initializer_list<V> il, A&&... a ): variant_base( I(), il, std::forward<A>(a)... )
|
||||
{
|
||||
}
|
||||
|
||||
template<std::size_t I, class... A, class E = typename std::enable_if<std::is_constructible<mp11::mp_at_c<variant<T...>, I>, A...>::value>::type>
|
||||
template<std::size_t I, class... A, class E = typename std::enable_if<std::is_constructible<mp11::mp_at_c<variant<T...>, I>, A&&...>::value>::type>
|
||||
constexpr explicit variant( in_place_index_t<I>, A&&... a ): variant_base( mp11::mp_size_t<I>(), std::forward<A>(a)... )
|
||||
{
|
||||
}
|
||||
|
||||
template<std::size_t I, class V, class... A, class E = typename std::enable_if<std::is_constructible<mp11::mp_at_c<variant<T...>, I>, std::initializer_list<V>&, A...>::value>::type>
|
||||
template<std::size_t I, class V, class... A, class E = typename std::enable_if<std::is_constructible<mp11::mp_at_c<variant<T...>, I>, std::initializer_list<V>&, A&&...>::value>::type>
|
||||
constexpr explicit variant( in_place_index_t<I>, std::initializer_list<V> il, A&&... a ): variant_base( mp11::mp_size_t<I>(), il, std::forward<A>(a)... )
|
||||
{
|
||||
}
|
||||
@@ -1226,14 +1168,7 @@ private:
|
||||
|
||||
template<class I> void operator()( I i ) const
|
||||
{
|
||||
if( this_->index() == i )
|
||||
{
|
||||
this_->_get_impl( i ) = r._get_impl( i );
|
||||
}
|
||||
else
|
||||
{
|
||||
this_->variant_base::template emplace<I::value>( r._get_impl( i ) );
|
||||
}
|
||||
this_->variant_base::template emplace<I::value>( r._get_impl( i ) );
|
||||
}
|
||||
};
|
||||
|
||||
@@ -1244,7 +1179,7 @@ public:
|
||||
class E3 = mp11::mp_if<mp11::mp_all<std::is_copy_constructible<T>..., std::is_copy_assignable<T>...>, E1>
|
||||
>
|
||||
BOOST_CXX14_CONSTEXPR variant& operator=( variant const & r )
|
||||
noexcept( mp11::mp_all<std::is_nothrow_copy_constructible<T>..., std::is_nothrow_copy_assignable<T>...>::value )
|
||||
noexcept( mp11::mp_all<std::is_nothrow_copy_constructible<T>...>::value )
|
||||
{
|
||||
mp11::mp_with_index<sizeof...(T)>( r.index(), L3{ this, r } );
|
||||
return *this;
|
||||
@@ -1268,14 +1203,7 @@ private:
|
||||
|
||||
template<class I> void operator()( I i ) const
|
||||
{
|
||||
if( this_->index() == i )
|
||||
{
|
||||
this_->_get_impl( i ) = std::move( r._get_impl( i ) );
|
||||
}
|
||||
else
|
||||
{
|
||||
this_->variant_base::template emplace<I::value>( std::move( r._get_impl( i ) ) );
|
||||
}
|
||||
this_->variant_base::template emplace<I::value>( std::move( r._get_impl( i ) ) );
|
||||
}
|
||||
};
|
||||
|
||||
@@ -1286,7 +1214,7 @@ public:
|
||||
class E3 = mp11::mp_if<mp11::mp_all<std::is_move_constructible<T>..., std::is_move_assignable<T>...>, E1>
|
||||
>
|
||||
variant& operator=( variant && r )
|
||||
noexcept( mp11::mp_all<std::is_nothrow_move_constructible<T>..., std::is_nothrow_move_assignable<T>...>::value )
|
||||
noexcept( mp11::mp_all<std::is_nothrow_move_constructible<T>...>::value )
|
||||
{
|
||||
mp11::mp_with_index<sizeof...(T)>( r.index(), L4{ this, r } );
|
||||
return *this;
|
||||
@@ -1295,29 +1223,20 @@ public:
|
||||
template<class U,
|
||||
class E1 = typename std::enable_if<!std::is_same<typename std::decay<U>::type, variant>::value>::type,
|
||||
class V = detail::resolve_overload_type<U, T...>,
|
||||
class E2 = typename std::enable_if<std::is_assignable<V&, U>::value && std::is_constructible<V, U>::value>::type
|
||||
class E2 = typename std::enable_if<std::is_assignable<V&, U&&>::value && std::is_constructible<V, U&&>::value>::type
|
||||
>
|
||||
BOOST_CXX14_CONSTEXPR variant& operator=( U&& u )
|
||||
noexcept( std::is_nothrow_assignable<V&, U>::value && std::is_nothrow_constructible<V, U>::value )
|
||||
noexcept( std::is_nothrow_constructible<V, U&&>::value )
|
||||
{
|
||||
std::size_t const I = detail::resolve_overload_index<U, T...>::value;
|
||||
|
||||
if( index() == I )
|
||||
{
|
||||
_get_impl( mp11::mp_size_t<I>() ) = std::forward<U>(u);
|
||||
}
|
||||
else
|
||||
{
|
||||
this->template emplace<I>( std::forward<U>(u) );
|
||||
}
|
||||
|
||||
this->template emplace<I>( std::forward<U>(u) );
|
||||
return *this;
|
||||
}
|
||||
|
||||
// modifiers
|
||||
|
||||
template<class U, class... A,
|
||||
class E = typename std::enable_if< mp11::mp_count<variant<T...>, U>::value == 1 && std::is_constructible<U, A...>::value >::type>
|
||||
class E = typename std::enable_if< mp11::mp_count<variant<T...>, U>::value == 1 && std::is_constructible<U, A&&...>::value >::type>
|
||||
BOOST_CXX14_CONSTEXPR U& emplace( A&&... a )
|
||||
{
|
||||
using I = mp11::mp_find<variant<T...>, U>;
|
||||
@@ -1326,7 +1245,7 @@ public:
|
||||
}
|
||||
|
||||
template<class U, class V, class... A,
|
||||
class E = typename std::enable_if< mp11::mp_count<variant<T...>, U>::value == 1 && std::is_constructible<U, std::initializer_list<V>&, A...>::value >::type>
|
||||
class E = typename std::enable_if< mp11::mp_count<variant<T...>, U>::value == 1 && std::is_constructible<U, std::initializer_list<V>&, A&&...>::value >::type>
|
||||
BOOST_CXX14_CONSTEXPR U& emplace( std::initializer_list<V> il, A&&... a )
|
||||
{
|
||||
using I = mp11::mp_find<variant<T...>, U>;
|
||||
@@ -1334,14 +1253,14 @@ public:
|
||||
return _get_impl( I() );
|
||||
}
|
||||
|
||||
template<std::size_t I, class... A, class E = typename std::enable_if<std::is_constructible<mp11::mp_at_c<variant<T...>, I>, A...>::value>::type>
|
||||
template<std::size_t I, class... A, class E = typename std::enable_if<std::is_constructible<mp11::mp_at_c<variant<T...>, I>, A&&...>::value>::type>
|
||||
BOOST_CXX14_CONSTEXPR variant_alternative_t<I, variant<T...>>& emplace( A&&... a )
|
||||
{
|
||||
variant_base::template emplace<I>( std::forward<A>(a)... );
|
||||
return _get_impl( mp11::mp_size_t<I>() );
|
||||
}
|
||||
|
||||
template<std::size_t I, class V, class... A, class E = typename std::enable_if<std::is_constructible<mp11::mp_at_c<variant<T...>, I>, std::initializer_list<V>&, A...>::value>::type>
|
||||
template<std::size_t I, class V, class... A, class E = typename std::enable_if<std::is_constructible<mp11::mp_at_c<variant<T...>, I>, std::initializer_list<V>&, A&&...>::value>::type>
|
||||
BOOST_CXX14_CONSTEXPR variant_alternative_t<I, variant<T...>>& emplace( std::initializer_list<V> il, A&&... a )
|
||||
{
|
||||
variant_base::template emplace<I>( il, std::forward<A>(a)... );
|
||||
@@ -1350,6 +1269,11 @@ public:
|
||||
|
||||
// value status
|
||||
|
||||
constexpr bool valueless_by_exception() const noexcept
|
||||
{
|
||||
return false;
|
||||
}
|
||||
|
||||
using variant_base::index;
|
||||
|
||||
// swap
|
||||
|
||||
16
test/Jamfile
16
test/Jamfile
@@ -1,6 +1,6 @@
|
||||
# Boost.Variant2 Library Test Jamfile
|
||||
#
|
||||
# Copyright 2015-2017 Peter Dimov
|
||||
# Copyright 2015-2019 Peter Dimov
|
||||
#
|
||||
# Distributed under the Boost Software License, Version 1.0.
|
||||
# See accompanying file LICENSE_1_0.txt or copy at
|
||||
@@ -9,7 +9,19 @@
|
||||
import testing ;
|
||||
import ../../config/checks/config : requires ;
|
||||
|
||||
project : requirements [ requires cxx11_variadic_templates cxx11_template_aliases cxx11_decltype cxx11_constexpr ] ;
|
||||
project
|
||||
: default-build
|
||||
|
||||
<warnings>all
|
||||
|
||||
: requirements
|
||||
|
||||
[ requires cxx11_variadic_templates cxx11_template_aliases cxx11_decltype cxx11_constexpr ]
|
||||
|
||||
<toolset>msvc:<warnings-as-errors>on
|
||||
<toolset>gcc:<warnings-as-errors>on
|
||||
<toolset>clang:<warnings-as-errors>on
|
||||
;
|
||||
|
||||
run variant_size.cpp ;
|
||||
run variant_alternative.cpp ;
|
||||
|
||||
@@ -6,6 +6,10 @@
|
||||
// See accompanying file LICENSE_1_0.txt or copy at
|
||||
// http://www.boost.org/LICENSE_1_0.txt
|
||||
|
||||
#if defined(_MSC_VER)
|
||||
# pragma warning( disable: 4702 ) // unreachable code
|
||||
#endif
|
||||
|
||||
#include <boost/variant2/variant.hpp>
|
||||
#include <boost/core/lightweight_test.hpp>
|
||||
#include <stdexcept>
|
||||
|
||||
@@ -6,6 +6,10 @@
|
||||
// See accompanying file LICENSE_1_0.txt or copy at
|
||||
// http://www.boost.org/LICENSE_1_0.txt
|
||||
|
||||
#if defined(_MSC_VER)
|
||||
# pragma warning( disable: 4702 ) // unreachable code
|
||||
#endif
|
||||
|
||||
#include <boost/variant2/variant.hpp>
|
||||
#include <boost/core/lightweight_test.hpp>
|
||||
#include <stdexcept>
|
||||
|
||||
@@ -6,6 +6,10 @@
|
||||
// See accompanying file LICENSE_1_0.txt or copy at
|
||||
// http://www.boost.org/LICENSE_1_0.txt
|
||||
|
||||
#if defined(_MSC_VER)
|
||||
# pragma warning( disable: 4702 ) // unreachable code
|
||||
#endif
|
||||
|
||||
#include <boost/variant2/variant.hpp>
|
||||
#include <boost/core/lightweight_test.hpp>
|
||||
#include <stdexcept>
|
||||
|
||||
@@ -57,6 +57,21 @@ STATIC_ASSERT( !std::is_nothrow_move_constructible<X2>::value );
|
||||
STATIC_ASSERT( !std::is_nothrow_copy_assignable<X2>::value );
|
||||
STATIC_ASSERT( !std::is_nothrow_move_assignable<X2>::value );
|
||||
|
||||
struct Y1
|
||||
{
|
||||
};
|
||||
|
||||
struct Y2
|
||||
{
|
||||
~Y2() {}
|
||||
};
|
||||
|
||||
struct Guard
|
||||
{
|
||||
explicit Guard(int) {}
|
||||
Guard(Guard&&) = delete;
|
||||
};
|
||||
|
||||
int main()
|
||||
{
|
||||
{
|
||||
@@ -165,5 +180,15 @@ int main()
|
||||
BOOST_TEST_EQ( get<0>(v).v, 4 );
|
||||
}
|
||||
|
||||
{
|
||||
variant<Y1, Guard> v;
|
||||
v.emplace<Guard>( 1 );
|
||||
}
|
||||
|
||||
{
|
||||
variant<Y2, Guard> v;
|
||||
v.emplace<Guard>( 1 );
|
||||
}
|
||||
|
||||
return boost::report_errors();
|
||||
}
|
||||
|
||||
@@ -6,6 +6,10 @@
|
||||
// See accompanying file LICENSE_1_0.txt or copy at
|
||||
// http://www.boost.org/LICENSE_1_0.txt
|
||||
|
||||
#if defined(_MSC_VER)
|
||||
# pragma warning( disable: 4702 ) // unreachable code
|
||||
#endif
|
||||
|
||||
#include <boost/variant2/variant.hpp>
|
||||
#include <boost/core/lightweight_test.hpp>
|
||||
#include <stdexcept>
|
||||
|
||||
@@ -6,6 +6,10 @@
|
||||
// See accompanying file LICENSE_1_0.txt or copy at
|
||||
// http://www.boost.org/LICENSE_1_0.txt
|
||||
|
||||
#if defined(_MSC_VER)
|
||||
# pragma warning( disable: 4702 ) // unreachable code
|
||||
#endif
|
||||
|
||||
#include <boost/variant2/variant.hpp>
|
||||
#include <boost/core/lightweight_test.hpp>
|
||||
#include <stdexcept>
|
||||
|
||||
@@ -6,6 +6,10 @@
|
||||
// See accompanying file LICENSE_1_0.txt or copy at
|
||||
// http://www.boost.org/LICENSE_1_0.txt
|
||||
|
||||
#if defined(_MSC_VER)
|
||||
# pragma warning( disable: 4702 ) // unreachable code
|
||||
#endif
|
||||
|
||||
#include <boost/variant2/variant.hpp>
|
||||
#include <boost/core/lightweight_test.hpp>
|
||||
#include <boost/core/lightweight_test_trait.hpp>
|
||||
|
||||
@@ -6,6 +6,10 @@
|
||||
// See accompanying file LICENSE_1_0.txt or copy at
|
||||
// http://www.boost.org/LICENSE_1_0.txt
|
||||
|
||||
#if defined(_MSC_VER)
|
||||
# pragma warning( disable: 4702 ) // unreachable code
|
||||
#endif
|
||||
|
||||
#include <boost/variant2/variant.hpp>
|
||||
#include <boost/core/lightweight_test.hpp>
|
||||
#include <type_traits>
|
||||
@@ -111,8 +115,8 @@ int main()
|
||||
}
|
||||
catch( std::exception const& )
|
||||
{
|
||||
// basic guarantee; X1 is nothrow default-constructible
|
||||
BOOST_TEST_EQ( v.index(), 1 );
|
||||
// strong guarantee
|
||||
BOOST_TEST_EQ( v.index(), 0 );
|
||||
}
|
||||
}
|
||||
|
||||
@@ -128,8 +132,8 @@ int main()
|
||||
}
|
||||
catch( std::exception const& )
|
||||
{
|
||||
// basic guarantee; X1 is nothrow default-constructible
|
||||
BOOST_TEST_EQ( v.index(), 0 );
|
||||
// strong guarantee
|
||||
BOOST_TEST_EQ( v.index(), 1 );
|
||||
}
|
||||
}
|
||||
|
||||
@@ -145,8 +149,8 @@ int main()
|
||||
}
|
||||
catch( std::exception const& )
|
||||
{
|
||||
// basic guarantee; monostate
|
||||
BOOST_TEST_EQ( v.index(), 2 );
|
||||
// strong guarantee
|
||||
BOOST_TEST_EQ( v.index(), 0 );
|
||||
}
|
||||
}
|
||||
|
||||
@@ -162,8 +166,8 @@ int main()
|
||||
}
|
||||
catch( std::exception const& )
|
||||
{
|
||||
// basic guarantee; monostate
|
||||
BOOST_TEST_EQ( v.index(), 2 );
|
||||
// strong guarantee
|
||||
BOOST_TEST_EQ( v.index(), 1 );
|
||||
}
|
||||
}
|
||||
|
||||
@@ -179,8 +183,8 @@ int main()
|
||||
}
|
||||
catch( std::exception const& )
|
||||
{
|
||||
// basic guarantee; X1 is nothrow default-constructible
|
||||
BOOST_TEST_EQ( v.index(), 2 );
|
||||
// strong guarantee
|
||||
BOOST_TEST_EQ( v.index(), 0 );
|
||||
}
|
||||
}
|
||||
|
||||
@@ -196,8 +200,8 @@ int main()
|
||||
}
|
||||
catch( std::exception const& )
|
||||
{
|
||||
// basic guarantee; monostate
|
||||
BOOST_TEST_EQ( v.index(), 3 );
|
||||
// strong guarantee
|
||||
BOOST_TEST_EQ( v.index(), 0 );
|
||||
}
|
||||
}
|
||||
|
||||
@@ -230,18 +234,8 @@ int main()
|
||||
}
|
||||
catch( std::exception const& )
|
||||
{
|
||||
// X3 is not v2d::trivially_move_assignable on libstdc++ 4.x
|
||||
|
||||
if( v2d::is_trivially_move_assignable<X3>::value )
|
||||
{
|
||||
// all trivially destructible and move-assignable, no change
|
||||
BOOST_TEST_EQ( v.index(), 0 );
|
||||
}
|
||||
else
|
||||
{
|
||||
// basic guarantee; X1 is nothrow default-constructible
|
||||
BOOST_TEST_EQ( v.index(), 1 );
|
||||
}
|
||||
// strong guarantee
|
||||
BOOST_TEST_EQ( v.index(), 0 );
|
||||
}
|
||||
}
|
||||
|
||||
@@ -257,18 +251,8 @@ int main()
|
||||
}
|
||||
catch( std::exception const& )
|
||||
{
|
||||
// X3 is not v2d::trivially_move_assignable on libstdc++ 4.x
|
||||
|
||||
if( v2d::is_trivially_move_assignable<X3>::value )
|
||||
{
|
||||
// all trivially destructible and move-assignable, no change
|
||||
BOOST_TEST_EQ( v.index(), 0 );
|
||||
}
|
||||
else
|
||||
{
|
||||
// basic guarantee; monostate
|
||||
BOOST_TEST_EQ( v.index(), 2 );
|
||||
}
|
||||
// strong guarantee
|
||||
BOOST_TEST_EQ( v.index(), 0 );
|
||||
}
|
||||
}
|
||||
|
||||
|
||||
Reference in New Issue
Block a user