<!DOCTYPE html>

<html lang="en">

<head>
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=no">
    <meta name="apple-mobile-web-app-capable" content="yes">
    <meta name="apple-mobile-web-app-status-bar-style" content="black">
    <meta name="mobile-web-app-capable" content="yes">
    <title>
        invoke_r - HackMD
    </title>
    <link rel="icon" type="image/png" href="https://hackmd.io/favicon.png">
    <link rel="apple-touch-icon" href="https://hackmd.io/apple-touch-icon.png">

    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.7/css/bootstrap.min.css" integrity="sha256-916EbMg70RQy9LHiGkXzG8hSg9EdNy97GazNG/aiY1w=" crossorigin="anonymous" />
    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css" integrity="sha256-eZrrJcwDc/3uDhsdt61sL2oOBY362qM3lon1gyExkL0=" crossorigin="anonymous" />
    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/ionicons/2.0.1/css/ionicons.min.css" integrity="sha256-3iu9jgsy9TpTwXKb7bNQzqWekRX7pPK+2OLj3R922fo=" crossorigin="anonymous" />
    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/octicons/3.5.0/octicons.min.css" integrity="sha256-QiWfLIsCT02Sdwkogf6YMiQlj4NE84MKkzEMkZnMGdg=" crossorigin="anonymous" />
    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/prism/1.5.1/themes/prism.min.css" integrity="sha256-vtR0hSWRc3Tb26iuN2oZHt3KRUomwTufNIf5/4oeCyg=" crossorigin="anonymous" />
    <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/@hackmd/emojify.js@2.1.0/dist/css/basic/emojify.min.css" integrity="sha256-UOrvMOsSDSrW6szVLe8ZDZezBxh5IoIfgTwdNDgTjiU=" crossorigin="anonymous" />
    <style>
        @import url(https://fonts.googleapis.com/css?family=Roboto:300,300i,400,400i,500,500i|Source+Code+Pro:300,400,500|Source+Sans+Pro:300,300i,400,400i,600,600i|Source+Serif+Pro&subset=latin-ext);.hljs{display:block;background:#fff;padding:.5em;color:#333;overflow-x:auto}.hljs-comment,.hljs-meta{color:#969896}.hljs-emphasis,.hljs-quote,.hljs-string,.hljs-strong,.hljs-template-variable,.hljs-variable{color:#df5000}.hljs-keyword,.hljs-selector-tag,.hljs-type{color:#a71d5d}.hljs-attribute,.hljs-bullet,.hljs-literal,.hljs-number,.hljs-symbol{color:#0086b3}.hljs-built_in,.hljs-builtin-name{color:#005cc5}.hljs-name,.hljs-section{color:#63a35c}.hljs-tag{color:#333}.hljs-attr,.hljs-selector-attr,.hljs-selector-class,.hljs-selector-id,.hljs-selector-pseudo,.hljs-title{color:#795da3}.hljs-addition{color:#55a532;background-color:#eaffea}.hljs-deletion{color:#bd2c00;background-color:#ffecec}.hljs-link{text-decoration:underline}.markdown-body{font-size:16px;line-height:1.5;word-wrap:break-word}.markdown-body:after,.markdown-body:before{display:table;content:""}.markdown-body:after{clear:both}.markdown-body>:first-child{margin-top:0!important}.markdown-body>:last-child{margin-bottom:0!important}.markdown-body a:not([href]){color:inherit;text-decoration:none}.markdown-body .absent{color:#c00}.markdown-body .anchor{float:left;padding-right:4px;margin-left:-20px;line-height:1}.markdown-body .anchor:focus{outline:none}.markdown-body blockquote,.markdown-body dl,.markdown-body ol,.markdown-body p,.markdown-body pre,.markdown-body table,.markdown-body ul{margin-top:0;margin-bottom:16px}.markdown-body hr{height:.25em;padding:0;margin:24px 0;background-color:#e7e7e7;border:0}.markdown-body blockquote{font-size:16px;padding:0 1em;color:#777;border-left:.25em solid #ddd}.markdown-body blockquote>:first-child{margin-top:0}.markdown-body blockquote>:last-child{margin-bottom:0}.markdown-body kbd,.popover kbd{display:inline-block;padding:3px 5px;font-size:11px;line-height:10px;color:#555;vertical-align:middle;background-color:#fcfcfc;border:1px solid #ccc;border-bottom-color:#bbb;border-radius:3px;box-shadow:inset 0 -1px 0 #bbb}.markdown-body .loweralpha{list-style-type:lower-alpha}.markdown-body h1,.markdown-body h2,.markdown-body h3,.markdown-body h4,.markdown-body h5,.markdown-body h6{margin-top:24px;margin-bottom:16px;font-weight:600;line-height:1.25}.markdown-body h1 .octicon-link,.markdown-body h2 .octicon-link,.markdown-body h3 .octicon-link,.markdown-body h4 .octicon-link,.markdown-body h5 .octicon-link,.markdown-body h6 .octicon-link{color:#000;vertical-align:middle;visibility:hidden}.markdown-body h1:hover .anchor,.markdown-body h2:hover .anchor,.markdown-body h3:hover .anchor,.markdown-body h4:hover .anchor,.markdown-body h5:hover .anchor,.markdown-body h6:hover .anchor{text-decoration:none}.markdown-body h1:hover .anchor .octicon-link,.markdown-body h2:hover .anchor .octicon-link,.markdown-body h3:hover .anchor .octicon-link,.markdown-body h4:hover .anchor .octicon-link,.markdown-body h5:hover .anchor .octicon-link,.markdown-body h6:hover .anchor .octicon-link{visibility:visible}.markdown-body h1 code,.markdown-body h1 tt,.markdown-body h2 code,.markdown-body h2 tt,.markdown-body h3 code,.markdown-body h3 tt,.markdown-body h4 code,.markdown-body h4 tt,.markdown-body h5 code,.markdown-body h5 tt,.markdown-body h6 code,.markdown-body h6 tt{font-size:inherit}.markdown-body h1{font-size:2em}.markdown-body h1,.markdown-body h2{padding-bottom:.3em;border-bottom:1px solid #eee}.markdown-body h2{font-size:1.5em}.markdown-body h3{font-size:1.25em}.markdown-body h4{font-size:1em}.markdown-body h5{font-size:.875em}.markdown-body h6{font-size:.85em;color:#777}.markdown-body ol,.markdown-body ul{padding-left:2em}.markdown-body ol.no-list,.markdown-body ul.no-list{padding:0;list-style-type:none}.markdown-body ol ol,.markdown-body ol ul,.markdown-body ul ol,.markdown-body ul ul{margin-top:0;margin-bottom:0}.markdown-body li>p{margin-top:16px}.markdown-body li+li{padding-top:.25em}.markdown-body dl{padding:0}.markdown-body dl dt{padding:0;margin-top:16px;font-size:1em;font-style:italic;font-weight:700}.markdown-body dl dd{padding:0 16px;margin-bottom:16px}.markdown-body table{display:block;width:100%;overflow:auto;word-break:normal;word-break:keep-all}.markdown-body table th{font-weight:700}.markdown-body table td,.markdown-body table th{padding:6px 13px;border:1px solid #ddd}.markdown-body table tr{background-color:#fff;border-top:1px solid #ccc}.markdown-body table tr:nth-child(2n){background-color:#f8f8f8}.markdown-body img{max-width:100%;box-sizing:content-box;background-color:#fff}.markdown-body img[align=right]{padding-left:20px}.markdown-body img[align=left]{padding-right:20px}.markdown-body .emoji{max-width:none;vertical-align:text-top;background-color:transparent}.markdown-body span.frame{display:block;overflow:hidden}.markdown-body span.frame>span{display:block;float:left;width:auto;padding:7px;margin:13px 0 0;overflow:hidden;border:1px solid #ddd}.markdown-body span.frame span img{display:block;float:left}.markdown-body span.frame span span{display:block;padding:5px 0 0;clear:both;color:#333}.markdown-body span.align-center{display:block;overflow:hidden;clear:both}.markdown-body span.align-center>span{display:block;margin:13px auto 0;overflow:hidden;text-align:center}.markdown-body span.align-center span img{margin:0 auto;text-align:center}.markdown-body span.align-right{display:block;overflow:hidden;clear:both}.markdown-body span.align-right>span{display:block;margin:13px 0 0;overflow:hidden;text-align:right}.markdown-body span.align-right span img{margin:0;text-align:right}.markdown-body span.float-left{display:block;float:left;margin-right:13px;overflow:hidden}.markdown-body span.float-left span{margin:13px 0 0}.markdown-body span.float-right{display:block;float:right;margin-left:13px;overflow:hidden}.markdown-body span.float-right>span{display:block;margin:13px auto 0;overflow:hidden;text-align:right}.markdown-body code,.markdown-body tt{padding:0;padding-top:.2em;padding-bottom:.2em;margin:0;font-size:85%;background-color:rgba(0,0,0,.04);border-radius:3px}.markdown-body code:after,.markdown-body code:before,.markdown-body tt:after,.markdown-body tt:before{letter-spacing:-.2em;content:"\00a0"}.markdown-body code br,.markdown-body tt br{display:none}.markdown-body del code{text-decoration:inherit}.markdown-body pre{word-wrap:normal}.markdown-body pre>code{padding:0;margin:0;font-size:100%;word-break:normal;white-space:pre;background:transparent;border:0}.markdown-body .highlight{margin-bottom:16px}.markdown-body .highlight pre{margin-bottom:0;word-break:normal}.markdown-body .highlight pre,.markdown-body pre{padding:16px;overflow:auto;font-size:85%;line-height:1.45;background-color:#f7f7f7;border-radius:3px}.markdown-body pre code,.markdown-body pre tt{display:inline;max-width:auto;padding:0;margin:0;overflow:visible;line-height:inherit;word-wrap:normal;background-color:transparent;border:0}.markdown-body pre code:after,.markdown-body pre code:before,.markdown-body pre tt:after,.markdown-body pre tt:before{content:normal}.markdown-body .csv-data td,.markdown-body .csv-data th{padding:5px;overflow:hidden;font-size:12px;line-height:1;text-align:left;white-space:nowrap}.markdown-body .csv-data .blob-line-num{padding:10px 8px 9px;text-align:right;background:#fff;border:0}.markdown-body .csv-data tr{border-top:0}.markdown-body .csv-data th{font-weight:700;background:#f8f8f8;border-top:0}.news .alert .markdown-body blockquote{padding:0 0 0 40px;border:0 none}.activity-tab .news .alert .commits,.activity-tab .news .markdown-body blockquote{padding-left:0}.task-list-item{list-style-type:none}.task-list-item label{font-weight:400}.task-list-item.enabled label{cursor:pointer}.task-list-item+.task-list-item{margin-top:3px}.task-list-item-checkbox{float:left;margin:.31em 0 .2em -1.3em!important;vertical-align:middle;cursor:default!important}.markdown-body{padding-top:40px;padding-bottom:40px;max-width:758px;overflow:visible!important;position:relative}.markdown-body .emoji{vertical-align:top}.markdown-body pre{border:inherit!important}.markdown-body code{color:inherit!important}.markdown-body pre code .wrapper{display:-moz-inline-flex;display:-ms-inline-flex;display:-o-inline-flex;display:inline-flex}.markdown-body pre code .gutter{float:left;overflow:hidden;-webkit-user-select:none;user-select:none}.markdown-body pre code .gutter.linenumber{text-align:right;position:relative;display:inline-block;cursor:default;z-index:4;padding:0 8px 0 0;min-width:20px;box-sizing:content-box;color:#afafaf!important;border-right:3px solid #6ce26c!important}.markdown-body pre code .gutter.linenumber>span:before{content:attr(data-linenumber)}.markdown-body pre code .code{float:left;margin:0 0 0 16px}.markdown-body .gist .line-numbers{border-left:none;border-top:none;border-bottom:none}.markdown-body .gist .line-data{border:none}.markdown-body .gist table{border-spacing:0;border-collapse:inherit!important}.markdown-body code[data-gist-id]{background:none;padding:0}.markdown-body code[data-gist-id]:after,.markdown-body code[data-gist-id]:before{content:""}.markdown-body code[data-gist-id] .blob-num{border:unset}.markdown-body code[data-gist-id] table{overflow:unset;margin-bottom:unset}.markdown-body code[data-gist-id] table tr{background:unset}.markdown-body[dir=rtl] pre{direction:ltr}.markdown-body[dir=rtl] code{direction:ltr;unicode-bidi:embed}.markdown-body .alert>p{margin-bottom:0}.markdown-body pre.abc,.markdown-body pre.flow-chart,.markdown-body pre.graphviz,.markdown-body pre.mermaid,.markdown-body pre.sequence-diagram,.markdown-body pre.vega{text-align:center;background-color:inherit;border-radius:0;white-space:inherit;overflow:visible}.markdown-body pre.abc>code,.markdown-body pre.flow-chart>code,.markdown-body pre.graphviz>code,.markdown-body pre.mermaid>code,.markdown-body pre.sequence-diagram>code,.markdown-body pre.vega>code{text-align:left}.markdown-body pre.abc>svg,.markdown-body pre.flow-chart>svg,.markdown-body pre.graphviz>svg,.markdown-body pre.mermaid>svg,.markdown-body pre.sequence-diagram>svg,.markdown-body pre.vega>svg{max-width:100%;height:100%}.markdown-body pre>code.wrap{white-space:pre-wrap;white-space:-moz-pre-wrap;white-space:-pre-wrap;white-space:-o-pre-wrap;word-wrap:break-word}.markdown-body .alert>p,.markdown-body .alert>ul{margin-bottom:0}.markdown-body summary{display:list-item}.markdown-body summary:focus{outline:none}.markdown-body details summary{cursor:pointer}.markdown-body details:not([open])>:not(summary){display:none}.markdown-body figure{margin:1em 40px}.markdown-body .mark,.markdown-body mark{background-color:#fff1a7}.vimeo,.youtube{cursor:pointer;display:table;text-align:center;background-position:50%;background-repeat:no-repeat;background-size:contain;background-color:#000;overflow:hidden}.vimeo,.youtube{position:relative;width:100%}.youtube{padding-bottom:56.25%}.vimeo img{width:100%;object-fit:contain;z-index:0}.youtube img{object-fit:cover;z-index:0}.vimeo iframe,.youtube iframe,.youtube img{width:100%;height:100%;position:absolute;top:0;left:0}.vimeo iframe,.youtube iframe{vertical-align:middle;z-index:1}.vimeo .icon,.youtube .icon{position:absolute;height:auto;width:auto;top:50%;left:50%;transform:translate(-50%,-50%);color:#fff;opacity:.3;transition:opacity .2s;z-index:0}.vimeo:hover .icon,.youtube:hover .icon{opacity:.6;transition:opacity .2s}.slideshare .inner,.speakerdeck .inner{position:relative;width:100%}.slideshare .inner iframe,.speakerdeck .inner iframe{position:absolute;top:0;bottom:0;left:0;right:0;width:100%;height:100%}.MJX_Assistive_MathML{display:none}#MathJax_Message{z-index:1000!important}.ui-infobar{position:relative;z-index:2;max-width:760px;margin:25px auto -25px;color:#777}.toc .invisable-node{list-style-type:none}.ui-toc{position:fixed;bottom:20px;z-index:998}.ui-toc.both-mode{margin-left:8px}.ui-toc.both-mode .ui-toc-label{height:40px;padding:10px 4px;border-top-left-radius:0;border-bottom-left-radius:0}.ui-toc-label{background-color:#e6e6e6;border:none;color:#868686;transition:opacity .2s}.ui-toc .open .ui-toc-label{opacity:1;color:#fff;transition:opacity .2s}.ui-toc-label:focus{opacity:.3;background-color:#ccc;color:#000}.ui-toc-label:hover{opacity:1;background-color:#ccc;transition:opacity .2s}.ui-toc-dropdown{margin-top:20px;margin-bottom:20px;padding-left:10px;padding-right:10px;max-width:45vw;width:25vw;max-height:70vh;overflow:auto;text-align:inherit}.ui-toc-dropdown>.toc{max-height:calc(70vh - 100px);overflow:auto}.ui-toc-dropdown[dir=rtl] .nav{padding-right:0;letter-spacing:.0029em}.ui-toc-dropdown a{overflow:hidden;text-overflow:ellipsis;white-space:pre}.ui-toc-dropdown .nav>li>a{display:block;padding:4px 20px;font-size:13px;font-weight:500;color:#767676}.ui-toc-dropdown .nav>li:first-child:last-child>ul,.ui-toc-dropdown .toc.expand ul{display:block}.ui-toc-dropdown .nav>li>a:focus,.ui-toc-dropdown .nav>li>a:hover{padding-left:19px;color:#000;text-decoration:none;background-color:transparent;border-left:1px solid #000}.ui-toc-dropdown[dir=rtl] .nav>li>a:focus,.ui-toc-dropdown[dir=rtl] .nav>li>a:hover{padding-right:19px;border-left:none;border-right:1px solid #000}.ui-toc-dropdown .nav>.active:focus>a,.ui-toc-dropdown .nav>.active:hover>a,.ui-toc-dropdown .nav>.active>a{padding-left:18px;font-weight:700;color:#000;background-color:transparent;border-left:2px solid #000}.ui-toc-dropdown[dir=rtl] .nav>.active:focus>a,.ui-toc-dropdown[dir=rtl] .nav>.active:hover>a,.ui-toc-dropdown[dir=rtl] .nav>.active>a{padding-right:18px;border-left:none;border-right:2px solid #000}.ui-toc-dropdown .nav .nav{display:none;padding-bottom:10px}.ui-toc-dropdown .nav>.active>ul{display:block}.ui-toc-dropdown .nav .nav>li>a{padding-top:1px;padding-bottom:1px;padding-left:30px;font-size:12px;font-weight:400}.ui-toc-dropdown[dir=rtl] .nav .nav>li>a{padding-right:30px}.ui-toc-dropdown .nav .nav>li>ul>li>a{padding-top:1px;padding-bottom:1px;padding-left:40px;font-size:12px;font-weight:400}.ui-toc-dropdown[dir=rtl] .nav .nav>li>ul>li>a{padding-right:40px}.ui-toc-dropdown .nav .nav>li>a:focus,.ui-toc-dropdown .nav .nav>li>a:hover{padding-left:29px}.ui-toc-dropdown[dir=rtl] .nav .nav>li>a:focus,.ui-toc-dropdown[dir=rtl] .nav .nav>li>a:hover{padding-right:29px}.ui-toc-dropdown .nav .nav>li>ul>li>a:focus,.ui-toc-dropdown .nav .nav>li>ul>li>a:hover{padding-left:39px}.ui-toc-dropdown[dir=rtl] .nav .nav>li>ul>li>a:focus,.ui-toc-dropdown[dir=rtl] .nav .nav>li>ul>li>a:hover{padding-right:39px}.ui-toc-dropdown .nav .nav>.active:focus>a,.ui-toc-dropdown .nav .nav>.active:hover>a,.ui-toc-dropdown .nav .nav>.active>a{padding-left:28px;font-weight:500}.ui-toc-dropdown[dir=rtl] .nav .nav>.active:focus>a,.ui-toc-dropdown[dir=rtl] .nav .nav>.active:hover>a,.ui-toc-dropdown[dir=rtl] .nav .nav>.active>a{padding-right:28px}.ui-toc-dropdown .nav .nav>.active>.nav>.active:focus>a,.ui-toc-dropdown .nav .nav>.active>.nav>.active:hover>a,.ui-toc-dropdown .nav .nav>.active>.nav>.active>a{padding-left:38px;font-weight:500}.ui-toc-dropdown[dir=rtl] .nav .nav>.active>.nav>.active:focus>a,.ui-toc-dropdown[dir=rtl] .nav .nav>.active>.nav>.active:hover>a,.ui-toc-dropdown[dir=rtl] .nav .nav>.active>.nav>.active>a{padding-right:38px}.markdown-body{font-family:-apple-system,BlinkMacSystemFont,Segoe UI,Helvetica Neue,Helvetica,Roboto,Arial,sans-serif}html[lang^=ja] .markdown-body{font-family:-apple-system,BlinkMacSystemFont,Segoe UI,Helvetica Neue,Helvetica,Roboto,Arial,Hiragino Kaku Gothic Pro,ヒラギノ角ゴ Pro W3,Osaka,Meiryo,メイリオ,MS Gothic,ＭＳ\ ゴシック,sans-serif}html[lang=zh-tw] .markdown-body{font-family:-apple-system,BlinkMacSystemFont,Segoe UI,Helvetica Neue,Helvetica,Roboto,Arial,PingFang TC,Microsoft JhengHei,微軟正黑,sans-serif}html[lang=zh-cn] .markdown-body{font-family:-apple-system,BlinkMacSystemFont,Segoe UI,Helvetica Neue,Helvetica,Roboto,Arial,PingFang SC,Microsoft YaHei,微软雅黑,sans-serif}html .markdown-body[lang^=ja]{font-family:-apple-system,BlinkMacSystemFont,Segoe UI,Helvetica Neue,Helvetica,Roboto,Arial,Hiragino Kaku Gothic Pro,ヒラギノ角ゴ Pro W3,Osaka,Meiryo,メイリオ,MS Gothic,ＭＳ\ ゴシック,sans-serif}html .markdown-body[lang=zh-tw]{font-family:-apple-system,BlinkMacSystemFont,Segoe UI,Helvetica Neue,Helvetica,Roboto,Arial,PingFang TC,Microsoft JhengHei,微軟正黑,sans-serif}html .markdown-body[lang=zh-cn]{font-family:-apple-system,BlinkMacSystemFont,Segoe UI,Helvetica Neue,Helvetica,Roboto,Arial,PingFang SC,Microsoft YaHei,微软雅黑,sans-serif}html[lang^=ja] .ui-toc-dropdown{font-family:Source Sans Pro,Helvetica,Arial,Meiryo UI,MS PGothic,ＭＳ\ Ｐゴシック,sans-serif}html[lang=zh-tw] .ui-toc-dropdown{font-family:Source Sans Pro,Helvetica,Arial,Microsoft JhengHei UI,微軟正黑UI,sans-serif}html[lang=zh-cn] .ui-toc-dropdown{font-family:Source Sans Pro,Helvetica,Arial,Microsoft YaHei UI,微软雅黑UI,sans-serif}html .ui-toc-dropdown[lang^=ja]{font-family:Source Sans Pro,Helvetica,Arial,Meiryo UI,MS PGothic,ＭＳ\ Ｐゴシック,sans-serif}html .ui-toc-dropdown[lang=zh-tw]{font-family:Source Sans Pro,Helvetica,Arial,Microsoft JhengHei UI,微軟正黑UI,sans-serif}html .ui-toc-dropdown[lang=zh-cn]{font-family:Source Sans Pro,Helvetica,Arial,Microsoft YaHei UI,微软雅黑UI,sans-serif}.ui-affix-toc{position:fixed;top:0;max-width:15vw;max-height:70vh;overflow:auto}.back-to-top,.expand-toggle,.go-to-bottom{display:block;padding:4px 10px;margin-top:10px;margin-left:10px;font-size:12px;font-weight:500;color:#999}.back-to-top:focus,.back-to-top:hover,.expand-toggle:focus,.expand-toggle:hover,.go-to-bottom:focus,.go-to-bottom:hover{color:#563d7c;text-decoration:none}.back-to-top,.go-to-bottom{margin-top:0}.ui-user-icon{width:20px;height:20px;display:block;border-radius:50%;margin-top:2px;margin-bottom:2px;margin-right:5px;background-position:50%;background-repeat:no-repeat;background-size:cover}.ui-user-icon.small{width:18px;height:18px;display:inline-block;vertical-align:middle;margin:0 0 .2em}.ui-infobar>small>span{line-height:22px}.ui-infobar>small .dropdown{display:inline-block}.ui-infobar>small .dropdown a:focus,.ui-infobar>small .dropdown a:hover{text-decoration:none}.ui-more-info{color:#888;cursor:pointer;vertical-align:middle}.ui-more-info .fa{font-size:16px}.ui-connectedGithub,.ui-published-note{color:#888}.ui-connectedGithub{line-height:23px;white-space:nowrap}.ui-connectedGithub a.file-path{color:#888;text-decoration:none;padding-left:22px}.ui-connectedGithub a.file-path:active,.ui-connectedGithub a.file-path:hover{color:#888;text-decoration:underline}.ui-connectedGithub .fa{font-size:20px}.ui-published-note .fa{font-size:20px;vertical-align:top}.unselectable{-webkit-user-select:none;-o-user-select:none;user-select:none}.selectable{-webkit-user-select:text;-o-user-select:text;user-select:text}@media print{blockquote,div,img,pre,table{page-break-inside:avoid!important}a[href]:after{font-size:12px!important}}.markdown-body.slides{position:relative;z-index:1;color:#222}.markdown-body.slides:before{content:"";display:block;position:absolute;top:0;left:0;right:0;bottom:0;z-index:-1;background-color:currentColor;box-shadow:0 0 0 50vw}.markdown-body.slides section[data-markdown]{position:relative;margin-bottom:1.5em;background-color:#fff;text-align:center}.markdown-body.slides section[data-markdown] code{text-align:left}.markdown-body.slides section[data-markdown]:before{content:"";display:block;padding-bottom:56.23%}.markdown-body.slides section[data-markdown]>div:first-child{position:absolute;top:50%;left:1em;right:1em;transform:translateY(-50%);max-height:100%;overflow:hidden}.markdown-body.slides section[data-markdown]>ul{display:inline-block}.markdown-body.slides>section>section+section:after{content:"";position:absolute;top:-1.5em;right:1em;height:1.5em;border:3px solid #777}.site-ui-font{font-family:Source Sans Pro,Helvetica,Arial,sans-serif}html[lang^=ja] .site-ui-font{font-family:Source Sans Pro,Helvetica,Arial,Hiragino Kaku Gothic Pro,ヒラギノ角ゴ Pro W3,Osaka,Meiryo,メイリオ,MS Gothic,ＭＳ\ ゴシック,sans-serif}html[lang=zh-tw] .site-ui-font{font-family:Source Sans Pro,Helvetica,Arial,PingFang TC,Microsoft JhengHei,微軟正黑,sans-serif}html[lang=zh-cn] .site-ui-font{font-family:Source Sans Pro,Helvetica,Arial,PingFang SC,Microsoft YaHei,微软雅黑,sans-serif}body{font-smoothing:subpixel-antialiased!important;-webkit-font-smoothing:subpixel-antialiased!important;-moz-osx-font-smoothing:auto!important;text-shadow:0 0 1em transparent,1px 1px 1.2px rgba(0,0,0,.004);-webkit-overflow-scrolling:touch;letter-spacing:.025em;font-family:Source Sans Pro,Helvetica,Arial,sans-serif}html[lang^=ja] body{font-family:Source Sans Pro,Helvetica,Arial,Hiragino Kaku Gothic Pro,ヒラギノ角ゴ Pro W3,Osaka,Meiryo,メイリオ,MS Gothic,ＭＳ\ ゴシック,sans-serif}html[lang=zh-tw] body{font-family:Source Sans Pro,Helvetica,Arial,PingFang TC,Microsoft JhengHei,微軟正黑,sans-serif}html[lang=zh-cn] body{font-family:Source Sans Pro,Helvetica,Arial,PingFang SC,Microsoft YaHei,微软雅黑,sans-serif}abbr[title]{border-bottom:none;text-decoration:underline;-webkit-text-decoration:underline dotted;text-decoration:underline dotted}abbr[data-original-title],abbr[title]{cursor:help}body.modal-open{overflow-y:auto;padding-right:0!important}
    </style>
    <!-- HTML5 shim and Respond.js for IE8 support of HTML5 elements and media queries -->
    <!-- WARNING: Respond.js doesn't work if you view the page via file:// -->
    <!--[if lt IE 9]>
    	<script src="https://cdnjs.cloudflare.com/ajax/libs/html5shiv/3.7.3/html5shiv.min.js" integrity="sha256-3Jy/GbSLrg0o9y5Z5n1uw0qxZECH7C6OQpVBgNFYa0g=" crossorigin="anonymous"></script>
    	<script src="https://cdnjs.cloudflare.com/ajax/libs/respond.js/1.4.2/respond.min.js" integrity="sha256-g6iAfvZp+nDQ2TdTR/VVKJf3bGro4ub5fvWSWVRi2NE=" crossorigin="anonymous"></script>
		<script src="https://cdnjs.cloudflare.com/ajax/libs/es5-shim/4.5.9/es5-shim.min.js" integrity="sha256-8E4Is26QH0bD52WoQpcB+R/tcWQtpzlCojrybUd7Mxo=" crossorigin="anonymous"></script>
    <![endif]-->
</head>

<body>
    <div id="doc" class="markdown-body container-fluid comment-inner comment-enabled" data-hard-breaks="true" style=""><style>
ins { background-color: #A0FFA0 }
s { background-color: #FFA0A0 }
blockquote { color: inherit !important }
</style><table><tbody>
<tr><th>Doc. no.:</th>    <td>P2136R3</td></tr>
<tr><th>Date:</th>        <td>2021-4-29</td></tr>
<tr><th>Audience:</th>    <td>LWG</td></tr>
<tr><th>Reply-to:</th>    <td>Zhihao Yuan &lt;zy at miator dot net&gt;</td></tr>
</tbody></table><h1 id="invoke_r" data-id="invoke_r" style=""><a class="anchor hidden-xs" href="#invoke_r" title="invoke_r"><span class="octicon octicon-link"></span></a><code>invoke_r</code></h1><h2 id="Changes-Since-R2" data-id="Changes-Since-R2" style=""><a class="anchor hidden-xs" href="#Changes-Since-R2" title="Changes-Since-R2"><span class="octicon octicon-link"></span></a><span>Changes Since R2</span></h2><ul>
<li><span>add feature testing macro</span></li>
</ul><h2 id="Changes-Since-R1" data-id="Changes-Since-R1" style=""><a class="anchor hidden-xs" href="#Changes-Since-R1" title="Changes-Since-R1"><span class="octicon octicon-link"></span></a><span>Changes Since R1</span></h2><ul>
<li><span>update wording</span></li>
</ul><h2 id="Changes-Since-R0" data-id="Changes-Since-R0" style=""><a class="anchor hidden-xs" href="#Changes-Since-R0" title="Changes-Since-R0"><span class="octicon octicon-link"></span></a><span>Changes Since R0</span></h2><ul>
<li><span>rename to </span><code>invoke_r</code><span>; the proposed facility is no longer overloaded with </span><code>std::invoke</code></li>
</ul><h2 id="Introduction" data-id="Introduction" style=""><a class="anchor hidden-xs" href="#Introduction" title="Introduction"><span class="octicon octicon-link"></span></a><span>Introduction</span></h2><p><span>This paper proposes </span><code>invoke_r</code><span>, a variant of </span><code>std::invoke</code><span> that allows specifying the return type, realizing the semantics of </span><code><em><span>INVOKE</span></em><span>&lt;R&gt;</span></code><span> rather than </span><em><code>INVOKE</code></em><span>.</span></p><h2 id="History" data-id="History" style=""><a class="anchor hidden-xs" href="#History" title="History"><span class="octicon octicon-link"></span></a><span>History</span></h2><p><span>When </span><code>std::invoke</code><span> was introduced in N4169</span><sup class="footnote-ref"><a href="#fn1" id="fnref1">[1]</a></sup><span>, </span><code>invoke&lt;R&gt;</code><span> was dropped from the proposal with the belief that such a form is unnecessary, stating:</span></p><blockquote>
<p><span>Mentioned version is leftover from TR1 implementation, were the result type was determined using </span><code>result_of</code><span> protocol or has to be specified at the call side and, after the introduction of type interference in C++11, it becomes obsolete.</span></p>
</blockquote><p><span>But in 2015, LWG 2420</span><sup class="footnote-ref"><a href="#fn2" id="fnref2">[2]</a></sup><span> was applied to the working draft. </span><code><em><span>INVOKE</span></em><span>(f, args…, void)</span></code><span>'s capability of casting away the return value is confirmed and specified.</span></p><p><span>In 2016, the author of this paper opened LWG 2690</span><sup class="footnote-ref"><a href="#fn3" id="fnref3">[3]</a></sup><span>, proposing </span><code>std::invoke&lt;R&gt;</code><span>.  The author of N4169 commented on that issue, confirmed that:</span></p><blockquote>
<p><span>The lack of </span><code>invoke&lt;R&gt;</code><span> was basically a result of the concurrent publication of the never revision of the paper and additional special semantics of </span><code><em><span>INVOKE</span></em><span>(f, args…, void)</span></code><span>.</span></p>
</blockquote><p><span>In 2017, </span><code><em><span>INVOKE</span></em><span>(f, args…, void)</span></code><span> gained the current spelling </span><code><em><span>INVOKE</span></em><span>&lt;R&gt;(f, args…)</span></code><span> in P0604R0</span><sup class="footnote-ref"><a href="#fn4" id="fnref4">[4]</a></sup><span>.  In the same paper, all the new invocation traits get </span><code>_r</code><span> variants that allow specifying the return type.</span></p><p><span>In 2018, </span><code>std::visit&lt;R&gt;</code><sup class="footnote-ref"><a href="#fn5" id="fnref5">[5]</a></sup><span> is added to the working draft. The usefulness of </span><code><em><span>INVOKE</span></em><span>&lt;R&gt;</span></code><span> keeps getting attention.</span></p><h2 id="Discussion" data-id="Discussion" style=""><a class="anchor hidden-xs" href="#Discussion" title="Discussion"><span class="octicon octicon-link"></span></a><span>Discussion</span></h2><h3 id="How-useful-invoke_r-is" data-id="How-useful-invoke_r-is" style=""><a class="anchor hidden-xs" href="#How-useful-invoke_r-is" title="How-useful-invoke_r-is"><span class="octicon octicon-link"></span></a><span>How useful </span><code>invoke_r</code><span> is?</span></h3><p><code>invoke_r&lt;R&gt;(...)</code><span> does three things that </span><code>std::invoke(...)</code><span> does not:</span></p><ol>
<li><span>In a call forwarder that allows specifying the return type or the full signature, putting </span><code>void</code><span> as the return type naturally discards the return value, as implied by </span><code>std::is_invocable_r</code><span> and </span><code>std::is_nothrow_invocable_r</code><span>.</span></li>
<li><span>When </span><code>R</code><span> is not </span><em><span>cv</span></em><span> </span><code>void</code><span>, you can specify a compatible return type that is different from the callable entity. For example, you can request a function that returns </span><code>T&amp;&amp;</code><span> to return a prvalue of type </span><code>T</code><span> by calling </span><code>invoke_r&lt;T&gt;</code><span>.</span></li>
<li><span>If the callable entity has overloaded call operators that may return different types, they may agree on a return type that allows you to specify. For example, you can perform an upcast for covariant return types.</span></li>
</ol><h3 id="Why-not-to-spell-it-invokeltRgt" data-id="Why-not-to-spell-it-invokeltRgt" style=""><a class="anchor hidden-xs" href="#Why-not-to-spell-it-invokeltRgt" title="Why-not-to-spell-it-invokeltRgt"><span class="octicon octicon-link"></span></a><span>Why not to spell it </span><code>invoke&lt;R&gt;</code><span>?</span></h3><p><span>LEWG reached consensus to name the facility differently to avoid ambiguity when </span><code>R</code><span> is the callable type, for the following reasons:</span></p><ol>
<li><code>std::invoke_r&lt;R&gt;</code><span> meant to be a low-level facility, therefore it supposes to be usable in any condition, unlike </span><code>std::bind&lt;R&gt;</code><span> and </span><code>std::visit&lt;R&gt;</code><span>.</span></li>
<li><span>Being consistent with an internal name for library specification, i.e., </span><code><em><span>INVOKE</span></em><span>&lt;R&gt;</span></code><span>, isn’t nessasry.</span></li>
<li><code>invoke</code><span> with an explicit return type shouldn’t belong to the </span><code>std::invoke</code><span> overload set, since an end-user never meant to get a different form when spelled a particular one.</span></li>
</ol><p><span>To not to miss any bikeshedding opportunity, our naming candidates include:</span></p><ol>
<li><code>invoke_r</code></li>
<li><code>invoke_argh</code></li>
</ol><p><span>The author prefers (1) because users may correctly correlate </span><code>std::invoke_r</code><span>, </span><code>std::is_invocable_r</code><span>, and </span><code>std::is_nothrow_invocable_r</code><span> given the similarity.</span></p><h2 id="Wording" data-id="Wording" style=""><a class="anchor hidden-xs" href="#Wording" title="Wording"><span class="octicon octicon-link"></span></a><span>Wording</span></h2><p><span>The wording is relative to N4885.</span></p><p><span>Modify 20.14.2 [functional.syn], header </span><code>&lt;functional&gt;</code><span> synopsis, as indicated:</span></p><pre><code>namespace std {
  <i>// 20.14.5 [func.invoke], invoke</i>
  template&lt;class F, class... Args&gt;
    constexpr invoke_result_t&lt;F, Args...&gt;   invoke(F&amp;&amp; f, Args&amp;&amp;... args)
      noexcept(is_nothrow_invocable_v&lt;F, Args...&gt;);
<ins>  template &lt;class R, class F, class... Args&gt;
    constexpr R invoke_r(F&amp;&amp; f, Args&amp;&amp;... args)
      noexcept(is_nothrow_invocable_r_v&lt;R, F, Args...&gt;);</ins>
</code></pre><p><span>Modify 20.14.5 [func.invoke] as follows:</span></p><blockquote>
<h3 id="20145-Function-template-invoke-functions" data-id="20145-Function-template-invoke-functions"><a class="anchor hidden-xs" href="#20145-Function-template-invoke-functions" title="20145-Function-template-invoke-functions"><span class="octicon octicon-link"></span></a>20.14.5 <s>Function template </s><code>invoke</code><ins> functions</ins></h3>
</blockquote><pre><code>template&lt;class F, class... Args&gt;
  constexpr invoke_result_t&lt;F, Args...&gt; invoke(F&amp;&amp; f, Args&amp;&amp;... args)
    noexcept(is_nothrow_invocable_v&lt;F, Args...&gt;);
</code></pre><div class="alert alert-info" data-original-title="" title="">
<p><em><span>[Drafting note:</span></em>
<span>The constraint is implied by </span><code>invoke_result_t</code><span>.</span>
<em><span>–end note]</span></em></p>
</div><blockquote>
<p><ins><em><span>Constraints:</span></em><span> </span><code>is_invocable_v&lt;F, Args...&gt;</code><span> is </span><code>true</code><span>.</span></ins></p>
<p><em><span>Returns:</span></em><span> </span><code><em><span>INVOKE</span></em><span>(std::forward&lt;F&gt;(f), std::forward&lt;Args&gt;(args)...)</span></code><span> (20.14.4 [func.require]).</span></p>
</blockquote><pre><code><ins>template&lt;class R, class F, class... Args&gt;
  constexpr R invoke_r(F&amp;&amp; f, Args&amp;&amp;... args)
    noexcept(is_nothrow_invocable_r_v&lt;R, F, Args...&gt;);</ins>
</code></pre><blockquote>
<p><ins><em><span>Constraints:</span></em><span> </span><code>is_invocable_r_v&lt;R, F, Args...&gt;</code><span> is </span><code>true</code><span>.</span></ins></p>
<p><ins><em><span>Returns:</span></em><span> </span><code><em><span>INVOKE</span></em><span>&lt;R&gt;(std::forward&lt;F&gt;(f), std::forward&lt;Args&gt;(args)...)</span></code><span> (20.14.4 [func.require]).</span></ins></p>
</blockquote><p><span>Add the following macro definition to 17.3.2 [version.syn]:</span></p><blockquote>
<p><code>#define __cpp_lib_invoke_r 20XXXXL</code><span> </span><em><span>// also in </span><code>&lt;functional&gt;</code></em></p>
</blockquote><h2 id="References" data-id="References" style=""><a class="anchor hidden-xs" href="#References" title="References"><span class="octicon octicon-link"></span></a><span>References</span></h2><hr class="footnotes-sep"><section class="footnotes">
<ol class="footnotes-list">
<li id="fn1" class="footnote-item"><p><span>Kamiński, Tomasz. </span><em><span>A proposal to add invoke function template (Revision 1)</span></em><span>.</span>
<a href="http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2014/n4169.html" target="_blank" rel="noopener"><span>http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2014/n4169.html</span></a> <a href="#fnref1" class="footnote-backref">↩︎</a></p>
</li>
<li id="fn2" class="footnote-item"><p><span>Bergé, Agustín. LWG 2420 </span><em><code>function&lt;void(ArgTypes...)&gt;</code><span> does not discard the return value of the target object</span></em><span>.</span>
<a href="https://cplusplus.github.io/LWG/issue2420" target="_blank" rel="noopener"><span>https://cplusplus.github.io/LWG/issue2420</span></a> <a href="#fnref2" class="footnote-backref">↩︎</a></p>
</li>
<li id="fn3" class="footnote-item"><p><span>Yuan, Zhihao. LWG 2690 </span><em><code>invoke&lt;R&gt;</code></em><span>.</span>
<a href="https://cplusplus.github.io/LWG/lwg-active.html#2690" target="_blank" rel="noopener"><span>https://cplusplus.github.io/LWG/lwg-active.html#2690</span></a> <a href="#fnref3" class="footnote-backref">↩︎</a></p>
</li>
<li id="fn4" class="footnote-item"><p><span>Krügler, Daniel et al. </span><em><span>Resolving GB 55, US 84, US 85, US 86</span></em><span>.</span>
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0604r0.html" target="_blank" rel="noopener"><span>http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0604r0.html</span></a> <a href="#fnref4" class="footnote-backref">↩︎</a></p>
</li>
<li id="fn5" class="footnote-item"><p><span>Park, Michael and Agustín Bergé. </span><em><code>visit&lt;R&gt;</code><span>:  Explicit Return Type for </span><code>visit</code></em><span>.</span>
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0655r1.pdf" target="_blank" rel="noopener"><span>http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0655r1.pdf</span></a> <a href="#fnref5" class="footnote-backref">↩︎</a></p>
</li>
</ol>
</section></div>
    <div class="ui-toc dropup unselectable hidden-print" style="display:none;">
        <div class="pull-right dropdown">
            <a id="tocLabel" class="ui-toc-label btn btn-default" data-toggle="dropdown" href="#" role="button" aria-haspopup="true" aria-expanded="false" title="Table of content">
                <i class="fa fa-bars"></i>
            </a>
            <ul id="ui-toc" class="ui-toc-dropdown dropdown-menu" aria-labelledby="tocLabel">
                <div class="toc"><ul class="nav">
<li class=""><a href="#invoke_r" title="invoke_r">invoke_r</a><ul class="nav">
<li><a href="#Changes-Since-R2" title="Changes Since R2">Changes Since R2</a></li>
<li><a href="#Changes-Since-R1" title="Changes Since R1">Changes Since R1</a></li>
<li><a href="#Changes-Since-R0" title="Changes Since R0">Changes Since R0</a></li>
<li><a href="#Introduction" title="Introduction">Introduction</a></li>
<li><a href="#History" title="History">History</a></li>
<li><a href="#Discussion" title="Discussion">Discussion</a><ul class="nav">
<li><a href="#How-useful-invoke_r-is" title="How useful invoke_r is?">How useful invoke_r is?</a></li>
<li><a href="#Why-not-to-spell-it-invokeltRgt" title="Why not to spell it invoke<R>?">Why not to spell it invoke&lt;R&gt;?</a></li>
</ul>
</li>
<li class=""><a href="#Wording" title="Wording">Wording</a></li>
<li><a href="#References" title="References">References</a></li>
</ul>
</li>
</ul>
</div><div class="toc-menu"><a class="expand-toggle" href="#">Expand all</a><a class="back-to-top" href="#">Back to top</a><a class="go-to-bottom" href="#">Go to bottom</a></div>
            </ul>
        </div>
    </div>
    <div id="ui-toc-affix" class="ui-affix-toc ui-toc-dropdown unselectable hidden-print" data-spy="affix" style="top:17px;display:none;" null null>
        <div class="toc"><ul class="nav">
<li class=""><a href="#invoke_r" title="invoke_r">invoke_r</a><ul class="nav">
<li><a href="#Changes-Since-R2" title="Changes Since R2">Changes Since R2</a></li>
<li><a href="#Changes-Since-R1" title="Changes Since R1">Changes Since R1</a></li>
<li><a href="#Changes-Since-R0" title="Changes Since R0">Changes Since R0</a></li>
<li><a href="#Introduction" title="Introduction">Introduction</a></li>
<li><a href="#History" title="History">History</a></li>
<li><a href="#Discussion" title="Discussion">Discussion</a><ul class="nav">
<li><a href="#How-useful-invoke_r-is" title="How useful invoke_r is?">How useful invoke_r is?</a></li>
<li><a href="#Why-not-to-spell-it-invokeltRgt" title="Why not to spell it invoke<R>?">Why not to spell it invoke&lt;R&gt;?</a></li>
</ul>
</li>
<li class=""><a href="#Wording" title="Wording">Wording</a></li>
<li><a href="#References" title="References">References</a></li>
</ul>
</li>
</ul>
</div><div class="toc-menu"><a class="expand-toggle" href="#">Expand all</a><a class="back-to-top" href="#">Back to top</a><a class="go-to-bottom" href="#">Go to bottom</a></div>
    </div>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.1.1/jquery.min.js" integrity="sha256-hVVnYaiADRTO2PzUGmuLJr8BLUSjGIZsDYGmIJLv2b8=" crossorigin="anonymous"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.7/js/bootstrap.min.js" integrity="sha256-U5ZEeKfGNOja007MMD3YBI0A3OSZOQbeG6z2f2Y0hu8=" crossorigin="anonymous" defer></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/gist-embed/2.6.0/gist-embed.min.js" integrity="sha256-KyF2D6xPIJUW5sUDSs93vWyZm+1RzIpKCexxElmxl8g=" crossorigin="anonymous" defer></script>
    <script>
        var markdown = $(".markdown-body");
        //smooth all hash trigger scrolling
        function smoothHashScroll() {
            var hashElements = $("a[href^='#']").toArray();
            for (var i = 0; i < hashElements.length; i++) {
                var element = hashElements[i];
                var $element = $(element);
                var hash = element.hash;
                if (hash) {
                    $element.on('click', function (e) {
                        // store hash
                        var hash = this.hash;
                        if ($(hash).length <= 0) return;
                        // prevent default anchor click behavior
                        e.preventDefault();
                        // animate
                        $('body, html').stop(true, true).animate({
                            scrollTop: $(hash).offset().top
                        }, 100, "linear", function () {
                            // when done, add hash to url
                            // (default click behaviour)
                            window.location.hash = hash;
                        });
                    });
                }
            }
        }

        smoothHashScroll();
        var toc = $('.ui-toc');
        var tocAffix = $('.ui-affix-toc');
        var tocDropdown = $('.ui-toc-dropdown');
        //toc
        tocDropdown.click(function (e) {
            e.stopPropagation();
        });

        var enoughForAffixToc = true;

        function generateScrollspy() {
            $(document.body).scrollspy({
                target: ''
            });
            $(document.body).scrollspy('refresh');
            if (enoughForAffixToc) {
                toc.hide();
                tocAffix.show();
            } else {
                tocAffix.hide();
                toc.show();
            }
            $(document.body).scroll();
        }

        function windowResize() {
            //toc right
            var paddingRight = parseFloat(markdown.css('padding-right'));
            var right = ($(window).width() - (markdown.offset().left + markdown.outerWidth() - paddingRight));
            toc.css('right', right + 'px');
            //affix toc left
            var newbool;
            var rightMargin = (markdown.parent().outerWidth() - markdown.outerWidth()) / 2;
            //for ipad or wider device
            if (rightMargin >= 133) {
                newbool = true;
                var affixLeftMargin = (tocAffix.outerWidth() - tocAffix.width()) / 2;
                var left = markdown.offset().left + markdown.outerWidth() - affixLeftMargin;
                tocAffix.css('left', left + 'px');
            } else {
                newbool = false;
            }
            if (newbool != enoughForAffixToc) {
                enoughForAffixToc = newbool;
                generateScrollspy();
            }
        }
        $(window).resize(function () {
            windowResize();
        });
        $(document).ready(function () {
            windowResize();
            generateScrollspy();
        });

        //remove hash
        function removeHash() {
            window.location.hash = '';
        }

        var backtotop = $('.back-to-top');
        var gotobottom = $('.go-to-bottom');

        backtotop.click(function (e) {
            e.preventDefault();
            e.stopPropagation();
            if (scrollToTop)
                scrollToTop();
            removeHash();
        });
        gotobottom.click(function (e) {
            e.preventDefault();
            e.stopPropagation();
            if (scrollToBottom)
                scrollToBottom();
            removeHash();
        });

        var toggle = $('.expand-toggle');
        var tocExpand = false;

        checkExpandToggle();
        toggle.click(function (e) {
            e.preventDefault();
            e.stopPropagation();
            tocExpand = !tocExpand;
            checkExpandToggle();
        })

        function checkExpandToggle () {
            var toc = $('.ui-toc-dropdown .toc');
            var toggle = $('.expand-toggle');
            if (!tocExpand) {
                toc.removeClass('expand');
                toggle.text('Expand all');
            } else {
                toc.addClass('expand');
                toggle.text('Collapse all');
            }
        }

        function scrollToTop() {
            $('body, html').stop(true, true).animate({
                scrollTop: 0
            }, 100, "linear");
        }

        function scrollToBottom() {
            $('body, html').stop(true, true).animate({
                scrollTop: $(document.body)[0].scrollHeight
            }, 100, "linear");
        }
    </script>
</body>

</html>
