1<?xml version="1.0" encoding="utf-8" ?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> 4<head> 5<meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> 6<meta name="generator" content="Docutils 0.7: http://docutils.sourceforge.net/" /> 7<title>The MPL Reference Manual: void_</title> 8<link rel="stylesheet" href="../style.css" type="text/css" /> 9</head> 10<body class="docframe refmanual"> 11<table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./empty-base.html" class="navigation-link">Prev</a> <a href="./macros.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./empty-base.html" class="navigation-link">Back</a> Along</span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./data-types-miscellaneous.html" class="navigation-link">Up</a> <a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td> 12<td class="header-group page-location"><a href="../refmanual.html" class="navigation-link">Front Page</a> / <a href="./data-types.html" class="navigation-link">Data Types</a> / <a href="./data-types-miscellaneous.html" class="navigation-link">Miscellaneous</a> / <a href="./void.html" class="navigation-link">void_</a></td> 13</tr></table><div class="header-separator"></div> 14<div class="section" id="void"> 15<h1><a class="toc-backref" href="./data-types-miscellaneous.html#id1585">void_</a></h1> 16<div class="section" id="id1280"> 17<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3> 18<pre class="literal-block"> 19struct <a href="./void.html" class="identifier">void_</a> 20{ 21 typedef <a href="./void.html" class="identifier">void_</a> type; 22}; 23 24template< typename T > struct is_void; 25</pre> 26</div> 27<div class="section" id="id1281"> 28<h3><a class="subsection-title" href="#description" name="description">Description</a></h3> 29<p><tt class="literal"><span class="pre"><a href="./void.html" class="identifier">void_</a></span></tt> is a generic type placeholder representing "nothing".</p> 30<!-- In many cases, returning ``void_`` from a metafunction to signal 31an absence of the requested data leads to a simpler user code than 32having a separate metafunction specifically for the purpose of 33performing the corresponding check. --> 34</div> 35<div class="section" id="id1282"> 36<h3><a class="subsection-title" href="#header" name="header">Header</a></h3> 37<pre class="literal-block"> 38#include <<a href="../../../../boost/mpl/void.hpp" class="header">boost/mpl/void.hpp</a>> 39</pre> 40</div> 41<div class="section" id="id1283"> 42<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3> 43<p><a class="reference internal" href="./data-types.html">Data Types</a>, <a class="reference internal" href="./pair.html">pair</a>, <a class="reference internal" href="./empty-base.html">empty_base</a>, <a class="reference internal" href="./bool.html">bool_</a>, <a class="reference internal" href="./int.html">int_</a>, <a class="reference internal" href="./integral-c.html">integral_c</a></p> 44</div> 45</div> 46 47<div class="footer-separator"></div> 48<table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./empty-base.html" class="navigation-link">Prev</a> <a href="./macros.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./empty-base.html" class="navigation-link">Back</a> Along</span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./data-types-miscellaneous.html" class="navigation-link">Up</a> <a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td> 49<td><div class="copyright-footer"><div class="copyright">Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</div> 50Distributed under the Boost Software License, Version 1.0. (See accompanying 51file LICENSE_1_0.txt or copy at <a class="reference external" href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)</div></td></tr></table></body> 52</html> 53