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: empty</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="./clear.html" class="navigation-link">Prev</a> <a href="./end.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./clear.html" class="navigation-link">Back</a> <a href="./end.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./intrinsic-metafunctions.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="./sequences.html" class="navigation-link">Sequences</a> / <a href="./intrinsic-metafunctions.html" class="navigation-link">Intrinsic Metafunctions</a> / <a href="./empty.html" class="navigation-link">empty</a></td> 13</tr></table><div class="header-separator"></div> 14<div class="section" id="empty"> 15<h1><a class="toc-backref" href="./intrinsic-metafunctions.html#id1430">empty</a></h1> 16<div class="section" id="id220"> 17<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3> 18<pre class="literal-block"> 19template< 20 typename Sequence 21 > 22struct <a href="./empty.html" class="identifier">empty</a> 23{ 24 typedef <em>unspecified</em> type; 25}; 26</pre> 27</div> 28<div class="section" id="id221"> 29<h3><a class="subsection-title" href="#description" name="description">Description</a></h3> 30<p>Returns an <a class="reference internal" href="./integral-constant.html">Integral Constant</a> <tt class="literal"><span class="pre">c</span></tt> such that <tt class="literal"><span class="pre">c::value</span> <span class="pre">==</span> <span class="pre">true</span></tt> if 31and only if the sequence is empty.</p> 32</div> 33<div class="section" id="id222"> 34<h3><a class="subsection-title" href="#header" name="header">Header</a></h3> 35<pre class="literal-block"> 36#include <<a href="../../../../boost/mpl/empty.hpp" class="header">boost/mpl/empty.hpp</a>> 37</pre> 38</div> 39<div class="section" id="id223"> 40<h3><a class="subsection-title" href="#model-of" name="model-of">Model of</a></h3> 41<p><a class="reference internal" href="./tag-dispatched-metafunction.html">Tag Dispatched Metafunction</a></p> 42</div> 43<div class="section" id="id224"> 44<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3> 45<table border="1" class="docutils table"> 46<colgroup> 47<col width="21%" /> 48<col width="32%" /> 49<col width="48%" /> 50</colgroup> 51<thead valign="bottom"> 52<tr><th class="head">Parameter</th> 53<th class="head">Requirement</th> 54<th class="head">Description</th> 55</tr> 56</thead> 57<tbody valign="top"> 58<tr><td><tt class="literal"><span class="pre">Sequence</span></tt></td> 59<td><a class="reference internal" href="./forward-sequence.html">Forward Sequence</a></td> 60<td>A sequence to test.</td> 61</tr> 62</tbody> 63</table> 64</div> 65<div class="section" id="id225"> 66<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3> 67<p>For any <a class="reference internal" href="./forward-sequence.html">Forward Sequence</a> <tt class="literal"><span class="pre">s</span></tt>:</p> 68<pre class="literal-block"> 69typedef <a href="./empty.html" class="identifier">empty</a><s>::type c; 70</pre> 71<table class="docutils field-list" frame="void" rules="none"> 72<col class="field-name" /> 73<col class="field-body" /> 74<tbody valign="top"> 75<tr class="field"><th class="field-name">Return type:</th><td class="field-body">Boolean <a class="reference internal" href="./integral-constant.html">Integral Constant</a>.</td> 76</tr> 77<tr class="field"><th class="field-name">Semantics:</th><td class="field-body">Equivalent to <tt class="literal"><span class="pre">typedef</span> <span class="pre">is_same<</span> <span class="pre"><a href="./begin.html" class="identifier">begin</a><s>::type,<a href="./end.html" class="identifier">end</a><s>::type</span> <span class="pre">>::type</span> <span class="pre">c;</span></tt>.</td> 78</tr> 79<tr class="field"><th class="field-name">Postcondition:</th><td class="field-body"><tt class="literal"><span class="pre"><a href="./empty.html" class="identifier">empty</a><s>::value</span> <span class="pre">==</span> <span class="pre">(</span> <span class="pre"><a href="./size.html" class="identifier">size</a><s>::value</span> <span class="pre">==</span> <span class="pre">0</span> <span class="pre">)</span></tt>.</td> 80</tr> 81</tbody> 82</table> 83</div> 84<div class="section" id="id226"> 85<h3><a class="subsection-title" href="#complexity" name="complexity">Complexity</a></h3> 86<p>Amortized constant time.</p> 87</div> 88<div class="section" id="id227"> 89<h3><a class="subsection-title" href="#example" name="example">Example</a></h3> 90<pre class="literal-block"> 91typedef <a href="./range-c.html" class="identifier">range_c</a><int,0,0> empty_range; 92typedef <a href="./vector.html" class="identifier">vector</a><long,float,double> types; 93 94<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>( <a href="./empty.html" class="identifier">empty</a><empty_range> ); 95<a href="./assert-not.html" class="identifier">BOOST_MPL_ASSERT_NOT</a>( <a href="./empty.html" class="identifier">empty</a><types> ); 96</pre> 97</div> 98<div class="section" id="id228"> 99<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3> 100<p><a class="reference internal" href="./forward-sequence.html">Forward Sequence</a>, <a class="reference internal" href="./integral-constant.html">Integral Constant</a>, <a class="reference internal" href="./size.html">size</a>, <a class="reference internal" href="./begin.html">begin</a> / <a class="reference internal" href="./end.html">end</a></p> 101<!-- Sequences/Intrinsic Metafunctions//end --> 102</div> 103</div> 104 105<div class="footer-separator"></div> 106<table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./clear.html" class="navigation-link">Prev</a> <a href="./end.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./clear.html" class="navigation-link">Back</a> <a href="./end.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./intrinsic-metafunctions.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> 107<td><div class="copyright-footer"><div class="copyright">Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</div> 108Distributed under the Boost Software License, Version 1.0. (See accompanying 109file 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> 110</html> 111