1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>empty</title> 5<link rel="stylesheet" href="../../../../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../../../index.html" title="Chapter 1. Fusion 2.2"> 8<link rel="up" href="../metafunctions.html" title="Metafunctions"> 9<link rel="prev" href="end.html" title="end"> 10<link rel="next" href="front.html" title="front"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="end.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../metafunctions.html"><img src="../../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../../index.html"><img src="../../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="front.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h5 class="title"> 27<a name="fusion.sequence.intrinsic.metafunctions.empty"></a><a class="link" href="empty.html" title="empty">empty</a> 28</h5></div></div></div> 29<h6> 30<a name="fusion.sequence.intrinsic.metafunctions.empty.h0"></a> 31 <span class="phrase"><a name="fusion.sequence.intrinsic.metafunctions.empty.description"></a></span><a class="link" href="empty.html#fusion.sequence.intrinsic.metafunctions.empty.description">Description</a> 32 </h6> 33<p> 34 Returns the result type of <a class="link" href="../functions/empty.html" title="empty"><code class="computeroutput"><span class="identifier">empty</span></code></a>. 35 </p> 36<h6> 37<a name="fusion.sequence.intrinsic.metafunctions.empty.h1"></a> 38 <span class="phrase"><a name="fusion.sequence.intrinsic.metafunctions.empty.synopsis"></a></span><a class="link" href="empty.html#fusion.sequence.intrinsic.metafunctions.empty.synopsis">Synopsis</a> 39 </h6> 40<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Seq</span><span class="special">></span> 41<span class="keyword">struct</span> <span class="identifier">empty</span> 42<span class="special">{</span> 43 <span class="keyword">typedef</span> <span class="emphasis"><em>unspecified</em></span> <span class="identifier">type</span><span class="special">;</span> 44<span class="special">};</span> 45</pre> 46<div class="table"> 47<a name="fusion.sequence.intrinsic.metafunctions.empty.t0"></a><p class="title"><b>Table 1.24. Parameters</b></p> 48<div class="table-contents"><table class="table" summary="Parameters"> 49<colgroup> 50<col> 51<col> 52<col> 53</colgroup> 54<thead><tr> 55<th> 56 <p> 57 Parameter 58 </p> 59 </th> 60<th> 61 <p> 62 Requirement 63 </p> 64 </th> 65<th> 66 <p> 67 Description 68 </p> 69 </th> 70</tr></thead> 71<tbody><tr> 72<td> 73 <p> 74 <code class="computeroutput"><span class="identifier">Seq</span></code> 75 </p> 76 </td> 77<td> 78 <p> 79 A model of <a class="link" href="../../concepts/forward_sequence.html" title="Forward Sequence">Forward 80 Sequence</a> 81 </p> 82 </td> 83<td> 84 <p> 85 Argument sequence 86 </p> 87 </td> 88</tr></tbody> 89</table></div> 90</div> 91<br class="table-break"><h6> 92<a name="fusion.sequence.intrinsic.metafunctions.empty.h2"></a> 93 <span class="phrase"><a name="fusion.sequence.intrinsic.metafunctions.empty.expression_semantics"></a></span><a class="link" href="empty.html#fusion.sequence.intrinsic.metafunctions.empty.expression_semantics">Expression 94 Semantics</a> 95 </h6> 96<pre class="programlisting"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">empty</span><span class="special"><</span><span class="identifier">Seq</span><span class="special">>::</span><span class="identifier">type</span> 97</pre> 98<p> 99 <span class="bold"><strong>Return type</strong></span>: An <a href="http://www.boost.org/libs/mpl/doc/refmanual/integral-constant.html" target="_top">MPL 100 Integral Constant</a> 101 </p> 102<p> 103 <span class="bold"><strong>Semantics</strong></span>: Returns <code class="computeroutput"><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">true_</span></code> 104 if <code class="computeroutput"><span class="identifier">Seq</span></code> has zero elements, 105 <code class="computeroutput"><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">false_</span></code> otherwise. 106 </p> 107<h6> 108<a name="fusion.sequence.intrinsic.metafunctions.empty.h3"></a> 109 <span class="phrase"><a name="fusion.sequence.intrinsic.metafunctions.empty.header"></a></span><a class="link" href="empty.html#fusion.sequence.intrinsic.metafunctions.empty.header">Header</a> 110 </h6> 111<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">fusion</span><span class="special">/</span><span class="identifier">sequence</span><span class="special">/</span><span class="identifier">intrinsic</span><span class="special">/</span><span class="identifier">empty</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 112<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">fusion</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">empty</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 113</pre> 114<h6> 115<a name="fusion.sequence.intrinsic.metafunctions.empty.h4"></a> 116 <span class="phrase"><a name="fusion.sequence.intrinsic.metafunctions.empty.example"></a></span><a class="link" href="empty.html#fusion.sequence.intrinsic.metafunctions.empty.example">Example</a> 117 </h6> 118<pre class="programlisting"><span class="keyword">typedef</span> <a class="link" href="../../../container/vector.html" title="vector"><code class="computeroutput"><span class="identifier">vector</span></code></a><span class="special"><></span> <span class="identifier">empty_vec</span><span class="special">;</span> 119<span class="keyword">typedef</span> <a class="link" href="../../../container/vector.html" title="vector"><code class="computeroutput"><span class="identifier">vector</span></code></a><span class="special"><</span><span class="keyword">int</span><span class="special">,</span><span class="keyword">float</span><span class="special">,</span><span class="keyword">char</span><span class="special">></span> <span class="identifier">vec</span><span class="special">;</span> 120 121<span class="identifier">BOOST_MPL_ASSERT</span><span class="special">((</span><a class="link" href="empty.html" title="empty"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">empty</span></code></a><span class="special"><</span><span class="identifier">empty_vec</span><span class="special">>));</span> 122<span class="identifier">BOOST_MPL_ASSERT_NOT</span><span class="special">((</span><a class="link" href="empty.html" title="empty"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">empty</span></code></a><span class="special"><</span><span class="identifier">vec</span><span class="special">>));</span> 123</pre> 124</div> 125<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 126<td align="left"></td> 127<td align="right"><div class="copyright-footer">Copyright © 2001-2006, 2011, 2012 Joel de Guzman, 128 Dan Marsden, Tobias Schwinger<p> 129 Distributed under the Boost Software License, Version 1.0. (See accompanying 130 file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) 131 </p> 132</div></td> 133</tr></table> 134<hr> 135<div class="spirit-nav"> 136<a accesskey="p" href="end.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../metafunctions.html"><img src="../../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../../index.html"><img src="../../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="front.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> 137</div> 138</body> 139</html> 140
