1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>filter_if</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="../functions.html" title="Functions"> 9<link rel="prev" href="filter.html" title="filter"> 10<link rel="next" href="transform.html" title="transform"> 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="filter.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../functions.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="transform.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.algorithm.transformation.functions.filter_if"></a><a class="link" href="filter_if.html" title="filter_if">filter_if</a> 28</h5></div></div></div> 29<h6> 30<a name="fusion.algorithm.transformation.functions.filter_if.h0"></a> 31 <span class="phrase"><a name="fusion.algorithm.transformation.functions.filter_if.description"></a></span><a class="link" href="filter_if.html#fusion.algorithm.transformation.functions.filter_if.description">Description</a> 32 </h6> 33<p> 34 For a given sequence, <a class="link" href="filter_if.html" title="filter_if"><code class="computeroutput"><span class="identifier">filter_if</span></code></a> returns a new sequences 35 containing only the elements with types for which a given <a href="http://www.boost.org/libs/mpl/doc/refmanual/lambda-expression.html" target="_top">MPL 36 Lambda Expression</a> evaluates to <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">true_</span></code>. 37 </p> 38<h6> 39<a name="fusion.algorithm.transformation.functions.filter_if.h1"></a> 40 <span class="phrase"><a name="fusion.algorithm.transformation.functions.filter_if.synopsis"></a></span><a class="link" href="filter_if.html#fusion.algorithm.transformation.functions.filter_if.synopsis">Synopsis</a> 41 </h6> 42<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span> 43 <span class="keyword">typename</span> <span class="identifier">Pred</span><span class="special">,</span> 44 <span class="keyword">typename</span> <span class="identifier">Sequence</span> 45 <span class="special">></span> 46<span class="keyword">typename</span> <a class="link" href="../metafunctions/filter_if.html" title="filter_if"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">filter_if</span></code></a><span class="special"><</span><span class="identifier">Sequence</span> <span class="keyword">const</span><span class="special">,</span> <span class="identifier">Pred</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">filter_if</span><span class="special">(</span><span class="identifier">Sequence</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">seq</span><span class="special">);</span> 47</pre> 48<div class="table"> 49<a name="fusion.algorithm.transformation.functions.filter_if.t0"></a><p class="title"><b>Table 1.67. Parameters</b></p> 50<div class="table-contents"><table class="table" summary="Parameters"> 51<colgroup> 52<col> 53<col> 54<col> 55</colgroup> 56<thead><tr> 57<th> 58 <p> 59 Parameter 60 </p> 61 </th> 62<th> 63 <p> 64 Requirement 65 </p> 66 </th> 67<th> 68 <p> 69 Description 70 </p> 71 </th> 72</tr></thead> 73<tbody> 74<tr> 75<td> 76 <p> 77 <code class="computeroutput"><span class="identifier">seq</span></code> 78 </p> 79 </td> 80<td> 81 <p> 82 A model of <a class="link" href="../../../sequence/concepts/forward_sequence.html" title="Forward Sequence">Forward 83 Sequence</a> 84 </p> 85 </td> 86<td> 87 <p> 88 Operation's argument 89 </p> 90 </td> 91</tr> 92<tr> 93<td> 94 <p> 95 <code class="computeroutput"><span class="identifier">Pred</span></code> 96 </p> 97 </td> 98<td> 99 <p> 100 A unary <a href="http://www.boost.org/libs/mpl/doc/refmanual/lambda-expression.html" target="_top">MPL 101 Lambda Expression</a> 102 </p> 103 </td> 104<td> 105 <p> 106 The predicate to filter by 107 </p> 108 </td> 109</tr> 110</tbody> 111</table></div> 112</div> 113<br class="table-break"><h6> 114<a name="fusion.algorithm.transformation.functions.filter_if.h2"></a> 115 <span class="phrase"><a name="fusion.algorithm.transformation.functions.filter_if.expression_semantics"></a></span><a class="link" href="filter_if.html#fusion.algorithm.transformation.functions.filter_if.expression_semantics">Expression 116 Semantics</a> 117 </h6> 118<pre class="programlisting"><a class="link" href="filter_if.html" title="filter_if"><code class="computeroutput"><span class="identifier">filter_if</span></code></a><span class="special"><</span><span class="identifier">Pred</span><span class="special">>(</span><span class="identifier">seq</span><span class="special">);</span> 119</pre> 120<p> 121 <span class="bold"><strong>Return type</strong></span>: 122 </p> 123<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 124<li class="listitem"> 125 A model of <a class="link" href="../../../sequence/concepts/forward_sequence.html" title="Forward Sequence">Forward 126 Sequence</a>. 127 </li> 128<li class="listitem"> 129 A model of <a class="link" href="../../../sequence/concepts/associative_sequence.html" title="Associative Sequence">Associative 130 Sequence</a> if <code class="computeroutput"><span class="identifier">seq</span></code> 131 implements the <a class="link" href="../../../sequence/concepts/associative_sequence.html" title="Associative Sequence">Associative 132 Sequence</a> model. 133 </li> 134</ul></div> 135<p> 136 <span class="bold"><strong>Semantics</strong></span>: Returns a sequence containing 137 all the elements of <code class="computeroutput"><span class="identifier">seq</span></code> 138 with types for which <code class="computeroutput"><span class="identifier">Pred</span></code> 139 evaluates to <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">true_</span></code>. The order of the retained elements 140 is the same as in the original sequence. 141 </p> 142<h6> 143<a name="fusion.algorithm.transformation.functions.filter_if.h3"></a> 144 <span class="phrase"><a name="fusion.algorithm.transformation.functions.filter_if.complexity"></a></span><a class="link" href="filter_if.html#fusion.algorithm.transformation.functions.filter_if.complexity">Complexity</a> 145 </h6> 146<p> 147 Constant. Returns a view which is lazily evaluated. 148 </p> 149<h6> 150<a name="fusion.algorithm.transformation.functions.filter_if.h4"></a> 151 <span class="phrase"><a name="fusion.algorithm.transformation.functions.filter_if.header"></a></span><a class="link" href="filter_if.html#fusion.algorithm.transformation.functions.filter_if.header">Header</a> 152 </h6> 153<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">algorithm</span><span class="special">/</span><span class="identifier">transformation</span><span class="special">/</span><span class="identifier">filter_if</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 154<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">filter_if</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 155</pre> 156<h6> 157<a name="fusion.algorithm.transformation.functions.filter_if.h5"></a> 158 <span class="phrase"><a name="fusion.algorithm.transformation.functions.filter_if.example"></a></span><a class="link" href="filter_if.html#fusion.algorithm.transformation.functions.filter_if.example">Example</a> 159 </h6> 160<pre class="programlisting"><span class="keyword">const</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">int</span><span class="special">,</span><span class="keyword">double</span><span class="special">,</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">vec</span><span class="special">(</span><span class="number">1</span><span class="special">,</span><span class="number">2</span><span class="special">,</span><span class="number">3.0</span><span class="special">,</span><span class="number">4.0</span><span class="special">);</span> 161<span class="identifier">assert</span><span class="special">(</span><a class="link" href="filter_if.html" title="filter_if"><code class="computeroutput"><span class="identifier">filter_if</span></code></a><span class="special"><</span><span class="identifier">is_integral</span><span class="special"><</span><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">_</span><span class="special">></span> <span class="special">>(</span><span class="identifier">vec</span><span class="special">)</span> <span class="special">==</span> <a class="link" href="../../../container/generation/functions/make_vector.html" title="make_vector"><code class="computeroutput"><span class="identifier">make_vector</span></code></a><span class="special">(</span><span class="number">1</span><span class="special">,</span><span class="number">2</span><span class="special">));</span> 162</pre> 163</div> 164<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 165<td align="left"></td> 166<td align="right"><div class="copyright-footer">Copyright © 2001-2006, 2011, 2012 Joel de Guzman, 167 Dan Marsden, Tobias Schwinger<p> 168 Distributed under the Boost Software License, Version 1.0. (See accompanying 169 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>) 170 </p> 171</div></td> 172</tr></table> 173<hr> 174<div class="spirit-nav"> 175<a accesskey="p" href="filter.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../functions.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="transform.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> 176</div> 177</body> 178</html> 179
