1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>find_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="find.html" title="find"> 10<link rel="next" href="count.html" title="count"> 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="find.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="count.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.query.functions.find_if"></a><a class="link" href="find_if.html" title="find_if">find_if</a> 28</h5></div></div></div> 29<h6> 30<a name="fusion.algorithm.query.functions.find_if.h0"></a> 31 <span class="phrase"><a name="fusion.algorithm.query.functions.find_if.description"></a></span><a class="link" href="find_if.html#fusion.algorithm.query.functions.find_if.description">Description</a> 32 </h6> 33<p> 34 Finds the first element within a sequence with a type for which a given 35 <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.query.functions.find_if.h1"></a> 40 <span class="phrase"><a name="fusion.algorithm.query.functions.find_if.synopsis"></a></span><a class="link" href="find_if.html#fusion.algorithm.query.functions.find_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">F</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/find_if.html" title="find_if"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">find_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">F</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">find_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 48<span class="keyword">template</span><span class="special"><</span> 49 <span class="keyword">typename</span> <span class="identifier">F</span><span class="special">,</span> 50 <span class="keyword">typename</span> <span class="identifier">Sequence</span> 51 <span class="special">></span> 52<span class="keyword">typename</span> <a class="link" href="../metafunctions/find_if.html" title="find_if"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">find_if</span></code></a><span class="special"><</span><span class="identifier">Sequence</span><span class="special">,</span> <span class="identifier">F</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">find_if</span><span class="special">(</span><span class="identifier">Sequence</span><span class="special">&</span> <span class="identifier">seq</span><span class="special">);</span> 53</pre> 54<div class="table"> 55<a name="fusion.algorithm.query.functions.find_if.t0"></a><p class="title"><b>Table 1.56. Parameters</b></p> 56<div class="table-contents"><table class="table" summary="Parameters"> 57<colgroup> 58<col> 59<col> 60<col> 61</colgroup> 62<thead><tr> 63<th> 64 <p> 65 Parameter 66 </p> 67 </th> 68<th> 69 <p> 70 Requirement 71 </p> 72 </th> 73<th> 74 <p> 75 Description 76 </p> 77 </th> 78</tr></thead> 79<tbody> 80<tr> 81<td> 82 <p> 83 <code class="computeroutput"><span class="identifier">seq</span></code> 84 </p> 85 </td> 86<td> 87 <p> 88 A model of <a class="link" href="../../../sequence/concepts/forward_sequence.html" title="Forward Sequence">Forward 89 Sequence</a> 90 </p> 91 </td> 92<td> 93 <p> 94 The sequence to search 95 </p> 96 </td> 97</tr> 98<tr> 99<td> 100 <p> 101 <code class="computeroutput"><span class="identifier">F</span></code> 102 </p> 103 </td> 104<td> 105 <p> 106 A unary <a href="http://www.boost.org/libs/mpl/doc/refmanual/lambda-expression.html" target="_top">MPL 107 Lambda Expression</a> 108 </p> 109 </td> 110<td> 111 <p> 112 The search predicate 113 </p> 114 </td> 115</tr> 116</tbody> 117</table></div> 118</div> 119<br class="table-break"><h6> 120<a name="fusion.algorithm.query.functions.find_if.h2"></a> 121 <span class="phrase"><a name="fusion.algorithm.query.functions.find_if.expression_semantics"></a></span><a class="link" href="find_if.html#fusion.algorithm.query.functions.find_if.expression_semantics">Expression 122 Semantics</a> 123 </h6> 124<pre class="programlisting"><a class="link" href="find_if.html" title="find_if"><code class="computeroutput"><span class="identifier">find_if</span></code></a><span class="special"><</span><span class="identifier">F</span><span class="special">>(</span><span class="identifier">seq</span><span class="special">)</span> 125</pre> 126<p> 127 <span class="bold"><strong>Return type</strong></span>: An iterator of the same 128 iterator category as the iterators of <code class="computeroutput"><span class="identifier">seq</span></code>. 129 </p> 130<p> 131 <span class="bold"><strong>Semantics</strong></span>: Returns the first element 132 of <code class="computeroutput"><span class="identifier">seq</span></code> for which <a href="http://www.boost.org/libs/mpl/doc/refmanual/lambda-expression.html" target="_top">MPL 133 Lambda Expression</a> <code class="computeroutput"><span class="identifier">F</span></code> 134 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>, or <code class="computeroutput"><a class="link" href="../../../sequence/intrinsic/functions/end.html" title="end"><code class="computeroutput"><span class="identifier">end</span></code></a><span class="special">(</span><span class="identifier">seq</span><span class="special">)</span></code> 135 if there is no such element. 136 </p> 137<h6> 138<a name="fusion.algorithm.query.functions.find_if.h3"></a> 139 <span class="phrase"><a name="fusion.algorithm.query.functions.find_if.complexity"></a></span><a class="link" href="find_if.html#fusion.algorithm.query.functions.find_if.complexity">Complexity</a> 140 </h6> 141<p> 142 Linear. At most <code class="computeroutput"><a class="link" href="../../../sequence/intrinsic/metafunctions/size.html" title="size"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">size</span></code></a><span class="special"><</span><span class="identifier">Sequence</span><span class="special">>::</span><span class="identifier">value</span></code> comparisons. 143 </p> 144<h6> 145<a name="fusion.algorithm.query.functions.find_if.h4"></a> 146 <span class="phrase"><a name="fusion.algorithm.query.functions.find_if.header"></a></span><a class="link" href="find_if.html#fusion.algorithm.query.functions.find_if.header">Header</a> 147 </h6> 148<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">query</span><span class="special">/</span><span class="identifier">find_if</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 149<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">find_if</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 150</pre> 151<h6> 152<a name="fusion.algorithm.query.functions.find_if.h5"></a> 153 <span class="phrase"><a name="fusion.algorithm.query.functions.find_if.example"></a></span><a class="link" href="find_if.html#fusion.algorithm.query.functions.find_if.example">Example</a> 154 </h6> 155<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">double</span><span class="special">,</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">vec</span><span class="special">(</span><span class="number">1.0</span><span class="special">,</span><span class="number">2</span><span class="special">);</span> 156<span class="identifier">assert</span><span class="special">(*</span><a class="link" href="find_if.html" title="find_if"><code class="computeroutput"><span class="identifier">find_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> <span class="number">2</span><span class="special">);</span> 157<span class="identifier">assert</span><span class="special">(</span><a class="link" href="find_if.html" title="find_if"><code class="computeroutput"><span class="identifier">find_if</span></code></a><span class="special"><</span><span class="identifier">is_class</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="../../../sequence/intrinsic/functions/end.html" title="end"><code class="computeroutput"><span class="identifier">end</span></code></a><span class="special">(</span><span class="identifier">vec</span><span class="special">));</span> 158</pre> 159</div> 160<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 161<td align="left"></td> 162<td align="right"><div class="copyright-footer">Copyright © 2001-2006, 2011, 2012 Joel de Guzman, 163 Dan Marsden, Tobias Schwinger<p> 164 Distributed under the Boost Software License, Version 1.0. (See accompanying 165 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>) 166 </p> 167</div></td> 168</tr></table> 169<hr> 170<div class="spirit-nav"> 171<a accesskey="p" href="find.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="count.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> 172</div> 173</body> 174</html> 175
