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  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 <p>
  30             Finds the first element within a sequence with a type for which a given
  31             <a href="http://www.boost.org/libs/mpl/doc/refmanual/lambda-expression.html" target="_top">MPL
  32             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>.
  33           </p>
  34 <h6>
  35 <a name="fusion.algorithm.query.functions.find_if.h0"></a>
  36             <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>
  37           </h6>
  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">&lt;</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">&gt;</span>
  46 <span class="emphasis"><em>unspecified</em></span> <span class="identifier">find_if</span><span class="special">(</span><span class="identifier">Sequence</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">seq</span><span class="special">);</span>
  47
  48 <span class="keyword">template</span><span class="special">&lt;</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">&gt;</span>
  52 <span class="emphasis"><em>unspecified</em></span> <span class="identifier">find_if</span><span class="special">(</span><span class="identifier">Sequence</span><span class="special">&amp;</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&#160;1.54.&#160;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">&lt;</span><span class="identifier">F</span><span class="special">&gt;(</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">&lt;</span><span class="identifier">Sequence</span><span class="special">&gt;::</span><span class="identifier">value</span></code> comparisons.
 143           </p>
 144 <div class="orderedlist"><ol class="orderedlist" type="1">
 145 <li class="listitem">
 146                 include &lt;boost/fusion/algorithm/query/find_if.hpp&gt;
 147               </li>
 148 <li class="listitem">
 149                 include &lt;boost/fusion/include/find_if.hpp&gt;
 150               </li>
 151 </ol></div>
 152 <h6>
 153 <a name="fusion.algorithm.query.functions.find_if.h4"></a>
 154             <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>
 155           </h6>
 156 <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">&lt;</span><span class="keyword">double</span><span class="special">,</span><span class="keyword">int</span><span class="special">&gt;</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>
 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">&lt;</span><span class="identifier">is_integral</span><span class="special">&lt;</span><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">_</span><span class="special">&gt;</span> <span class="special">&gt;(</span><span class="identifier">vec</span><span class="special">)</span> <span class="special">==</span> <span class="number">2</span><span class="special">);</span>
 158 <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">&lt;</span><span class="identifier">is_class</span><span class="special">&lt;</span><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">_</span><span class="special">&gt;</span> <span class="special">&gt;(</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>
 159 </pre>
 160 </div>
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 162 <td align="left"></td>
 163 <td align="right"><div class="copyright-footer">Copyright &#169; 2001-2006, 2011, 2012 Joel de Guzman,
 164       Dan Marsden, Tobias Schwinger<p>
 165         Distributed under the Boost Software License, Version 1.0. (See accompanying
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