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  27 <a name="boost.proto.child_idp930674992"></a><div class="titlepage"></div>
  28 <div class="refnamediv">
  29 <h2><span class="refentrytitle">Function child</span></h2>
  30 <p>boost::proto::child &#8212; Return the <em class="replaceable"><code>N</code></em><sup>th</sup> child of the specified Proto expression. </p>
  31 </div>
  32 <h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
  33 <div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link" href="../../proto/reference.html#header.boost.proto.traits_hpp" title="Header &lt;boost/proto/traits.hpp&gt;">boost/proto/traits.hpp</a>&gt;
  34
  35 </span>
  36 <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> N<span class="special">,</span> <span class="keyword">typename</span> <a class="link" href="../../Expr.html" title="Concept Expr">Expr</a><span class="special">&gt;</span>
  37   <span class="keyword">typename</span> <a class="link" href="result_of/child.html" title="Struct template child">proto::result_of::child</a><span class="special">&lt;</span> <span class="identifier">Expr</span> <span class="special">&amp;</span><span class="special">,</span> <span class="identifier">N</span> <span class="special">&gt;</span><span class="special">::</span><span class="identifier">type</span> <span class="identifier">child</span><span class="special">(</span><span class="identifier">Expr</span> <span class="special">&amp;</span> expr<span class="special">)</span><span class="special">;</span>
  38 <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> N<span class="special">,</span> <span class="keyword">typename</span> <a class="link" href="../../Expr.html" title="Concept Expr">Expr</a><span class="special">&gt;</span>
  39   <span class="keyword">typename</span> <a class="link" href="result_of/child.html" title="Struct template child">proto::result_of::child</a><span class="special">&lt;</span> <span class="identifier">Expr</span> <span class="keyword">const</span> <span class="special">&amp;</span><span class="special">,</span> <span class="identifier">N</span> <span class="special">&gt;</span><span class="special">::</span><span class="identifier">type</span>
  40   <span class="identifier">child</span><span class="special">(</span><span class="identifier">Expr</span> <span class="keyword">const</span> <span class="special">&amp;</span> expr<span class="special">)</span><span class="special">;</span>
  41 <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <a class="link" href="../../Expr.html" title="Concept Expr">Expr</a><span class="special">&gt;</span>
  42   <span class="keyword">typename</span> <a class="link" href="result_of/child.html" title="Struct template child">proto::result_of::child</a><span class="special">&lt;</span> <span class="identifier">Expr</span> <span class="special">&amp;</span> <span class="special">&gt;</span><span class="special">::</span><span class="identifier">type</span> <span class="identifier">child</span><span class="special">(</span><span class="identifier">Expr</span> <span class="special">&amp;</span> expr<span class="special">)</span><span class="special">;</span>
  43 <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <a class="link" href="../../Expr.html" title="Concept Expr">Expr</a><span class="special">&gt;</span>
  44   <span class="keyword">typename</span> <a class="link" href="result_of/child.html" title="Struct template child">proto::result_of::child</a><span class="special">&lt;</span> <span class="identifier">Expr</span> <span class="keyword">const</span> <span class="special">&amp;</span> <span class="special">&gt;</span><span class="special">::</span><span class="identifier">type</span>
  45   <span class="identifier">child</span><span class="special">(</span><span class="identifier">Expr</span> <span class="keyword">const</span> <span class="special">&amp;</span> expr<span class="special">)</span><span class="special">;</span></pre></div>
  46 <div class="refsect1">
  47 <a name="idp566273776"></a><h2>Description</h2>
  48 <p>
  49             Return the <em class="replaceable"><code>N</code></em><sup>th</sup> child of the specified Proto expression.
  50             If <code class="computeroutput">N</code> is not specified, as in <code class="computeroutput">proto::child(expr)</code>,
  51             then <code class="computeroutput">N</code> is assumed to be <code class="computeroutput">mpl::long_&lt;0&gt;</code>.
  52             The child is returned by reference.
  53           </p>
  54 <div class="variablelist"><table border="0" class="variablelist compact">
  55 <colgroup>
  56 <col align="left" valign="top">
  57 <col>
  58 </colgroup>
  59 <tbody>
  60 <tr>
  61 <td><p><span class="term">Parameters:</span></p></td>
  62 <td><div class="variablelist"><table border="0" class="variablelist compact">
  63 <colgroup>
  64 <col align="left" valign="top">
  65 <col>
  66 </colgroup>
  67 <tbody><tr>
  68 <td><p><span class="term"><code class="computeroutput">expr</code></span></p></td>
  69 <td><p>The Proto expression. </p></td>
  70 </tr></tbody>
  71 </table></div></td>
  72 </tr>
  73 <tr>
  74 <td><p><span class="term">Requires:</span></p></td>
  75 <td>
  76 <p>
  77             <code class="computeroutput"><a class="link" href="is_expr.html" title="Struct template is_expr">proto::is_expr</a>&lt;Expr&gt;::value</code> is
  78             <code class="computeroutput">true</code>.
  79           </p>
  80 <p>
  81             <code class="computeroutput">N</code> is an MPL Integral Constant.
  82           </p>
  83 <p>
  84             <code class="computeroutput">N::value &lt; Expr::proto_arity::value</code>
  85           </p>
  86 </td>
  87 </tr>
  88 <tr>
  89 <td><p><span class="term">Returns:</span></p></td>
  90 <td><p>A reference to the <em class="replaceable"><code>N</code></em><sup>th</sup> child
  91           of <code class="computeroutput">expr</code>.</p></td>
  92 </tr>
  93 <tr>
  94 <td><p><span class="term">Throws:</span></p></td>
  95 <td>Will not throw.</td>
  96 </tr>
  97 </tbody>
  98 </table></div>
  99 </div>
 100 </div>
 101 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 102 <td align="left"></td>
 103 <td align="right"><div class="copyright-footer">Copyright &#169; 2008 Eric Niebler<p>
 104         Distributed under the Boost Software License, Version 1.0. (See accompanying
 105         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>)
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