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  27 <a name="boost.proto.when_Grammar,_idp705850352.impl"></a><div class="titlepage"></div>
  28 <div class="refnamediv">
  29 <h2><span class="refentrytitle">Struct template impl</span></h2>
  30 <p>boost::proto::when&lt;Grammar, &gt;::impl</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.transform.when_hpp" title="Header &lt;boost/proto/transform/when.hpp&gt;">boost/proto/transform/when.hpp</a>&gt;
  34
  35 </span>
  36 <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">,</span> <span class="keyword">typename</span> State<span class="special">,</span> <span class="keyword">typename</span> Data<span class="special">&gt;</span>
  37 <span class="keyword">struct</span> <a class="link" href="impl.html" title="Struct template impl">impl</a> <span class="special">:</span> <span class="keyword"></span>
  38     <span class="identifier">boost</span><span class="special">::</span><span class="identifier">remove_reference</span><span class="special">&lt;</span>
  39       <span class="keyword">typename</span> <span class="identifier">mpl</span><span class="special">::</span><span class="identifier">eval_if_c</span><span class="special">&lt;</span>
  40         <a class="link" href="../result_of/has_env_var.html" title="Struct template has_env_var">proto::result_of::has_env_var</a><span class="special">&lt;</span><span class="identifier">Data</span><span class="special">,</span> <a class="link" href="../transforms_type.html" title="Struct transforms_type">proto::transforms_type</a><span class="special">&gt;</span><span class="special">::</span><span class="identifier">value</span><span class="special">,</span>
  41         <a class="link" href="../result_of/env_var.html" title="Struct template env_var">proto::result_of::env_var</a><span class="special">&lt;</span><span class="identifier">Data</span><span class="special">,</span> <a class="link" href="../transforms_type.html" title="Struct transforms_type">proto::transforms_type</a><span class="special">&gt;</span><span class="special">,</span>
  42         <a class="link" href="../result_of/env_var.html" title="Struct template env_var">proto::result_of::env_var</a><span class="special">&lt;</span><span class="identifier">Data</span><span class="special">,</span> <a class="link" href="../data_type.html" title="Struct data_type">proto::data_type</a><span class="special">&gt;</span>
  43       <span class="special">&gt;</span><span class="special">::</span><span class="identifier">type</span>
  44     <span class="special">&gt;</span><span class="special">::</span><span class="identifier">type</span>
  45       <span class="special">::</span><span class="keyword">template</span> <span class="identifier">when</span><span class="special">&lt;</span> <span class="identifier">Grammar</span> <span class="special">&gt;</span>
  46         <span class="special">::</span><span class="keyword">template</span> <span class="identifier">impl</span><span class="special">&lt;</span> <span class="identifier">Expr</span><span class="special">,</span> <span class="identifier">State</span><span class="special">,</span> <span class="identifier">Data</span> <span class="special">&gt;</span>
  47 <span class="special">{</span>
  48 <span class="special">}</span><span class="special">;</span></pre></div>
  49 <div class="refsect1">
  50 <a name="idp485280896"></a><h2>Description</h2>
  51 <p>
  52               The implementation of the <code class="computeroutput">impl</code> struct depends on whether the <code class="computeroutput">Data</code>
  53               parameter is a transform environment that contains a value corresponding to the
  54               <a class="link" href="../transforms_type.html" title="Struct transforms_type">proto::transforms_type</a> key. If so, that value is treated as a
  55               map from rules to transforms. Otherwise, the <code class="computeroutput">Data</code> type itself is treated
  56               as such a map.
  57             </p>
  58 </div>
  59 </div>
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  61 <td align="left"></td>
  62 <td align="right"><div class="copyright-footer">Copyright &#169; 2008 Eric Niebler<p>
  63         Distributed under the Boost Software License, Version 1.0. (See accompanying
  64         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>)
  65       </p>
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