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  25 <div class="refentry">
  26 <a name="boost.proto.nullary_expr"></a><div class="titlepage"></div>
  27 <div class="refnamediv">
  28 <h2><span class="refentrytitle">Struct template nullary_expr</span></h2>
  29 <p>boost::proto::nullary_expr &#8212; A metafunction for generating nullary expression types, a grammar element for matching
  30           nullary expressions, and
  31           a <a class="link" href="../../PrimitiveTransform.html" title="Concept PrimitiveTransform">PrimitiveTransform</a> that returns the current expression unchanged. </p>
  32 </div>
  33 <h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
  34 <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;
  35
  36 </span><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Tag<span class="special">,</span> <span class="keyword">typename</span> T<span class="special">&gt;</span>
  37 <span class="keyword">struct</span> <a class="link" href="nullary_expr.html" title="Struct template nullary_expr">nullary_expr</a> <span class="special">:</span> <span class="keyword"></span> <a class="link" href="transform.html" title="Struct template transform">proto::transform</a><span class="special">&lt;</span> <span class="identifier">nullary_expr</span><span class="special">&lt;</span><span class="identifier">Tag</span><span class="special">,</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="special">&gt;</span> <span class="special">{</span>
  38   <span class="comment">// types</span>
  39   <span class="keyword">typedef</span> <a class="link" href="expr.html" title="Struct template expr">proto::expr</a><span class="special">&lt;</span> <span class="identifier">Tag</span><span class="special">,</span> <a class="link" href="term.html" title="Struct template term">proto::term</a><span class="special">&lt;</span> <span class="identifier">T</span> <span class="special">&gt;</span> <span class="special">&gt;</span>       <a name="boost.proto.nullary_expr.type"></a><span class="identifier">type</span><span class="special">;</span>
  40   <span class="keyword">typedef</span> <a class="link" href="basic_expr.html" title="Struct template basic_expr">proto::basic_expr</a><span class="special">&lt;</span> <span class="identifier">Tag</span><span class="special">,</span> <a class="link" href="term.html" title="Struct template term">proto::term</a><span class="special">&lt;</span> <span class="identifier">T</span> <span class="special">&gt;</span> <span class="special">&gt;</span> <a name="boost.proto.nullary_expr.proto_grammar"></a><span class="identifier">proto_grammar</span><span class="special">;</span>
  41
  42   <span class="comment">// member classes/structs/unions</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">,</span> <span class="keyword">typename</span> State<span class="special">,</span> <span class="keyword">typename</span> Data<span class="special">&gt;</span>
  44   <span class="keyword">struct</span> <a class="link" href="nullary_expr/impl.html" title="Struct template impl">impl</a> <span class="special">:</span> <span class="keyword"></span> <a class="link" href="transform_impl.html" title="Struct template transform_impl">proto::transform_impl</a><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> <span class="special">{</span>
  45     <span class="comment">// types</span>
  46     <span class="keyword">typedef</span> <span class="identifier">Expr</span> <a class="link" href="nullary_expr/impl.html#boost.proto.nullary_expr.impl.result_type"><span class="identifier">result_type</span></a><span class="special">;</span>
  47
  48     <span class="comment">// <a class="link" href="nullary_expr/impl.html#idp227426784-bb">public member functions</a></span>
  49     <span class="identifier">Expr</span> <a class="link" href="nullary_expr/impl.html#idp227427344-bb"><span class="keyword">operator</span><span class="special">(</span><span class="special">)</span></a><span class="special">(</span><span class="keyword">typename</span> <span class="identifier">impl</span><span class="special">::</span><span class="identifier">expr_param</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">impl</span><span class="special">::</span><span class="identifier">state_param</span><span class="special">,</span>
  50                     <span class="keyword">typename</span> <span class="identifier">impl</span><span class="special">::</span><span class="identifier">data_param</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
  51   <span class="special">}</span><span class="special">;</span>
  52 <span class="special">}</span><span class="special">;</span></pre></div>
  53 <div class="refsect1">
  54 <a name="idp385417024"></a><h2>Description</h2>
  55 <p>
  56             Use <code class="computeroutput">proto::nullary_expr&lt;<a class="link" href="_.html" title="Struct _">proto::_</a>, <a class="link" href="_.html" title="Struct _">proto::_</a>&gt;</code>
  57             as a grammar element to match any nullary expression.
  58           </p>
  59 </div>
  60 </div>
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  63 <td align="right"><div class="copyright-footer">Copyright &#169; 2008 Eric Niebler<p>
  64         Distributed under the Boost Software License, Version 1.0. (See accompanying
  65         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>)
  66       </p>
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