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27 <a name="boost.proto.is_expr"></a><div class="titlepage"></div>
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29 <h2><span class="refentrytitle">Struct template is_expr</span></h2>
30 <p>boost::proto::is_expr — A Boolean metafunction that indicates whether a given type <code class="computeroutput">T</code>
31 is a Proto expression type.</p>
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: <<a class="link" href="../../proto/reference.html#header.boost.proto.traits_hpp" title="Header <boost/proto/traits.hpp>">boost/proto/traits.hpp</a>>
36 </span><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span>
37 <span class="keyword">struct</span> <a class="link" href="is_expr.html" title="Struct template is_expr">is_expr</a> <span class="special">:</span> <span class="keyword"></span> mpl::bool_<<em class="replaceable"><code>true-or-false</code></em>> <span class="special">{</span>
38 <span class="special">}</span><span class="special">;</span></pre></div>
39 <div class="refsect1">
40 <a name="idp478370368"></a><h2>Description</h2>
42 If <code class="computeroutput">T</code> is an instantiation of
43 <code class="computeroutput"><a class="link" href="expr.html" title="Struct template expr">proto::expr<></a></code> or
44 <code class="computeroutput"><a class="link" href="basic_expr.html" title="Struct template basic_expr">proto::basic_expr<></a></code> or is an extension
45 (via <a class="link" href="extends.html" title="Struct template extends">proto::extends<></a> or
46 <a class="link" href="../../BOOST_PROTO_EXTENDS.html" title="Macro BOOST_PROTO_EXTENDS">BOOST_PROTO_EXTENDS</a>()) of such an instantiation,
47 <code class="computeroutput"><a class="link" href="is_expr.html" title="Struct template is_expr">proto::is_expr</a><T>::value</code>
48 is <code class="computeroutput">true</code>.
49 Otherwise, <code class="computeroutput"><a class="link" href="is_expr.html" title="Struct template is_expr">proto::is_expr</a><T>::value</code>
50 is <code class="computeroutput">false</code>.
54 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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56 <td align="right"><div class="copyright-footer">Copyright © 2008 Eric Niebler<p>
57 Distributed under the Boost Software License, Version 1.0. (See accompanying
58 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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