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<a name="boost.proto.is_proto_expr"></a><div class="titlepage"></div>
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<h2><span class="refentrytitle">Struct is_proto_expr</span></h2>
<p>boost::proto::is_proto_expr — Empty type to be used as a dummy template parameter of POD expression wrappers. It allows
argument-dependent lookup to find Proto's operator overloads.</p>
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<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
<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.extends_hpp" title="Header <boost/proto/extends.hpp>">boost/proto/extends.hpp</a>>
</span>
<span class="keyword">struct</span> <a class="link" href="is_proto_expr.html" title="Struct is_proto_expr">is_proto_expr</a> <span class="special">{</span>
<span class="special">}</span><span class="special">;</span></pre></div>
<div class="refsect1">
<a name="idm45555191213952"></a><h2>Description</h2>
<p>
<code class="computeroutput">proto::is_proto_expr</code> allows argument-dependent lookup to find Proto's operator overloads. For example:
</p>
<p>
</p>
<pre class="programlisting"> <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Dummy</span> <span class="special">=</span> <a class="link" href="is_proto_expr.html" title="Struct is_proto_expr">proto::is_proto_expr</a><span class="special">></span>
<span class="keyword">struct</span> <span class="identifier">my_terminal</span>
<span class="special">{</span>
<a class="link" href="../../BOOST_PROTO_BASIC_EXTENDS.html" title="Macro BOOST_PROTO_BASIC_EXTENDS">BOOST_PROTO_BASIC_EXTENDS</a><span class="special">(</span>
<span class="keyword">typename</span> <a class="link" href="terminal.html" title="Struct template terminal">proto::terminal</a><span class="special"><</span><span class="identifier">T</span><span class="special">></span><span class="special">::</span><span class="identifier">type</span>
<span class="special">,</span> <span class="identifier">my_terminal</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span>
<span class="special">,</span> <a class="link" href="default_domain.html" title="Struct default_domain">proto::default_domain</a>
<span class="special">)</span>
<span class="special">}</span><span class="special">;</span>
<span class="comment">// ...</span>
<span class="identifier">my_terminal</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">_1</span><span class="special">,</span> <span class="identifier">_2</span><span class="special">;</span>
<span class="identifier">_1</span> <span class="special">+</span> <span class="identifier">_2</span><span class="special">;</span> <span class="comment">// OK, uses proto::operator+</span></pre>
<p>
</p>
<p>
Without the second <code class="computeroutput">Dummy</code> template parameter, Proto's operator overloads
would not be considered by name lookup.
</p>
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<td align="right"><div class="copyright-footer">Copyright © 2008 Eric Niebler<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
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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