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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>> |
| |
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| <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="id2283867"></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> |
| </div> |
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| <td align="left"></td> |
| <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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