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30 Phoenix uses
<code class=
"computeroutput"><span class=
"identifier">boost
</span><span class=
"special">::
</span><span class=
"identifier">is_placeholder
</span></code> for recognizing placeholders:
32 <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>
33 <span class=
"keyword">struct
</span> <span class=
"identifier">is_placeholder
</span>
34 <span class=
"special">{
</span>
35 <span class=
"keyword">static
</span> <span class=
"keyword">const
</span> <span class=
"keyword">int
</span> <span class=
"identifier">value
</span> <span class=
"special">=
</span> <span class=
"number">0</span><span class=
"special">;
</span>
36 <span class=
"special">};
</span>
39 To adapt your own placeholder, the nested value needs to be greater than
40 0 for your types. This is done by specializing this trait.
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© 2002-
2005,
2010,
2014,
2015 Joel de Guzman, Dan Marsden, Thomas
46 Heller, John Fletcher
<p>
47 Distributed under the Boost Software License, Version
1.0. (See accompanying
48 file LICENSE_1_0.txt or copy at
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