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| Phoenix uses <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">is_placeholder</span></code> for recognizing placeholders: |
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| <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">struct</span> <span class="identifier">is_placeholder</span> |
| <span class="special">{</span> |
| <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> |
| <span class="special">};</span> |
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| To adapt your own placeholder, the nested value needs to be greater than |
| 0 for your types. This is done by specializing this trait. |
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