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<title>Getting the type of data</title>
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<div class="titlepage"><div><div><h3 class="title">
<a name="variadic_macro_data.vmd_generic.vmd_convert_sequence"></a><a class="link" href="vmd_convert_sequence.html" title="Getting the type of data">Getting
      the type of data</a>
</h3></div></div></div>
<p>
        VMD has the ability to retrieve the type of any data which it can parse,
        which means any VMD sequence. The macro to do this is called BOOST_VMD_GET_TYPE
        and it takes a single required parameter, which is a VMD sequence.
      </p>
<p>
        It returns one of the types previously discussed when introducing v-types
        as an identifier subset. As explained previously in that topic a v-type is
        fully recognized by VMD macros and can be part of a sequence and passed as
        VMD data just like all the other data types VMD recognizes.
      </p>
<p>
        When BOOST_VMD_GET_TYPE returns the type of data it returns by default the
        most specific type that the data can be. This means that non-empty lists
        and arrays are returned as such, not as tuples, and numbers and types and
        empty lists are returned as such, not as identifiers.
      </p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">vmd</span><span class="special">/</span><span class="identifier">get_type</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>

<span class="preprocessor">#define</span> <span class="identifier">BOOST_VMD_REGISTER_ANID</span> <span class="special">(</span><span class="identifier">ANID</span><span class="special">)</span>
<span class="preprocessor">#define</span> <span class="identifier">SEQUENCE_EMPTY</span>
<span class="preprocessor">#define</span> <span class="identifier">SEQUENCE_MULTI</span> <span class="special">(</span><span class="number">1</span><span class="special">,</span><span class="number">2</span><span class="special">,</span><span class="number">3</span><span class="special">)</span> <span class="number">88</span>
<span class="preprocessor">#define</span> <span class="identifier">SEQUENCE1</span> <span class="special">(</span><span class="number">3</span><span class="special">,(</span><span class="number">1</span><span class="special">,</span><span class="number">2</span><span class="special">,</span><span class="number">3</span><span class="special">))</span>
<span class="preprocessor">#define</span> <span class="identifier">SEQUENCE2</span> <span class="identifier">ANID</span>
<span class="preprocessor">#define</span> <span class="identifier">SEQUENCE3</span> <span class="special">(</span><span class="number">1</span><span class="special">,(</span><span class="number">2</span><span class="special">,(</span><span class="number">3</span><span class="special">,</span><span class="identifier">BOOST_PP_NIL</span><span class="special">)))</span>
<span class="preprocessor">#define</span> <span class="identifier">SEQUENCE4</span> <span class="number">1</span>
<span class="preprocessor">#define</span> <span class="identifier">SEQUENCE5</span> <span class="special">(</span><span class="number">1</span><span class="special">)(</span><span class="number">2</span><span class="special">)(</span><span class="number">3</span><span class="special">)</span>
<span class="preprocessor">#define</span> <span class="identifier">SEQUENCE6</span> <span class="special">(</span><span class="number">1</span><span class="special">,</span><span class="number">2</span><span class="special">,</span><span class="number">3</span><span class="special">)</span>
<span class="preprocessor">#define</span> <span class="identifier">SEQUENCE7</span> <span class="identifier">BOOST_VMD_TYPE_NUMBER</span>

<span class="identifier">BOOST_VMD_GET_TYPE</span><span class="special">(</span><span class="identifier">SEQUENCE_EMPTY</span><span class="special">)</span> <span class="identifier">will</span> <span class="keyword">return</span> <span class="identifier">BOOST_VMD_TYPE_EMPTY</span>
<span class="identifier">BOOST_VMD_GET_TYPE</span><span class="special">(</span><span class="identifier">SEQUENCE_MULTI</span><span class="special">)</span> <span class="identifier">will</span> <span class="keyword">return</span> <span class="identifier">BOOST_VMD_TYPE_SEQUENCE</span>
<span class="identifier">BOOST_VMD_GET_TYPE</span><span class="special">(</span><span class="identifier">SEQUENCE1</span><span class="special">)</span> <span class="identifier">will</span> <span class="keyword">return</span> <span class="identifier">BOOST_VMD_TYPE_ARRAY</span>
<span class="identifier">BOOST_VMD_GET_TYPE</span><span class="special">(</span><span class="identifier">SEQUENCE2</span><span class="special">)</span> <span class="identifier">will</span> <span class="keyword">return</span> <span class="identifier">BOOST_VMD_TYPE_IDENTIFIER</span>
<span class="identifier">BOOST_VMD_GET_TYPE</span><span class="special">(</span><span class="identifier">SEQUENCE3</span><span class="special">)</span> <span class="identifier">will</span> <span class="keyword">return</span> <span class="identifier">BOOST_VMD_TYPE_LIST</span>
<span class="identifier">BOOST_VMD_GET_TYPE</span><span class="special">(</span><span class="identifier">SEQUENCE4</span><span class="special">)</span> <span class="identifier">will</span> <span class="keyword">return</span> <span class="identifier">BOOST_VMD_TYPE_NUMBER</span>
<span class="identifier">BOOST_VMD_GET_TYPE</span><span class="special">(</span><span class="identifier">SEQUENCE5</span><span class="special">)</span> <span class="identifier">will</span> <span class="keyword">return</span> <span class="identifier">BOOST_VMD_TYPE_SEQ</span>
<span class="identifier">BOOST_VMD_GET_TYPE</span><span class="special">(</span><span class="identifier">SEQUENCE6</span><span class="special">)</span> <span class="identifier">will</span> <span class="keyword">return</span> <span class="identifier">BOOST_VMD_TYPE_TUPLE</span>
<span class="identifier">BOOST_VMD_GET_TYPE</span><span class="special">(</span><span class="identifier">SEQUENCE7</span><span class="special">)</span> <span class="identifier">will</span> <span class="keyword">return</span> <span class="identifier">BOOST_VMD_TYPE_TYPE</span>
</pre>
<h5>
<a name="variadic_macro_data.vmd_generic.vmd_convert_sequence.h0"></a>
        <span class="phrase"><a name="variadic_macro_data.vmd_generic.vmd_convert_sequence.usage"></a></span><a class="link" href="vmd_convert_sequence.html#variadic_macro_data.vmd_generic.vmd_convert_sequence.usage">Usage</a>
      </h5>
<p>
        You can use the general header file:
      </p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">vmd</span><span class="special">/</span><span class="identifier">vmd</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
</pre>
<p>
        or you can use the individual header file:
      </p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">vmd</span><span class="special">/</span><span class="identifier">get_type</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
</pre>
<p>
        for the BOOST_VMD_GET_TYPE macro.
      </p>
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