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- <div class="section">
- <div class="titlepage"><div><div><h3 class="title">
- <a name="boost_typetraits.reference.function_traits"></a><a class="link" href="function_traits.html" title="function_traits">function_traits</a>
- </h3></div></div></div>
- <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span>
- <span class="keyword">struct</span> <span class="identifier">function_traits</span>
- <span class="special">{</span>
- <span class="keyword">static</span> <span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">arity</span> <span class="special">=</span> <em class="replaceable"><code>see-below</code></em><span class="special">;</span>
- <span class="keyword">typedef</span> <em class="replaceable"><code>see-below</code></em> <span class="identifier">result_type</span><span class="special">;</span>
- <span class="keyword">typedef</span> <em class="replaceable"><code>see-below</code></em> arg<em class="replaceable"><code>N</code></em>_type<span class="special">;</span>
- <span class="special">};</span>
- </pre>
- <p>
- The class template function_traits will only compile if:
- </p>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- The compiler supports partial specialization of class templates.
- </li>
- <li class="listitem">
- The template argument <code class="computeroutput"><span class="identifier">F</span></code>
- is a <span class="emphasis"><em>function type</em></span>, note that this <span class="emphasis"><em><span class="bold"><strong>is not</strong></span></em></span> the same thing as a <span class="emphasis"><em>pointer
- to a function</em></span>.
- </li>
- </ul></div>
- <div class="tip"><table border="0" summary="Tip">
- <tr>
- <td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="../../../../../../doc/src/images/tip.png"></td>
- <th align="left">Tip</th>
- </tr>
- <tr><td align="left" valign="top"><p>
- function_traits is intended to introspect only C++ functions of the form
- R (), R( A1 ), R ( A1, ... etc. ) and not function pointers or class member
- functions. To convert a function pointer type to a suitable type use <a class="link" href="remove_pointer.html" title="remove_pointer">remove_pointer</a>.
- </p></td></tr>
- </table></div>
- <div class="table">
- <a name="boost_typetraits.reference.function_traits.function_traits_members"></a><p class="title"><b>Table 1.22. Function Traits Members</b></p>
- <div class="table-contents"><table class="table" summary="Function Traits Members">
- <colgroup>
- <col>
- <col>
- </colgroup>
- <thead><tr>
- <th>
- <p>
- Member
- </p>
- </th>
- <th>
- <p>
- Description
- </p>
- </th>
- </tr></thead>
- <tbody>
- <tr>
- <td>
- <p>
- <code class="computeroutput"><span class="identifier">function_traits</span><span class="special"><</span><span class="identifier">F</span><span class="special">>::</span><span class="identifier">arity</span></code>
- </p>
- </td>
- <td>
- <p>
- An integral constant expression that gives the number of arguments
- accepted by the function type <code class="computeroutput"><span class="identifier">F</span></code>.
- </p>
- </td>
- </tr>
- <tr>
- <td>
- <p>
- <code class="computeroutput"><span class="identifier">function_traits</span><span class="special"><</span><span class="identifier">F</span><span class="special">>::</span><span class="identifier">result_type</span></code>
- </p>
- </td>
- <td>
- <p>
- The type returned by function type <code class="computeroutput"><span class="identifier">F</span></code>.
- </p>
- </td>
- </tr>
- <tr>
- <td>
- <p>
- <code class="computeroutput"><span class="identifier">function_traits</span><span class="special"><</span><span class="identifier">F</span><span class="special">>::</span>arg<em class="replaceable"><code>N</code></em>_type</code>
- </p>
- </td>
- <td>
- <p>
- The <em class="replaceable"><code>N</code></em>th argument type of function type <code class="computeroutput"><span class="identifier">F</span></code>,
- where <code class="computeroutput"><span class="number">1</span> <span class="special"><=</span>
- <span class="identifier">N</span> <span class="special"><=</span>
- <span class="identifier">arity</span></code> of <code class="computeroutput"><span class="identifier">F</span></code>.
- </p>
- </td>
- </tr>
- </tbody>
- </table></div>
- </div>
- <br class="table-break"><div class="table">
- <a name="boost_typetraits.reference.function_traits.examples"></a><p class="title"><b>Table 1.23. Examples</b></p>
- <div class="table-contents"><table class="table" summary="Examples">
- <colgroup>
- <col>
- <col>
- </colgroup>
- <thead><tr>
- <th>
- <p>
- Expression
- </p>
- </th>
- <th>
- <p>
- Result
- </p>
- </th>
- </tr></thead>
- <tbody>
- <tr>
- <td>
- <p>
- <code class="computeroutput"><span class="identifier">function_traits</span><span class="special"><</span><span class="keyword">void</span>
- <span class="special">(</span><span class="keyword">void</span><span class="special">)>::</span><span class="identifier">arity</span></code>
- </p>
- </td>
- <td>
- <p>
- An integral constant expression that has the value 0.
- </p>
- </td>
- </tr>
- <tr>
- <td>
- <p>
- <code class="computeroutput"><span class="identifier">function_traits</span><span class="special"><</span><span class="keyword">long</span>
- <span class="special">(</span><span class="keyword">int</span><span class="special">)>::</span><span class="identifier">arity</span></code>
- </p>
- </td>
- <td>
- <p>
- An integral constant expression that has the value 1.
- </p>
- </td>
- </tr>
- <tr>
- <td>
- <p>
- <code class="computeroutput"><span class="identifier">function_traits</span><span class="special"><</span><span class="keyword">long</span>
- <span class="special">(</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">long</span><span class="special">,</span> <span class="keyword">double</span><span class="special">,</span> <span class="keyword">void</span><span class="special">*)>::</span><span class="identifier">arity</span></code>
- </p>
- </td>
- <td>
- <p>
- An integral constant expression that has the value 4.
- </p>
- </td>
- </tr>
- <tr>
- <td>
- <p>
- <code class="computeroutput"><span class="identifier">function_traits</span><span class="special"><</span><span class="keyword">void</span>
- <span class="special">(</span><span class="keyword">void</span><span class="special">)>::</span><span class="identifier">result_type</span></code>
- </p>
- </td>
- <td>
- <p>
- The type <code class="computeroutput"><span class="keyword">void</span></code>.
- </p>
- </td>
- </tr>
- <tr>
- <td>
- <p>
- <code class="computeroutput"><span class="identifier">function_traits</span><span class="special"><</span><span class="keyword">long</span>
- <span class="special">(</span><span class="keyword">int</span><span class="special">)>::</span><span class="identifier">result_type</span></code>
- </p>
- </td>
- <td>
- <p>
- The type <code class="computeroutput"><span class="keyword">long</span></code>.
- </p>
- </td>
- </tr>
- <tr>
- <td>
- <p>
- <code class="computeroutput"><span class="identifier">function_traits</span><span class="special"><</span><span class="keyword">long</span>
- <span class="special">(</span><span class="keyword">int</span><span class="special">)>::</span><span class="identifier">arg1_type</span></code>
- </p>
- </td>
- <td>
- <p>
- The type <code class="computeroutput"><span class="keyword">int</span></code>.
- </p>
- </td>
- </tr>
- <tr>
- <td>
- <p>
- <code class="computeroutput"><span class="identifier">function_traits</span><span class="special"><</span><span class="keyword">long</span>
- <span class="special">(</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">long</span><span class="special">,</span> <span class="keyword">double</span><span class="special">,</span> <span class="keyword">void</span><span class="special">*)>::</span><span class="identifier">arg4_type</span></code>
- </p>
- </td>
- <td>
- <p>
- The type <code class="computeroutput"><span class="keyword">void</span><span class="special">*</span></code>.
- </p>
- </td>
- </tr>
- <tr>
- <td>
- <p>
- <code class="computeroutput"><span class="identifier">function_traits</span><span class="special"><</span><span class="keyword">long</span>
- <span class="special">(</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">long</span><span class="special">,</span> <span class="keyword">double</span><span class="special">,</span> <span class="keyword">void</span><span class="special">*)>::</span><span class="identifier">arg5_type</span></code>
- </p>
- </td>
- <td>
- <p>
- A compiler error: there is no <code class="computeroutput"><span class="identifier">arg5_type</span></code>
- since there are only four arguments.
- </p>
- </td>
- </tr>
- <tr>
- <td>
- <p>
- <code class="computeroutput"><span class="identifier">function_traits</span><span class="special"><</span><span class="keyword">long</span>
- <span class="special">(*)(</span><span class="keyword">void</span><span class="special">)>::</span><span class="identifier">arity</span></code>
- </p>
- </td>
- <td>
- <p>
- A compiler error: argument type is a <span class="emphasis"><em>function pointer</em></span>,
- and not a <span class="emphasis"><em>function type</em></span>.
- </p>
- </td>
- </tr>
- </tbody>
- </table></div>
- </div>
- <br class="table-break"><p>
- <span class="bold"><strong>Compiler Compatibility:</strong></span> All current compilers
- are supported by this trait.
- </p>
- </div>
- <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
- <td align="left"></td>
- <td align="right"><div class="copyright-footer">Copyright © 2000, 2011 Adobe Systems Inc, David Abrahams,
- Frederic Bron, Steve Cleary, Beman Dawes, Aleksey Gurtovoy, Howard Hinnant,
- Jesse Jones, Mat Marcus, Itay Maman, John Maddock, Alexander Nasonov, Thorsten
- Ottosen, Roman Perepelitsa, Robert Ramey, Jeremy Siek, Robert Stewart and Steven
- Watanabe<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>)
- </p>
- </div></td>
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