ceph/src/boost/libs/type_traits/doc/html/boost_typetraits/reference/function_traits.html

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  26 <div class="titlepage"><div><div><h3 class="title">
  27 <a name="boost_typetraits.reference.function_traits"></a><a class="link" href="function_traits.html" title="function_traits">function_traits</a>
  28 </h3></div></div></div>
  29 <pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">&gt;</span>
  30 <span class="keyword">struct</span> <span class="identifier">function_traits</span>
  31 <span class="special">{</span>
  32    <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>
  33    <span class="keyword">typedef</span> <em class="replaceable"><code>see-below</code></em>           <span class="identifier">result_type</span><span class="special">;</span>
  34    <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>
  35 <span class="special">};</span>
  36 </pre>
  37 <p>
  38         The class template function_traits will only compile if:
  39       </p>
  40 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
  41 <li class="listitem">
  42             The compiler supports partial specialization of class templates.
  43           </li>
  44 <li class="listitem">
  45             The template argument <code class="computeroutput"><span class="identifier">F</span></code>
  46             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
  47             to a function</em></span>.
  48           </li>
  49 </ul></div>
  50 <div class="tip"><table border="0" summary="Tip">
  51 <tr>
  52 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="../../../../../../doc/src/images/tip.png"></td>
  53 <th align="left">Tip</th>
  54 </tr>
  55 <tr><td align="left" valign="top"><p>
  56           function_traits is intended to introspect only C++ functions of the form
  57           R (), R( A1 ), R ( A1, ... etc. ) and not function pointers or class member
  58           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>.
  59         </p></td></tr>
  60 </table></div>
  61 <div class="table">
  62 <a name="boost_typetraits.reference.function_traits.function_traits_members"></a><p class="title"><b>Table&#160;1.20.&#160;Function Traits Members</b></p>
  63 <div class="table-contents"><table class="table" summary="Function Traits Members">
  64 <colgroup>
  65 <col>
  66 <col>
  67 </colgroup>
  68 <thead><tr>
  69 <th>
  70                 <p>
  71                   Member
  72                 </p>
  73               </th>
  74 <th>
  75                 <p>
  76                   Description
  77                 </p>
  78               </th>
  79 </tr></thead>
  80 <tbody>
  81 <tr>
  82 <td>
  83                 <p>
  84                   <code class="computeroutput"><span class="identifier">function_traits</span><span class="special">&lt;</span><span class="identifier">F</span><span class="special">&gt;::</span><span class="identifier">arity</span></code>
  85                 </p>
  86               </td>
  87 <td>
  88                 <p>
  89                   An integral constant expression that gives the number of arguments
  90                   accepted by the function type <code class="computeroutput"><span class="identifier">F</span></code>.
  91                 </p>
  92               </td>
  93 </tr>
  94 <tr>
  95 <td>
  96                 <p>
  97                   <code class="computeroutput"><span class="identifier">function_traits</span><span class="special">&lt;</span><span class="identifier">F</span><span class="special">&gt;::</span><span class="identifier">result_type</span></code>
  98                 </p>
  99               </td>
 100 <td>
 101                 <p>
 102                   The type returned by function type <code class="computeroutput"><span class="identifier">F</span></code>.
 103                 </p>
 104               </td>
 105 </tr>
 106 <tr>
 107 <td>
 108                 <p>
 109                   <code class="computeroutput"><span class="identifier">function_traits</span><span class="special">&lt;</span><span class="identifier">F</span><span class="special">&gt;::</span>arg<em class="replaceable"><code>N</code></em>_type</code>
 110                 </p>
 111               </td>
 112 <td>
 113                 <p>
 114                   The <em class="replaceable"><code>N</code></em>th argument type of function type <code class="computeroutput"><span class="identifier">F</span></code>,
 115                   where <code class="computeroutput"><span class="number">1</span> <span class="special">&lt;=</span>
 116                   <span class="identifier">N</span> <span class="special">&lt;=</span>
 117                   <span class="identifier">arity</span></code> of <code class="computeroutput"><span class="identifier">F</span></code>.
 118                 </p>
 119               </td>
 120 </tr>
 121 </tbody>
 122 </table></div>
 123 </div>
 124 <br class="table-break"><div class="table">
 125 <a name="boost_typetraits.reference.function_traits.examples"></a><p class="title"><b>Table&#160;1.21.&#160;Examples</b></p>
 126 <div class="table-contents"><table class="table" summary="Examples">
 127 <colgroup>
 128 <col>
 129 <col>
 130 </colgroup>
 131 <thead><tr>
 132 <th>
 133                 <p>
 134                   Expression
 135                 </p>
 136               </th>
 137 <th>
 138                 <p>
 139                   Result
 140                 </p>
 141               </th>
 142 </tr></thead>
 143 <tbody>
 144 <tr>
 145 <td>
 146                 <p>
 147                   <code class="computeroutput"><span class="identifier">function_traits</span><span class="special">&lt;</span><span class="keyword">void</span>
 148                   <span class="special">(</span><span class="keyword">void</span><span class="special">)&gt;::</span><span class="identifier">arity</span></code>
 149                 </p>
 150               </td>
 151 <td>
 152                 <p>
 153                   An integral constant expression that has the value 0.
 154                 </p>
 155               </td>
 156 </tr>
 157 <tr>
 158 <td>
 159                 <p>
 160                   <code class="computeroutput"><span class="identifier">function_traits</span><span class="special">&lt;</span><span class="keyword">long</span>
 161                   <span class="special">(</span><span class="keyword">int</span><span class="special">)&gt;::</span><span class="identifier">arity</span></code>
 162                 </p>
 163               </td>
 164 <td>
 165                 <p>
 166                   An integral constant expression that has the value 1.
 167                 </p>
 168               </td>
 169 </tr>
 170 <tr>
 171 <td>
 172                 <p>
 173                   <code class="computeroutput"><span class="identifier">function_traits</span><span class="special">&lt;</span><span class="keyword">long</span>
 174                   <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">*)&gt;::</span><span class="identifier">arity</span></code>
 175                 </p>
 176               </td>
 177 <td>
 178                 <p>
 179                   An integral constant expression that has the value 4.
 180                 </p>
 181               </td>
 182 </tr>
 183 <tr>
 184 <td>
 185                 <p>
 186                   <code class="computeroutput"><span class="identifier">function_traits</span><span class="special">&lt;</span><span class="keyword">void</span>
 187                   <span class="special">(</span><span class="keyword">void</span><span class="special">)&gt;::</span><span class="identifier">result_type</span></code>
 188                 </p>
 189               </td>
 190 <td>
 191                 <p>
 192                   The type <code class="computeroutput"><span class="keyword">void</span></code>.
 193                 </p>
 194               </td>
 195 </tr>
 196 <tr>
 197 <td>
 198                 <p>
 199                   <code class="computeroutput"><span class="identifier">function_traits</span><span class="special">&lt;</span><span class="keyword">long</span>
 200                   <span class="special">(</span><span class="keyword">int</span><span class="special">)&gt;::</span><span class="identifier">result_type</span></code>
 201                 </p>
 202               </td>
 203 <td>
 204                 <p>
 205                   The type <code class="computeroutput"><span class="keyword">long</span></code>.
 206                 </p>
 207               </td>
 208 </tr>
 209 <tr>
 210 <td>
 211                 <p>
 212                   <code class="computeroutput"><span class="identifier">function_traits</span><span class="special">&lt;</span><span class="keyword">long</span>
 213                   <span class="special">(</span><span class="keyword">int</span><span class="special">)&gt;::</span><span class="identifier">arg1_type</span></code>
 214                 </p>
 215               </td>
 216 <td>
 217                 <p>
 218                   The type <code class="computeroutput"><span class="keyword">int</span></code>.
 219                 </p>
 220               </td>
 221 </tr>
 222 <tr>
 223 <td>
 224                 <p>
 225                   <code class="computeroutput"><span class="identifier">function_traits</span><span class="special">&lt;</span><span class="keyword">long</span>
 226                   <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">*)&gt;::</span><span class="identifier">arg4_type</span></code>
 227                 </p>
 228               </td>
 229 <td>
 230                 <p>
 231                   The type <code class="computeroutput"><span class="keyword">void</span><span class="special">*</span></code>.
 232                 </p>
 233               </td>
 234 </tr>
 235 <tr>
 236 <td>
 237                 <p>
 238                   <code class="computeroutput"><span class="identifier">function_traits</span><span class="special">&lt;</span><span class="keyword">long</span>
 239                   <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">*)&gt;::</span><span class="identifier">arg5_type</span></code>
 240                 </p>
 241               </td>
 242 <td>
 243                 <p>
 244                   A compiler error: there is no <code class="computeroutput"><span class="identifier">arg5_type</span></code>
 245                   since there are only four arguments.
 246                 </p>
 247               </td>
 248 </tr>
 249 <tr>
 250 <td>
 251                 <p>
 252                   <code class="computeroutput"><span class="identifier">function_traits</span><span class="special">&lt;</span><span class="keyword">long</span>
 253                   <span class="special">(*)(</span><span class="keyword">void</span><span class="special">)&gt;::</span><span class="identifier">arity</span></code>
 254                 </p>
 255               </td>
 256 <td>
 257                 <p>
 258                   A compiler error: argument type is a <span class="emphasis"><em>function pointer</em></span>,
 259                   and not a <span class="emphasis"><em>function type</em></span>.
 260                 </p>
 261               </td>
 262 </tr>
 263 </tbody>
 264 </table></div>
 265 </div>
 266 <br class="table-break"><p>
 267         <span class="bold"><strong>Compiler Compatibility:</strong></span> All current compilers
 268         are supported by this trait.
 269       </p>
 270 </div>
 271 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 272 <td align="left"></td>
 273 <td align="right"><div class="copyright-footer">Copyright &#169; 2000, 2011 Adobe Systems Inc, David Abrahams,
 274       Frederic Bron, Steve Cleary, Beman Dawes, Aleksey Gurtovoy, Howard Hinnant,
 275       Jesse Jones, Mat Marcus, Itay Maman, John Maddock, Alexander Nasonov, Thorsten
 276       Ottosen, Roman Perepelitsa, Robert Ramey, Jeremy Siek, Robert Stewart and Steven
 277       Watanabe<p>
 278         Distributed under the Boost Software License, Version 1.0. (See accompanying
 279         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>)
 280       </p>
 281 </div></td>
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