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  26 <div class="titlepage"><div><div><h5 class="title">
  27 <a name="range.reference.adaptors.reference.type_erased"></a><a class="link" href="type_erased.html" title="type_erased">type_erased</a>
  28 </h5></div></div></div>
  29 <div class="toc"><dl><dt><span class="section"><a href="type_erased.html#range.reference.adaptors.reference.type_erased.type_erased_example">type-erased
  30             example</a></span></dt></dl></div>
  31 <div class="informaltable"><table class="table">
  32 <colgroup>
  33 <col>
  34 <col>
  35 </colgroup>
  36 <thead><tr>
  37 <th>
  38                     <p>
  39                       Syntax
  40                     </p>
  41                   </th>
  42 <th>
  43                     <p>
  44                       Code
  45                     </p>
  46                   </th>
  47 </tr></thead>
  48 <tbody>
  49 <tr>
  50 <td>
  51                     <p>
  52                       Pipe
  53                     </p>
  54                   </td>
  55 <td>
  56                     <p>
  57                       <code class="computeroutput"><span class="identifier">rng</span> <span class="special">|</span>
  58                       <span class="identifier">boost</span><span class="special">::</span><span class="identifier">adaptors</span><span class="special">::</span><span class="identifier">type_erased</span><span class="special">&lt;</span><span class="identifier">Value</span><span class="special">,</span>
  59                       <span class="identifier">Traversal</span><span class="special">,</span>
  60                       <span class="identifier">Reference</span><span class="special">,</span>
  61                       <span class="identifier">Difference</span><span class="special">,</span>
  62                       <span class="identifier">Buffer</span><span class="special">&gt;()</span></code>
  63                     </p>
  64                   </td>
  65 </tr>
  66 <tr>
  67 <td>
  68                     <p>
  69                       Function
  70                     </p>
  71                   </td>
  72 <td>
  73                     <p>
  74                       <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">adaptors</span><span class="special">::</span><span class="identifier">type_erase</span><span class="special">(</span><span class="identifier">rng</span><span class="special">,</span>
  75                       <span class="identifier">boost</span><span class="special">::</span><span class="identifier">adaptors</span><span class="special">::</span><span class="identifier">type_erased</span><span class="special">&lt;</span><span class="identifier">Value</span><span class="special">,</span>
  76                       <span class="identifier">Traversal</span><span class="special">,</span>
  77                       <span class="identifier">Reference</span><span class="special">,</span>
  78                       <span class="identifier">Difference</span><span class="special">,</span>
  79                       <span class="identifier">Buffer</span><span class="special">&gt;)</span></code>
  80                     </p>
  81                   </td>
  82 </tr>
  83 </tbody>
  84 </table></div>
  85 <p>
  86             Please note that it is frequently unnecessary to use the <code class="computeroutput"><span class="identifier">type_erased</span></code> adaptor. It is often better
  87             to use the implicit conversion to <code class="computeroutput"><span class="identifier">any_range</span></code>.
  88           </p>
  89 <p>
  90             Let <code class="computeroutput"><span class="identifier">Rng</span></code> be the type of
  91             <code class="computeroutput"><span class="identifier">rng</span></code>.
  92           </p>
  93 <div class="itemizedlist"><ul class="itemizedlist" type="disc">
  94 <li class="listitem">
  95 <p class="simpara">
  96                 <span class="bold"><strong>Template parameters:</strong></span>
  97               </p>
  98 <div class="itemizedlist"><ul class="itemizedlist" type="circle">
  99 <li class="listitem">
 100                     <code class="computeroutput"><span class="identifier">Value</span></code> is the
 101                     <code class="computeroutput"><span class="identifier">value_type</span></code> for
 102                     the <code class="computeroutput"><span class="identifier">any_range</span></code>.
 103                     If this is set to boost::use_default, <code class="computeroutput"><span class="identifier">Value</span></code>
 104                     will be calculated from the range type when the adaptor is applied.
 105                   </li>
 106 <li class="listitem">
 107                     <code class="computeroutput"><span class="identifier">Traversal</span></code> is
 108                     the tag used to identify the traversal of the resultant range.
 109                     Frequently it is desireable to set a traversal category lower
 110                     than the source container or range to maximize the number of
 111                     ranges that can convert to the <code class="computeroutput"><span class="identifier">any_range</span></code>.
 112                     If this is left as boost::use_default then <code class="computeroutput"><span class="identifier">Traversal</span></code>
 113                     will be <code class="computeroutput"><span class="keyword">typename</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">iterator_traversal</span><span class="special">&lt;</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">range_iterator</span><span class="special">&lt;</span><span class="identifier">Rng</span><span class="special">&gt;::</span><span class="identifier">type</span><span class="special">&gt;::</span><span class="identifier">type</span></code>
 114                   </li>
 115 <li class="listitem">
 116                     <code class="computeroutput"><span class="identifier">Reference</span></code> is
 117                     the <code class="computeroutput"><span class="identifier">reference</span></code>
 118                     for the <code class="computeroutput"><span class="identifier">any_range</span></code>.
 119                     <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">use_default</span></code> will equate to
 120                     <code class="computeroutput"><span class="keyword">typename</span> <span class="identifier">range_reference</span><span class="special">&lt;</span><span class="identifier">Rng</span><span class="special">&gt;::</span><span class="identifier">type</span></code>.
 121                   </li>
 122 <li class="listitem">
 123                     <code class="computeroutput"><span class="identifier">Difference</span></code> is
 124                     the <code class="computeroutput"><span class="identifier">difference_type</span></code>
 125                     for the any_range. <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">use_default</span></code>
 126                     will equate to <code class="computeroutput"><span class="keyword">typename</span>
 127                     <span class="identifier">boost</span><span class="special">::</span><span class="identifier">range_difference</span><span class="special">&lt;</span><span class="identifier">Rng</span><span class="special">&gt;::</span><span class="identifier">type</span></code>
 128                   </li>
 129 <li class="listitem">
 130                     <code class="computeroutput"><span class="identifier">Buffer</span></code> is the
 131                     storage used to allocate the underlying iterator wrappers. This
 132                     can typically be ignored, but is available as a template parameter
 133                     for customization. Buffer must be a model of the <code class="computeroutput"><span class="identifier">AnyIteratorBufferConcept</span></code>.
 134                   </li>
 135 </ul></div>
 136 </li>
 137 <li class="listitem">
 138                 <span class="bold"><strong>Precondition:</strong></span> <code class="computeroutput"><span class="identifier">Traversal</span></code>
 139                 is one of <code class="computeroutput"><span class="special">{</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">use_default</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">single_pass_traversal_tag</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">forward_traversal_tag</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">bidirectional_traversal_tag</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">random_access_traversal_tag</span>
 140                 <span class="special">}</span></code>
 141               </li>
 142 <li class="listitem">
 143                 <span class="bold"><strong>Returns:</strong></span> The returned value is the
 144                 same as <code class="computeroutput"><span class="keyword">typename</span> <span class="identifier">any_range_type_generator</span><span class="special">&lt;</span> <span class="identifier">Rng</span><span class="special">,</span> <span class="identifier">Value</span><span class="special">,</span> <span class="identifier">Traversal</span><span class="special">,</span> <span class="identifier">Reference</span><span class="special">,</span> <span class="identifier">Difference</span><span class="special">,</span> <span class="identifier">Buffer</span>
 145                 <span class="special">&gt;</span></code> that represents <code class="computeroutput"><span class="identifier">rng</span></code> in a type-erased manner.
 146               </li>
 147 <li class="listitem">
 148                 <span class="bold"><strong>Range Category:</strong></span> <a class="link" href="../../../concepts/single_pass_range.html" title="Single Pass Range">Single
 149                 Pass Range</a>
 150               </li>
 151 <li class="listitem">
 152                 <span class="bold"><strong>Returned Range Category:</strong></span> if <code class="computeroutput"><span class="identifier">Traversal</span></code> was specified as <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">use_default</span></code> then <code class="computeroutput"><span class="keyword">typename</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">iterator_traversal</span><span class="special">&lt;</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">range_iterator</span><span class="special">&lt;</span><span class="identifier">Rng</span><span class="special">&gt;::</span><span class="identifier">type</span><span class="special">&gt;::</span><span class="identifier">type</span></code>,
 153                 otherwise <code class="computeroutput"><span class="identifier">Traversal</span></code>.
 154               </li>
 155 </ul></div>
 156 <a name="range.reference.adaptors.reference.type_erased.anyiteratorbufferconcept"></a><h6>
 157 <a name="id677095"></a>
 158             <a class="link" href="type_erased.html#range.reference.adaptors.reference.type_erased.anyiteratorbufferconcept">AnyIteratorBufferConcept</a>
 159           </h6>
 160 <p>
 161
 162 </p>
 163 <pre class="programlisting"><span class="keyword">class</span> <span class="identifier">AnyIteratorBufferConcept</span>
 164 <span class="special">{</span>
 165 <span class="keyword">public</span><span class="special">:</span>
 166     <span class="identifier">AnyIteratorBufferConcept</span><span class="special">();</span>
 167     <span class="special">~</span><span class="identifier">AnyIteratorBufferConcept</span><span class="special">();</span>
 168
 169     <span class="comment">// bytes is the requested size to allocate. This function
 170 </span>    <span class="comment">// must return a pointer to an adequate area of memory.
 171 </span>    <span class="comment">// throws: bad_alloc
 172 </span>    <span class="comment">//
 173 </span>    <span class="comment">// The buffer will only ever have zero or one
 174 </span>    <span class="comment">// outstanding memory allocations.
 175 </span>    <span class="keyword">void</span><span class="special">*</span> <span class="identifier">allocate</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">bytes</span><span class="special">);</span>
 176
 177     <span class="comment">// deallocate this buffer
 178 </span>    <span class="keyword">void</span> <span class="identifier">deallocate</span><span class="special">();</span>
 179 <span class="special">};</span>
 180 </pre>
 181 <p>
 182           </p>
 183 <div class="section">
 184 <div class="titlepage"><div><div><h6 class="title">
 185 <a name="range.reference.adaptors.reference.type_erased.type_erased_example"></a><a class="link" href="type_erased.html#range.reference.adaptors.reference.type_erased.type_erased_example" title="type-erased example">type-erased
 186             example</a>
 187 </h6></div></div></div>
 188 <p>
 189
 190 </p>
 191 <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">range</span><span class="special">/</span><span class="identifier">adaptor</span><span class="special">/</span><span class="identifier">type_erased</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 192 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">range</span><span class="special">/</span><span class="identifier">algorithm</span><span class="special">/</span><span class="identifier">copy</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 193 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">assign</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 194 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">foreach</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 195 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">algorithm</span><span class="special">&gt;</span>
 196 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">iostream</span><span class="special">&gt;</span>
 197 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">list</span><span class="special">&gt;</span>
 198 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">vector</span><span class="special">&gt;</span>
 199
 200 <span class="comment">// The client interface from an OO perspective merely requires a sequence
 201 </span><span class="comment">// of integers that can be forward traversed
 202 </span><span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">any_range</span><span class="special">&lt;</span>
 203     <span class="keyword">int</span>
 204   <span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">forward_traversal_tag</span>
 205   <span class="special">,</span> <span class="keyword">int</span>
 206   <span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">ptrdiff_t</span>
 207 <span class="special">&gt;</span> <span class="identifier">integer_range</span><span class="special">;</span>
 208
 209 <span class="keyword">namespace</span> <span class="identifier">server</span>
 210 <span class="special">{</span>
 211     <span class="keyword">void</span> <span class="identifier">display_integers</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">integer_range</span><span class="special">&amp;</span> <span class="identifier">rng</span><span class="special">)</span>
 212     <span class="special">{</span>
 213         <span class="identifier">boost</span><span class="special">::</span><span class="identifier">copy</span><span class="special">(</span><span class="identifier">rng</span><span class="special">,</span>
 214                     <span class="identifier">std</span><span class="special">::</span><span class="identifier">ostream_iterator</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span><span class="special">,</span> <span class="string">","</span><span class="special">));</span>
 215
 216         <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 217     <span class="special">}</span>
 218 <span class="special">}</span>
 219
 220 <span class="keyword">namespace</span> <span class="identifier">client</span>
 221 <span class="special">{</span>
 222     <span class="keyword">void</span> <span class="identifier">run</span><span class="special">()</span>
 223     <span class="special">{</span>
 224         <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">assign</span><span class="special">;</span>
 225         <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">adaptors</span><span class="special">;</span>
 226
 227         <span class="comment">// Under most conditions one would simply use an appropriate
 228 </span>        <span class="comment">// any_range as a function parameter. The type_erased adaptor
 229 </span>        <span class="comment">// is often superfluous. However because the type_erased
 230 </span>        <span class="comment">// adaptor is applied to a range, we can use default template
 231 </span>        <span class="comment">// arguments that are generated in conjunction with the
 232 </span>        <span class="comment">// range type to which we are applying the adaptor.
 233 </span>
 234         <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">input</span><span class="special">;</span>
 235         <span class="identifier">input</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">4</span><span class="special">,</span><span class="number">5</span><span class="special">;</span>
 236
 237         <span class="comment">// Note that this call is to a non-template function
 238 </span>        <span class="identifier">server</span><span class="special">::</span><span class="identifier">display_integers</span><span class="special">(</span><span class="identifier">input</span><span class="special">);</span>
 239
 240         <span class="identifier">std</span><span class="special">::</span><span class="identifier">list</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">input2</span><span class="special">;</span>
 241         <span class="identifier">input2</span> <span class="special">+=</span> <span class="number">6</span><span class="special">,</span><span class="number">7</span><span class="special">,</span><span class="number">8</span><span class="special">,</span><span class="number">9</span><span class="special">,</span><span class="number">10</span><span class="special">;</span>
 242
 243         <span class="comment">// Note that this call is to the same non-tempate function
 244 </span>        <span class="identifier">server</span><span class="special">::</span><span class="identifier">display_integers</span><span class="special">(</span><span class="identifier">input2</span><span class="special">);</span>
 245
 246         <span class="identifier">input2</span><span class="special">.</span><span class="identifier">clear</span><span class="special">();</span>
 247         <span class="identifier">input2</span> <span class="special">+=</span> <span class="number">11</span><span class="special">,</span><span class="number">12</span><span class="special">,</span><span class="number">13</span><span class="special">,</span><span class="number">14</span><span class="special">,</span><span class="number">15</span><span class="special">;</span>
 248
 249         <span class="comment">// Calling using the adaptor looks like this:
 250 </span>        <span class="comment">// Notice that here I have a type_erased that would be a
 251 </span>        <span class="comment">// bidirectional_traversal_tag, but this is convertible
 252 </span>        <span class="comment">// to the forward_traversal_tag equivalent hence this
 253 </span>        <span class="comment">// works.
 254 </span>        <span class="identifier">server</span><span class="special">::</span><span class="identifier">display_integers</span><span class="special">(</span><span class="identifier">input2</span> <span class="special">|</span> <span class="identifier">type_erased</span><span class="special">&lt;&gt;());</span>
 255
 256         <span class="comment">// However we may simply wish to define an adaptor that
 257 </span>        <span class="comment">// takes a range and makes it into an appropriate
 258 </span>        <span class="comment">// forward_traversal any_range...
 259 </span>        <span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">adaptors</span><span class="special">::</span><span class="identifier">type_erased</span><span class="special">&lt;</span>
 260             <span class="identifier">boost</span><span class="special">::</span><span class="identifier">use_default</span>
 261           <span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">forward_traversal_tag</span>
 262         <span class="special">&gt;</span> <span class="identifier">type_erased_forward</span><span class="special">;</span>
 263
 264         <span class="comment">// This adaptor can turn other containers with different
 265 </span>        <span class="comment">// value_types and reference_types into the appropriate
 266 </span>        <span class="comment">// any_range.
 267 </span>
 268         <span class="identifier">server</span><span class="special">::</span><span class="identifier">display_integers</span><span class="special">(</span><span class="identifier">input2</span> <span class="special">|</span> <span class="identifier">type_erased_forward</span><span class="special">());</span>
 269     <span class="special">}</span>
 270 <span class="special">}</span>
 271
 272 <span class="keyword">int</span> <span class="identifier">main</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">argc</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">argv</span><span class="special">[])</span>
 273 <span class="special">{</span>
 274     <span class="identifier">client</span><span class="special">::</span><span class="identifier">run</span><span class="special">();</span>
 275     <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
 276 <span class="special">}</span>
 277 </pre>
 278 <p>
 279             </p>
 280 </div>
 281 <p>
 282             This would produce the output:
 283 </p>
 284 <pre class="programlisting"><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">4</span><span class="special">,</span><span class="number">5</span>
 285 <span class="number">6</span><span class="special">,</span><span class="number">7</span><span class="special">,</span><span class="number">8</span><span class="special">,</span><span class="number">9</span><span class="special">,</span><span class="number">10</span>
 286 <span class="number">11</span><span class="special">,</span><span class="number">12</span><span class="special">,</span><span class="number">13</span><span class="special">,</span><span class="number">14</span><span class="special">,</span><span class="number">15</span>
 287 <span class="number">11</span><span class="special">,</span><span class="number">12</span><span class="special">,</span><span class="number">13</span><span class="special">,</span><span class="number">14</span><span class="special">,</span><span class="number">15</span>
 288 </pre>
 289 <p>
 290           </p>
 291 </div>
 292 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 293 <td align="left"></td>
 294 <td align="right"><div class="copyright-footer">Copyright &#169; 2003 -2010 Thorsten Ottosen, Neil Groves<p>
 295         Distributed under the Boost Software License, Version 1.0. (See accompanying
 296         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>)
 297       </p>
 298 </div></td>
 299 </tr></table>
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