1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>type_erased</title> 5<link rel="stylesheet" href="../../../../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../../../index.html" title="Chapter 1. Range 2.0"> 8<link rel="up" href="../reference.html" title="Reference"> 9<link rel="prev" href="strided.html" title="strided"> 10<link rel="next" href="tokenized.html" title="tokenized"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="strided.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../../index.html"><img src="../../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="tokenized.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 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 class="toc"><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"><</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">>()</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"><</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">>)</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" style="list-style-type: disc; "> 94<li class="listitem"> 95 <span class="bold"><strong>Template parameters:</strong></span> 96 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; "> 97<li class="listitem"> 98 <code class="computeroutput"><span class="identifier">Value</span></code> is the 99 <code class="computeroutput"><span class="identifier">value_type</span></code> 100 for the <code class="computeroutput"><span class="identifier">any_range</span></code>. 101 If this is set to boost::use_default, <code class="computeroutput"><span class="identifier">Value</span></code> 102 will be calculated from the range type when the adaptor is 103 applied. 104 </li> 105<li class="listitem"> 106 <code class="computeroutput"><span class="identifier">Traversal</span></code> is 107 the tag used to identify the traversal of the resultant range. 108 Frequently it is desirable to set a traversal category lower 109 than the source container or range to maximize the number of 110 ranges that can convert to the <code class="computeroutput"><span class="identifier">any_range</span></code>. 111 If this is left as boost::use_default then <code class="computeroutput"><span class="identifier">Traversal</span></code> 112 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"><</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">range_iterator</span><span class="special"><</span><span class="identifier">Rng</span><span class="special">>::</span><span class="identifier">type</span><span class="special">>::</span><span class="identifier">type</span></code> 113 </li> 114<li class="listitem"> 115 <code class="computeroutput"><span class="identifier">Reference</span></code> is 116 the <code class="computeroutput"><span class="identifier">reference</span></code> 117 for the <code class="computeroutput"><span class="identifier">any_range</span></code>. 118 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">use_default</span></code> will equate to 119 <code class="computeroutput"><span class="keyword">typename</span> <span class="identifier">range_reference</span><span class="special"><</span><span class="identifier">Rng</span><span class="special">>::</span><span class="identifier">type</span></code>. 120 </li> 121<li class="listitem"> 122 <code class="computeroutput"><span class="identifier">Difference</span></code> 123 is the <code class="computeroutput"><span class="identifier">difference_type</span></code> 124 for the any_range. <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">use_default</span></code> 125 will equate to <code class="computeroutput"><span class="keyword">typename</span> 126 <span class="identifier">boost</span><span class="special">::</span><span class="identifier">range_difference</span><span class="special"><</span><span class="identifier">Rng</span><span class="special">>::</span><span class="identifier">type</span></code> 127 </li> 128<li class="listitem"> 129 <code class="computeroutput"><span class="identifier">Buffer</span></code> is the 130 storage used to allocate the underlying iterator wrappers. 131 This can typically be ignored, but is available as a template 132 parameter for customization. Buffer must be a model of the 133 <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"><</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">></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"><</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">range_iterator</span><span class="special"><</span><span class="identifier">Rng</span><span class="special">>::</span><span class="identifier">type</span><span class="special">>::</span><span class="identifier">type</span></code>, 153 otherwise <code class="computeroutput"><span class="identifier">Traversal</span></code>. 154 </li> 155</ul></div> 156<h6> 157<a name="range.reference.adaptors.reference.type_erased.h0"></a> 158 <span class="phrase"><a name="range.reference.adaptors.reference.type_erased.anyiteratorbufferconcept"></a></span><a class="link" href="type_erased.html#range.reference.adaptors.reference.type_erased.anyiteratorbufferconcept">AnyIteratorBufferConcept</a> 159 </h6> 160<p> 161</p> 162<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">AnyIteratorBufferConcept</span> 163<span class="special">{</span> 164<span class="keyword">public</span><span class="special">:</span> 165 <span class="identifier">AnyIteratorBufferConcept</span><span class="special">();</span> 166 <span class="special">~</span><span class="identifier">AnyIteratorBufferConcept</span><span class="special">();</span> 167 168 <span class="comment">// bytes is the requested size to allocate. This function</span> 169 <span class="comment">// must return a pointer to an adequate area of memory.</span> 170 <span class="comment">// throws: bad_alloc</span> 171 <span class="comment">//</span> 172 <span class="comment">// The buffer will only ever have zero or one</span> 173 <span class="comment">// outstanding memory allocations.</span> 174 <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> 175 176 <span class="comment">// deallocate this buffer</span> 177 <span class="keyword">void</span> <span class="identifier">deallocate</span><span class="special">();</span> 178<span class="special">};</span> 179</pre> 180<p> 181 </p> 182<div class="section"> 183<div class="titlepage"><div><div><h6 class="title"> 184<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 185 example</a> 186</h6></div></div></div> 187<p> 188</p> 189<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</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">></span> 190<span class="preprocessor">#include</span> <span class="special"><</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">></span> 191<span class="preprocessor">#include</span> <span class="special"><</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">></span> 192<span class="preprocessor">#include</span> <span class="special"><</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">></span> 193<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">iterator</span><span class="special">></span> 194<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">iostream</span><span class="special">></span> 195<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">list</span><span class="special">></span> 196<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">vector</span><span class="special">></span> 197 198<span class="comment">// The client interface from an OO perspective merely requires a sequence</span> 199<span class="comment">// of integers that can be forward traversed</span> 200<span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">any_range</span><span class="special"><</span> 201 <span class="keyword">int</span> 202 <span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">forward_traversal_tag</span> 203 <span class="special">,</span> <span class="keyword">int</span> 204 <span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">ptrdiff_t</span> 205<span class="special">></span> <span class="identifier">integer_range</span><span class="special">;</span> 206 207<span class="keyword">namespace</span> <span class="identifier">server</span> 208<span class="special">{</span> 209 <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">&</span> <span class="identifier">rng</span><span class="special">)</span> 210 <span class="special">{</span> 211 <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> 212 <span class="identifier">std</span><span class="special">::</span><span class="identifier">ostream_iterator</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(</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> 213 214 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 215 <span class="special">}</span> 216<span class="special">}</span> 217 218<span class="keyword">namespace</span> <span class="identifier">client</span> 219<span class="special">{</span> 220 <span class="keyword">void</span> <span class="identifier">run</span><span class="special">()</span> 221 <span class="special">{</span> 222 <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> 223 <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> 224 225 <span class="comment">// Under most conditions one would simply use an appropriate</span> 226 <span class="comment">// any_range as a function parameter. The type_erased adaptor</span> 227 <span class="comment">// is often superfluous. However because the type_erased</span> 228 <span class="comment">// adaptor is applied to a range, we can use default template</span> 229 <span class="comment">// arguments that are generated in conjunction with the</span> 230 <span class="comment">// range type to which we are applying the adaptor.</span> 231 232 <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">input</span><span class="special">;</span> 233 <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> 234 235 <span class="comment">// Note that this call is to a non-template function</span> 236 <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> 237 238 <span class="identifier">std</span><span class="special">::</span><span class="identifier">list</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">input2</span><span class="special">;</span> 239 <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> 240 241 <span class="comment">// Note that this call is to the same non-tempate function</span> 242 <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> 243 244 <span class="identifier">input2</span><span class="special">.</span><span class="identifier">clear</span><span class="special">();</span> 245 <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> 246 247 <span class="comment">// Calling using the adaptor looks like this:</span> 248 <span class="comment">// Notice that here I have a type_erased that would be a</span> 249 <span class="comment">// bidirectional_traversal_tag, but this is convertible</span> 250 <span class="comment">// to the forward_traversal_tag equivalent hence this</span> 251 <span class="comment">// works.</span> 252 <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"><>());</span> 253 254 <span class="comment">// However we may simply wish to define an adaptor that</span> 255 <span class="comment">// takes a range and makes it into an appropriate</span> 256 <span class="comment">// forward_traversal any_range...</span> 257 <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"><</span> 258 <span class="identifier">boost</span><span class="special">::</span><span class="identifier">use_default</span> 259 <span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">forward_traversal_tag</span> 260 <span class="special">></span> <span class="identifier">type_erased_forward</span><span class="special">;</span> 261 262 <span class="comment">// This adaptor can turn other containers with different</span> 263 <span class="comment">// value_types and reference_types into the appropriate</span> 264 <span class="comment">// any_range.</span> 265 266 <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> 267 <span class="special">}</span> 268<span class="special">}</span> 269 270<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> 271<span class="special">{</span> 272 <span class="identifier">client</span><span class="special">::</span><span class="identifier">run</span><span class="special">();</span> 273 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 274<span class="special">}</span> 275</pre> 276<p> 277 </p> 278</div> 279<p> 280 This would produce the output: 281</p> 282<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><span class="special">,</span> 283<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> 284<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> 285<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> 286</pre> 287<p> 288 </p> 289</div> 290<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 291<td align="left"></td> 292<td align="right"><div class="copyright-footer">Copyright © 2003-2010 Thorsten Ottosen, 293 Neil Groves<p> 294 Distributed under the Boost Software License, Version 1.0. (See accompanying 295 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>) 296 </p> 297</div></td> 298</tr></table> 299<hr> 300<div class="spirit-nav"> 301<a accesskey="p" href="strided.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../../index.html"><img src="../../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="tokenized.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> 302</div> 303</body> 304</html> 305
