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25</div> 26<div class="refentry"> 27<a name="boost.recursive_wrapper"></a><div class="titlepage"></div> 28<div class="refnamediv"> 29<h2><span class="refentrytitle">Class template recursive_wrapper</span></h2> 30<p>boost::recursive_wrapper — Solves circular dependencies, enabling recursive types.</p> 31</div> 32<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2> 33<div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: <<a class="link" href="../variant/reference.html#header.boost.variant.recursive_wrapper_hpp" title="Header <boost/variant/recursive_wrapper.hpp>">boost/variant/recursive_wrapper.hpp</a>> 34 35</span><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span> 36<span class="keyword">class</span> <a class="link" href="recursive_wrapper.html" title="Class template recursive_wrapper">recursive_wrapper</a> <span class="special">{</span> 37<span class="keyword">public</span><span class="special">:</span> 38 <span class="comment">// types</span> 39 <span class="keyword">typedef</span> <span class="identifier">T</span> <a name="boost.recursive_wrapper.type"></a><span class="identifier">type</span><span class="special">;</span> 40 41 <span class="comment">// <a class="link" href="recursive_wrapper.html#boost.recursive_wrapperconstruct-copy-destruct">construct/copy/destruct</a></span> 42 <a class="link" href="recursive_wrapper.html#id-1_3_46_5_6_1_1_6-bb"><span class="identifier">recursive_wrapper</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span> 43 <a class="link" href="recursive_wrapper.html#id-1_3_46_5_6_1_1_7-bb"><span class="identifier">recursive_wrapper</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">recursive_wrapper</span> <span class="special">&</span><span class="special">)</span><span class="special">;</span> 44 <a class="link" href="recursive_wrapper.html#id-1_3_46_5_6_1_1_8-bb"><span class="identifier">recursive_wrapper</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">T</span> <span class="special">&</span><span class="special">)</span><span class="special">;</span> 45 <a class="link" href="recursive_wrapper.html#id-1_3_46_5_6_1_1_5-bb"><span class="special">~</span><span class="identifier">recursive_wrapper</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span> 46 47 <span class="comment">// <a class="link" href="recursive_wrapper.html#id-1_3_46_5_6_1_1_9-bb">modifiers</a></span> 48 <span class="keyword">void</span> <a class="link" href="recursive_wrapper.html#id-1_3_46_5_6_1_1_9_1-bb"><span class="identifier">swap</span></a><span class="special">(</span><span class="identifier">recursive_wrapper</span> <span class="special">&</span><span class="special">)</span><span class="special">;</span> 49 <span class="identifier">recursive_wrapper</span> <span class="special">&</span> <a class="link" href="recursive_wrapper.html#id-1_3_46_5_6_1_1_9_2-bb"><span class="keyword">operator</span><span class="special">=</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">recursive_wrapper</span> <span class="special">&</span><span class="special">)</span><span class="special">;</span> 50 <span class="identifier">recursive_wrapper</span> <span class="special">&</span> <a class="link" href="recursive_wrapper.html#id-1_3_46_5_6_1_1_9_3-bb"><span class="keyword">operator</span><span class="special">=</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">T</span> <span class="special">&</span><span class="special">)</span><span class="special">;</span> 51 52 <span class="comment">// <a class="link" href="recursive_wrapper.html#id-1_3_46_5_6_1_1_10-bb">queries</a></span> 53 <span class="identifier">T</span> <span class="special">&</span> <a class="link" href="recursive_wrapper.html#id-1_3_46_5_6_1_1_10_1_1-bb"><span class="identifier">get</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span> 54 <span class="keyword">const</span> <span class="identifier">T</span> <span class="special">&</span> <a class="link" href="recursive_wrapper.html#id-1_3_46_5_6_1_1_10_1_2-bb"><span class="identifier">get</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> 55 <span class="identifier">T</span> <span class="special">*</span> <a class="link" href="recursive_wrapper.html#id-1_3_46_5_6_1_1_10_2_1-bb"><span class="identifier">get_pointer</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span> 56 <span class="keyword">const</span> <span class="identifier">T</span> <span class="special">*</span> <a class="link" href="recursive_wrapper.html#id-1_3_46_5_6_1_1_10_2_2-bb"><span class="identifier">get_pointer</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> 57<span class="special">}</span><span class="special">;</span></pre></div> 58<div class="refsect1"> 59<a name="id-1.3.46.5.7.3.4"></a><h2>Description</h2> 60<p>The <code class="computeroutput">recursive_wrapper</code> class template has an 61 interface similar to a simple value container, but its content is 62 allocated dynamically. This allows <code class="computeroutput">recursive_wrapper</code> to 63 hold types <code class="computeroutput">T</code> whose member data leads to a circular 64 dependency (e.g., a data member of <code class="computeroutput">T</code> has a data member 65 of type <code class="computeroutput">T</code>).</p> 66<p>The application of <code class="computeroutput">recursive_wrapper</code> is easiest 67 understood in context. See 68 <a class="xref" href="../variant/tutorial.html#variant.tutorial.recursive.recursive-wrapper" title="Recursive types with recursive_wrapper">the section called “Recursive types with <code class="computeroutput">recursive_wrapper</code>”</a> for a 69 demonstration of a common use of the class template.</p> 70<p><span class="bold"><strong>Notes</strong></span>:</p> 71<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">Any type specified as the template argument to 72 <code class="computeroutput">recursive_wrapper</code> must be capable of construction via 73 <code class="computeroutput">operator new</code>. Thus, for instance, references are not 74 supported.</li></ul></div> 75<div class="refsect2"> 76<a name="id-1.3.46.5.7.3.4.6"></a><h3> 77<a name="boost.recursive_wrapperconstruct-copy-destruct"></a><code class="computeroutput">recursive_wrapper</code> 78 public 79 construct/copy/destruct</h3> 80<div class="orderedlist"><ol class="orderedlist" type="1"> 81<li class="listitem"> 82<pre class="literallayout"><a name="id-1_3_46_5_6_1_1_6-bb"></a><span class="identifier">recursive_wrapper</span><span class="special">(</span><span class="special">)</span><span class="special">;</span></pre>Default constructor.<p class="simpara">Initializes <code class="computeroutput">*this</code> by default construction of 83 <code class="computeroutput">T</code>.</p> 84<div class="variablelist"><table border="0" class="variablelist compact"> 85<colgroup> 86<col align="left" valign="top"> 87<col> 88</colgroup> 89<tbody> 90<tr> 91<td><p><span class="term">Requires:</span></p></td> 92<td> 93<code class="computeroutput">T</code> must fulfill the requirements of the 94 <span class="emphasis"><em>DefaultConstructible</em></span> [20.1.4] 95 concept.</td> 96</tr> 97<tr> 98<td><p><span class="term">Throws:</span></p></td> 99<td>May fail with any exceptions arising from the default 100 constructor of <code class="computeroutput">T</code> or, in the event of 101 insufficient memory, with <code class="computeroutput">std::bad_alloc</code>.</td> 102</tr> 103</tbody> 104</table></div> 105</li> 106<li class="listitem"> 107<pre class="literallayout"><a name="id-1_3_46_5_6_1_1_7-bb"></a><span class="identifier">recursive_wrapper</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">recursive_wrapper</span> <span class="special">&</span> other<span class="special">)</span><span class="special">;</span></pre>Copy constructor.<p class="simpara">Copies the content of <code class="computeroutput">other</code> into 108 <code class="computeroutput">*this</code>.</p> 109<div class="variablelist"><table border="0" class="variablelist compact"> 110<colgroup> 111<col align="left" valign="top"> 112<col> 113</colgroup> 114<tbody><tr> 115<td><p><span class="term">Throws:</span></p></td> 116<td>May fail with any exceptions arising from the 117 copy constructor of <code class="computeroutput">T</code> or, in the event of 118 insufficient memory, with <code class="computeroutput">std::bad_alloc</code>.</td> 119</tr></tbody> 120</table></div> 121</li> 122<li class="listitem"> 123<pre class="literallayout"><a name="id-1_3_46_5_6_1_1_8-bb"></a><span class="identifier">recursive_wrapper</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">T</span> <span class="special">&</span> operand<span class="special">)</span><span class="special">;</span></pre>Value constructor.<p class="simpara">Copies <code class="computeroutput">operand</code> into 124 <code class="computeroutput">*this</code>.</p> 125<div class="variablelist"><table border="0" class="variablelist compact"> 126<colgroup> 127<col align="left" valign="top"> 128<col> 129</colgroup> 130<tbody><tr> 131<td><p><span class="term">Throws:</span></p></td> 132<td>May fail with any exceptions arising from the 133 copy constructor of <code class="computeroutput">T</code> or, in the event of 134 insufficient memory, with <code class="computeroutput">std::bad_alloc</code>.</td> 135</tr></tbody> 136</table></div> 137</li> 138<li class="listitem"> 139<pre class="literallayout"><a name="id-1_3_46_5_6_1_1_5-bb"></a><span class="special">~</span><span class="identifier">recursive_wrapper</span><span class="special">(</span><span class="special">)</span><span class="special">;</span></pre>Destructor.<p class="simpara">Deletes the content of <code class="computeroutput">*this</code>.</p> 140<div class="variablelist"><table border="0" class="variablelist compact"> 141<colgroup> 142<col align="left" valign="top"> 143<col> 144</colgroup> 145<tbody><tr> 146<td><p><span class="term">Throws:</span></p></td> 147<td>Will not throw.</td> 148</tr></tbody> 149</table></div> 150</li> 151</ol></div> 152</div> 153<div class="refsect2"> 154<a name="id-1.3.46.5.7.3.4.7"></a><h3> 155<a name="id-1_3_46_5_6_1_1_9-bb"></a><code class="computeroutput">recursive_wrapper</code> modifiers</h3> 156<div class="orderedlist"><ol class="orderedlist" type="1"> 157<li class="listitem"> 158<pre class="literallayout"><span class="keyword">void</span> <a name="id-1_3_46_5_6_1_1_9_1-bb"></a><span class="identifier">swap</span><span class="special">(</span><span class="identifier">recursive_wrapper</span> <span class="special">&</span> other<span class="special">)</span><span class="special">;</span></pre> 159<p class="simpara">Exchanges contents of <code class="computeroutput">*this</code> and 160 <code class="computeroutput">other</code>.</p> 161<div class="variablelist"><table border="0" class="variablelist compact"> 162<colgroup> 163<col align="left" valign="top"> 164<col> 165</colgroup> 166<tbody><tr> 167<td><p><span class="term">Throws:</span></p></td> 168<td>Will not throw.</td> 169</tr></tbody> 170</table></div> 171</li> 172<li class="listitem"> 173<pre class="literallayout"><span class="identifier">recursive_wrapper</span> <span class="special">&</span> <a name="id-1_3_46_5_6_1_1_9_2-bb"></a><span class="keyword">operator</span><span class="special">=</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">recursive_wrapper</span> <span class="special">&</span> rhs<span class="special">)</span><span class="special">;</span></pre>Copy assignment operator.<p class="simpara">Assigns the content of <code class="computeroutput">rhs</code> to the content of 174 <code class="computeroutput">*this</code>.</p> 175<div class="variablelist"><table border="0" class="variablelist compact"> 176<colgroup> 177<col align="left" valign="top"> 178<col> 179</colgroup> 180<tbody> 181<tr> 182<td><p><span class="term">Requires:</span></p></td> 183<td> 184<code class="computeroutput">T</code> must fulfill the requirements of 185 the <a class="link" href="../Assignable.html" title="Concept Assignable">Assignable</a> 186 concept.</td> 187</tr> 188<tr> 189<td><p><span class="term">Throws:</span></p></td> 190<td>May fail with any exceptions arising from the assignment 191 operator of <code class="computeroutput">T</code>.</td> 192</tr> 193</tbody> 194</table></div> 195</li> 196<li class="listitem"> 197<pre class="literallayout"><span class="identifier">recursive_wrapper</span> <span class="special">&</span> <a name="id-1_3_46_5_6_1_1_9_3-bb"></a><span class="keyword">operator</span><span class="special">=</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">T</span> <span class="special">&</span> rhs<span class="special">)</span><span class="special">;</span></pre>Value assignment operator.<p class="simpara">Assigns <code class="computeroutput">rhs</code> into the content of 198 <code class="computeroutput">*this</code>.</p> 199<div class="variablelist"><table border="0" class="variablelist compact"> 200<colgroup> 201<col align="left" valign="top"> 202<col> 203</colgroup> 204<tbody> 205<tr> 206<td><p><span class="term">Requires:</span></p></td> 207<td> 208<code class="computeroutput">T</code> must fulfill the requirements of the 209 <a class="link" href="../Assignable.html" title="Concept Assignable">Assignable</a> 210 concept.</td> 211</tr> 212<tr> 213<td><p><span class="term">Throws:</span></p></td> 214<td>May fail with any exceptions arising from the assignment 215 operator of <code class="computeroutput">T</code>.</td> 216</tr> 217</tbody> 218</table></div> 219</li> 220</ol></div> 221</div> 222<div class="refsect2"> 223<a name="id-1.3.46.5.7.3.4.8"></a><h3> 224<a name="id-1_3_46_5_6_1_1_10-bb"></a><code class="computeroutput">recursive_wrapper</code> queries</h3> 225<div class="orderedlist"><ol class="orderedlist" type="1"> 226<li class="listitem"> 227<pre class="literallayout"><a name="id-1_3_46_5_6_1_1_10_1-bb"></a><span class="identifier">T</span> <span class="special">&</span> <a name="id-1_3_46_5_6_1_1_10_1_1-bb"></a><span class="identifier">get</span><span class="special">(</span><span class="special">)</span><span class="special">;</span> 228<span class="keyword">const</span> <span class="identifier">T</span> <span class="special">&</span> <a name="id-1_3_46_5_6_1_1_10_1_2-bb"></a><span class="identifier">get</span><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre> 229<p class="simpara">Returns a reference to the content of 230 <code class="computeroutput">*this</code>.</p> 231<div class="variablelist"><table border="0" class="variablelist compact"> 232<colgroup> 233<col align="left" valign="top"> 234<col> 235</colgroup> 236<tbody><tr> 237<td><p><span class="term">Throws:</span></p></td> 238<td>Will not throw.</td> 239</tr></tbody> 240</table></div> 241</li> 242<li class="listitem"> 243<pre class="literallayout"><a name="id-1_3_46_5_6_1_1_10_2-bb"></a><span class="identifier">T</span> <span class="special">*</span> <a name="id-1_3_46_5_6_1_1_10_2_1-bb"></a><span class="identifier">get_pointer</span><span class="special">(</span><span class="special">)</span><span class="special">;</span> 244<span class="keyword">const</span> <span class="identifier">T</span> <span class="special">*</span> <a name="id-1_3_46_5_6_1_1_10_2_2-bb"></a><span class="identifier">get_pointer</span><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre> 245<p class="simpara">Returns a pointer to the content of 246 <code class="computeroutput">*this</code>.</p> 247<div class="variablelist"><table border="0" class="variablelist compact"> 248<colgroup> 249<col align="left" valign="top"> 250<col> 251</colgroup> 252<tbody><tr> 253<td><p><span class="term">Throws:</span></p></td> 254<td>Will not throw.</td> 255</tr></tbody> 256</table></div> 257</li> 258</ol></div> 259</div> 260</div> 261</div> 262<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 263<td align="left"></td> 264<td align="right"><div class="copyright-footer">Copyright © 2002, 2003 Eric Friedman, Itay Maman<br>Copyright © 2014-2020 Antony Polukhin<p>Distributed under the Boost Software License, Version 1.0. 265 (See accompanying file <code class="filename">LICENSE_1_0.txt</code> or copy at 266 <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) 267 </p> 268</div></td> 269</tr></table> 270<hr> 271<div class="spirit-nav"> 272<a accesskey="p" href="make_recurs_1_3_46_5_5_1_3.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../variant/reference.html#header.boost.variant.recursive_wrapper_hpp"><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="is_recursive_wrapper.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> 273</div> 274</body> 275</html> 276
