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  4. <title>Chapter&#160;7.&#160;Utility and Infrastructure</title>
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  18. <div class="chapter">
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  19. <div class="titlepage"><div><div><h1 class="title">
    20. 

  20. <a name="utility_and_infrastructure"></a>Chapter&#160;7.&#160;Utility and Infrastructure</h1></div></div></div>
    21. 

  21. <div class="toc">
    22. 

  22. <p><b>Table of Contents</b></p>
    23. 

  23. <dl class="toc">
    24. 

  24. <dt><span class="section"><a href="utility_and_infrastructure.html#utility_and_infrastructure.boost_python_has_back_reference_">boost/python/has_back_reference.hpp</a></span></dt>
    25. 

  25. <dd><dl>
    26. 

  26. <dt><span class="section"><a href="utility_and_infrastructure.html#utility_and_infrastructure.boost_python_has_back_reference_.introduction">Introduction</a></span></dt>
    27. 

  27. <dt><span class="section"><a href="utility_and_infrastructure.html#utility_and_infrastructure.boost_python_has_back_reference_.class_template_has_back_referenc">Class
    28. 

  28.         template <code class="computeroutput"><span class="identifier">has_back_reference</span></code></a></span></dt>
    29. 

  29. <dt><span class="section"><a href="utility_and_infrastructure.html#utility_and_infrastructure.boost_python_has_back_reference_.examples">Examples</a></span></dt>
    30. 

  30. </dl></dd>
    31. 

  31. <dt><span class="section"><a href="utility_and_infrastructure/boost_python_instance_holder_hpp.html">boost/python/instance_holder.hpp</a></span></dt>
    32. 

  32. <dd><dl>
    33. 

  33. <dt><span class="section"><a href="utility_and_infrastructure/boost_python_instance_holder_hpp.html#utility_and_infrastructure.boost_python_instance_holder_hpp.introduction">Introduction</a></span></dt>
    34. 

  34. <dt><span class="section"><a href="utility_and_infrastructure/boost_python_instance_holder_hpp.html#utility_and_infrastructure.boost_python_instance_holder_hpp.class_template_instance_holder">Class
    35. 

  35.         template <code class="computeroutput"><span class="identifier">instance_holder</span></code></a></span></dt>
    36. 

  36. <dt><span class="section"><a href="utility_and_infrastructure/boost_python_instance_holder_hpp.html#utility_and_infrastructure.boost_python_instance_holder_hpp.examples">Examples</a></span></dt>
    37. 

  37. </dl></dd>
    38. 

  38. <dt><span class="section"><a href="utility_and_infrastructure/boost_python_pointee_hpp.html">boost/python/pointee.hpp</a></span></dt>
    39. 

  39. <dd><dl>
    40. 

  40. <dt><span class="section"><a href="utility_and_infrastructure/boost_python_pointee_hpp.html#utility_and_infrastructure.boost_python_pointee_hpp.introduction">Introduction</a></span></dt>
    41. 

  41. <dt><span class="section"><a href="utility_and_infrastructure/boost_python_pointee_hpp.html#utility_and_infrastructure.boost_python_pointee_hpp.class_template_pointee">Class
    42. 

  42.         template <code class="computeroutput"><span class="identifier">pointee</span></code></a></span></dt>
    43. 

  43. <dt><span class="section"><a href="utility_and_infrastructure/boost_python_pointee_hpp.html#utility_and_infrastructure.boost_python_pointee_hpp.examples">Examples</a></span></dt>
    44. 

  44. </dl></dd>
    45. 

  45. <dt><span class="section"><a href="utility_and_infrastructure/boost_python_handle_hpp.html">boost/python/handle.hpp</a></span></dt>
    46. 

  46. <dd><dl>
    47. 

  47. <dt><span class="section"><a href="utility_and_infrastructure/boost_python_handle_hpp.html#utility_and_infrastructure.boost_python_handle_hpp.introduction">Introduction</a></span></dt>
    48. 

  48. <dt><span class="section"><a href="utility_and_infrastructure/boost_python_handle_hpp.html#utility_and_infrastructure.boost_python_handle_hpp.class_template_handle">Class
    49. 

  49.         template <code class="computeroutput"><span class="identifier">handle</span></code></a></span></dt>
    50. 

  50. <dt><span class="section"><a href="utility_and_infrastructure/boost_python_handle_hpp.html#utility_and_infrastructure.boost_python_handle_hpp.function_borrowed">Function
    51. 

  51.         <code class="computeroutput"><span class="identifier">borrowed</span></code></a></span></dt>
    52. 

  52. <dt><span class="section"><a href="utility_and_infrastructure/boost_python_handle_hpp.html#utility_and_infrastructure.boost_python_handle_hpp.function_allow_null">Function
    53. 

  53.         <code class="computeroutput"><span class="identifier">allow_null</span></code></a></span></dt>
    54. 

  54. </dl></dd>
    55. 

  55. <dt><span class="section"><a href="utility_and_infrastructure/boost_python_type_id_hpp.html">boost/python/type_id.hpp</a></span></dt>
    56. 

  56. <dd><dl>
    57. 

  57. <dt><span class="section"><a href="utility_and_infrastructure/boost_python_type_id_hpp.html#utility_and_infrastructure.boost_python_type_id_hpp.introduction">Introduction</a></span></dt>
    58. 

  58. <dt><span class="section"><a href="utility_and_infrastructure/boost_python_type_id_hpp.html#utility_and_infrastructure.boost_python_type_id_hpp.class_template_type_info">Class
    59. 

  59.         template <code class="computeroutput"><span class="identifier">type_info</span></code></a></span></dt>
    60. 

  60. <dt><span class="section"><a href="utility_and_infrastructure/boost_python_type_id_hpp.html#utility_and_infrastructure.boost_python_type_id_hpp.functions">Functions</a></span></dt>
    61. 

  61. <dt><span class="section"><a href="utility_and_infrastructure/boost_python_type_id_hpp.html#utility_and_infrastructure.boost_python_type_id_hpp.example">Example</a></span></dt>
    62. 

  62. </dl></dd>
    63. 

  63. <dt><span class="section"><a href="utility_and_infrastructure/boost_python_ssize_t_hpp.html">boost/python/ssize_t.hpp</a></span></dt>
    64. 

  64. <dd><dl>
    65. 

  65. <dt><span class="section"><a href="utility_and_infrastructure/boost_python_ssize_t_hpp.html#utility_and_infrastructure.boost_python_ssize_t_hpp.introduction">Introduction</a></span></dt>
    66. 

  66. <dt><span class="section"><a href="utility_and_infrastructure/boost_python_ssize_t_hpp.html#utility_and_infrastructure.boost_python_ssize_t_hpp.typedefs">Typedefs</a></span></dt>
    67. 

  67. <dt><span class="section"><a href="utility_and_infrastructure/boost_python_ssize_t_hpp.html#utility_and_infrastructure.boost_python_ssize_t_hpp.constants">Constants</a></span></dt>
    68. 

  68. </dl></dd>
    69. 

  69. </dl>
    70. 

  70. </div>
    71. 

  71. <div class="section">
    72. 

  72. <div class="titlepage"><div><div><h2 class="title" style="clear: both">
    73. 

  73. <a name="utility_and_infrastructure.boost_python_has_back_reference_"></a><a class="link" href="utility_and_infrastructure.html#utility_and_infrastructure.boost_python_has_back_reference_" title="boost/python/has_back_reference.hpp">boost/python/has_back_reference.hpp</a>
    74. 

  74. </h2></div></div></div>
    75. 

  75. <div class="toc"><dl class="toc">
    76. 

  76. <dt><span class="section"><a href="utility_and_infrastructure.html#utility_and_infrastructure.boost_python_has_back_reference_.introduction">Introduction</a></span></dt>
    77. 

  77. <dt><span class="section"><a href="utility_and_infrastructure.html#utility_and_infrastructure.boost_python_has_back_reference_.class_template_has_back_referenc">Class
    78. 

  78.         template <code class="computeroutput"><span class="identifier">has_back_reference</span></code></a></span></dt>
    79. 

  79. <dt><span class="section"><a href="utility_and_infrastructure.html#utility_and_infrastructure.boost_python_has_back_reference_.examples">Examples</a></span></dt>
    80. 

  80. </dl></div>
    81. 

  81. <div class="section">
    82. 

  82. <div class="titlepage"><div><div><h3 class="title">
    83. 

  83. <a name="utility_and_infrastructure.boost_python_has_back_reference_.introduction"></a><a class="link" href="utility_and_infrastructure.html#utility_and_infrastructure.boost_python_has_back_reference_.introduction" title="Introduction">Introduction</a>
    84. 

  84. </h3></div></div></div>
    85. 

  85. <p>
    86. 

  86.           &lt;boost/python/has_back_reference.hpp&gt; defines the predicate metafunction
    87. 

  87.           <code class="computeroutput"><span class="identifier">has_back_reference</span><span class="special">&lt;&gt;</span></code>,
    88. 

  88.           which can be specialized by the user to indicate that a wrapped class instance
    89. 

  89.           holds a <code class="computeroutput"><span class="identifier">PyObject</span><span class="special">*</span></code>
    90. 

  90.           corresponding to a Python object.
    91. 

  91.         </p>
    92. 

  92. </div>
    93. 

  93. <div class="section">
    94. 

  94. <div class="titlepage"><div><div><h3 class="title">
    95. 

  95. <a name="utility_and_infrastructure.boost_python_has_back_reference_.class_template_has_back_referenc"></a><a class="link" href="utility_and_infrastructure.html#utility_and_infrastructure.boost_python_has_back_reference_.class_template_has_back_referenc" title="Class template has_back_reference">Class
    96. 

  96.         template <code class="computeroutput"><span class="identifier">has_back_reference</span></code></a>
    97. 

  97. </h3></div></div></div>
    98. 

  98. <p>
    99. 

  99.           A unary metafunction whose value is true iff its argument is a <code class="computeroutput"><span class="identifier">pointer_wrapper</span><span class="special">&lt;&gt;</span></code>.
    100. 

  100.         </p>
    101. 

  101. <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">python</span>
    102. 

  102. <span class="special">{</span>
    103. 

  103.     <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">WrappedClass</span><span class="special">&gt;</span> <span class="keyword">class</span> <span class="identifier">has_back_reference</span>
    104. 

  104.     <span class="special">{</span>
    105. 

  105.         <span class="keyword">typedef</span> <span class="identifier">mpl</span><span class="special">::</span><span class="identifier">false_</span> <span class="identifier">type</span><span class="special">;</span>
    106. 

  106.     <span class="special">};</span>
    107. 

  107. <span class="special">}}</span>
    108. 

  108. </pre>
    109. 

  109. <p>
    110. 

  110.           A metafunction that is inspected by Boost.Python to determine how wrapped
    111. 

  111.           classes can be constructed.
    112. 

  112.         </p>
    113. 

  113. <p>
    114. 

  114.           <code class="computeroutput"><span class="identifier">type</span><span class="special">::</span><span class="identifier">value</span></code> is an integral constant convertible
    115. 

  115.           to bool of unspecified type. Specializations may substitute a true-valued
    116. 

  116.           integral constant wrapper for type iff for each invocation of <code class="computeroutput"><span class="identifier">class_</span><span class="special">&lt;</span><span class="identifier">WrappedClass</span><span class="special">&gt;::</span><span class="identifier">def</span><span class="special">(</span><span class="identifier">init</span><span class="special">&lt;</span> <span class="identifier">type</span><span class="special">-</span><span class="identifier">sequence</span><span class="special">...&gt;())</span></code>
    117. 

  117.           and the implicitly wrapped copy constructor (unless it is noncopyable),
    118. 

  118.           there exists a corresponding constructor <code class="computeroutput"><span class="identifier">WrappedClass</span><span class="special">::</span><span class="identifier">WrappedClass</span><span class="special">(</span><span class="identifier">PyObject</span><span class="special">*,</span> <span class="identifier">type</span><span class="special">-</span><span class="identifier">sequence</span><span class="special">...)</span></code>. If such a specialization exists, the
    119. 

  119.           WrappedClass constructors will be called with a "back reference"
    120. 

  120.           pointer to the corresponding Python object whenever they are invoked from
    121. 

  121.           Python. The easiest way to provide this nested type is to derive the specialization
    122. 

  122.           from <code class="computeroutput"><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">true_</span></code>.
    123. 

  123.         </p>
    124. 

  124. </div>
    125. 

  125. <div class="section">
    126. 

  126. <div class="titlepage"><div><div><h3 class="title">
    127. 

  127. <a name="utility_and_infrastructure.boost_python_has_back_reference_.examples"></a><a class="link" href="utility_and_infrastructure.html#utility_and_infrastructure.boost_python_has_back_reference_.examples" title="Examples">Examples</a>
    128. 

  128. </h3></div></div></div>
    129. 

  129. <p>
    130. 

  130.           In C++:
    131. 

  131.         </p>
    132. 

  132. <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">python</span><span class="special">/</span><span class="keyword">class</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
    133. 

  133. <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">python</span><span class="special">/</span><span class="identifier">module</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
    134. 

  134. <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">python</span><span class="special">/</span><span class="identifier">has_back_reference</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
    135. 

  135. <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">python</span><span class="special">/</span><span class="identifier">handle</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
    136. 

  136. <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">shared_ptr</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
    137. 

  137. 

  138. <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">python</span><span class="special">;</span>
    139. 

  139. <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">shared_ptr</span><span class="special">;</span>
    140. 

  140. 

  141. <span class="keyword">struct</span> <span class="identifier">X</span>
    142. 

  142. <span class="special">{</span>
    143. 

  143.     <span class="identifier">X</span><span class="special">(</span><span class="identifier">PyObject</span><span class="special">*</span> <span class="identifier">self</span><span class="special">)</span> <span class="special">:</span> <span class="identifier">m_self</span><span class="special">(</span><span class="identifier">self</span><span class="special">),</span> <span class="identifier">m_x</span><span class="special">(</span><span class="number">0</span><span class="special">)</span> <span class="special">{}</span>
    144. 

  144.     <span class="identifier">X</span><span class="special">(</span><span class="identifier">PyObject</span><span class="special">*</span> <span class="identifier">self</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">x</span><span class="special">)</span> <span class="special">:</span> <span class="identifier">m_self</span><span class="special">(</span><span class="identifier">self</span><span class="special">),</span> <span class="identifier">m_x</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">{}</span>
    145. 

  145.     <span class="identifier">X</span><span class="special">(</span><span class="identifier">PyObject</span><span class="special">*</span> <span class="identifier">self</span><span class="special">,</span> <span class="identifier">X</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="special">:</span> <span class="identifier">m_self</span><span class="special">(</span><span class="identifier">self</span><span class="special">),</span> <span class="identifier">m_x</span><span class="special">(</span><span class="identifier">other</span><span class="special">.</span><span class="identifier">m_x</span><span class="special">)</span> <span class="special">{}</span>
    146. 

  146. 

  147.     <span class="identifier">handle</span><span class="special">&lt;&gt;</span> <span class="identifier">self</span><span class="special">()</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">handle</span><span class="special">&lt;&gt;(</span><span class="identifier">borrowed</span><span class="special">(</span><span class="identifier">m_self</span><span class="special">));</span> <span class="special">}</span>
    148. 

  148.     <span class="keyword">int</span> <span class="identifier">get</span><span class="special">()</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">m_x</span><span class="special">;</span> <span class="special">}</span>
    149. 

  149.     <span class="keyword">void</span> <span class="identifier">set</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">x</span><span class="special">)</span> <span class="special">{</span> <span class="identifier">m_x</span> <span class="special">=</span> <span class="identifier">x</span><span class="special">;</span> <span class="special">}</span>
    150. 

  150. 

  151.     <span class="identifier">PyObject</span><span class="special">*</span> <span class="identifier">m_self</span><span class="special">;</span>
    152. 

  152.     <span class="keyword">int</span> <span class="identifier">m_x</span><span class="special">;</span>
    153. 

  153. <span class="special">};</span>
    154. 

  154. 

  155. <span class="comment">// specialize has_back_reference for X</span>
    156. 

  156. <span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">python</span>
    157. 

  157. <span class="special">{</span>
    158. 

  158.   <span class="keyword">template</span> <span class="special">&lt;&gt;</span>
    159. 

  159.   <span class="keyword">struct</span> <span class="identifier">has_back_reference</span><span class="special">&lt;</span><span class="identifier">X</span><span class="special">&gt;</span>
    160. 

  160.     <span class="special">:</span> <span class="identifier">mpl</span><span class="special">::</span><span class="identifier">true_</span>
    161. 

  161.   <span class="special">{};</span>
    162. 

  162. <span class="special">}}</span>
    163. 

  163. 

  164. <span class="keyword">struct</span> <span class="identifier">Y</span>
    165. 

  165. <span class="special">{</span>
    166. 

  166.     <span class="identifier">Y</span><span class="special">()</span> <span class="special">:</span> <span class="identifier">m_x</span><span class="special">(</span><span class="number">0</span><span class="special">)</span> <span class="special">{}</span>
    167. 

  167.     <span class="identifier">Y</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">x</span><span class="special">)</span> <span class="special">:</span> <span class="identifier">m_x</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">{}</span>
    168. 

  168.     <span class="keyword">int</span> <span class="identifier">get</span><span class="special">()</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">m_x</span><span class="special">;</span> <span class="special">}</span>
    169. 

  169.     <span class="keyword">void</span> <span class="identifier">set</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">x</span><span class="special">)</span> <span class="special">{</span> <span class="identifier">m_x</span> <span class="special">=</span> <span class="identifier">x</span><span class="special">;</span> <span class="special">}</span>
    170. 

  170. 

  171.     <span class="keyword">int</span> <span class="identifier">m_x</span><span class="special">;</span>
    172. 

  172. <span class="special">};</span>
    173. 

  173. 

  174. <span class="identifier">shared_ptr</span><span class="special">&lt;</span><span class="identifier">Y</span><span class="special">&gt;</span>
    175. 

  175. <span class="identifier">Y_self</span><span class="special">(</span><span class="identifier">shared_ptr</span><span class="special">&lt;</span><span class="identifier">Y</span><span class="special">&gt;</span> <span class="identifier">self</span><span class="special">)</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">self</span><span class="special">;</span> <span class="special">}</span>
    176. 

  176. 

  177. <span class="identifier">BOOST_PYTHON_MODULE</span><span class="special">(</span><span class="identifier">back_references</span><span class="special">)</span>
    178. 

  178. <span class="special">{</span>
    179. 

  179.     <span class="identifier">class_</span><span class="special">&lt;</span><span class="identifier">X</span><span class="special">&gt;(</span><span class="string">"X"</span><span class="special">)</span>
    180. 

  180.        <span class="special">.</span><span class="identifier">def</span><span class="special">(</span><span class="identifier">init</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;())</span>
    181. 

  181.        <span class="special">.</span><span class="identifier">def</span><span class="special">(</span><span class="string">"self"</span><span class="special">,</span> <span class="special">&amp;</span><span class="identifier">X</span><span class="special">::</span><span class="identifier">self</span><span class="special">)</span>
    182. 

  182.        <span class="special">.</span><span class="identifier">def</span><span class="special">(</span><span class="string">"get"</span><span class="special">,</span> <span class="special">&amp;</span><span class="identifier">X</span><span class="special">::</span><span class="identifier">get</span><span class="special">)</span>
    183. 

  183.        <span class="special">.</span><span class="identifier">def</span><span class="special">(</span><span class="string">"set"</span><span class="special">,</span> <span class="special">&amp;</span><span class="identifier">X</span><span class="special">::</span><span class="identifier">set</span><span class="special">)</span>
    184. 

  184.        <span class="special">;</span>
    185. 

  185. 

  186.     <span class="identifier">class_</span><span class="special">&lt;</span><span class="identifier">Y</span><span class="special">,</span> <span class="identifier">shared_ptr</span><span class="special">&lt;</span><span class="identifier">Y</span><span class="special">&gt;</span> <span class="special">&gt;(</span><span class="string">"Y"</span><span class="special">)</span>
    187. 

  187.        <span class="special">.</span><span class="identifier">def</span><span class="special">(</span><span class="identifier">init</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;())</span>
    188. 

  188.        <span class="special">.</span><span class="identifier">def</span><span class="special">(</span><span class="string">"get"</span><span class="special">,</span> <span class="special">&amp;</span><span class="identifier">Y</span><span class="special">::</span><span class="identifier">get</span><span class="special">)</span>
    189. 

  189.        <span class="special">.</span><span class="identifier">def</span><span class="special">(</span><span class="string">"set"</span><span class="special">,</span> <span class="special">&amp;</span><span class="identifier">Y</span><span class="special">::</span><span class="identifier">set</span><span class="special">)</span>
    190. 

  190.        <span class="special">.</span><span class="identifier">def</span><span class="special">(</span><span class="string">"self"</span><span class="special">,</span> <span class="identifier">Y_self</span><span class="special">)</span>
    191. 

  191.        <span class="special">;</span>
    192. 

  192. <span class="special">}</span>
    193. 

  193. </pre>
    194. 

  194. <p>
    195. 

  195.           The following Python session illustrates that x.self() returns the same
    196. 

  196.           Python object on which it is invoked, while y.self() must create a new
    197. 

  197.           Python object which refers to the same Y instance.
    198. 

  198.         </p>
    199. 

  199. <p>
    200. 

  200.           In Python:
    201. 

  201.         </p>
    202. 

  202. <pre class="programlisting"><span class="special">&gt;&gt;&gt;</span> <span class="identifier">from</span> <span class="identifier">back_references</span> <span class="identifier">import</span> <span class="special">*</span>
    203. 

  203. <span class="special">&gt;&gt;&gt;</span> <span class="identifier">x</span> <span class="special">=</span> <span class="identifier">X</span><span class="special">(</span><span class="number">1</span><span class="special">)</span>
    204. 

  204. <span class="special">&gt;&gt;&gt;</span> <span class="identifier">x2</span> <span class="special">=</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">self</span><span class="special">()</span>
    205. 

  205. <span class="special">&gt;&gt;&gt;</span> <span class="identifier">x2</span> <span class="identifier">is</span> <span class="identifier">x</span>
    206. 

  206. <span class="number">1</span>
    207. 

  207. <span class="special">&gt;&gt;&gt;</span> <span class="special">(</span><span class="identifier">x</span><span class="special">.</span><span class="identifier">get</span><span class="special">(),</span> <span class="identifier">x2</span><span class="special">.</span><span class="identifier">get</span><span class="special">())</span>
    208. 

  208. <span class="special">(</span><span class="number">1</span><span class="special">,</span> <span class="number">1</span><span class="special">)</span>
    209. 

  209. <span class="special">&gt;&gt;&gt;</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">set</span><span class="special">(</span><span class="number">10</span><span class="special">)</span>
    210. 

  210. <span class="special">&gt;&gt;&gt;</span> <span class="special">(</span><span class="identifier">x</span><span class="special">.</span><span class="identifier">get</span><span class="special">(),</span> <span class="identifier">x2</span><span class="special">.</span><span class="identifier">get</span><span class="special">())</span>
    211. 

  211. <span class="special">(</span><span class="number">10</span><span class="special">,</span> <span class="number">10</span><span class="special">)</span>
    212. 

  212. <span class="special">&gt;&gt;&gt;</span>
    213. 

  213. <span class="special">&gt;&gt;&gt;</span>
    214. 

  214. <span class="special">&gt;&gt;&gt;</span> <span class="identifier">y</span> <span class="special">=</span> <span class="identifier">Y</span><span class="special">(</span><span class="number">2</span><span class="special">)</span>
    215. 

  215. <span class="special">&gt;&gt;&gt;</span> <span class="identifier">y2</span> <span class="special">=</span> <span class="identifier">y</span><span class="special">.</span><span class="identifier">self</span><span class="special">()</span>
    216. 

  216. <span class="special">&gt;&gt;&gt;</span> <span class="identifier">y2</span> <span class="identifier">is</span> <span class="identifier">y</span>
    217. 

  217. <span class="number">0</span>
    218. 

  218. <span class="special">&gt;&gt;&gt;</span> <span class="special">(</span><span class="identifier">y</span><span class="special">.</span><span class="identifier">get</span><span class="special">(),</span> <span class="identifier">y2</span><span class="special">.</span><span class="identifier">get</span><span class="special">())</span>
    219. 

  219. <span class="special">(</span><span class="number">2</span><span class="special">,</span> <span class="number">2</span><span class="special">)</span>
    220. 

  220. <span class="special">&gt;&gt;&gt;</span> <span class="identifier">y</span><span class="special">.</span><span class="identifier">set</span><span class="special">(</span><span class="number">20</span><span class="special">)</span>
    221. 

  221. <span class="special">&gt;&gt;&gt;</span> <span class="special">(</span><span class="identifier">y</span><span class="special">.</span><span class="identifier">get</span><span class="special">(),</span> <span class="identifier">y2</span><span class="special">.</span><span class="identifier">get</span><span class="special">())</span>
    222. 

  222. <span class="special">(</span><span class="number">20</span><span class="special">,</span> <span class="number">20</span><span class="special">)</span>
    223. 

  223. </pre>
    224. 

  224. </div>
    225. 

  225. </div>
    226. 

  226. </div>
    227. 

  227. <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
    228. 

  228. <td align="left"></td>
    229. 

  229. <td align="right"><div class="copyright-footer">Copyright &#169; 2002-2005, 2015 David Abrahams, Stefan Seefeld<p>
    230. 

  230.         Distributed under the Boost Software License, Version 1.0. (See accompanying
    231. 

  231.         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>
    232. 

  232.       </p>
    233. 

  233. </div></td>
    234. 

  234. </tr></table>
    235. 

  235. <hr>
    236. 

  236. <div class="spirit-nav">
    237. 

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    238. 

  238. </div>
    239. 

  239. </body>
    240. 

  240. </html>
    241.