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- <div class="section">
- <div class="titlepage"><div><div><h2 class="title" style="clear: both">
- <a name="utility_and_infrastructure.boost_python_instance_holder_hpp"></a><a class="link" href="boost_python_instance_holder_hpp.html" title="boost/python/instance_holder.hpp">boost/python/instance_holder.hpp</a>
- </h2></div></div></div>
- <div class="toc"><dl class="toc">
- <dt><span class="section"><a href="boost_python_instance_holder_hpp.html#utility_and_infrastructure.boost_python_instance_holder_hpp.introduction">Introduction</a></span></dt>
- <dt><span class="section"><a href="boost_python_instance_holder_hpp.html#utility_and_infrastructure.boost_python_instance_holder_hpp.class_template_instance_holder">Class
- template <code class="computeroutput"><span class="identifier">instance_holder</span></code></a></span></dt>
- <dt><span class="section"><a href="boost_python_instance_holder_hpp.html#utility_and_infrastructure.boost_python_instance_holder_hpp.examples">Examples</a></span></dt>
- </dl></div>
- <div class="section">
- <div class="titlepage"><div><div><h3 class="title">
- <a name="utility_and_infrastructure.boost_python_instance_holder_hpp.introduction"></a><a class="link" href="boost_python_instance_holder_hpp.html#utility_and_infrastructure.boost_python_instance_holder_hpp.introduction" title="Introduction">Introduction</a>
- </h3></div></div></div>
- <p>
- <boost/python/instance_holder.hpp> provides class <code class="computeroutput"><span class="identifier">instance_holder</span></code>,
- the base class for types which hold C++ instances of wrapped classes.
- </p>
- </div>
- <div class="section">
- <div class="titlepage"><div><div><h3 class="title">
- <a name="utility_and_infrastructure.boost_python_instance_holder_hpp.class_template_instance_holder"></a><a class="link" href="boost_python_instance_holder_hpp.html#utility_and_infrastructure.boost_python_instance_holder_hpp.class_template_instance_holder" title="Class template instance_holder">Class
- template <code class="computeroutput"><span class="identifier">instance_holder</span></code></a>
- </h3></div></div></div>
- <div class="toc"><dl class="toc">
- <dt><span class="section"><a href="boost_python_instance_holder_hpp.html#utility_and_infrastructure.boost_python_instance_holder_hpp.class_template_instance_holder.class_intance_holder_destructor">Class
- <code class="computeroutput"><span class="identifier">intance_holder</span></code> destructor</a></span></dt>
- <dt><span class="section"><a href="boost_python_instance_holder_hpp.html#utility_and_infrastructure.boost_python_instance_holder_hpp.class_template_instance_holder.class_intance_holder_modifiers">Class
- <code class="computeroutput"><span class="identifier">intance_holder</span></code> modifiers</a></span></dt>
- <dt><span class="section"><a href="boost_python_instance_holder_hpp.html#utility_and_infrastructure.boost_python_instance_holder_hpp.class_template_instance_holder.class_intance_holder_observers">Class
- <code class="computeroutput"><span class="identifier">intance_holder</span></code> observers</a></span></dt>
- </dl></div>
- <p>
- <code class="computeroutput"><span class="identifier">instance_holder</span></code> is an abstract
- base class whose concrete derived classes hold C++ class instances within
- their Python object wrappers. To allow multiple inheritance in Python from
- C++ class wrappers, each such Python object contains a chain of instance_holders.
- When an <code class="computeroutput"><span class="identifier">__init__</span></code> function
- for a wrapped C++ class is invoked, a new <code class="computeroutput"><span class="identifier">instance_holder</span></code>
- instance is created and installed in the Python object using its <code class="computeroutput"><span class="identifier">install</span><span class="special">()</span></code>
- function. Each concrete class derived from <code class="computeroutput"><span class="identifier">instance_holder</span></code>
- must provide a <code class="computeroutput"><span class="identifier">holds</span><span class="special">()</span></code>
- implementation which allows Boost.Python to query it for the type(s) it
- is holding. In order to support the held type's wrapped constructor(s),
- the class must also provide constructors that can accept an initial <code class="computeroutput"><span class="identifier">PyObject</span><span class="special">*</span></code>
- argument referring to the owning Python object, and which forward the rest
- of their arguments to the constructor of the held type. The initial argument
- is needed to enable virtual function overriding in Python, and may be ignored,
- depending on the specific <code class="computeroutput"><span class="identifier">instance_holder</span></code>
- subclass.
- </p>
- <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>
- <span class="special">{</span>
- <span class="keyword">class</span> <span class="identifier">instance_holder</span> <span class="special">:</span> <span class="identifier">noncopyable</span>
- <span class="special">{</span>
- <span class="keyword">public</span><span class="special">:</span>
- <span class="comment">// destructor</span>
- <span class="keyword">virtual</span> <span class="special">~</span><span class="identifier">instance_holder</span><span class="special">();</span>
- <span class="comment">// instance_holder modifiers</span>
- <span class="keyword">void</span> <span class="identifier">install</span><span class="special">(</span><span class="identifier">PyObject</span><span class="special">*</span> <span class="identifier">inst</span><span class="special">)</span> <span class="keyword">throw</span><span class="special">();</span>
- <span class="comment">// instance_holder observers</span>
- <span class="keyword">virtual</span> <span class="keyword">void</span><span class="special">*</span> <span class="identifier">holds</span><span class="special">(</span><span class="identifier">type_info</span><span class="special">)</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
- <span class="special">};</span>
- <span class="special">}}</span>
- </pre>
- <div class="section">
- <div class="titlepage"><div><div><h4 class="title">
- <a name="utility_and_infrastructure.boost_python_instance_holder_hpp.class_template_instance_holder.class_intance_holder_destructor"></a><a class="link" href="boost_python_instance_holder_hpp.html#utility_and_infrastructure.boost_python_instance_holder_hpp.class_template_instance_holder.class_intance_holder_destructor" title="Class intance_holder destructor">Class
- <code class="computeroutput"><span class="identifier">intance_holder</span></code> destructor</a>
- </h4></div></div></div>
- <pre class="programlisting"><span class="keyword">virtual</span> <span class="special">~</span><span class="identifier">instance_holder</span><span class="special">();</span></pre>
- <div class="variablelist">
- <p class="title"><b></b></p>
- <dl class="variablelist">
- <dt><span class="term">Effects</span></dt>
- <dd><p>
- destroys the object
- </p></dd>
- </dl>
- </div>
- </div>
- <div class="section">
- <div class="titlepage"><div><div><h4 class="title">
- <a name="utility_and_infrastructure.boost_python_instance_holder_hpp.class_template_instance_holder.class_intance_holder_modifiers"></a><a class="link" href="boost_python_instance_holder_hpp.html#utility_and_infrastructure.boost_python_instance_holder_hpp.class_template_instance_holder.class_intance_holder_modifiers" title="Class intance_holder modifiers">Class
- <code class="computeroutput"><span class="identifier">intance_holder</span></code> modifiers</a>
- </h4></div></div></div>
- <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">install</span><span class="special">(</span><span class="identifier">PyObject</span><span class="special">*</span> <span class="identifier">inst</span><span class="special">)</span> <span class="keyword">throw</span><span class="special">();</span></pre>
- <div class="variablelist">
- <p class="title"><b></b></p>
- <dl class="variablelist">
- <dt><span class="term">Requires</span></dt>
- <dd><p>
- <code class="computeroutput"><span class="identifier">inst</span></code> is a Python
- instance of a wrapped C++ class type, or is a type derived from
- a wrapped C++ class type.
- </p></dd>
- <dt><span class="term">Effects</span></dt>
- <dd><p>
- installs the new instance at the head of the Python object's chain
- of held instances.
- </p></dd>
- <dt><span class="term">Throws</span></dt>
- <dd><p>
- nothing
- </p></dd>
- </dl>
- </div>
- </div>
- <div class="section">
- <div class="titlepage"><div><div><h4 class="title">
- <a name="utility_and_infrastructure.boost_python_instance_holder_hpp.class_template_instance_holder.class_intance_holder_observers"></a><a class="link" href="boost_python_instance_holder_hpp.html#utility_and_infrastructure.boost_python_instance_holder_hpp.class_template_instance_holder.class_intance_holder_observers" title="Class intance_holder observers">Class
- <code class="computeroutput"><span class="identifier">intance_holder</span></code> observers</a>
- </h4></div></div></div>
- <pre class="programlisting"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="special">*</span><span class="identifier">holds</span><span class="special">(</span><span class="identifier">type_info</span> <span class="identifier">x</span><span class="special">)</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span></pre>
- <div class="variablelist">
- <p class="title"><b></b></p>
- <dl class="variablelist">
- <dt><span class="term">Returns</span></dt>
- <dd><p>
- A pointer to an object of the type described by <code class="computeroutput"><span class="identifier">x</span></code>
- if <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
- contains such an object, 0 otherwise.
- </p></dd>
- </dl>
- </div>
- </div>
- </div>
- <div class="section">
- <div class="titlepage"><div><div><h3 class="title">
- <a name="utility_and_infrastructure.boost_python_instance_holder_hpp.examples"></a><a class="link" href="boost_python_instance_holder_hpp.html#utility_and_infrastructure.boost_python_instance_holder_hpp.examples" title="Examples">Examples</a>
- </h3></div></div></div>
- <p>
- The following is a simplified version of the instance holder template used
- by Boost.Python to wrap classes held by smart pointers:
- </p>
- <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">SmartPtr</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">Value</span><span class="special">></span>
- <span class="keyword">struct</span> <span class="identifier">pointer_holder</span> <span class="special">:</span> <span class="identifier">instance_holder</span>
- <span class="special">{</span>
- <span class="comment">// construct from the SmartPtr type</span>
- <span class="identifier">pointer_holder</span><span class="special">(</span><span class="identifier">SmartPtr</span> <span class="identifier">p</span><span class="special">)</span>
- <span class="special">:</span><span class="identifier">m_p</span><span class="special">(</span><span class="identifier">p</span><span class="special">)</span>
- <span class="comment">// Forwarding constructors for the held type</span>
- <span class="identifier">pointer_holder</span><span class="special">(</span><span class="identifier">PyObject</span><span class="special">*)</span>
- <span class="special">:</span><span class="identifier">m_p</span><span class="special">(</span><span class="keyword">new</span> <span class="identifier">Value</span><span class="special">())</span>
- <span class="special">{</span>
- <span class="special">}</span>
- <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">A0</span><span class="special">></span>
- <span class="identifier">pointer_holder</span><span class="special">(</span><span class="identifier">PyObject</span><span class="special">*,</span><span class="identifier">A0</span> <span class="identifier">a0</span><span class="special">)</span>
- <span class="special">:</span><span class="identifier">m_p</span><span class="special">(</span><span class="keyword">new</span> <span class="identifier">Value</span><span class="special">(</span><span class="identifier">a0</span><span class="special">))</span>
- <span class="special">{</span>
- <span class="special">}</span>
- <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">A0</span><span class="special">,</span><span class="keyword">class</span> <span class="identifier">A1</span><span class="special">></span>
- <span class="identifier">pointer_holder</span><span class="special">(</span><span class="identifier">PyObject</span><span class="special">*,</span><span class="identifier">A0</span> <span class="identifier">a0</span><span class="special">,</span><span class="identifier">A1</span> <span class="identifier">a1</span><span class="special">)</span>
- <span class="special">:</span><span class="identifier">m_p</span><span class="special">(</span><span class="keyword">new</span> <span class="identifier">Value</span><span class="special">(</span><span class="identifier">a0</span><span class="special">,</span><span class="identifier">a1</span><span class="special">))</span>
- <span class="special">{</span>
- <span class="special">}</span>
- <span class="special">...</span>
- <span class="keyword">private</span><span class="special">:</span> <span class="comment">// required holder implementation</span>
- <span class="keyword">void</span><span class="special">*</span> <span class="identifier">holds</span><span class="special">(</span><span class="identifier">type_info</span> <span class="identifier">dst_t</span><span class="special">)</span>
- <span class="special">{</span>
- <span class="comment">// holds an instance of the SmartPtr type...</span>
- <span class="keyword">if</span> <span class="special">(</span><span class="identifier">dst_t</span> <span class="special">==</span> <span class="identifier">python</span><span class="special">::</span><span class="identifier">type_id</span><span class="special"><</span><span class="identifier">SmartPtr</span><span class="special">>())</span>
- <span class="keyword">return</span> <span class="special">&</span><span class="keyword">this</span><span class="special">-></span><span class="identifier">m_p</span><span class="special">;</span>
- <span class="comment">// ...and an instance of the SmartPtr's element_type, if the</span>
- <span class="comment">// pointer is non-null</span>
- <span class="keyword">return</span> <span class="identifier">python</span><span class="special">::</span><span class="identifier">type_id</span><span class="special"><</span><span class="identifier">Value</span><span class="special">>()</span> <span class="special">==</span> <span class="identifier">dst_t</span> <span class="special">?</span> <span class="special">&*</span><span class="keyword">this</span><span class="special">-></span><span class="identifier">m_p</span> <span class="special">:</span> <span class="number">0</span><span class="special">;</span>
- <span class="special">}</span>
- <span class="keyword">private</span><span class="special">:</span> <span class="comment">// data members</span>
- <span class="identifier">SmartPtr</span> <span class="identifier">m_p</span><span class="special">;</span>
- <span class="special">};</span>
- </pre>
- </div>
- </div>
- <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
- <td align="left"></td>
- <td align="right"><div class="copyright-footer">Copyright © 2002-2005, 2015 David Abrahams, Stefan Seefeld<p>
- Distributed under the Boost Software License, Version 1.0. (See accompanying
- 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>
- </p>
- </div></td>
- </tr></table>
- <hr>
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