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diff --git a/libs/python/doc/v2/reference_existing_object.html b/libs/python/doc/v2/reference_existing_object.html new file mode 100644 index 000000000..12e228f50 --- /dev/null +++ b/libs/python/doc/v2/reference_existing_object.html @@ -0,0 +1,180 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> + +<!-- Copyright David Abrahams 2006. Distributed under the Boost --> +<!-- Software License, Version 1.0. (See accompanying --> +<!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) --> +<html> + <head> + <meta name="generator" content= + "HTML Tidy for Windows (vers 1st August 2002), see www.w3.org"> + <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> + <link rel="stylesheet" type="text/css" href="../boost.css"> + + <title>Boost.Python - + <boost/python/reference_existing_object.hpp></title> + </head> + + <body> + <table border="0" cellpadding="7" cellspacing="0" width="100%" summary= + "header"> + <tr> + <td valign="top" width="300"> + <h3><a href="../../../../index.htm"><img height="86" width="277" + alt="C++ Boost" src="../../../../boost.png" border="0"></a></h3> + </td> + + <td valign="top"> + <h1 align="center"><a href="../index.html">Boost.Python</a></h1> + + <h2 align="center">Header + <boost/python/reference_existing_object.hpp></h2> + </td> + </tr> + </table> + <hr> + + <h2>Contents</h2> + + <dl class="page-index"> + <dt><a href="#classes">Classes</a></dt> + + <dd> + <dl class="page-index"> + <dt><a href="#reference_existing_object-spec">Class + <code>reference_existing_object</code></a></dt> + + <dd> + <dl class="page-index"> + <dt><a href="#reference_existing_object-spec-synopsis">Class + <code>reference_existing_object</code> synopsis</a></dt> + + <dt><a href= + "#reference_existing_object-spec-metafunctions">Class + <code>reference_existing_object</code> metafunctions</a></dt> + </dl> + </dd> + </dl> + </dd> + + <dt><a href="#examples">Example</a></dt> + </dl> + <hr> + + <h2><a name="classes"></a>Classes</h2> + + <h3><a name="reference_existing_object-spec"></a>Class + <code>reference_existing_object</code></h3> + + <p><code>reference_existing_object</code> is a model of <a href= + "ResultConverter.html#ResultConverterGenerator-concept">ResultConverterGenerator</a> + which can be used to wrap C++ functions which return a reference or + pointer to a C++ object. When the wrapped function is called, the value + referenced by its return value is not copied. A new Python object is + created which contains a pointer to the referent, and no attempt is made + to ensure that the lifetime of the referent is at least as long as that + of the corresponding Python object. Thus, it can be <font color= + "#ff0000"><b>highly dangerous</b></font> to use + <code>reference_existing_object</code> without additional lifetime + management from such models of <a href= + "CallPolicies.html">CallPolicies</a> as <a href= + "with_custodian_and_ward.html#with_custodian_and_ward-spec">with_custodian_and_ward</a>. + This class is used in the implementation of <a href= + "return_internal_reference.html#return_internal_reference-spec">return_internal_reference</a>.</p> + + <h4><a name="reference_existing_object-spec-synopsis"></a>Class + <code>reference_existing_object</code> synopsis</h4> +<pre> +namespace boost { namespace python +{ + struct reference_existing_object + { + template <class T> struct apply; + }; +}} +</pre> + + <h4><a name="reference_existing_object-spec-metafunctions"></a>Class + <code>reference_existing_object</code> metafunctions</h4> +<pre> +template <class T> struct apply +</pre> + + <dl class="metafunction-semantics"> + <dt><b>Requires:</b> <code>T</code> is <code>U&</code> or + <code>U*</code>for some <code>U</code>.</dt> + + <dt><b>Returns:</b> <code>typedef <a href= + "to_python_indirect.html#to_python_indirect-spec">to_python_indirect</a><T,V> + type</code>, where <code>V</code> is a class whose + static <code>execute</code> function constructs an instance + holder containing an <i>unowned</i> + <code>U*</code> pointing to the referent of the wrapped function's + return value.</dt> + </dl> + + <h2><a name="examples"></a>Example</h2> + + <p>In C++:</p> +<pre> +#include <boost/python/module.hpp> +#include <boost/python/class.hpp> +#include <boost/python/reference_existing_object.hpp> +#include <boost/python/return_value_policy.hpp> +#include <utility> + +// classes to wrap +struct Singleton +{ + Singleton() : x(0) {} + + int exchange(int n) // set x and return the old value + { + std::swap(n, x); + return n; + } + + int x; +}; + +Singleton& get_it() +{ + static Singleton just_one; + return just_one; +} + +// Wrapper code +using namespace boost::python; +BOOST_PYTHON_MODULE(singleton) +{ + def("get_it", get_it, + return_value_policy<reference_existing_object>()); + + class_<Singleton>("Singleton") + .def("exchange", &Singleton::exchange) + ; +} +</pre> + In Python: +<pre> +>>> import singleton +>>> s1 = singleton.get_it() +>>> s2 = singleton.get_it() +>>> id(s1) == id(s2) # s1 and s2 are not the same object +0 +>>> s1.exchange(42) # but they reference the same C++ Singleton +0 +>>> s2.exchange(99) +42 +</pre> + + <p>Revised + <!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan --> + 13 November, 2002 + <!--webbot bot="Timestamp" endspan i-checksum="39359" --> + </p> + + <p><i>© Copyright <a href= + "http://www.boost.org/people/dave_abrahams.htm">Dave Abrahams</a> 2002.</i></p> + </body> +</html> + |