<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <meta name="generator" content="HTML Tidy, 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/to_python_indirect.hpp></title> <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="../../../../c++boost.gif" border="0"></a></h3> <td valign="top"> <h1 align="center"><a href="../index.html">Boost.Python</a></h1> <h2 align="center">Header <boost/python/to_python_indirect.hpp></h2> </table> <hr> <h2>Contents</h2> <dl class="page-index"> <dt><a href="#introduction">Introduction</a> <dt><a href="#classes">Classes</a> <dd> <dl class="page-index"> <dt><a href="#to_python_indirect-spec">Class Template <code>to_python_indirect</code></a> <dd> <dl class="page-index"> <dt><a href="#to_python_indirect-spec-synopsis">Class Template <code>to_python_indirect</code> synopsis</a> <dt><a href="#to_python_indirect-spec-observers">Class Template <code>to_python_indirect</code> observer functions</a> <dt><a href="#to_python_indirect-spec-statics">Class Template <code>to_python_indirect</code> static functions</a> </dl> </dl> <dt><a href="#examples">Example</a> </dl> <hr> <h2><a name="introduction"></a>Introduction</h2> <code><boost/python/to_python_indirect.hpp></code> supplies a way to construct new Python objects that hold wrapped C++ class instances via a pointer or smart pointer. <h2><a name="classes"></a>Classes</h2> <h3><a name="to_python_indirect-spec"></a>Class template <code>to_python_indirect</code></h3> <p>Class template <code>to_python_indirect</code> converts objects of its first argument type to python as extension class instances, using the ownership policy provided by its 2nd argument. <p> <table border="1" summary="to_python_indirect template parameters"> <caption> <b><code>to_python_indirect</code> Requirements</b><br> In the table below, <b><code>x</code></b> denotes an object of type <code>T</code>, <b><code>h</code></b> denotes an object of type <code>boost::python::objects::instance_holder*</code>, and <b><code>p</code></b> denotes an object of type <code>U*</code>. </caption> <tr> <th>Parameter <th>Requirements <th>Description <tr> <td><code>T</code> <td>Either <code>U</code> <i>cv</i><code>&</code> (where <i>cv</i> is any optional cv-qualification) or a <a href="Dereferenceable.html">Dereferenceable</a> type such that <code>*x</code> is convertible to <code>U const&</code>, where <code>U</code> is a class type. <td>A type deferencing a C++ class exposed to Python using class template <code><a href="class.html#class_-spec">class_</a></code>. <tr> <td><code>MakeHolder</code> <td>h = MakeHolder::execute(p); <td>A class whose static <code>execute()</code> creates an <code>instance_holder</code>. </table> Instantiations of <code>to_python_indirect</code> are models of <a href="ResultConverter.html#ResultConverter-concept">ResultConverter</a>. <h4><a name="to_python_indirect-spec-synopsis"></a>Class template <code>to_python_indirect</code> synopsis</h4> <pre> namespace boost { namespace python { template <class T, class MakeHolder> struct to_python_indirect { static bool convertible(); PyObject* operator()(T ptr_or_reference) const; private: static PyTypeObject* type(); }; }} </pre> <h4><a name="to_python_indirect-spec-observers"></a>Class template <code>to_python_indirect</code> observers</h4> <pre> PyObject* operator()(T x) const; </pre> <dl class="function-semantics"> <dt><b>Requires:</b> <code>x</code> refers to an object (if it is a pointer type, it is non-null). <code>convertible() == true</code>. <dt><b>Effects:</b> Creates an appropriately-typed Boost.Python extension class instance, uses <code>MakeHolder</code> to create an <code>instance_holder</code> from <code>x</code>, installs the <code>instance_holder</code> in the new extension class instance, and returns a pointer to it. </dl> <h4><a name="to_python_indirect-spec-statics"></a>Class template <code>to_python_indirect</code> statics</h4> <pre> bool convertible(); </pre> <dt><b>Effects:</b> Returns <code>true</code> iff any module has registered a Python type corresponding to <code>U</code>. <h2><a name="examples"></a>Example</h2> This example replicates the functionality of <a href="reference_existing_object.html#reference_existing_object-spec">reference_existing_object</a>, but without some of the compile-time error checking. <pre> struct make_reference_holder { typedef boost::python::objects::instance_holder* result_type; template <class T> static result_type execute(T* p) { return new boost::python::objects::pointer_holder<T*, T>(p); } }; struct reference_existing_object { // metafunction returning the <a href="ResultConverter.html#ResultConverter-concept">ResultConverter</a> template <class T> struct apply { typedef boost::python::to_python_indirect<T,make_reference_holder> type; }; }; </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><i>© Copyright <a href="../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights Reserved.</i>