boost-react-native-bundle

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">    <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/to_python_converter.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/to_python_converter.hpp></h2> </td> </tr> </table> <hr> <h2>Contents</h2> <dl class="page-index"> <dt><a href="#introduction">Introduction</a></dt> <dt><a href="#classes">Classes</a></dt> <dd> <dl class="page-index"> <dt><a href="#to_python_converter-spec">Class Template <code>to_python_converter</code></a></dt> <dd> <dl class="page-index"> <dt><a href="#to_python_converter-spec-synopsis">Class Template <code>to_python_converter</code> synopsis</a></dt> <dt><a href="#to_python_converter-spec-ctors">Class Template <code>to_python_converter</code> constructor</a></dt> </dl> </dd> </dl> </dd> <dt><a href="#examples">Example</a></dt> </dl> <hr> <h2><a name="introduction"></a>Introduction</h2> <code>to_python_converter</code> registers a conversion from objects of a given C++ type into a Python object. <h2><a name="classes"></a>Classes</h2> <h3><a name="to_python_converter-spec"></a>Class template <code>to_python_converter</code></h3> <code>to_python_converter</code> adds a wrapper around a static member function of its second template parameter, handling low-level details such as insertion into the converter registry. <table border="1" summary="to_python_converter template parameters"> <caption> <b><code>to_python_converter</code> template parameters</b><br> In the table below, <b><code>x</code></b> denotes an object of type <code>T</code> </caption> <tr> <th>Parameter</th> <th>Requirements</th> <th>Description</th> </tr> <tr> <td><code>T</code></td> <td> </td> <td>The C++ type of the source object in the conversion</td> </tr> <tr> <td><code>Conversion</code></td> <td> <code>PyObject* p = Conversion::convert(x)</code>,<br> if <code>p == 0</code>, <code><a href= "http://www.python.org/doc/2.2/api/exceptionHandling.html#l2h-71">PyErr_Occurred</a>() != 0</code>.</td> <td>A class type whose static member function <code>convert</code> does the real work of the conversion.</td> </tr> <tr> <td><code>bool has_get_pytype = false</code></td> <td> <code>PyTypeObject const * p = Conversion::get_pytype() </code>.</td> <td><b>Optional member</b> - if <code>Conversion</code> has <code>get_pytype</code> member supply <code>true</code> for this parameters. If present <code>get_pytype</code> is used to document the return type of functions using this conversion. The <code>get_pytype</code> may be implemented using the classes and functions from <a href="pytype_function.html"><code>pytype_function.hpp</code></a> <b>NOTE :</b> For backward compatibility this parameter may be passed after checking if <code>BOOST_PYTHON_SUPPORTS_PY_SIGNATURES</code> is defined (see <a href="pytype_function.html#examples">here</a>). </td> </tr> </table> <h4><a name="to_python_converter-spec-synopsis"></a>Class template <code>to_python_converter</code> synopsis</h4> <pre> namespace boost { namespace python { template <class T, class Conversion, bool convertion_has_get_pytype_member=false> struct to_python_converter { to_python_converter(); }; }} </pre> <h4><a name="to_python_converter-spec-ctors"></a>Class template <code>to_python_converter</code> constructor</h4> <pre> to_python_converter(); </pre> <dl class="function-semantics"> <dt><b>Effects:</b> Registers a to_python converter which uses <code>Conversion::convert()</code> to do its work.</dt> </dl> <h2><a name="examples"></a>Example</h2> This example presumes that someone has implemented the standard <a href= "http://www.python.org/doc/2.2/ext/dnt-basics.html">noddy example module</a> from the Python documentation, and placed the corresponding declarations in <code>"noddy.h"</code>. Because <code>noddy_NoddyObject</code> is the ultimate trivial extension type, the example is a bit contrived: it wraps a function for which all information is contained in the <i>type</i> of its return value. <h3>C++ module definition</h3> <pre> #include <boost/python/reference.hpp> #include <boost/python/module.hpp> #include "noddy.h" struct tag {}; tag make_tag() { return tag(); } using namespace boost::python; struct tag_to_noddy { static PyObject* convert(tag const& x) { return PyObject_New(noddy_NoddyObject, &noddy_NoddyType); } static PyTypeObject const* get_pytype() { return &noddy_NoddyType; } }; BOOST_PYTHON_MODULE(to_python_converter) { def("make_tag", make_tag); to_python_converter<tag, tag_to_noddy, true>(); //"true" because tag_to_noddy has member get_pytype } </pre> <h3>Python code</h3> <pre> >>> import to_python_converter >>> def always_none(): ... return None ... >>> def choose_function(x): ... if (x % 2 != 0): ... return to_python_converter.make_tag ... else: ... return always_none ... >>> a = [ choose_function(x) for x in range(5) ] >>> b = [ f() for f in a ] >>> type(b[0]) <type 'NoneType'> >>> type(b[1]) <type 'Noddy'> >>> type(b[2]) <type 'NoneType'> >>> type(b[3]) <type 'Noddy'> </pre> <p>Revised  11 June, 2007  </p> <p><i>© Copyright <a href= "http://www.boost.org/people/dave_abrahams.htm">Dave Abrahams</a> 2002.</i></p> </body> </html>