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<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> <link rel="stylesheet" type="text/css" href="../boost.css"> <title>Boost.Python - <register_ptr_to_python.hpp></title> </head> <body link="#0000ff" vlink="#800080"> <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 <register_ptr_to_python.hpp></h2> </td> </tr> </table> <hr> <h2>Contents</h2> <dl class="page-index"> <dt><a href="#introduction">Introduction</a></dt> <dt><a href="#functions">Functions</a></dt> <dl class="page-index"> <dt><a href="#register_ptr_to_python-spec">register_ptr_to_python</a></dt> </dl> <dt><a href="#examples">Example(s)</a></dt> </dl> <hr> <h2><a name="introduction"></a>Introduction</h2> <p> <code><boost/python/register_ptr_to_python.hpp></code> supplies <code>register_ptr_to_python</code>, a function template which registers a conversion for smart pointers to Python. The resulting Python object holds a copy of the converted smart pointer, but behaves as though it were a wrapped copy of the pointee. If the pointee type has virtual functions and the class representing its dynamic (most-derived) type has been wrapped, the Python object will be an instance of the wrapper for the most-derived type. More than one smart pointer type for a pointee's class can be registered. </p> <p> Note that in order to convert a Python <code>X</code> object to a <code>smart_ptr<X>&</code> (non-const reference), the embedded C++ object must be held by <code>smart_ptr<X></code>, and that when wrapped objects are created by calling the constructor from Python, how they are held is determined by the <code>HeldType</code> parameter to <code>class_<...></code> instances. </p> <h2><a name="functions"></a>Functions</h2> <pre> <a name="register_ptr_to_python-spec">template <class P> void register_ptr_to_python() </pre> <dl class="function-semantics"> <dt><b>Requires:</b> <code>P</code> is <a href="Dereferenceable.html#Dereferenceable-concept">Dereferenceable</a>. </dt> <dt><b>Effects:</b> Allows conversions to-python of <code>P</code> instances. </dt> </dl> <h2><a name="examples"></a>Example(s)</h2> <h3>C++ Wrapper Code</h3> Here is an example of a module that contains a class <code>A</code> with virtual functions and some functions that work with <code>boost::shared_ptr<A></code>. <pre> struct A { virtual int f() { return 0; } }; shared_ptr<A> New() { return shared_ptr<A>( new A() ); } int Ok( const shared_ptr<A>& a ) { return a->f(); } int Fail( shared_ptr<A>& a ) { return a->f(); } struct A_Wrapper: A { A_Wrapper(PyObject* self_): self(self_) {} int f() { return call_method<int>(self, "f"); } int default_f() { return A::f(); } PyObject* self; }; BOOST_PYTHON_MODULE(register_ptr) { class_<A, A_Wrapper>("A") .def("f", &A::f, &A_Wrapper::default_f) ; def("New", &New); def("Ok", &Call); def("Fail", &Fail); register_ptr_to_python< shared_ptr<A> >(); } </pre> <h3>Python Code</h3> <pre> >>> from register_ptr import * >>> a = A() >>> Ok(a) # ok, passed as shared_ptr<A> 0 >>> Fail(a) # passed as shared_ptr<A>&, and was created in Python! Traceback (most recent call last): File "<stdin>", line 1, in ? TypeError: bad argument type for built-in operation >>> >>> na = New() # now "na" is actually a shared_ptr<A> >>> Ok(a) 0 >>> Fail(a) 0 >>> </pre> If <code>shared_ptr<A></code> is registered as follows: <pre> class_<A, A_Wrapper, shared_ptr<A> >("A") .def("f", &A::f, &A_Wrapper::default_f) ; </pre> There will be an error when trying to convert <code>shared_ptr<A></code> to <code>shared_ptr<A_Wrapper></code>: <pre> >>> a = New() Traceback (most recent call last): File "<stdin>", line 1, in ? TypeError: No to_python (by-value) converter found for C++ type: class boost::shared_ptr<struct A> >>> </pre> <p>Revised  24 Jun, 2003  </p> <p><i>© Copyright <a href="http://www.boost.org/people/dave_abrahams.htm">Dave Abrahams</a> 2002. </i></p> </body> </html>