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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<title>Boost.Python - <wrapper.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="../../../../boost.png" border="0"></a></h3>
<td valign="top">
<h1 align="center"><a href="../index.html">Boost.Python</a></h1>
<h2 align="center">Header <wrapper.hpp></h2>
</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="#override-spec">Class template
<code>override</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#override-spec-synopsis">Class
<code>override</code> synopsis</a></dt>
<dt><a href="#override-spec-observers">Class
<code>override</code> observer functions</a></dt>
</dl>
</dd>
<dt><a href="#wrapper-spec">Class template
<code>wrapper</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#wrapper-spec-synopsis">Class <code>wrapper</code>
synopsis</a></dt>
<dt><a href="#wrapper-spec-observers">Class
<code>wrapper</code> observer functions</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="#examples">Example(s)</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p>To wrap a class <code>T</code> such that its virtual functions can be
"overridden in Python"—so that the corresponding method of a Python
derived class will be called when the virtual function is invoked from
C++—you must create a C++ wrapper class derived from ``T`` that
overrides those virtual functions so that they call into Python. This
header contains classes that can be used to make that job easier.</p>
<h2><a name="classes"></a>Classes</h2>
<h3><a name="override-spec"></a>Class <code>override</code></h3>
<p>Encapsulates a Python override of a C++ virtual function. An
<code>override</code> object either holds a callable Python object or
<code>None</code>.</p>
<h4><a name="override-spec-synopsis"></a>Class <code>override</code>
synopsis</h4>
<pre>
namespace boost
{
class override : object
{
public:
<i>unspecified</i> operator() const;
template <class A0>
<i>unspecified</i> operator(A0) const;
template <class A0, class A1>
<i>unspecified</i> operator(A0, A1) const;
...
template <class A0, class A1, ...class A<i>n</i>>
<i>unspecified</i> operator(A0, A1, ...A<i>n</i>) const;
};
};
</pre>
<h4><a name="override-spec-observers"></a>Class <code>override</code>
observer functions</h4>
<pre>
<i>unspecified</i> operator() const;
template <class A0>
<i>unspecified</i> operator(A0) const;
template <class A0, class A1>
<i>unspecified</i> operator(A0, A1) const;
...
template <class A0, class A1, ...class A<i>n</i>>
<i>unspecified</i> operator(A0, A1, ...A<i>n</i>) const;
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> If <code>*this</code> holds a callable Python
object, it is invoked with the specified arguments in the manner
specified <a href="callbacks.html">here</a>. Otherwise, throws <code><a
href="errors.html#error_already_set-spec">error_already_set</a></code>
.</dt>
<dt><b>Returns:</b> An object of unspecified type that holds the Python
result of the invocation and, when converted to a C++ type
<code>R</code>, attempts to convert that result object to
<code>R</code>. If that conversion fails, throws <code><a href=
"errors.html#error_already_set-spec">error_already_set</a></code>
.</dt>
</dl>
<h3><a name="wrapper-spec"></a>Class template <code>wrapper</code></h3>
<p>Deriving your wrapper class from both ``T`` <i>and</i>
``wrapper<T> makes writing that derived class easier.</p>
<h4><a name="wrapper-spec-synopsis"></a>Class template
<code>wrapper</code> synopsis</h4>
<pre>
namespace boost
{
class wrapper
{
protected:
override get_override(char const* name) const;
};
};
</pre>
<h4><a name="wrapper-spec-observers"></a>Class <code>wrapper</code>
observer functions</h4>
<pre>
override get_override(char const* name) const;
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>name</code> is a <a href=
"definitions.html#ntbs">ntbs</a>.</dt>
<dt><b>Returns:</b> If <code>*this</code> is the C++ base class
subobject of a Python derived class instance that overrides the named
function, returns an <code>override</code> object that delegates to the
Python override. Otherwise, returns an <code>override</code> object
that holds <code>None</code>.</dt>
</dl>
<h2><a name="examples"></a>Example</h2>
<pre>
#include <boost/python/module.hpp>
#include <boost/python/class.hpp>
#include <boost/python/wrapper.hpp>
#include <boost/python/call.hpp>
using namespace boost::python;
// Class with one pure virtual function
struct P
{
virtual ~P(){}
virtual char const* f() = 0;
char const* g() { return "P::g()"; }
};
struct PCallback : P, wrapper<P>
{
char const* f()
{
#if BOOST_WORKAROUND(BOOST_MSVC, <= 1300) // Workaround for vc6/vc7
return call<char const*>(this->get_override("f").ptr());
#else
return this->get_override("f")();
#endif
}
};
// Class with one non-pure virtual function
struct A
{
virtual ~A(){}
virtual char const* f() { return "A::f()"; }
};
struct ACallback : A, wrapper<A>
{
char const* f()
{
if (override f = this->get_override("f"))
#if BOOST_WORKAROUND(BOOST_MSVC, <= 1300) // Workaround for vc6/vc7
return call<char const*>(f.ptr());
#else
return f();
#endif
return A::f();
}
char const* default_f() { return this->A::f(); }
};
BOOST_PYTHON_MODULE_INIT(polymorphism)
{
class_<PCallback,boost::noncopyable>("P")
.def("f", pure_virtual(&P::f))
;
class_<ACallback,boost::noncopyable>("A")
.def("f", &A::f, &ACallback::default_f)
;
}
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
31 October, 2004
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
<p><i>© Copyright <a href="../../../../people/dave_abrahams.htm">Dave
Abrahams</a> 2004</i>
|
