1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
|
<!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=utf-8">
<link rel="stylesheet" type="text/css" href="../boost.css">
<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="http://www.boost.org/people/dave_abrahams.htm">Dave
Abrahams</a> 2004</i> 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)</p>
|
