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
|
<!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/implicit.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/implicit.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>
<dd>
<dl class="page-index">
<dt><a href="#implicitly_convertible-spec">Function Template
<code>implicitly_convertible</code></a></dt>
</dl>
</dd>
<dt><a href="#examples">Example</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<code>implicitly_convertible</code> allows Boost.Python to implicitly
take advantage of a C++ implicit or explicit conversion when matching
Python objects to C++ argument types.
<h2><a name="functions"></a>Functions</h2>
<h3><a name="implicitly_convertible-spec"></a>Function template
<code>implicitly_convertible</code></h3>
<pre>
template <class Source, class Target>
void implicitly_convertible();
</pre>
<table border="1" summary="implicitly_convertible template parameters">
<caption>
<b><code>implicitly_convertible</code> template parameters</b><br>
</caption>
<tr>
<th>Parameter</th>
<th>Description</th>
</tr>
<tr>
<td><code>Source</code></td>
<td>The source type of the implicit conversion</td>
</tr>
<tr>
<td><code>Target</code></td>
<td>The target type of the implicit conversion</td>
</tr>
</table>
<dl class="function-semantics">
<dt><b>Requires:</b> The declaration <code>Target t(s);</code>, where
<code>s</code> is of type <code>Source</code>, is valid.</dt>
<dt><b>Effects:</b> registers an rvalue <code>from_python</code>
converter to <code>Target</code> which can succeed for any
<code>PyObject* p</code> iff there exists any registered converter
which can produce <code>Source</code> rvalues</dt>
<dt><b>Rationale:</b> C++ users expect to be able to take advantage of
the same sort of interoperability in Python as they do in C++.</dt>
</dl>
<h2><a name="examples"></a>Example</h2>
<h3>C++ module definition</h3>
<pre>
#include <boost/python/class.hpp>
#include <boost/python/implicit.hpp>
#include <boost/python/module.hpp>
using namespace boost::python;
struct X
{
X(int x) : v(x) {}
operator int() { return v; }
int v;
};
int x_value(X const& x)
{
return x.v;
}
X make_x(int n) { return X(n); }
BOOST_PYTHON_MODULE(implicit_ext)
{
def("x_value", x_value);
def("make_x", make_x);
class_<X>("X",
init<int>())
;
implicitly_convertible<X,int>();
implicitly_convertible<int,X>();
}
</pre>
<h3>Python code</h3>
<pre>
>>> from implicit_ext import *
>>> x_value(X(42))
42
>>> x_value(42)
42
>>> x = make_x(X(42))
>>> x_value(x)
42
</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>
<p><i>© Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002.</i></p>
</body>
</html>
|
