| 1 | <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> |
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| 2 | |
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| 3 | <!-- Copyright David Abrahams 2006. Distributed under the Boost --> |
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| 4 | <!-- Software License, Version 1.0. (See accompanying --> |
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| 5 | <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) --> |
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| 6 | <html> |
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| 7 | <head> |
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| 8 | <meta name="generator" content= |
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| 9 | "HTML Tidy for Windows (vers 1st August 2002), see www.w3.org"> |
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| 10 | <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> |
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| 11 | <link rel="stylesheet" type="text/css" href="../boost.css"> |
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| 12 | |
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| 13 | <title>Boost.Python - <boost/python/implicit.hpp></title> |
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| 14 | </head> |
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| 15 | |
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| 16 | <body> |
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| 17 | <table border="0" cellpadding="7" cellspacing="0" width="100%" summary= |
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| 18 | "header"> |
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| 19 | <tr> |
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| 20 | <td valign="top" width="300"> |
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| 21 | <h3><a href="../../../../index.htm"><img height="86" width="277" |
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| 22 | alt="C++ Boost" src="../../../../boost.png" border="0"></a></h3> |
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| 23 | </td> |
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| 24 | |
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| 25 | <td valign="top"> |
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| 26 | <h1 align="center"><a href="../index.html">Boost.Python</a></h1> |
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| 27 | |
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| 28 | <h2 align="center">Header <boost/python/implicit.hpp></h2> |
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| 29 | </td> |
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| 30 | </tr> |
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| 31 | </table> |
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| 32 | <hr> |
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| 33 | |
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| 34 | <h2>Contents</h2> |
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| 35 | |
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| 36 | <dl class="page-index"> |
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| 37 | <dt><a href="#introduction">Introduction</a></dt> |
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| 38 | |
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| 39 | <dt><a href="#functions">Functions</a></dt> |
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| 40 | |
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| 41 | <dd> |
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| 42 | <dl class="page-index"> |
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| 43 | <dt><a href="#implicitly_convertible-spec">Function Template |
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| 44 | <code>implicitly_convertible</code></a></dt> |
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| 45 | </dl> |
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| 46 | </dd> |
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| 47 | |
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| 48 | <dt><a href="#examples">Example</a></dt> |
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| 49 | </dl> |
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| 50 | <hr> |
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| 51 | |
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| 52 | <h2><a name="introduction"></a>Introduction</h2> |
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| 53 | <code>implicitly_convertible</code> allows Boost.Python to implicitly |
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| 54 | take advantage of a C++ implicit or explicit conversion when matching |
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| 55 | Python objects to C++ argument types. |
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| 56 | |
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| 57 | <h2><a name="functions"></a>Functions</h2> |
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| 58 | |
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| 59 | <h3><a name="implicitly_convertible-spec"></a>Function template |
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| 60 | <code>implicitly_convertible</code></h3> |
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| 61 | <pre> |
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| 62 | template <class Source, class Target> |
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| 63 | void implicitly_convertible(); |
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| 64 | </pre> |
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| 65 | |
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| 66 | <table border="1" summary="implicitly_convertible template parameters"> |
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| 67 | <caption> |
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| 68 | <b><code>implicitly_convertible</code> template parameters</b><br> |
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| 69 | </caption> |
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| 70 | |
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| 71 | <tr> |
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| 72 | <th>Parameter</th> |
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| 73 | |
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| 74 | <th>Description</th> |
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| 75 | </tr> |
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| 76 | |
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| 77 | <tr> |
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| 78 | <td><code>Source</code></td> |
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| 79 | |
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| 80 | <td>The source type of the implicit conversion</td> |
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| 81 | </tr> |
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| 82 | |
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| 83 | <tr> |
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| 84 | <td><code>Target</code></td> |
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| 85 | |
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| 86 | <td>The target type of the implicit conversion</td> |
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| 87 | </tr> |
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| 88 | </table> |
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| 89 | |
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| 90 | <dl class="function-semantics"> |
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| 91 | <dt><b>Requires:</b> The declaration <code>Target t(s);</code>, where |
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| 92 | <code>s</code> is of type <code>Source</code>, is valid.</dt> |
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| 93 | |
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| 94 | <dt><b>Effects:</b> registers an rvalue <code>from_python</code> |
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| 95 | converter to <code>Target</code> which can succeed for any |
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| 96 | <code>PyObject* p</code> iff there exists any registered converter |
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| 97 | which can produce <code>Source</code> rvalues</dt> |
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| 98 | |
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| 99 | <dt><b>Rationale:</b> C++ users expect to be able to take advantage of |
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| 100 | the same sort of interoperability in Python as they do in C++.</dt> |
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| 101 | </dl> |
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| 102 | |
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| 103 | <h2><a name="examples"></a>Example</h2> |
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| 104 | |
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| 105 | <h3>C++ module definition</h3> |
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| 106 | <pre> |
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| 107 | #include <boost/python/class.hpp> |
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| 108 | #include <boost/python/implicit.hpp> |
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| 109 | #include <boost/python/module.hpp> |
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| 110 | |
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| 111 | using namespace boost::python; |
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| 112 | |
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| 113 | struct X |
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| 114 | { |
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| 115 | X(int x) : v(x) {} |
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| 116 | operator int() const { return v; } |
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| 117 | int v; |
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| 118 | }; |
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| 119 | |
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| 120 | int x_value(X const& x) |
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| 121 | { |
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| 122 | return x.v; |
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| 123 | } |
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| 124 | |
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| 125 | X make_x(int n) { return X(n); } |
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| 126 | |
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| 127 | BOOST_PYTHON_MODULE(implicit_ext) |
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| 128 | { |
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| 129 | def("x_value", x_value); |
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| 130 | def("make_x", make_x); |
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| 131 | |
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| 132 | class_<X>("X", |
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| 133 | init<int>()) |
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| 134 | ; |
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| 135 | |
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| 136 | implicitly_convertible<X,int>(); |
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| 137 | implicitly_convertible<int,X>(); |
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| 138 | } |
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| 139 | </pre> |
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| 140 | |
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| 141 | <h3>Python code</h3> |
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| 142 | <pre> |
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| 143 | >>> from implicit_ext import * |
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| 144 | >>> x_value(X(42)) |
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| 145 | 42 |
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| 146 | >>> x_value(42) |
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| 147 | 42 |
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| 148 | >>> x = make_x(X(42)) |
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| 149 | >>> x_value(x) |
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| 150 | 42 |
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| 151 | </pre> |
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| 152 | |
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| 153 | <p>Revised |
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| 154 | <!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan --> |
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| 155 | 13 November, 2002 |
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| 156 | <!--webbot bot="Timestamp" endspan i-checksum="39359" --> |
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| 157 | </p> |
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| 158 | |
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| 159 | <p><i>© Copyright <a href= |
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| 160 | "../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002.</i></p> |
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| 161 | </body> |
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| 162 | </html> |
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| 163 | |
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