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161 lines
4.1 KiB
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<meta name="generator" content=
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"HTML Tidy for Windows (vers 1st August 2002), see www.w3.org">
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<link rel="stylesheet" type="text/css" href="../boost.css">
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<title>Boost.Python - <boost/python/implicit.hpp></title>
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</head>
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<body>
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<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
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"header">
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<tr>
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<td valign="top" width="300">
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<h3><a href="../../../../index.htm"><img height="86" width="277"
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alt="C++ Boost" src="../../../../boost.png" border="0"></a></h3>
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</td>
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<td valign="top">
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<h1 align="center"><a href="../index.html">Boost.Python</a></h1>
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<h2 align="center">Header <boost/python/implicit.hpp></h2>
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</td>
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</tr>
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</table>
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<hr>
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<h2>Contents</h2>
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<dl class="page-index">
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<dt><a href="#introduction">Introduction</a></dt>
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<dt><a href="#functions">Functions</a></dt>
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<dd>
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<dl class="page-index">
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<dt><a href="#implicitly_convertible-spec">Function Template
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<code>implicitly_convertible</code></a></dt>
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</dl>
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</dd>
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<dt><a href="#examples">Example</a></dt>
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</dl>
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<hr>
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<h2><a name="introduction"></a>Introduction</h2>
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<code>implicitly_convertible</code> allows Boost.Python to implicitly
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take advantage of a C++ implicit or explicit conversion when matching
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Python objects to C++ argument types.
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<h2><a name="functions"></a>Functions</h2>
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<h3><a name="implicitly_convertible-spec"></a>Function template
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<code>implicitly_convertible</code></h3>
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<pre>
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template <class Source, class Target>
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void implicitly_convertible();
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</pre>
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<table border="1" summary="implicitly_convertible template parameters">
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<caption>
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<b><code>implicitly_convertible</code> template parameters</b><br>
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</caption>
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<tr>
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<th>Parameter</th>
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<th>Description</th>
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</tr>
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<tr>
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<td><code>Source</code></td>
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<td>The source type of the implicit conversion</td>
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</tr>
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<tr>
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<td><code>Target</code></td>
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<td>The target type of the implicit conversion</td>
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</tr>
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</table>
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<dl class="function-semantics">
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<dt><b>Requires:</b> The declaration <code>Target t(s);</code>, where
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<code>s</code> is of type <code>Source</code>, is valid.</dt>
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<dt><b>Effects:</b> registers an rvalue <code>from_python</code>
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converter to <code>Target</code> which can succeed for any
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<code>PyObject* p</code> iff there exists any registered converter
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which can produce <code>Source</code> rvalues</dt>
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<dt><b>Rationale:</b> C++ users expect to be able to take advantage of
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the same sort of interoperability in Python as they do in C++.</dt>
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</dl>
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<h2><a name="examples"></a>Example</h2>
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<h3>C++ module definition</h3>
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<pre>
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#include <boost/python/class.hpp>
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#include <boost/python/implicit.hpp>
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#include <boost/python/module.hpp>
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using namespace boost::python;
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struct X
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{
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X(int x) : v(x) {}
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operator int() const { return v; }
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int v;
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};
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int x_value(X const& x)
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{
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return x.v;
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}
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X make_x(int n) { return X(n); }
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BOOST_PYTHON_MODULE(implicit_ext)
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{
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def("x_value", x_value);
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def("make_x", make_x);
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class_<X>("X",
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init<int>())
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;
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implicitly_convertible<X,int>();
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implicitly_convertible<int,X>();
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}
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</pre>
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<h3>Python code</h3>
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<pre>
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>>> from implicit_ext import *
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>>> x_value(X(42))
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42
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>>> x_value(42)
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42
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>>> x = make_x(X(42))
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>>> x_value(x)
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42
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</pre>
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<p>Revised
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<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
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13 November, 2002
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<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
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</p>
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<p><i>© Copyright <a href=
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"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002.</i></p>
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</body>
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</html>
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