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<h3><a href="../../../../index.htm"><img height="86" width="277"
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<h1 align="center"><a href="../index.html">Boost.Python</a></h1>
<h2 align="center">Header <boost/python/implicit.hpp></h2>
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<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() const { 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=
"http://www.boost.org/people/dave_abrahams.htm">Dave Abrahams</a> 2002.</i></p>
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