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<title>Boost.Python - <boost/python/def_visitor.hpp></title>
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<h3><a href="../../../../index.htm"><img height="86" width="277" alt=
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<h1 align="center"><a href="../index.html"><font size="7">Boost.Python</font></a></h1>
<h2 align="center">Header <boost/python/def_visitor.hpp></h2>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a>
<dt><a href="#classes">Classes</a>
<dd>
<dl class="page-index">
<dt><a href="#def_visitor-spec">Class <code>def_visitor</code></a>
<dd> <a href="#def_visitor-synopsis">Class <code>def_visitor</code>
synopsis</a></dd>
<dd> <a href="#def_visitor-requirements">Class <code>def_visitor</code>
requirements</a></dd>
</dl>
<dt><a href="#examples">Example</a>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p><code><boost/python/def_visitor.hpp></code> provides a generic visitation
interface through which the <a href="class.html">class_</a> <b>def</b> member
functionality can be extended non-intrusively to avoid cluttering the <a href="class.html">class_</a>
interface. It declares the <code>def_visitor<T> </code>class template,
which is parameterized on the derived type <tt>DerivedVisitor</tt>, which provides
the actual <b>def</b> functionality through its <b>visit</b> member functions.
<h2><a name="classes"></a>Classes</h2>
<h3><a name="def_visitor-spec"></a>Class template <code>def_visitor<DerivedVisitor></code></h3>
<p>The class def_visitor is a base class paramaterized by its derived class. The
def_visitor class is a protocol class. Its derived class, DerivedVisitor, is
expected to have a member function visit. The def_visitor class is never instantiated
directly. Instead, an instance of its subclass, DerivedVisitor, is passed
on as an argument to the <a href="class.html">class_</a> def member function.
<h4>
<a name="def_visitor-synopsis" id="def_visitor-synopsis"></a>Class <code>def_visitor </code>synopsis</h4>
<pre>namespace boost { namespace python {
template <class DerivedVisitor>
class def_visitor {};
}</pre>
<h3><a name="def_visitor-requirements"></a><code>def_visitor </code>requirements</h3>
<p>The <span class="pre">client supplied class </span><span class="pre"></span><tt class="literal"><span class="pre">DerivedVisitor</span></tt>
template parameter is expected to:
<ul>
<li>be privately derived from def_visitor</li>
<li>grant friend access to class def_visitor_access</li>
<li>define either or both visit member functions listed in the table below:</li>
</ul>
<table border class="table">
<tr>
<td width="181" nowrap><b>Expression</b></td>
<td width="85"><b>Return Type</b></td>
<td width="330"><b>Requirements</b></td>
<td width="259"><b>Effects</b></td>
</tr>
<tr>
<td nowrap>visitor.visit(cls)</td>
<td>void</td>
<td>cls is an instance of a <a href="class.html">class_</a> being wrapped
to Python. visitor is a def_visitor derived class.</td>
<td>A call to cls.def(visitor) forwards to this member function.</td>
</tr>
<tr>
<td nowrap>visitor.visit(cls, name, options)</td>
<td>void</td>
<td>cls is a class_ instance, name is a C string. visitor is a def_visitor
derived class. options is a context specific optional argument.</td>
<td>A call to cls.def(name, visitor) or cls.def(name, visitor, options) forwards
to this member function. </td>
</tr>
</table>
<h2><a name="examples"></a>Example</h2>
<pre>class X {/*...*/};<br>
class my_def_visitor : boost::python::def_visitor<my_def_visitor>
{
friend class def_visitor_access;
template <class classT>
void visit(classT& c) const
{
c
.def("foo", &my_def_visitor::foo)
.def("bar", &my_def_visitor::bar)
;
}
static void foo(X& self);
static void bar(X& self);
};
BOOST_PYTHON_MODULE(my_ext)
{
class_<X>("X")
.def(my_def_visitor())
;
}
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->27 August, 2003<!--webbot bot="Timestamp" endspan i-checksum="34484" -->
</p>
<p><i>© Copyright Joel de Guzman 2003. </i>
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