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- [section boost/python/def_visitor.hpp]
- [section Introduction]
- <boost/python/def_visitor.hpp> provides a generic visitation interface through which the [link high_level_components.boost_python_class_hpp.class_template_class_t_bases_hel class_] def member functionality can be extended non-intrusively to avoid cluttering the [link high_level_components.boost_python_class_hpp.class_template_class_t_bases_hel class_] interface. It declares the `def_visitor<T>` class template, which is parameterized on the derived type `DerivedVisitor`, which provides the actual `def` functionality through its `visit` member functions.
- [endsect]
- [section Class `def_visitor`]
- 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 [link high_level_components.boost_python_class_hpp.class_template_class_t_bases_hel class_] `def` member function.
- ``
- namespace boost { namespace python {
- template <class DerivedVisitor>
- class def_visitor {};
- }
- ``
- [variablelist
- [[Requires][The client supplied class DerivedVisitor template parameter is expected to:
- * be privately derived from def_visitor
- * grant friend access to class def_visitor_access
- * define either or both visit member functions listed in the table below:
- [table
- [[Expression][Return Type][Requirements][Effects]]
- [[`visitor.visit(cls)`][`void`]
- [`cls` is an instance of a [link high_level_components.boost_python_class_hpp.class_template_class_t_bases_hel class_] being wrapped to Python. `visitor` is a `def_visitor` derived class.]
- [A call to `cls.def(visitor)` forwards to this member function.]]
- [[`visitor.visit(cls, name, options)`][`void`]
- [`cls` is a [link high_level_components.boost_python_class_hpp.class_template_class_t_bases_hel class_] instance, name is a C string. `visitor` is a `def_visitor` derived class. options is a context specific optional argument.]
- [A call to `cls.def(name, visitor)` or `cls.def(name, visitor, options)` forwards to this member function. ]]]
- ]]
- ]
- [endsect]
- [section Example]
- ``
- class X {/*...*/};
- 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);
- c.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());
- }
- ``
- [endsect]
- [endsect]
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