1[section boost/python/def_visitor.hpp] 2[section Introduction] 3<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. 4[endsect] 5[section Class `def_visitor`] 6The 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. 7 8`` 9namespace boost { namespace python { 10 11 template <class DerivedVisitor> 12 class def_visitor {}; 13} 14`` 15 16[variablelist 17 [[Requires][The client supplied class DerivedVisitor template parameter is expected to: 18 * be privately derived from def_visitor 19 * grant friend access to class def_visitor_access 20 * define either or both visit member functions listed in the table below: 21 [table 22 [[Expression][Return Type][Requirements][Effects]] 23 [[`visitor.visit(cls)`][`void`] 24 [`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.] 25 [A call to `cls.def(visitor)` forwards to this member function.]] 26 [[`visitor.visit(cls, name, options)`][`void`] 27 [`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.] 28 [A call to `cls.def(name, visitor)` or `cls.def(name, visitor, options)` forwards to this member function. ]]] 29 ]] 30 ] 31[endsect] 32[section Example] 33`` 34class X {/*...*/}; 35 36class my_def_visitor : boost::python::def_visitor<my_def_visitor> 37{ 38 friend class def_visitor_access; 39 40 template <class classT> 41 void visit(classT& c) const 42 { 43 c.def("foo", &my_def_visitor::foo); 44 c.def("bar", &my_def_visitor::bar); 45 } 46 47 static void foo(X& self); 48 static void bar(X& self); 49}; 50 51BOOST_PYTHON_MODULE(my_ext) 52{ 53 class_<X>("X") 54 .def(my_def_visitor()); 55} 56`` 57[endsect] 58[endsect] 59