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1 | [section boost/python/return_arg.hpp] |
2 | [section Introduction] | |
3 | `return_arg` and `return_self` instantiations are models of [link concepts.callpolicies `CallPolicies`] which return the specified argument parameter (usually `*this`) of a wrapped (member) function. | |
4 | [endsect] | |
5 | [section Class `return_arg`] | |
6 | [table | |
7 | [[Parameter][Requirements][Description][Default]] | |
8 | [[arg_pos][A positive compile-time constant of type `std::size_t`.][the position of the argument to be returned.][1]] | |
9 | [[Base][A model of [link concepts.callpolicies `CallPolicies`]][Used for policy composition. Any `result_converter` it supplies will be overridden by `return_arg`, but its `precall` and `postcall` policies are composed as described here [link concepts.callpolicies `CallPolicies`].][default_call_policies]] | |
10 | ] | |
11 | `` | |
12 | namespace boost { namespace python | |
13 | { | |
14 | template <size_t arg_pos=1, class Base = default_call_policies> | |
15 | struct return_arg : Base | |
16 | { | |
17 | static PyObject* postcall(PyObject*, PyObject* result); | |
18 | struct result_converter{ template <class T> struct apply; }; | |
19 | template <class Sig> struct extract_return_type : mpl::at_c<Sig, arg_pos>{}; | |
20 | ||
21 | }; | |
22 | }} | |
23 | `` | |
24 | [endsect] | |
25 | [section Class `return_arg` static functions] | |
26 | ``PyObject* postcall(PyObject* args, PyObject* result);`` | |
27 | [variablelist | |
28 | [[Requires][`PyTuple_Check(args) != 0` and `PyTuple_Size(args) != 0`]] | |
29 | [[Returns][PyTuple_GetItem(args,arg_pos-1)]] | |
30 | ] | |
31 | [endsect] | |
32 | [section Class template `return_self`] | |
33 | `` | |
34 | namespace boost { namespace python | |
35 | { | |
36 | template <class Base = default_call_policies> | |
37 | struct return_self | |
38 | : return_arg<1,Base> | |
39 | {}; | |
40 | }} | |
41 | `` | |
42 | [endsect] | |
43 | [section Example] | |
44 | C++ module definition: | |
45 | `` | |
46 | #include <boost/python/module.hpp> | |
47 | #include <boost/python/class.hpp> | |
48 | #include <boost/python/return_arg.hpp> | |
49 | ||
50 | struct Widget | |
51 | { | |
52 | Widget() :sensitive_(true){} | |
53 | bool get_sensitive() const { return sensitive_; } | |
54 | void set_sensitive(bool s) { this->sensitive_ = s; } | |
55 | private: | |
56 | bool sensitive_; | |
57 | }; | |
58 | ||
59 | struct Label : Widget | |
60 | { | |
61 | Label() {} | |
62 | ||
63 | std::string get_label() const { return label_; } | |
64 | void set_label(const std::string &l){ label_ = l; } | |
65 | ||
66 | private: | |
67 | std::string label_; | |
68 | }; | |
69 | ||
70 | using namespace boost::python; | |
71 | BOOST_PYTHON_MODULE(return_self_ext) | |
72 | { | |
73 | class_<widget>("Widget") | |
74 | .def("sensitive", &Widget::get_sensitive) | |
75 | .def("sensitive", &Widget::set_sensitive, return_self<>()) | |
76 | ; | |
77 | ||
78 | class_<Label, bases<Widget> >("Label") | |
79 | .def("label", &Label::get_label) | |
80 | .def("label", &Label::set_label, return_self<>()) | |
81 | ; | |
82 | } | |
83 | `` | |
84 | Python code: | |
85 | `` | |
86 | >>> from return_self_ext import * | |
87 | >>> l1 = Label().label("foo").sensitive(false) | |
88 | >>> l2 = Label().sensitive(false).label("foo") | |
89 | `` | |
90 | [endsect] | |
91 | [endsect] |