ceph/src/boost/libs/python/doc/reference/return_by_value.qbk

   1 [section boost/python/return_by_value.hpp]
   2 [section Class `return_by_value`]
   3 `return_by_value` is a model of [link concepts.resultconverter.resultconvertergenerator_concept ResultConverterGenerator] which can be used to wrap C++ functions returning any reference or value type such that the return value is copied into a new Python object.
   4 ``
   5 namespace boost { namespace python
   6 {
   7     struct return_by_value
   8     {
   9         template <class T> struct apply;
  10     };
  11 }}
  12 ``
  13 [endsect]
  14 [section Class `return_by_value` metafunctions]
  15 ``template <class T> struct apply``
  16 [variablelist
  17 [[Returns][`typedef to_python_value<T> type;`]]
  18 ]
  19 [endsect]
  20 [section Example]
  21 In C++:
  22 ``
  23 #include <boost/python/module.hpp>
  24 #include <boost/python/class.hpp>
  25 #include <boost/python/return_by_value.hpp>
  26 #include <boost/python/return_value_policy.hpp>
  27
  28 // classes to wrap
  29 struct Bar { };
  30
  31 Bar global_bar;
  32
  33 // functions to wrap:
  34 Bar b1();
  35 Bar& b2();
  36 Bar const& b3();
  37
  38 // Wrapper code
  39 using namespace boost::python;
  40 template <class R>
  41 void def_void_function(char const* name, R (*f)())
  42 {
  43    def(name, f, return_value_policy<return_by_value>());
  44 }
  45
  46 BOOST_PYTHON_MODULE(my_module)
  47 {
  48     class_<Bar>("Bar");
  49     def_void_function("b1", b1);
  50     def_void_function("b2", b2);
  51     def_void_function("b3", b3);
  52 }
  53 ``
  54 Python code:
  55 ``
  56 >>> from my_module import *
  57 >>> b = b1() # each of these calls
  58 >>> b = b2() # creates a brand
  59 >>> b = b3() # new Bar object
  60 ``
  61 [endsect]
  62 [endsect]