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

   1 [section boost/python/copy_const_reference.hpp]
   2 [section Class `copy_const_reference`]
   3 `copy_const_reference` is a model of [link concepts.resultconverter.resultconvertergenerator_concept ResultConverterGenerator] which can be used to wrap C++ functions returning a reference-to-const type such that the referenced value is copied into a new Python object.
   4 ``
   5 namespace boost { namespace python
   6 {
   7     struct copy_const_reference
   8     {
   9         template <class T> struct apply;
  10     };
  11 }}
  12 ``
  13 [endsect]
  14 [section Class `copy_const_reference` metafunctions]
  15 ``template <class T> struct apply``
  16 [variablelist
  17 [[Requires][`T` is `U const&` for some `U`.]]
  18 [[Returns][`typedef to_python_value<T> type;`]]
  19 ]
  20 [endsect]
  21 [section Example]
  22 C++ module definition:
  23 ``
  24 #include <boost/python/module.hpp>
  25 #include <boost/python/class.hpp>
  26 #include <boost/python/copy_const_reference.hpp>
  27 #include <boost/python/return_value_policy.hpp>
  28
  29 // classes to wrap
  30 struct Bar { int x; }
  31
  32 struct Foo {
  33    Foo(int x) : { b.x = x; }
  34    Bar const& get_bar() const { return b; }
  35  private:
  36    Bar b;
  37 };
  38
  39 // Wrapper code
  40 using namespace boost::python;
  41 BOOST_PYTHON_MODULE(my_module)
  42 {
  43     class_<Bar>("Bar");
  44
  45      class_<Foo>("Foo", init<int>())
  46         .def("get_bar", &Foo::get_bar
  47             , return_value_policy<copy_const_reference>())
  48        ;
  49 }
  50 ``
  51 Python code:
  52 ``
  53 >>> from my_module import *
  54 >>> f = Foo(3)         # create a Foo object
  55 >>> b = f.get_bar()    # make a copy of the internal Bar object
  56 ``
  57 [endsect]
  58 [endsect]