1[section boost/python/to_python_indirect.hpp] 2[section Introduction] 3 <boost/python/to_python_indirect.hpp> supplies a way to construct new Python objects that hold wrapped C++ class instances via a pointer or smart pointer. 4 [endsect] 5[section Class `to_python_indirect`] 6Class template `to_python_indirect` converts objects of its first argument type to python as extension class instances, using the ownership policy provided by its 2nd argument. 7[table 8[[Parameter][Requirements][Description]] 9 [[T][Either `U cv&` (where cv is any optional cv-qualification) or a [link concepts.dereferenceable Dereferenceable] type such that `*x` is convertible to `U const&`, where `U` is a class type. ][`A` type deferencing a C++ class exposed to Python using class template [link high_level_components.boost_python_class_hpp.class_template_class_t_bases_hel `class_`]. ]] 10[[MakeHolder][`h = MakeHolder::execute(p);` ][A class whose static `execute()` creates an `instance_holder`. ]] 11 ] 12Instantiations of to_python_indirect are models of [link concepts.resultconverter `ResultConverter`]. 13`` 14namespace boost { namespace python 15{ 16 template <class T, class MakeHolder> 17 struct to_python_indirect 18 { 19 static bool convertible(); 20 PyObject* operator()(T ptr_or_reference) const; 21 private: 22 static PyTypeObject* type(); 23 }; 24}} 25`` 26[endsect] 27[section Class `to_python_indirect` observers] 28``PyObject* operator()(T x) const;`` 29[variablelist 30[[Requires][`x` refers to an object (if it is a pointer type, it is non-null). `convertible() == true`.]] 31[[Effects][Creates an appropriately-typed Boost.Python extension class instance, uses MakeHolder to create an instance_holder from x, installs the instance_holder in the new extension class instance, and returns a pointer to it.]] 32] 33[endsect] 34[section Class `to_python_indirect` statics] 35``bool convertible()`` 36[variablelist 37[[Effects][Returns true iff any module has registered a Python type corresponding to U. ]] 38] 39[endsect] 40[endsect] 41[section Example] 42This example replicates the functionality of [link function_invocation_and_creation.models_of_resultconvertergenerat.boost_python_reference_existing_.class_reference_existing_object `reference_existing_object`], but without some of the compile-time error checking. 43`` 44struct make_reference_holder 45{ 46 typedef boost::python::objects::instance_holder* result_type; 47 template <class T> 48 static result_type execute(T* p) 49 { 50 return new boost::python::objects::pointer_holder<T*, T>(p); 51 } 52}; 53 54struct reference_existing_object 55{ 56 // metafunction returning the ResultConverter 57 template <class T> 58 struct apply 59 { 60 typedef boost::python::to_python_indirect<T,make_reference_holder> type; 61 }; 62}; 63`` 64[endsect] 65[endsect] 66