[section boost/python/to_python_indirect.hpp]

[section Introduction]

<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.

[endsect]

[section Class `to_python_indirect`]

Class 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.

[table

[[Parameter][Requirements][Description]]

[[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_`]. ]]

[[MakeHolder][`h = MakeHolder::execute(p);` ][A class whose static `execute()` creates an `instance_holder`. ]]

]

Instantiations of to_python_indirect are models of [link concepts.resultconverter `ResultConverter`].

``

namespace boost { namespace python

{

template <class T, class MakeHolder>

struct to_python_indirect

{

static bool convertible();

PyObject* operator()(T ptr_or_reference) const;

private:

static PyTypeObject* type();

};

}}

``

[endsect]

[section Class `to_python_indirect` observers]

``PyObject* operator()(T x) const;``

[variablelist

[[Requires][`x` refers to an object (if it is a pointer type, it is non-null). `convertible() == true`.]]

[[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.]]

]

[endsect]

[section Class `to_python_indirect` statics]

``bool convertible()``

[variablelist

[[Effects][Returns true iff any module has registered a Python type corresponding to U. ]]

]

[endsect]

[endsect]

[section Example]

This 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.

``

struct make_reference_holder

{

typedef boost::python::objects::instance_holder* result_type;

template <class T>

static result_type execute(T* p)

{

return new boost::python::objects::pointer_holder<T*, T>(p);

}

};

struct reference_existing_object

{

// metafunction returning the ResultConverter

template <class T>

struct apply

{

typedef boost::python::to_python_indirect<T,make_reference_holder> type;

};

};

``

[endsect]

[endsect]