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[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]
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