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// Copyright David Abrahams 2002.
// Distributed under the Boost Software License, Version 1.0. (See
// accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
#ifndef OBJECT_MANAGER_DWA2002614_HPP
# define OBJECT_MANAGER_DWA2002614_HPP
# include <boost/python/handle.hpp>
# include <boost/python/cast.hpp>
# include <boost/python/converter/pyobject_traits.hpp>
# include <boost/type_traits/object_traits.hpp>
# include <boost/mpl/if.hpp>
# include <boost/python/detail/indirect_traits.hpp>
# include <boost/mpl/bool.hpp>
// Facilities for dealing with types which always manage Python
// objects. Some examples are object, list, str, et. al. Different
// to_python/from_python conversion rules apply here because in
// contrast to other types which are typically embedded inside a
// Python object, these are wrapped around a Python object. For most
// object managers T, a C++ non-const T reference argument does not
// imply the existence of a T lvalue embedded in the corresponding
// Python argument, since mutating member functions on T actually only
// modify the held Python object.
//
// handle<T> is an object manager, though strictly speaking it should
// not be. In other words, even though mutating member functions of
// hanlde<T> actually modify the handle<T> and not the T object,
// handle<T>& arguments of wrapped functions will bind to "rvalues"
// wrapping the actual Python argument, just as with other object
// manager classes. Making an exception for handle<T> is simply not
// worth the trouble.
//
// borrowed<T> cv* is an object manager so that we can use the general
// to_python mechanisms to convert raw Python object pointers to
// python, without the usual semantic problems of using raw pointers.
// Object Manager Concept requirements:
//
// T is an Object Manager
// p is a PyObject*
// x is a T
//
// * object_manager_traits<T>::is_specialized == true
//
// * T(detail::borrowed_reference(p))
// Manages p without checking its type
//
// * get_managed_object(x, boost::python::tag)
// Convertible to PyObject*
//
// Additional requirements if T can be converted from_python:
//
// * T(object_manager_traits<T>::adopt(p))
// steals a reference to p, or throws a TypeError exception if
// p doesn't have an appropriate type. May assume p is non-null
//
// * X::check(p)
// convertible to bool. True iff T(X::construct(p)) will not
// throw.
// Forward declarations
//
namespace boost { namespace python
{
namespace api
{
class object;
}
}}
namespace boost { namespace python { namespace converter {
// Specializations for handle<T>
template <class T>
struct handle_object_manager_traits
: pyobject_traits<typename T::element_type>
{
private:
typedef pyobject_traits<typename T::element_type> base;
public:
BOOST_STATIC_CONSTANT(bool, is_specialized = true);
// Initialize with a null_ok pointer for efficiency, bypassing the
// null check since the source is always non-null.
static null_ok<typename T::element_type>* adopt(PyObject* p)
{
return python::allow_null(base::checked_downcast(p));
}
};
template <class T>
struct default_object_manager_traits
{
BOOST_STATIC_CONSTANT(
bool, is_specialized = python::detail::is_borrowed_ptr<T>::value
);
};
template <class T>
struct object_manager_traits
: mpl::if_c<
is_handle<T>::value
, handle_object_manager_traits<T>
, default_object_manager_traits<T>
>::type
{
};
//
// Traits for detecting whether a type is an object manager or a
// (cv-qualified) reference to an object manager.
//
template <class T>
struct is_object_manager
: mpl::bool_<object_manager_traits<T>::is_specialized>
{
};
# ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
template <class T>
struct is_reference_to_object_manager
: mpl::false_
{
};
template <class T>
struct is_reference_to_object_manager<T&>
: is_object_manager<T>
{
};
template <class T>
struct is_reference_to_object_manager<T const&>
: is_object_manager<T>
{
};
template <class T>
struct is_reference_to_object_manager<T volatile&>
: is_object_manager<T>
{
};
template <class T>
struct is_reference_to_object_manager<T const volatile&>
: is_object_manager<T>
{
};
# else
namespace detail
{
typedef char (&yes_reference_to_object_manager)[1];
typedef char (&no_reference_to_object_manager)[2];
// A number of nastinesses go on here in order to work around MSVC6
// bugs.
template <class T>
struct is_object_manager_help
{
typedef typename mpl::if_<
is_object_manager<T>
, yes_reference_to_object_manager
, no_reference_to_object_manager
>::type type;
// If we just use the type instead of the result of calling this
// function, VC6 will ICE.
static type call();
};
// A set of overloads for each cv-qualification. The same argument
// is passed twice: the first one is used to unwind the cv*, and the
// second one is used to avoid relying on partial ordering for
// overload resolution.
template <class U>
typename is_object_manager_help<U>
is_object_manager_helper(U*, void*);
template <class U>
typename is_object_manager_help<U>
is_object_manager_helper(U const*, void const*);
template <class U>
typename is_object_manager_help<U>
is_object_manager_helper(U volatile*, void volatile*);
template <class U>
typename is_object_manager_help<U>
is_object_manager_helper(U const volatile*, void const volatile*);
template <class T>
struct is_reference_to_object_manager_nonref
: mpl::false_
{
};
template <class T>
struct is_reference_to_object_manager_ref
{
static T sample_object;
BOOST_STATIC_CONSTANT(
bool, value
= (sizeof(is_object_manager_helper(&sample_object, &sample_object).call())
== sizeof(detail::yes_reference_to_object_manager)
)
);
typedef mpl::bool_<value> type;
};
}
template <class T>
struct is_reference_to_object_manager
: mpl::if_<
is_reference<T>
, detail::is_reference_to_object_manager_ref<T>
, detail::is_reference_to_object_manager_nonref<T>
>::type
{
};
# endif
}}} // namespace boost::python::converter
#endif // OBJECT_MANAGER_DWA2002614_HPP
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