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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 FROM_PYTHON_AUX_DATA_DWA2002128_HPP
 # define FROM_PYTHON_AUX_DATA_DWA2002128_HPP
 
 # include <boost/python/converter/constructor_function.hpp>
 # include <boost/python/detail/referent_storage.hpp>
 # include <boost/python/detail/destroy.hpp>
 # include <boost/python/detail/type_traits.hpp>
 # include <boost/align/align.hpp>
 # include <boost/static_assert.hpp>
 # include <cstddef>
 
 // Data management for potential rvalue conversions from Python to C++
 // types. When a client requests a conversion to T* or T&, we
 // generally require that an object of type T exists in the source
 // Python object, and the code here does not apply**. This implements
 // conversions which may create new temporaries of type T. The classic
 // example is a conversion which converts a Python tuple to a
 // std::vector. Since no std::vector lvalue exists in the Python
 // object -- it must be created "on-the-fly" by the converter, and
 // which must manage the lifetime of the created object.
 //
 // Note that the client is not precluded from using a registered
 // lvalue conversion to T in this case. In other words, we will
 // happily accept a Python object which /does/ contain a std::vector
 // lvalue, provided an appropriate converter is registered. So, while
 // this is an rvalue conversion from the client's point-of-view, the
 // converter registry may serve up lvalue or rvalue conversions for
 // the target type.
 //
 // ** C++ argument from_python conversions to T const& are an
 // exception to the rule for references: since in C++, const
 // references can bind to temporary rvalues, we allow rvalue
 // converters to be chosen when the target type is T const& for some
 // T.
 namespace boost { namespace python { namespace converter { 
 
 // Conversions begin by filling in and returning a copy of this
 // structure. The process looks up a converter in the rvalue converter
 // registry for the target type. It calls the convertible() function
 // of each registered converter, passing the source PyObject* as an
 // argument, until a non-null result is returned. This result goes in
 // the convertible field, and the converter's construct() function is
 // stored in the construct field.
 //
 // If no appropriate converter is found, conversion fails and the
 // convertible field is null. When used in argument conversion for
 // wrapped C++ functions, it causes overload resolution to reject the
 // current function but not to fail completely. If an exception is
 // thrown, overload resolution stops and the exception propagates back
 // through the caller.
 //
 // If an lvalue converter is matched, its convertible() function is
 // expected to return a pointer to the stored T object; its
 // construct() function will be NULL. The convertible() function of
 // rvalue converters may return any non-singular pointer; the actual
 // target object will only be available once the converter's
 // construct() function is called.
 struct rvalue_from_python_stage1_data
 {
     void* convertible;
     constructor_function construct;
 };
 
 // Augments rvalue_from_python_stage1_data by adding storage for
 // constructing an object of remove_reference<T>::type. The
 // construct() function of rvalue converters (stored in m_construct
 // above) will cast the rvalue_from_python_stage1_data to an
 // appropriate instantiation of this template in order to access that
 // storage.
 template <class T>
 struct rvalue_from_python_storage
 {
     rvalue_from_python_stage1_data stage1;
 
     // Storage for the result, in case an rvalue must be constructed
     typename python::detail::referent_storage<
         typename boost::python::detail::add_lvalue_reference<T>::type
     >::type storage;
 };
 
 // Augments rvalue_from_python_storage<T> with a destructor. If
 // stage1.convertible == storage.bytes, it indicates that an object of
 // remove_reference<T>::type has been constructed in storage and
 // should will be destroyed in ~rvalue_from_python_data(). It is
 // crucial that successful rvalue conversions establish this equality
 // and that unsuccessful ones do not.
 template <class T>
 struct rvalue_from_python_data : rvalue_from_python_storage<T>
 {
 # if (!defined(__MWERKS__) || __MWERKS__ >= 0x3000) \
         && (!defined(__EDG_VERSION__) || __EDG_VERSION__ >= 245) \
         && (!defined(__DECCXX_VER) || __DECCXX_VER > 60590014) \
         && !defined(BOOST_PYTHON_SYNOPSIS) /* Synopsis' OpenCXX has trouble parsing this */
     // This must always be a POD struct with m_data its first member.
     BOOST_STATIC_ASSERT(BOOST_PYTHON_OFFSETOF(rvalue_from_python_storage<T>,stage1) == 0);
 # endif
     
     // The usual constructor 
     rvalue_from_python_data(rvalue_from_python_stage1_data const&);
 
     // This constructor just sets m_convertible -- used by
     // implicitly_convertible<> to perform the final step of the
     // conversion, where the construct() function is already known.
     rvalue_from_python_data(void* convertible);
 
     // Destroys any object constructed in the storage.
     ~rvalue_from_python_data();
  private:
     typedef typename boost::python::detail::add_lvalue_reference<
                 typename boost::python::detail::add_cv<T>::type>::type ref_type;
 };
 
 //
 // Implementataions
 //
 template <class T>
 inline rvalue_from_python_data<T>::rvalue_from_python_data(rvalue_from_python_stage1_data const& _stage1)
 {
     this->stage1 = _stage1;
 }
 
 template <class T>
 inline rvalue_from_python_data<T>::rvalue_from_python_data(void* convertible)
 {
     this->stage1.convertible = convertible;
 }
 
 template <class T>
 inline rvalue_from_python_data<T>::~rvalue_from_python_data()
 {
     if (this->stage1.convertible == this->storage.bytes)
     {
         size_t allocated = sizeof(this->storage);
         void *ptr = this->storage.bytes;
         void *aligned_storage =
             ::boost::alignment::align(boost::python::detail::alignment_of<T>::value, 0, ptr, allocated);
         python::detail::destroy_referent<ref_type>(aligned_storage);
     }
 }
 
 }}} // namespace boost::python::converter
 
 #endif // FROM_PYTHON_AUX_DATA_DWA2002128_HPP

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