// 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 INSTANCE_HOLDER_DWA2002517_HPP

 # define INSTANCE_HOLDER_DWA2002517_HPP

 # include <boost/python/detail/prefix.hpp>

 # include <boost/utility.hpp>

 # include <boost/python/type_id.hpp>

 # include <cstddef>

 namespace boost { namespace python { 

 // Base class for all holders

 struct BOOST_PYTHON_DECL instance_holder : private noncopyable

 {

  public:

     instance_holder();

     virtual ~instance_holder();

     // return the next holder in a chain

     instance_holder* next() const;

     // When the derived holder actually holds by [smart] pointer and

     // null_ptr_only is set, only report that the type is held when

     // the pointer is null.  This is needed for proper shared_ptr

     // support, to prevent holding shared_ptrs from being found when

     // converting from python so that we can use the conversion method

     // that always holds the Python object.

     virtual void* holds(type_info, bool null_ptr_only) = 0;

     void install(PyObject* inst) throw();

     // These functions should probably be located elsewhere.

     // Allocate storage for an object of the given size at the given

     // offset in the Python instance<> object if bytes are available

     // there. Otherwise allocate size bytes of heap memory.

     static void* allocate(PyObject*, std::size_t offset, std::size_t size);

     // Deallocate storage from the heap if it was not carved out of

     // the given Python object by allocate(), above.

     static void deallocate(PyObject*, void* storage) throw();

  private:

     instance_holder* m_next;

 };

 // This macro is needed for implementation of derived holders

 # define BOOST_PYTHON_UNFORWARD(N,ignored) (typename unforward<A##N>::type)(a##N)

 //

 // implementation

 //

 inline instance_holder* instance_holder::next() const

 {

     return m_next;

 }

 }} // namespace boost::python

 #endif // INSTANCE_HOLDER_DWA2002517_HPP