boost/python/instance_holder.hpp

   1 // Copyright David Abrahams 2002.
   2 // Distributed under the Boost Software License, Version 1.0. (See
   3 // accompanying file LICENSE_1_0.txt or copy at
   4 // http://www.boost.org/LICENSE_1_0.txt)
   5 #ifndef INSTANCE_HOLDER_DWA2002517_HPP
   6 # define INSTANCE_HOLDER_DWA2002517_HPP
   7
   8 # include <boost/python/detail/prefix.hpp>
   9
  10 # include <boost/utility.hpp>
  11 # include <boost/python/type_id.hpp>
  12 # include <cstddef>
  13
  14 namespace boost { namespace python {
  15
  16 // Base class for all holders
  17 struct BOOST_PYTHON_DECL instance_holder : private noncopyable
  18 {
  19  public:
  20     instance_holder();
  21     virtual ~instance_holder();
  22
  23     // return the next holder in a chain
  24     instance_holder* next() const;
  25
  26     // When the derived holder actually holds by [smart] pointer and
  27     // null_ptr_only is set, only report that the type is held when
  28     // the pointer is null.  This is needed for proper shared_ptr
  29     // support, to prevent holding shared_ptrs from being found when
  30     // converting from python so that we can use the conversion method
  31     // that always holds the Python object.
  32     virtual void* holds(type_info, bool null_ptr_only) = 0;
  33
  34     void install(PyObject* inst) throw();
  35
  36     // These functions should probably be located elsewhere.
  37
  38     // Allocate storage for an object of the given size at the given
  39     // offset in the Python instance<> object if bytes are available
  40     // there. Otherwise allocate size bytes of heap memory.
  41     static void* allocate(PyObject*, std::size_t offset, std::size_t size);
  42
  43     // Deallocate storage from the heap if it was not carved out of
  44     // the given Python object by allocate(), above.
  45     static void deallocate(PyObject*, void* storage) throw();
  46  private:
  47     instance_holder* m_next;
  48 };
  49
  50 // This macro is needed for implementation of derived holders
  51 # define BOOST_PYTHON_UNFORWARD(N,ignored) (typename unforward<A##N>::type)(a##N)
  52
  53 //
  54 // implementation
  55 //
  56 inline instance_holder* instance_holder::next() const
  57 {
  58     return m_next;
  59 }
  60
  61 }} // namespace boost::python
  62
  63 #endif // INSTANCE_HOLDER_DWA2002517_HPP