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dcast.h
00001 // Filename: dcast.h
00002 // Created by:  drose (06Aug01)
00003 //
00004 ////////////////////////////////////////////////////////////////////
00005 //
00006 // PANDA 3D SOFTWARE
00007 // Copyright (c) Carnegie Mellon University.  All rights reserved.
00008 //
00009 // All use of this software is subject to the terms of the revised BSD
00010 // license.  You should have received a copy of this license along
00011 // with this source code in a file named "LICENSE."
00012 //
00013 ////////////////////////////////////////////////////////////////////
00014 
00015 #ifndef DCAST_H
00016 #define DCAST_H
00017 
00018 #include "pandabase.h"
00019 
00020 #include "typeHandle.h"
00021 #include "typedObject.h"
00022 #include "config_express.h"
00023 
00024 // The DCAST (downcast) macro is defined as a convenience for
00025 // downcasting from some TypedObject pointer (or a PointerTo).  It's
00026 // just a normal C++-style downcast, except it first checks get_type()
00027 // to make sure the downcasting is safe.  If you compile with NDEBUG,
00028 // or set verify-dcast to #f, this check is removed.
00029 
00030 // DCAST will return NULL if the downcasting is unsafe.  If you'd
00031 // rather it abort out of the function (a la nassertv/nassertr), then
00032 // see DCAST_INTO_V and DCAST_INTO_R, below.
00033 
00034 template<class WantType>
00035 INLINE WantType *_dcast(WantType *, TypedObject *ptr);
00036 template<class WantType>
00037 INLINE const WantType *_dcast(WantType *, const TypedObject *ptr);
00038 
00039 // Note: it is important that DCAST not repeat the pointer parameter,
00040 // since many users of DCAST may want to use the result of a function
00041 // as the pointer parameter, and it could be terribly confusing and
00042 // difficult to trace if the function were inadvertently executed
00043 // twice.  This happened!
00044 #define DCAST(want_type, pointer) _dcast((want_type*)0, pointer)
00045 
00046 // DCAST_INTO_V and DCAST_INTO_R are similar in purpose to DCAST,
00047 // except they: (a) automatically assign a variable instead of
00048 // returning the downcasted pointer, and (b) they immediately return
00049 // out of the function if the downcasting fails.  DCAST_INTO_V is for
00050 // use in a void function and returns nothing; DCAST_INTO_R is for use
00051 // in a non-void function and returns the indicated value.
00052 
00053 // Both DCAST_INTO_V and DCAST_INTO_R accept as the first parameter a
00054 // variable of type (want_type *) or (const want_type *), instead of
00055 // the name of the type.  This variable will be filled with the new
00056 // pointer.
00057 
00058 
00059 // _dcast_ref is used to implement DCAST_INTO_V and DCAST_INTO_R.  Its
00060 // difference from _dcast is that it takes a reference to a pointer as
00061 // a first parameter.  The main point of this is to shut up the
00062 // compiler about pointers used before their value is assigned.
00063 template<class WantType>
00064 INLINE WantType *_dcast_ref(WantType *&, TypedObject *ptr);
00065 template<class WantType>
00066 INLINE const WantType *_dcast_ref(WantType *&, const TypedObject *ptr);
00067 
00068 #ifdef DO_DCAST
00069 // _dcast_verify performs the actual verification.
00070 EXPCL_PANDAEXPRESS bool
00071 _dcast_verify(TypeHandle want_handle, size_t want_size, 
00072               const TypedObject *ptr);
00073 #endif  // DO_DCAST
00074 
00075 #define DCAST_INTO_V(to_pointer, from_pointer) \
00076   { \
00077     (to_pointer) = _dcast_ref(to_pointer, from_pointer); \
00078     nassertv((void *)(to_pointer) != (void *)NULL); \
00079   }
00080 
00081 #define DCAST_INTO_R(to_pointer, from_pointer, return_value) \
00082   { \
00083     (to_pointer) = _dcast_ref(to_pointer, from_pointer); \
00084     nassertr((void *)(to_pointer) != (void *)NULL, return_value); \
00085   }
00086 
00087 #include "dcast.T"
00088 
00089 #endif
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