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dcast.h
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1/**
2 * PANDA 3D SOFTWARE
3 * Copyright (c) Carnegie Mellon University. All rights reserved.
4 *
5 * All use of this software is subject to the terms of the revised BSD
6 * license. You should have received a copy of this license along
7 * with this source code in a file named "LICENSE."
8 *
9 * @file dcast.h
10 * @author drose
11 * @date 2001-08-06
12 */
13
14#ifndef DCAST_H
15#define DCAST_H
16
17#include "pandabase.h"
18
19#include "typeHandle.h"
20#include "typedObject.h"
21#include "config_express.h"
22
23// The DCAST (downcast) macro is defined as a convenience for downcasting from
24// some TypedObject pointer (or a PointerTo). It's just a normal C++-style
25// downcast, except it first checks get_type() to make sure the downcasting is
26// safe. If you compile with NDEBUG, or set verify-dcast to #f, this check is
27// removed.
28
29// DCAST will return NULL if the downcasting is unsafe. If you'd rather it
30// abort out of the function (a la nassertvnassertr), then see DCAST_INTO_V
31// and DCAST_INTO_R, below.
32
33template<class WantType>
34INLINE WantType *_dcast(WantType *, TypedObject *ptr);
35template<class WantType>
36INLINE const WantType *_dcast(WantType *, const TypedObject *ptr);
37
38// Note: it is important that DCAST not repeat the pointer parameter, since
39// many users of DCAST may want to use the result of a function as the pointer
40// parameter, and it could be terribly confusing and difficult to trace if the
41// function were inadvertently executed twice. This happened!
42#define DCAST(want_type, pointer) _dcast((want_type*)0, pointer)
43
44// DCAST_INTO_V and DCAST_INTO_R are similar in purpose to DCAST, except they:
45// (a) automatically assign a variable instead of returning the downcasted
46// pointer, and (b) they immediately return out of the function if the
47// downcasting fails. DCAST_INTO_V is for use in a void function and returns
48// nothing; DCAST_INTO_R is for use in a non-void function and returns the
49// indicated value.
50
51// Both DCAST_INTO_V and DCAST_INTO_R accept as the first parameter a variable
52// of type (want_type *) or (const want_type *), instead of the name of the
53// type. This variable will be filled with the new pointer.
54
55
56// _dcast_ref is used to implement DCAST_INTO_V and DCAST_INTO_R. Its
57// difference from _dcast is that it takes a reference to a pointer as a first
58// parameter. The main point of this is to shut up the compiler about
59// pointers used before their value is assigned.
60template<class WantType>
61INLINE WantType *_dcast_ref(WantType *&, TypedObject *ptr);
62template<class WantType>
63INLINE const WantType *_dcast_ref(WantType *&, const TypedObject *ptr);
64
65// _dcast_verify performs the actual verification. This is an empty function
66// when DO_DCAST is not set, but we still need to define it for ABI
67// compatibility reasons.
68EXPCL_PANDA_EXPRESS bool
69_dcast_verify(TypeHandle want_handle, size_t want_size,
70 const TypedObject *ptr);
71
72#define DCAST_INTO_V(to_pointer, from_pointer) \
73 { \
74 (to_pointer) = _dcast_ref(to_pointer, from_pointer); \
75 nassertv((void *)(to_pointer) != nullptr); \
76 }
77
78#define DCAST_INTO_R(to_pointer, from_pointer, return_value) \
79 { \
80 (to_pointer) = _dcast_ref(to_pointer, from_pointer); \
81 nassertr((void *)(to_pointer) != nullptr, return_value); \
82 }
83
84#include "dcast.T"
85
86#endif
TypeHandle is the identifier used to differentiate C++ class types.
Definition typeHandle.h:81
This is an abstract class that all classes which use TypeHandle, and also provide virtual functions t...
Definition typedObject.h:88
PANDA 3D SOFTWARE Copyright (c) Carnegie Mellon University.
EXPCL_PANDA_EXPRESS bool _dcast_verify(TypeHandle want_handle, size_t want_size, const TypedObject *ptr)
This function performs the actual check that the indicated TypedObject pointer is of the intended typ...
Definition dcast.cxx:29
PANDA 3D SOFTWARE Copyright (c) Carnegie Mellon University.
PANDA 3D SOFTWARE Copyright (c) Carnegie Mellon University.
PANDA 3D SOFTWARE Copyright (c) Carnegie Mellon University.