1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
|
/****************************************************************************
**
** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
** All rights reserved.
** Contact: Nokia Corporation (qt-info@nokia.com)
**
** This file is part of the QtXmlPatterns module of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** No Commercial Usage
** This file contains pre-release code and may not be distributed.
** You may use this file in accordance with the terms and conditions
** contained in the Technology Preview License Agreement accompanying
** this package.
**
** GNU Lesser General Public License Usage
** Alternatively, this file may be used under the terms of the GNU Lesser
** General Public License version 2.1 as published by the Free Software
** Foundation and appearing in the file LICENSE.LGPL included in the
** packaging of this file. Please review the following information to
** ensure the GNU Lesser General Public License version 2.1 requirements
** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
**
** In addition, as a special exception, Nokia gives you certain additional
** rights. These rights are described in the Nokia Qt LGPL Exception
** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
**
** If you have questions regarding the use of this file, please contact
** Nokia at qt-info@nokia.com.
**
**
**
**
**
**
**
**
** $QT_END_LICENSE$
**
****************************************************************************/
//
// W A R N I N G
// -------------
//
// This file is not part of the Qt API. It exists purely as an
// implementation detail. This header file may change from version to
// version without notice, or even be removed.
//
// We mean it.
#ifndef Patternist_CppCastingHelper_H
#define Patternist_CppCastingHelper_H
#include <QtCore/QtGlobal>
QT_BEGIN_HEADER
QT_BEGIN_NAMESPACE
namespace QPatternist
{
/**
* @short Provides convenience methods for performing static casts between C++ classes.
*
* In Patternist, it is very common to do up-casts from Expression or Item, which typically
* involves writing messy code. Such an old-way cast looks like this:
*
* @code
* static_cast<const MyClass *>(myInstance.data())->myClassMember()
* @endcode
*
* CppCastingHelper provides the convenience method as() for this, which is functionally
* equivalent to the above code, but simpler:
*
* @code
* myInstance->as<MyClass>()->myClassMember()
* @endcode
*
* The as() function performs a static cast.
*
* By using CppCastingHelper, this is achieved:
*
* - Const correctness is automatically taken care of
* - Less code to write
* - When compiling in debug mode, the as() functions uses a @c dynamic_cast to verify that the
* static casts are properly done, such that sensible error messages are given when the casts
* are invalid. It also traps invalid casts which nevertheless happen to work on a particular
* platform/compiler/hardware architecture.
*
* CppCastingHelper is a template class where the TSubClass parameter must be the class
* inheriting CppCastingHelper. See Item or Expression for demonstration.
*
* @author Frans Englich <frans.englich@nokia.com>
*/
template<typename TSubClass>
class CppCastingHelper
{
public:
/**
* Casts this instance to:
*
* @code
* const TCastTarget *
* @endcode
*
* and returns the result.
*
* When compiled in debug mode, this function perform a @c dynamic_cast, in order to
* check the correctness of the cast.
*/
template<typename TCastTarget>
inline const TCastTarget *as() const
{
#if defined(Patternist_DEBUG) && !defined(Q_CC_XLC)
/* At least on aix-xlc-64, the compiler cries when it sees dynamic_cast. */
Q_ASSERT_X(dynamic_cast<const TCastTarget *>(static_cast<const TSubClass *>(this)),
Q_FUNC_INFO,
"The cast is invalid. This class does not inherit the cast target.");
#endif
return static_cast<const TCastTarget *>(static_cast<const TSubClass *>(this));
}
/**
* Casts this instance to:
*
* @code
* TCastTarget *
* @endcode
*
* and returns the result.
*
* When compiled in debug mode, a @c dynamic_cast is attempted, in order to
* check the correctness of the cast.
*/
template<typename TCastTarget>
inline TCastTarget *as()
{
#if defined(Patternist_DEBUG) && !defined(Q_CC_XLC)
/* At least on aix-xlc-64, the compiler cries when it sees dynamic_cast. */
Q_ASSERT_X(dynamic_cast<TCastTarget *>(static_cast<TSubClass *>(this)),
Q_FUNC_INFO,
"The cast is invalid. This class does not inherit the cast target.");
#endif
return static_cast<TCastTarget *>(static_cast<TSubClass *>(this));
}
protected:
/**
* This constructor is protected because this class must be sub-classed.
*/
inline CppCastingHelper() {}
};
}
QT_END_NAMESPACE
QT_END_HEADER
#endif
|
