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scoped_restore.h
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1 /* scoped_restore, a simple class for saving and restoring a value
2
3 Copyright (C) 2016-2018 Free Software Foundation, Inc.
4
5 This file is part of GDB.
6
7 This program is free software; you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation; either version 3 of the License, or
10 (at your option) any later version.
11
12 This program is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
16
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>. */
19
20 #ifndef SCOPED_RESTORE_H
21 #define SCOPED_RESTORE_H
22
23 /* Base class for scoped_restore_tmpl. */
24 class scoped_restore_base
25 {
26 public:
27 /* This informs the (scoped_restore_tmpl<T>) dtor that you no longer
28 want the original value restored. */
29 void release () const
30 { m_saved_var = NULL; }
31
32 protected:
33 scoped_restore_base (void *saved_var)
34 : m_saved_var (saved_var)
35 {}
36
37 /* The type-erased saved variable. This is here so that clients can
38 call release() on a "scoped_restore" local, which is a typedef to
39 a scoped_restore_base. See below. */
40 mutable void *m_saved_var;
41 };
42
43 /* A convenience typedef. Users of make_scoped_restore declare the
44 local RAII object as having this type. */
45 typedef const scoped_restore_base &scoped_restore;
46
47 /* An RAII-based object that saves a variable's value, and then
48 restores it again when this object is destroyed. */
49 template<typename T>
50 class scoped_restore_tmpl : public scoped_restore_base
51 {
52 public:
53
54 /* Create a new scoped_restore object that saves the current value
55 of *VAR. *VAR will be restored when this scoped_restore object
56 is destroyed. */
57 scoped_restore_tmpl (T *var)
58 : scoped_restore_base (var),
59 m_saved_value (*var)
60 {
61 }
62
63 /* Create a new scoped_restore object that saves the current value
64 of *VAR, and sets *VAR to VALUE. *VAR will be restored when this
65 scoped_restore object is destroyed. This is templated on T2 to
66 allow passing VALUEs of types convertible to T.
67 E.g.: T='base'; T2='derived'. */
68 template <typename T2>
69 scoped_restore_tmpl (T *var, T2 value)
70 : scoped_restore_base (var),
71 m_saved_value (*var)
72 {
73 *var = value;
74 }
75
76 scoped_restore_tmpl (const scoped_restore_tmpl<T> &other)
77 : scoped_restore_base {other.m_saved_var},
78 m_saved_value (other.m_saved_value)
79 {
80 other.m_saved_var = NULL;
81 }
82
83 ~scoped_restore_tmpl ()
84 {
85 if (saved_var () != NULL)
86 *saved_var () = m_saved_value;
87 }
88
89 private:
90 /* Return a pointer to the saved variable with its type
91 restored. */
92 T *saved_var ()
93 { return static_cast<T *> (m_saved_var); }
94
95 /* No need for this. It is intentionally not defined anywhere. */
96 scoped_restore_tmpl &operator= (const scoped_restore_tmpl &);
97
98 /* The saved value. */
99 const T m_saved_value;
100 };
101
102 /* Make a scoped_restore. This is useful because it lets template
103 argument deduction work. */
104 template<typename T>
105 scoped_restore_tmpl<T> make_scoped_restore (T *var)
106 {
107 return scoped_restore_tmpl<T> (var);
108 }
109
110 /* Make a scoped_restore. This is useful because it lets template
111 argument deduction work. */
112 template<typename T, typename T2>
113 scoped_restore_tmpl<T> make_scoped_restore (T *var, T2 value)
114 {
115 return scoped_restore_tmpl<T> (var, value);
116 }
117
118 #endif /* SCOPED_RESTORE_H */
scoped_restore_tmpl::scoped_restore_tmpl
scoped_restore_tmpl(T *var, T2 value)
Definition: scoped_restore.h:69
scoped_restore
const scoped_restore_base & scoped_restore
Definition: scoped_restore.h:45
scoped_restore_base::release
void release() const
Definition: scoped_restore.h:29
scoped_restore_tmpl::m_saved_value
const T m_saved_value
Definition: scoped_restore.h:99
make_scoped_restore
scoped_restore_tmpl< T > make_scoped_restore(T *var)
Definition: scoped_restore.h:105
scoped_restore_tmpl::scoped_restore_tmpl
scoped_restore_tmpl(const scoped_restore_tmpl< T > &other)
Definition: scoped_restore.h:76
scoped_restore_tmpl::operator=
scoped_restore_tmpl & operator=(const scoped_restore_tmpl &)
scoped_restore_base
Definition: scoped_restore.h:24
scoped_restore_base::scoped_restore_base
scoped_restore_base(void *saved_var)
Definition: scoped_restore.h:33
value
Definition: value.c:169
scoped_restore_base::m_saved_var
void * m_saved_var
Definition: scoped_restore.h:40
scoped_restore_tmpl::~scoped_restore_tmpl
~scoped_restore_tmpl()
Definition: scoped_restore.h:83
scoped_restore_tmpl::scoped_restore_tmpl
scoped_restore_tmpl(T *var)
Definition: scoped_restore.h:57
scoped_restore_tmpl
Definition: scoped_restore.h:50
scoped_restore_tmpl::saved_var
T * saved_var()
Definition: scoped_restore.h:92