| 1 | /* scoped_restore, a simple class for saving and restoring a value |
| 2 | |
| 3 | Copyright (C) 2016-2019 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 COMMON_SCOPED_RESTORE_H |
| 21 | #define COMMON_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 /* COMMON_SCOPED_RESTORE_H */ |