gdb/common/scoped_restore.h

   1 /* scoped_restore, a simple class for saving and restoring a value
   2
   3    Copyright (C) 2016-2017 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 struct scoped_restore_base
  25 {
  26 };
  27
  28 /* A convenience typedef.  Users of make_scoped_restore declare the
  29    local RAII object as having this type.  */
  30 typedef const scoped_restore_base &scoped_restore;
  31
  32 /* An RAII-based object that saves a variable's value, and then
  33    restores it again when this object is destroyed. */
  34 template<typename T>
  35 class scoped_restore_tmpl : public scoped_restore_base
  36 {
  37  public:
  38
  39   /* Create a new scoped_restore object that saves the current value
  40      of *VAR.  *VAR will be restored when this scoped_restore object
  41      is destroyed.  */
  42   scoped_restore_tmpl (T *var)
  43     : m_saved_var (var),
  44       m_saved_value (*var)
  45   {
  46   }
  47
  48   /* Create a new scoped_restore object that saves the current value
  49      of *VAR, and sets *VAR to VALUE.  *VAR will be restored when this
  50      scoped_restore object is destroyed.  This is templated on T2 to
  51      allow passing VALUEs of types convertible to T.
  52      E.g.: T='base'; T2='derived'.  */
  53   template <typename T2>
  54   scoped_restore_tmpl (T *var, T2 value)
  55     : m_saved_var (var),
  56       m_saved_value (*var)
  57   {
  58     *var = value;
  59   }
  60
  61   scoped_restore_tmpl (const scoped_restore_tmpl<T> &other)
  62     : m_saved_var (other.m_saved_var),
  63       m_saved_value (other.m_saved_value)
  64   {
  65     other.m_saved_var = NULL;
  66   }
  67
  68   ~scoped_restore_tmpl ()
  69   {
  70     if (m_saved_var != NULL)
  71       *m_saved_var = m_saved_value;
  72   }
  73
  74  private:
  75
  76   /* No need for this.  It is intentionally not defined anywhere.  */
  77   scoped_restore_tmpl &operator= (const scoped_restore_tmpl &);
  78
  79   /* The saved variable.  */
  80   mutable T *m_saved_var;
  81
  82   /* The saved value.  */
  83   const T m_saved_value;
  84 };
  85
  86 /* Make a scoped_restore.  This is useful because it lets template
  87    argument deduction work.  */
  88 template<typename T>
  89 scoped_restore_tmpl<T> make_scoped_restore (T *var)
  90 {
  91   return scoped_restore_tmpl<T> (var);
  92 }
  93
  94 /* Make a scoped_restore.  This is useful because it lets template
  95    argument deduction work.  */
  96 template<typename T, typename T2>
  97 scoped_restore_tmpl<T> make_scoped_restore (T *var, T2 value)
  98 {
  99   return scoped_restore_tmpl<T> (var, value);
 100 }
 101
 102 #endif /* SCOPED_RESTORE_H */