gdbsupport/scoped_restore.h

   1 /* scoped_restore, a simple class for saving and restoring a value
   2
   3    Copyright (C) 2016-2020 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 */