gdbsupport/safe-iterator.h

   1 /* A safe iterator for GDB, the GNU debugger.
   2    Copyright (C) 2018-2020 Free Software Foundation, Inc.
   3
   4    This file is part of GDB.
   5
   6    This program is free software; you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 3 of the License, or
   9    (at your option) any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  18
  19 #ifndef COMMON_SAFE_ITERATOR_H
  20 #define COMMON_SAFE_ITERATOR_H
  21
  22 /* A forward iterator that wraps Iterator, such that when iterating
  23    with iterator IT, it is possible to delete *IT without invalidating
  24    IT.  Suitably wrapped in a range type and used with range-for, this
  25    allow convenient patterns like this:
  26
  27      // range_safe() returns a range type whose begin()/end() methods
  28      // return safe iterators.
  29      for (foo *f : range_safe ())
  30        {
  31          if (f->should_delete ())
  32            {
  33              // The ++it operation implicitly done by the range-for is
  34              // still OK after this.
  35              delete f;
  36            }
  37        }
  38 */
  39
  40 template<typename Iterator>
  41 class basic_safe_iterator
  42 {
  43 public:
  44   typedef basic_safe_iterator self_type;
  45   typedef typename Iterator::value_type value_type;
  46   typedef typename Iterator::reference reference;
  47   typedef typename Iterator::pointer pointer;
  48   typedef typename Iterator::iterator_category iterator_category;
  49   typedef typename Iterator::difference_type difference_type;
  50
  51   /* Construct using the given argument; the end iterator is default
  52      constructed.  */
  53   template<typename Arg>
  54   explicit basic_safe_iterator (Arg &&arg)
  55     : m_it (std::forward<Arg> (arg)),
  56       m_next (m_it)
  57   {
  58     if (m_it != m_end)
  59       ++m_next;
  60   }
  61
  62   /* Construct the iterator using the first argument, and construct
  63      the end iterator using the second argument.  */
  64   template<typename Arg>
  65   explicit basic_safe_iterator (Arg &&arg, Arg &&arg2)
  66     : m_it (std::forward<Arg> (arg)),
  67       m_next (m_it),
  68       m_end (std::forward<Arg> (arg2))
  69   {
  70     if (m_it != m_end)
  71       ++m_next;
  72   }
  73
  74   /* Create a one-past-end iterator.  */
  75   basic_safe_iterator ()
  76   {}
  77
  78   value_type operator* () const { return *m_it; }
  79
  80   self_type &operator++ ()
  81   {
  82     m_it = m_next;
  83     if (m_it != m_end)
  84       ++m_next;
  85     return *this;
  86   }
  87
  88   bool operator== (const self_type &other) const
  89   { return m_it == other.m_it; }
  90
  91   bool operator!= (const self_type &other) const
  92   { return m_it != other.m_it; }
  93
  94 private:
  95   /* The current element.  */
  96   Iterator m_it {};
  97
  98   /* The next element.  Always one element ahead of M_IT.  */
  99   Iterator m_next {};
 100
 101   /* A one-past-end iterator.  */
 102   Iterator m_end {};
 103 };
 104
 105 /* A range adapter that wraps another range, and then returns safe
 106    iterators wrapping the original range's iterators.  */
 107
 108 template<typename Range>
 109 class basic_safe_range
 110 {
 111 public:
 112
 113   typedef basic_safe_iterator<typename Range::iterator> iterator;
 114
 115   explicit basic_safe_range (Range range)
 116     : m_range (range)
 117   {
 118   }
 119
 120   iterator begin ()
 121   {
 122     return iterator (m_range.begin (), m_range.end ());
 123   }
 124
 125   iterator end ()
 126   {
 127     return iterator (m_range.end (), m_range.end ());
 128   }
 129
 130 private:
 131
 132   Range m_range;
 133 };
 134
 135 #endif /* COMMON_SAFE_ITERATOR_H */