gdbsupport/safe-iterator.h

   1 /* A safe iterator for GDB, the GNU debugger.
   2    Copyright (C) 2018-2024 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 #include <type_traits>
  23
  24 /* A forward iterator that wraps Iterator, such that when iterating
  25    with iterator IT, it is possible to delete *IT without invalidating
  26    IT.  Suitably wrapped in a range type and used with range-for, this
  27    allow convenient patterns like this:
  28
  29      // range_safe() returns a range type whose begin()/end() methods
  30      // return safe iterators.
  31      for (foo *f : range_safe ())
  32        {
  33          if (f->should_delete ())
  34            {
  35              // The ++it operation implicitly done by the range-for is
  36              // still OK after this.
  37              delete f;
  38            }
  39        }
  40 */
  41
  42 template<typename Iterator>
  43 class basic_safe_iterator
  44 {
  45 public:
  46   typedef basic_safe_iterator self_type;
  47   typedef typename Iterator::value_type value_type;
  48   typedef typename Iterator::reference reference;
  49   typedef typename Iterator::pointer pointer;
  50   typedef typename Iterator::iterator_category iterator_category;
  51   typedef typename Iterator::difference_type difference_type;
  52
  53   /* Construct the begin iterator using the given arguments; the end iterator is
  54      default constructed.  */
  55   template<typename... Args>
  56   explicit basic_safe_iterator (Args &&...args)
  57     : m_it (std::forward<Args> (args)...),
  58       m_next (m_it)
  59   {
  60     if (m_it != m_end)
  61       ++m_next;
  62   }
  63
  64   /* Construct the iterator using the first argument, and construct
  65      the end iterator using the second argument.  */
  66   template<typename Arg>
  67   explicit basic_safe_iterator (Arg &&arg, Arg &&arg2)
  68     : m_it (std::forward<Arg> (arg)),
  69       m_next (m_it),
  70       m_end (std::forward<Arg> (arg2))
  71   {
  72     if (m_it != m_end)
  73       ++m_next;
  74   }
  75
  76   /* Create a one-past-end iterator.  */
  77   basic_safe_iterator ()
  78   {}
  79
  80   typename std::invoke_result<decltype(&Iterator::operator*), Iterator>::type
  81     operator* () const
  82   { return *m_it; }
  83
  84   self_type &operator++ ()
  85   {
  86     m_it = m_next;
  87     if (m_it != m_end)
  88       ++m_next;
  89     return *this;
  90   }
  91
  92   bool operator== (const self_type &other) const
  93   { return m_it == other.m_it; }
  94
  95   bool operator!= (const self_type &other) const
  96   { return m_it != other.m_it; }
  97
  98 private:
  99   /* The current element.  */
 100   Iterator m_it {};
 101
 102   /* The next element.  Always one element ahead of M_IT.  */
 103   Iterator m_next {};
 104
 105   /* A one-past-end iterator.  */
 106   Iterator m_end {};
 107 };
 108
 109 /* A range adapter that wraps another range, and then returns safe
 110    iterators wrapping the original range's iterators.  */
 111
 112 template<typename Range>
 113 class basic_safe_range
 114 {
 115 public:
 116
 117   typedef basic_safe_iterator<typename Range::iterator> iterator;
 118
 119   explicit basic_safe_range (Range range)
 120     : m_range (range)
 121   {
 122   }
 123
 124   iterator begin ()
 125   {
 126     return iterator (m_range.begin (), m_range.end ());
 127   }
 128
 129   iterator end ()
 130   {
 131     return iterator (m_range.end (), m_range.end ());
 132   }
 133
 134 private:
 135
 136   Range m_range;
 137 };
 138
 139 #endif /* COMMON_SAFE_ITERATOR_H */