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      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 */
    140