src/indirectmap.h

   1 // Copyright (c) 2016 The Bitcoin Core developers
   2 // Distributed under the MIT software license, see the accompanying
   3 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
   4
   5 #ifndef BITCOIN_INDIRECTMAP_H
   6 #define BITCOIN_INDIRECTMAP_H
   7
   8 template <class T>
   9 struct DereferencingComparator { bool operator()(const T a, const T b) const { return *a < *b; } };
  10
  11 /* Map whose keys are pointers, but are compared by their dereferenced values.
  12  *
  13  * Differs from a plain std::map<const K*, T, DereferencingComparator<K*> > in
  14  * that methods that take a key for comparison take a K rather than taking a K*
  15  * (taking a K* would be confusing, since it's the value rather than the address
  16  * of the object for comparison that matters due to the dereferencing comparator).
  17  *
  18  * Objects pointed to by keys must not be modified in any way that changes the
  19  * result of DereferencingComparator.
  20  */
  21 template <class K, class T>
  22 class indirectmap {
  23 private:
  24     typedef std::map<const K*, T, DereferencingComparator<const K*> > base;
  25     base m;
  26 public:
  27     typedef typename base::iterator iterator;
  28     typedef typename base::const_iterator const_iterator;
  29     typedef typename base::size_type size_type;
  30     typedef typename base::value_type value_type;
  31
  32     // passthrough (pointer interface)
  33     std::pair<iterator, bool> insert(const value_type& value) { return m.insert(value); }
  34
  35     // pass address (value interface)
  36     iterator find(const K& key)                     { return m.find(&key); }
  37     const_iterator find(const K& key) const         { return m.find(&key); }
  38     iterator lower_bound(const K& key)              { return m.lower_bound(&key); }
  39     const_iterator lower_bound(const K& key) const  { return m.lower_bound(&key); }
  40     size_type erase(const K& key)                   { return m.erase(&key); }
  41     size_type count(const K& key) const             { return m.count(&key); }
  42
  43     // passthrough
  44     bool empty() const              { return m.empty(); }
  45     size_type size() const          { return m.size(); }
  46     size_type max_size() const      { return m.max_size(); }
  47     void clear()                    { m.clear(); }
  48     iterator begin()                { return m.begin(); }
  49     iterator end()                  { return m.end(); }
  50     const_iterator begin() const    { return m.begin(); }
  51     const_iterator end() const      { return m.end(); }
  52     const_iterator cbegin() const   { return m.cbegin(); }
  53     const_iterator cend() const     { return m.cend(); }
  54 };
  55
  56 #endif // BITCOIN_INDIRECTMAP_H