Re: maps, iterators, and const

"Alf P. Steinbach" <>
Fri, 21 May 2010 18:46:05 +0200
* John, on 21.05.2010 17:54:

Solve this by creating your own iterators which inherit privately from
the map's iterators and don't expose the map's iterators in your
custom interface.


Hmm. This would be more complicated than I would like since I don't want
to have to define additional classes. It's not ideal, but maybe I will
just go the const_cast route and define my map as std::map<int,const A*>
and use const_cast internally in the few places I need to alter an A.

Possibly you have design level problem, but possibly you have not.

You might consider something like the following:

#include <map>
#include <iostream>

class A {};

class B
     typedef std::map< int, A* > Map;
     Map map_;

     B( B const& other );
     B& operator=( B const& other );

         map_[1] = new A;
         map_[2] = new A;
         map_[3] = new A;

     class ConstIter
     friend class B;
         typedef std::pair< int, A const* > ConstPair;
         Map::const_iterator current_;

         ConstIter( Map::const_iterator start )
             : current_( start )

         ConstPair const* operator->() const; // No such.

         ConstIter& operator++()
             ++current_; return *this;

         ConstIter operator++( int )
             return ConstIter( current_++ );

         ConstPair const operator*() const
             return *current_;

         bool operator==( ConstIter const& other )
             return current_ == other.current_;

         bool operator!=( ConstIter const& other )
             return current_ != other.current_;

         int key() const { return current_->first; }
         A const* value() const { return current_->second; }

     ConstIter begin() const { return map_.begin(); }
     ConstIter end() const { return map_.end(); }

int main ()
     B b;
     for( B::ConstIter it = b.begin(); it != b.end(); ++it )
         std::cout << it.key() << std::endl;

Cheers & hth.,

- Alf

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