Re: [Boost-users] [Serialization] How to restore ref-counted strings

From: Robert Ramey (ramey_at_[hidden])
Date: 2007-03-09 14:47:21

Here is your proposal

> static map<string, bool> string_map;
>
> template <class Archive>
> void read_string(Archive ar, string& a_string) {
>    string s;
>    ar >> s;  // read from disk
>    map<string, bool>::iterator i = string_map.find(s);
>
>    if (i == string_map.end()) {
>        i = string_map.insert(make_pair(s, true));
>    }
>
>    a_string = i->first;
> }
>
> void destroy_map() { string_map.clear(); }

First I would use a set rather than map as I think it
would be sufficient.

Second I would make this a "helper class" .  Your
special "Lear Archive" would be derived from
an existing archive and the helper class using
multiple inheritance.  Look at the implemenation
of shared_ptr checked into the HEADof CVS
to see how to do this.

class LearHelper {
    std::set<std::string> m_strings;
};

class LearArchive : binary_oarchive_impl, LearHelper {
};

class lear_string : std::string {
    typedef  mpl:_true? boost::serialization:is_wrapper;

    template<class Archive>
    void save(Archive &ar, const unsigned int version) const {
        std::string::iterator it = m_strings.find(*this);
        // if the string isn't in the set
        if(it != std::string::end())
            m_strings.insert(*this);
       // serialize the one in the set
         ar << *it;
    }
    void load(Archive &ar, const unsigned int version) {
        // load the string to a temporary location
        std::string tstr;
        ar >> tsr;
        // look it up in the set;
        std::string::iterator it = m_strings.find(*this);
        // if the string isn't in the set
        if(it != std::string::end())
            it = m_strings.insert(tsr);
       // and copy from the one in the set
        *this = tsr;
        reset_object_address(... // in case someone loads a pointer to a 
string
    }
}

finally, whenever you serialize a string, you use the lear_string wrapper

some class ...
    std::sting my_string;
   ....
  save(...
        ar << lear_string(my_string);
        ...
    load(...
        ar >> lear_string(my_string);
};

Food for thought. This should keep you busy for a while.  Good Luck.

Robert Ramey