root/tlate/lazy_structured_value.hh

/*  This file is part of Alue, the multiprotocol Internet discussion daemon

    Copyright © 2009 Antti-Juhani Kaijanaho

    Alue is free software: you can redistribute it and/or modify it
    under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    Alue is distributed in the hope that it will be useful, but
    WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with Alue.  If not, see <http://www.gnu.org/licenses/>.

 */

#ifndef GUARD_TLATE_LAZY_STRUCTURED_VALUE_HH
#define GUARD_TLATE_LAZY_STRUCTURED_VALUE_HH

#include "missing_value.hh"
#include "structured_value.hh"

#include <boost/thread/mutex.hpp>
#include <map>

namespace tlate
{
        class lazy_structured_value : public structured_value
        {
        protected:
                mutable boost::mutex mt;
                structured_value::const_ptr computer;
                mutable std::map<std::string,value::const_ptr> memo;
        public:
                typedef boost::shared_ptr<lazy_structured_value> ptr;
                typedef boost::shared_ptr<const lazy_structured_value>
                const_ptr;

                explicit lazy_structured_value(structured_value::const_ptr computer)
                        : computer(computer)
                        {}
                
                value::const_ptr get(std::string) const;
        };
        inline
        value::const_ptr lazy_structured_value::get(std::string key) const
        {
                boost::lock_guard<boost::mutex> lg(mt);
                value::const_ptr &rv = memo[key];
                if (!rv) rv = computer->get(key);
                if (!rv) rv.reset(new missing_value);
                return rv;
        }
};

#endif /* GUARD_TLATE_LAZY_STRUCTURED_VALUE_HH */