root/tlate/value.hh

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

    Copyright © 2009, 2010 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_VALUE_HH
#define GUARD_TLATE_VALUE_HH

#include <boost/shared_ptr.hpp>
#include <string>
#include <sstream>

namespace tlate
{
        class sequential_value;
        class value 
        {
        protected:
                value() {}
                value(const value &) {}
                value &operator=(const value &);
        public:
                typedef boost::shared_ptr<value> ptr;
                typedef boost::shared_ptr<const value> const_ptr;

                virtual ~value() {}
                virtual bool is_missing() const { return false; }
                virtual
                value::const_ptr call(boost::shared_ptr<sequential_value>,
                                      std::string /*fname*/, int /*line*/)
                        const {
                        return value::ptr();
                }
                virtual void print(std::ostream &) const = 0;
                std::string to_string() const {
                        std::ostringstream ss;
                        print(ss);
                        return ss.str();
                }
        };

        inline std::ostream &operator<<(std::ostream &os, value::const_ptr v)
        {
                if (v) v->print(os);
                return os;
        }
}

#endif /* GUARD_TLATE_VALUE_HH */