mapnik/include/mapnik/attribute.hpp

/*****************************************************************************
 * 
 * This file is part of Mapnik (c++ mapping toolkit)
 *
 * Copyright (C) 2006 Artem Pavlenko
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 *
 *****************************************************************************/

//$Id: attribute.hpp 41 2005-04-13 20:21:56Z pavlenko $

#ifndef ATTRIBUTE_HPP
#define ATTRIBUTE_HPP

// boost
#include <boost/any.hpp>
// stl
#include <typeinfo>
#include <sstream>
#include <map>

namespace mapnik {
    template <typename T>
    struct attribute_traits
    {
        static std::string to_string(const T& value)
        {
            std::stringstream ss;
            ss << value;
            return ss.str();
        }
    };

    template <>
    struct attribute_traits<std::string>
    {
        static std::string to_string(const std::string& value)
        {
            return value;
        }
    };
    
    class MAPNIK_DECL attribute
    {	
    public:
        attribute()
            : base_(0) {}

        template <typename T>
        attribute(const T& value)
            : base_(new attribute_impl<T>(value)) 
        {}

        attribute(const attribute& rhs)
            : base_(rhs.base_ ? rhs.base_->clone() : 0)
        {}

        ~attribute() 
        {
            delete base_;
        }

        template<typename T>
        attribute& operator=(const T& rhs)
        {
            attribute(rhs).swap(*this);
            return *this;
        }

        attribute& operator=(const attribute& rhs)
        {
            attribute(rhs).swap(*this);
            return *this;
        }

        bool empty() const
        {
            return !base_;
        }

        const std::type_info & type() const
        {
            return base_ ? base_->type() : typeid(void);
        }

        const std::string to_string() const
        {
            return base_ ? base_->to_string() : "";
        }
    private:
        attribute& swap(attribute& rhs)
        {
            std::swap(base_,rhs.base_);
            return *this;
        }
	
        class attribute_base
        {
        public:
            virtual ~attribute_base() {}
            virtual attribute_base* clone() const=0;
            virtual std::string to_string() const=0;
            virtual const std::type_info& type()  const=0;
        };

        template <typename T,typename ATraits=attribute_traits<T> >
        class attribute_impl : public attribute_base
        {	    
        public:
            typedef T value_type;
            attribute_impl(const value_type& value)
                : value_(value) {}
	    
            virtual std::string to_string() const
            {
                return  ATraits::to_string(value_);
            }
	    
            virtual attribute_base* clone() const
            {
                return new attribute_impl(value_);
            }
            virtual const std::type_info& type() const 
            {
                return typeid(value_);
            }
            value_type value_;
        };
    private:
        template<typename value_type>
        friend value_type* attribute_cast(attribute*);
        attribute_base* base_;
    };
    
    
    template<typename T>
    struct bad_attribute_cast : public std::bad_cast
    {
        virtual const char* what() const throw()
        {
            return "attribute::failed conversion";
        }
    };
    
    template <typename T> 
    bool is_type(const attribute& attr)
    {
        return attr.type()==typeid(T);
    }
    
    template <typename T>
    T* attribute_cast(attribute* attr)
    {
        return attr && attr->type() == typeid(T)
            ? &static_cast<attribute::attribute_impl<T>*>(attr->base_)->value_
            : 0;
    }

    template <typename T>
    const T* attribute_cast(const attribute* attr)
    {
        return attribute_cast<T>(const_cast<attribute*>(attr));
    }
    
    template <typename T>
    T attribute_cast(const attribute& attr)
    {
        using namespace boost;
        typedef BOOST_DEDUCED_TYPENAME remove_reference<T>::type nonref;
        const nonref * result=attribute_cast<nonref>(&attr);
        if (!result)
        {
            throw bad_attribute_cast<T>();
        }
        return *result;
    }
    
    template <typename T>
    T attribute_cast(attribute& attr)
    {
        using namespace boost;
        typedef BOOST_DEDUCED_TYPENAME remove_reference<T>::type nonref;
        nonref * result=attribute_cast<nonref>(&attr);
        if (!result)
            throw bad_attribute_cast<T>();
        return *result;
    }
    
       
    template <typename T>
    attribute attribute_from_string(const std::string& val)
    {
        std::istringstream is(val);
        T t;
        is >> t;
        return attribute(t);
    }

    template <typename charT, typename traits>
    inline std::basic_ostream<charT,traits>& 
    operator << (std::basic_ostream<charT,traits>& out,
                 const attribute& attr)
    {
        out << attr.to_string();
        return out; 
    }
}

#endif //ATTRIBUTE_HPP