visitor.h

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/** @file
 *  @author Bram de Greve (bramz@users.sourceforge.net)
 *  @author Tom De Muer (tomdemuer@users.sourceforge.net)
 *
 *  *** BEGIN LICENSE INFORMATION ***
 *  
 *  The contents of this file are subject to the Common Public Attribution License 
 *  Version 1.0 (the "License"); you may not use this file except in compliance with 
 *  the License. You may obtain a copy of the License at 
 *  http://lass.sourceforge.net/cpal-license. The License is based on the 
 *  Mozilla Public License Version 1.1 but Sections 14 and 15 have been added to cover 
 *  use of software over a computer network and provide for limited attribution for 
 *  the Original Developer. In addition, Exhibit A has been modified to be consistent 
 *  with Exhibit B.
 *  
 *  Software distributed under the License is distributed on an "AS IS" basis, WITHOUT 
 *  WARRANTY OF ANY KIND, either express or implied. See the License for the specific 
 *  language governing rights and limitations under the License.
 *  
 *  The Original Code is LASS - Library of Assembled Shared Sources.
 *  
 *  The Initial Developer of the Original Code is Bram de Greve and Tom De Muer.
 *  The Original Developer is the Initial Developer.
 *  
 *  All portions of the code written by the Initial Developer are:
 *  Copyright (C) 2004-2007 the Initial Developer.
 *  All Rights Reserved.
 *  
 *  Contributor(s):
 *
 *  Alternatively, the contents of this file may be used under the terms of the 
 *  GNU General Public License Version 2 or later (the GPL), in which case the 
 *  provisions of GPL are applicable instead of those above.  If you wish to allow use
 *  of your version of this file only under the terms of the GPL and not to allow 
 *  others to use your version of this file under the CPAL, indicate your decision by 
 *  deleting the provisions above and replace them with the notice and other 
 *  provisions required by the GPL License. If you do not delete the provisions above,
 *  a recipient may use your version of this file under either the CPAL or the GPL.
 *  
 *  *** END LICENSE INFORMATION ***
 */

#ifndef LASS_GUARDIAN_OF_INCLUSION_UTIL_VISITOR_H
#define LASS_GUARDIAN_OF_INCLUSION_UTIL_VISITOR_H

namespace lass
{
namespace util
{

class BadVisit: public Exception
{
public:
    BadVisit(const std::string& msg, const std::string& loc): Exception(msg, loc) {}
private:
    LASS_UTIL_EXCEPTION_PRIVATE_IMPL(BadVisit)
};



class LASS_DLL VisitorBase
{
public:
    virtual ~VisitorBase();
protected:
    VisitorBase();
};



template <typename T>
class Visitor
{
public:
    void preVisit(T& visitable)
    {
        doPreVisit(visitable);
    }
    void postVisit(T& visitable)
    {
        doPostVisit(visitable);
    }
private:
    virtual void doPreVisit(T& visitable) = 0;
    virtual void doPostVisit(T& visitable) {}
};



struct ThrowOnUnknownVisit
{
    template <typename T> static void onUnknownPreVisit(VisitorBase& visitor, T& visitable)
    {
        LASS_THROW_EX(BadVisit, "unkown previsit on type '" << typeid(T).name() << "'.");
    }
    template <typename T> static void onUnknownPostVisit(VisitorBase& visitor, T& visitable)
    {
        LASS_THROW_EX(BadVisit, "unkown postvisit on type '" << typeid(T).name() << "'.");
    }
};


struct IgnoreUnknownVisit
{
    template <typename T> static void onUnknownPreVisit(VisitorBase& visitor, T& visitable) {}
    template <typename T> static void onUnknownPostVisit(VisitorBase& visitor, T& visitable) {}
};



template <typename CatchAll = ThrowOnUnknownVisit>
class VisitableBase
{
public:
    virtual ~VisitableBase() {}

    void accept(VisitorBase& visitor) { doAccept(visitor); }

    template <typename T>
    static void preAccept(VisitorBase& visitor, T& visitable)
    {
        if (Visitor<T>* p = dynamic_cast<Visitor<T>*>(&visitor))
        {
            p->preVisit(visitable);
        }
        else
        {
            CatchAll::onUnknownPreVisit(visitor, visitable);
        }
    }

    template <typename T>
    static void postAccept(VisitorBase& visitor, T& visitable)
    {
        if (Visitor<T>* p = dynamic_cast<Visitor<T>*>(&visitor))
        {
            p->postVisit(visitable);
        }
        else
        {
            CatchAll::onUnknownPostVisit(visitor, visitable);
        }
    }

private:

    virtual void doAccept(VisitorBase& visitor) = 0;
};

#define LASS_UTIL_VISITOR_DO_ACCEPT\
    void doAccept(::lass::util::VisitorBase& visitor)\
    {\
        preAccept(visitor, *this);\
        postAccept(visitor, *this);\
    }

}
}

#endif

// EOF