Visitor.h 11.9 KB
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////////////////////////////////////////////////////////////////////////////////
// The Loki Library
// Copyright (c) 2001 by Andrei Alexandrescu
// This code accompanies the book:
// Alexandrescu, Andrei. "Modern C++ Design: Generic Programming and Design 
//     Patterns Applied". Copyright (c) 2001. Addison-Wesley.
// Permission to use, copy, modify, distribute and sell this software for any 
//     purpose is hereby granted without fee, provided that the above copyright 
//     notice appear in all copies and that both that copyright notice and this 
//     permission notice appear in supporting documentation.
// The author or Addison-Wesley Longman make no representations about the 
//     suitability of this software for any purpose. It is provided "as is" 
//     without express or implied warranty.
////////////////////////////////////////////////////////////////////////////////

// $Header: /cvsroot-fuse/loki-lib/loki/include/loki/Visitor.h,v 1.7 2006/01/16 19:05:09 rich_sposato Exp $

///  \defgroup VisitorGroup Visitor

#ifndef LOKI_VISITOR_INC_
#define LOKI_VISITOR_INC_

#include <iostream>
#include <boost/shared_ptr.hpp>
#include "Typelist.h"
#include "HierarchyGenerators.h"

namespace Loki
{

////////////////////////////////////////////////////////////////////////////////
/// \class BaseVisitor
///  
/// \ingroup VisitorGroup
/// The base class of any Acyclic Visitor
////////////////////////////////////////////////////////////////////////////////

    class BaseVisitor
    {
    public:
        virtual ~BaseVisitor() {}
    };
    
////////////////////////////////////////////////////////////////////////////////
/// \class Visitor
///
/// \ingroup VisitorGroup
/// The building block of Acyclic Visitor
///
/// \par Usage
///
/// Defining the visitable class:
/// 
/// \code
/// class RasterBitmap : public BaseVisitable<>
/// {
/// public:
///     LOKI_DEFINE_VISITABLE()
/// };
/// \endcode
///
/// Way 1 to define a visitor:
/// \code
/// class SomeVisitor : 
///     public BaseVisitor // required
///     public Visitor<RasterBitmap>,
///     public Visitor<Paragraph>
/// {
/// public:
///     void Visit(RasterBitmap&); // visit a RasterBitmap
///     void Visit(Paragraph &);   // visit a Paragraph
/// };
/// \endcode
///
/// Way 2 to define the visitor:
/// \code
/// class SomeVisitor : 
///     public BaseVisitor // required
///     public Visitor<LOKI_TYPELIST_2(RasterBitmap, Paragraph)>
/// {
/// public:
///     void Visit(RasterBitmap&); // visit a RasterBitmap
///     void Visit(Paragraph &);   // visit a Paragraph
/// };
/// \endcode
///
/// Way 3 to define the visitor:
/// \code
/// class SomeVisitor : 
///     public BaseVisitor // required
///     public Visitor<Seq<RasterBitmap, Paragraph>::Type>
/// {
/// public:
///     void Visit(RasterBitmap&); // visit a RasterBitmap
///     void Visit(Paragraph &);   // visit a Paragraph
/// };
/// \endcode
///
/// \par Using const visit functions:
///
/// Defining the visitable class (true for const):
/// 
/// \code
/// class RasterBitmap : public BaseVisitable<void, DefaultCatchAll, true>
/// {
/// public:
///     LOKI_DEFINE_CONST_VISITABLE()
/// };
/// \endcode
///
/// Defining the visitor which only calls const member functions:
/// \code
/// class SomeVisitor : 
///     public BaseVisitor // required
///     public Visitor<RasterBitmap, void, true>,
/// {
/// public:
///     void Visit(const RasterBitmap&); // visit a RasterBitmap by a const member function
/// };
/// \endcode
///
/// \par Example:
///
/// test/Visitor/main.cpp 
////////////////////////////////////////////////////////////////////////////////

    template <class T, typename R = void, bool ConstVisit = false>
    class Visitor;

    template <class T, typename R>
    class Visitor<T, R, false>
    {
    public:
        typedef R ReturnType;
        typedef T ParamType;
        virtual ~Visitor() {}
        virtual ReturnType visit(ParamType&, boost::shared_ptr<BaseVisitor>) = 0;
    };

    template <class T, typename R>
    class Visitor<T, R, true>
    {
    public:
        typedef R ReturnType;
        typedef const T ParamType;
        virtual ~Visitor() {}
        virtual ReturnType visit(ParamType&, boost::shared_ptr<BaseVisitor>) = 0;
    };

////////////////////////////////////////////////////////////////////////////////
// class template Visitor (specialization)
// This specialization is not present in the book. It makes it easier to define
// Visitors for multiple types in a shot by using a typelist. Example:
//
// class SomeVisitor : 
//     public BaseVisitor // required
//     public Visitor<LOKI_TYPELIST_2(RasterBitmap, Paragraph)>
// {
// public:
//     void Visit(RasterBitmap&); // visit a RasterBitmap
//     void Visit(Paragraph &);   // visit a Paragraph
// };
////////////////////////////////////////////////////////////////////////////////

    template <class Head, class Tail, typename R>
    class Visitor<Typelist<Head, Tail>, R, false>
        : public Visitor<Head, R, false>, public Visitor<Tail, R, false>
    {
    public:
        typedef R ReturnType;
       // using Visitor<Head, R>::Visit;
       // using Visitor<Tail, R>::Visit;
    };
    
    template <class Head, typename R>
    class Visitor<Typelist<Head, NullType>, R, false> : public Visitor<Head, R, false>
    {
    public:
        typedef R ReturnType;
        using Visitor<Head, R, false>::Visit;
    };

    template <class Head, class Tail, typename R>
    class Visitor<Typelist<Head, Tail>, R, true>
        : public Visitor<Head, R, true>, public Visitor<Tail, R, true>
    {
    public:
        typedef R ReturnType;
       // using Visitor<Head, R>::Visit;
       // using Visitor<Tail, R>::Visit;
    };
    
    template <class Head, typename R>
    class Visitor<Typelist<Head, NullType>, R, true> : public Visitor<Head, R, true>
    {
    public:
        typedef R ReturnType;
        using Visitor<Head, R, true>::visit;
    };


////////////////////////////////////////////////////////////////////////////////
// class template BaseVisitorImpl
// Implements non-strict visitation (you can implement only part of the Visit
//     functions)
////////////////////////////////////////////////////////////////////////////////

    template <class TList, typename R = void> class BaseVisitorImpl;

    template <class Head, class Tail, typename R>
    class BaseVisitorImpl<Typelist<Head, Tail>, R>
        : public Visitor<Head, R>
        , public BaseVisitorImpl<Tail, R>
    {
    public:
       // using BaseVisitorImpl<Tail, R>::Visit;

        virtual R visit(Head&, boost::shared_ptr<BaseVisitor>)
        { return R(); }
    };
    
    template <class Head, typename R>
    class BaseVisitorImpl<Typelist<Head, NullType>, R>
        : public Visitor<Head, R>
    {
    public:
        virtual R visit(Head&, boost::shared_ptr<BaseVisitor>)
        { return R(); }
    };
    
////////////////////////////////////////////////////////////////////////////////
// class template BaseVisitable
////////////////////////////////////////////////////////////////////////////////

template <typename R, typename Visited>
struct DefaultCatchAll
{
    static R OnUnknownVisitor(Visited&, BaseVisitor&)
    { return R(); }
};

////////////////////////////////////////////////////////////////////////////////
// class template BaseVisitable
////////////////////////////////////////////////////////////////////////////////

	template
    <
        typename R = void,
        bool ConstVisitable = false
    >
    class BaseVisitable;

    template<typename R>
    class BaseVisitable<R, false>
    {
    public:
        typedef R ReturnType;
        virtual ~BaseVisitable() {}
        virtual ReturnType accept(boost::shared_ptr<BaseVisitor>) = 0;
        
    protected: // give access only to the hierarchy

        template <class T>
        static ReturnType acceptImpl(T& visited, boost::shared_ptr<BaseVisitor> guest)
        {
            // Apply the Acyclic Visitor
            if (Visitor<T,R>* p = dynamic_cast<Visitor<T,R>*>(guest.get()))
            {
                return p->visit(visited, guest);
            }
            return R();
        }
    };

    template<typename R>
    class BaseVisitable<R, true>
    {
    public:
        typedef R ReturnType;
        virtual ~BaseVisitable() {}
        virtual ReturnType accept(BaseVisitor&) const = 0;
        
    protected: // give access only to the hierarchy
        template <class T>
        static ReturnType acceptImpl(const T& visited, boost::shared_ptr<BaseVisitor> guest)
        {
            // Apply the Acyclic Visitor
            if (Visitor<T,R,true>* p = dynamic_cast<Visitor<T,R,true>*>(guest.get))
            {
                return p->visit(visited, guest);
            }
            return R();
        }
    };

////////////////////////////////////////////////////////////////////////////////
/// \def LOKI_DEFINE_VISITABLE()
/// \ingroup VisitorGroup
/// Put it in every class that you want to make visitable 
/// (in addition to deriving it from BaseVisitable<R>)
////////////////////////////////////////////////////////////////////////////////

#define LOKI_DEFINE_VISITABLE_BASE() \
    virtual ReturnType accept(boost::shared_ptr<Loki::BaseVisitor> guest) \
    { return acceptImpl(*this, guest); }

#define LOKI_DEFINE_VISITABLE(my_class, my_base) \
    virtual ReturnType accept(boost::shared_ptr<Loki::BaseVisitor> guest) \
    { \
        if (Loki::Visitor<my_class,ReturnType>* p = dynamic_cast<Loki::Visitor<my_class,ReturnType>*>(guest.get())) \
        { \
312
        	std::cout << "HERE" << std::endl; \
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            return p->visit(*this, guest); \
        } \
        else \
        { \
            return my_base::accept(guest); \
        } \
    }

////////////////////////////////////////////////////////////////////////////////
/// \def LOKI_DEFINE_CONST_VISITABLE()
/// \ingroup VisitorGroup
/// Put it in every class that you want to make visitable by const member 
/// functions (in addition to deriving it from BaseVisitable<R>)
////////////////////////////////////////////////////////////////////////////////

#define LOKI_DEFINE_CONST_VISITABLE() \
    virtual ReturnType accept(boost::shared_ptr<::Loki::BaseVisitor> guest) const \
    { return acceptImpl(*this, guest); }

////////////////////////////////////////////////////////////////////////////////
/// \class CyclicVisitor
///
/// \ingroup VisitorGroup
/// Put it in every class that you want to make visitable (in addition to 
/// deriving it from BaseVisitable<R>
////////////////////////////////////////////////////////////////////////////////

    template <typename R, class TList>
    class CyclicVisitor : public Visitor<TList, R>
    {
    public:
        typedef R ReturnType;
        // using Visitor<TList, R>::Visit;
        
        template <class Visited>
        ReturnType GenericVisit(Visited& host)
        {
            Visitor<Visited, ReturnType>& subObj = *this;
            return subObj.visit(host);
        }
    };
    
////////////////////////////////////////////////////////////////////////////////
/// \def LOKI_DEFINE_CYCLIC_VISITABLE(SomeVisitor)
/// \ingroup VisitorGroup
/// Put it in every class that you want to make visitable by a cyclic visitor
////////////////////////////////////////////////////////////////////////////////

#define LOKI_DEFINE_CYCLIC_VISITABLE(SomeVisitor) \
    virtual SomeVisitor::ReturnType accept(SomeVisitor& guest) \
    { return guest.GenericVisit(*this); }

} // namespace Loki

////////////////////////////////////////////////////////////////////////////////
// Change log:
// March     20, ????: add default argument DefaultCatchAll to BaseVisitable
// June      20, 2001: ported by Nick Thurn to gcc 2.95.3. Kudos, Nick!!!
// September 28, 2004: replaced Loki:: with ::Loki:: in DEFINE_VISITABLE
// January    2, 2006: add support for visiting constant member functions, Peter K�mmel
////////////////////////////////////////////////////////////////////////////////

#endif // VISITOR_INC_

// $Log: Visitor.h,v $
// Revision 1.7  2006/01/16 19:05:09  rich_sposato
// Added cvs keywords.
//