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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.
+////////////////////////////////////////////////////////////////////////////////
+#ifndef LOKI_VISITOR_INC_
+#define LOKI_VISITOR_INC_
+
+// $Id: Visitor.h 751 2006-10-17 19:50:37Z syntheticpp $
+
+
+///  \defgroup VisitorGroup Visitor
+
+#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&) = 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&) = 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&)
+        { return R(); }
+    };
+    
+    template <class Head, typename R>
+    class BaseVisitorImpl<Typelist<Head, NullType>, R>
+        : public Visitor<Head, R>
+    {
+    public:
+        virtual R Visit(Head&)
+        { 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, 
+        template <typename, class> class CatchAll = DefaultCatchAll,
+        bool ConstVisitable = false
+    >
+    class BaseVisitable;
+
+    template<typename R,template <typename, class> class CatchAll>
+    class BaseVisitable<R, CatchAll, false>
+    {
+    public:
+        typedef R ReturnType;
+        virtual ~BaseVisitable() {}
+        virtual ReturnType Accept(BaseVisitor&) = 0;
+        
+    protected: // give access only to the hierarchy
+        template <class T>
+        static ReturnType AcceptImpl(T& visited, BaseVisitor& guest)
+        {
+            // Apply the Acyclic Visitor
+            if (Visitor<T,R>* p = dynamic_cast<Visitor<T,R>*>(&guest))
+            {
+                return p->Visit(visited);
+            }
+            return CatchAll<R, T>::OnUnknownVisitor(visited, guest);
+        }
+    };
+
+    template<typename R,template <typename, class> class CatchAll>
+    class BaseVisitable<R, CatchAll, 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, BaseVisitor& guest)
+        {
+            // Apply the Acyclic Visitor
+            if (Visitor<T,R,true>* p = dynamic_cast<Visitor<T,R,true>*>(&guest))
+            {
+                return p->Visit(visited);
+            }
+            return CatchAll<R, T>::OnUnknownVisitor(const_cast<T&>(visited), guest);
+        }
+    };
+
+
+////////////////////////////////////////////////////////////////////////////////
+/// \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() \
+    virtual ReturnType Accept(::Loki::BaseVisitor& guest) \
+    { return AcceptImpl(*this, 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(::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
+
+
+
+#endif // end file guardian
+