different workaround for void returns than visitor.h
git-svn-id: svn://svn.code.sf.net/p/loki-lib/code/trunk@106 7ec92016-0320-0410-acc4-a06ded1c099a
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MSVC/1200/VisitorOld.h
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MSVC/1200/VisitorOld.h
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////////////////////////////////////////////////////////////////////////////////
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// The Loki Library
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// Copyright (c) 2001 by Andrei Alexandrescu
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// This code accompanies the book:
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// Alexandrescu, Andrei. "Modern C++ Design: Generic Programming and Design
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// Patterns Applied". Copyright (c) 2001. Addison-Wesley.
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// Permission to use, copy, modify, distribute and sell this software for any
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// purpose is hereby granted without fee, provided that the above copyright
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// notice appear in all copies and that both that copyright notice and this
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// permission notice appear in supporting documentation.
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// The author or Addison-Wesley Longman make no representations about the
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// suitability of this software for any purpose. It is provided "as is"
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// without express or implied warranty.
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////////////////////////////////////////////////////////////////////////////////
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// Last update: Feb 23, 2003
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//
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//
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// The original visitor implementation depends heavily on the possibility
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// to return an expression of type "cv void" from a functions with a return
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// type of cv void (6.6.3).
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// Unfortunately the MSVC 6.0 does not allow that. Because I could not think
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// of any transparent workaround I decided to create a set of complete new
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// classes for the void-case.
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// Of course this is a very unattractive solution :-(
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// If you know of a better solution, please let me know.
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//
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// The MSVC 6.0 does not allow void to be a default value for a template parameter.
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// I therefore changed all defaults to int.
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#ifndef VISITOR_INC_
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#define VISITOR_INC_
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#include "Typelist.h"
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#include "HierarchyGenerators.h"
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#include "MSVC6Helpers.h"
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namespace Loki
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{
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////////////////////////////////////////////////////////////////////////////////
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// class template BaseVisitor
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// The base class of any Acyclic Visitor
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////////////////////////////////////////////////////////////////////////////////
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class BaseVisitor
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{
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public:
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virtual ~BaseVisitor() {}
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};
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////////////////////////////////////////////////////////////////////////////////
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// class template Visitor
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// The building block of Acyclic Visitor
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////////////////////////////////////////////////////////////////////////////////
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template <class T, typename R = int/* = void */ >
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class Visitor;
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////////////////////////////////////////////////////////////////////////////////
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// class template Visitor (specialization)
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// This specialization is not present in the book. It makes it easier to define
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// Visitors for multiple types in a shot by using a typelist. Example:
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//
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// class SomeVisitor :
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// public BaseVisitor // required
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// public Visitor<TYPELIST_2(RasterBitmap, Paragraph)>,
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// public Visitor<Paragraph>
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// {
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// public:
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// void Visit(RasterBitmap&); // visit a RasterBitmap
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// void Visit(Paragraph &); // visit a Paragraph
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// };
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////////////////////////////////////////////////////////////////////////////////
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namespace Private
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{
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// helper for Visitor's the left base class
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template <unsigned int ListId>
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struct VisitorImplLeft
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{
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template <class TList, class R>
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struct In
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{
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typedef typename TList::ERROR_WRONG_SPECIALIZATION_SELECTED Result;
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};
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};
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// helper for Visitor's the right base class
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template <unsigned int ListId>
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struct VisitorImplRight
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{
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template <class TList, class R>
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struct In
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{
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typedef typename TList::ERROR_WRONG_SPECIALIZATION_SELECTED Result;
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};
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};
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// simulates specialization
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// class Visitor<Head, R>
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template <>
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struct VisitorImplLeft<TL::Private::NoneList_ID>
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{
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template <class T, class R>
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struct In
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{
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struct Result
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{
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typedef R ReturnType;
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virtual ReturnType Visit(T&) = 0;
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};
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};
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};
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// simulates the left base class for the specialization
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// class Visitor<Typelist<Head, Tail>, R>
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template <>
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struct VisitorImplLeft<TL::Private::Typelist_ID>
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{
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template <class TList, class R>
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struct In
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{
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typedef Visitor<typename TList::Head, R> Result;
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};
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};
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template <>
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struct VisitorImplRight<TL::Private::NoneList_ID>
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{
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template <class TList, class R>
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struct In
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{
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struct Result {};
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};
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};
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// simulates the right base class for the specialization
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// class Visitor<Typelist<Head, Tail>, R>
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template <>
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struct VisitorImplRight<TL::Private::Typelist_ID>
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{
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template <class TList, class R>
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struct In
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{
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typedef Visitor<typename TList::Tail, R> Result;
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};
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};
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template <>
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struct VisitorImplRight<TL::Private::AtomList_ID>
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{
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template <class TList, class R>
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struct In
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{
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struct Result {};
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};
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};
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// MSVC 6.0 will complain if we try to let Visitor inherit
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// directly from VisitorImplLeft/VisitorImplRight
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template <class T, class R>
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struct VisitorImplLeftWrap
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{
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struct Dummy{};
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typedef typename VisitorImplLeft
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<
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TL::Private::IsTypelist<T>::type_id == TL::Private::AtomList_ID ?
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TL::Private::Typelist_ID :
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TL::Private::IsTypelist<T>::type_id
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>::template In<T, R>::Result TempType;
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typedef VC_Base_Workaround<TempType, Dummy> Workaround;
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typedef Workaround::LeftBase Result;
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};
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template <class T, class R>
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struct VisitorImplRightWrap
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{
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struct Dummy{};
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typedef typename VisitorImplRight
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<
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TL::Private::IsTypelist<T>::type_id
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>::template In<T, R>::Result TempType;
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typedef VC_Base_Workaround<TempType, Dummy> Workaround;
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typedef Workaround::LeftBase Result;
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};
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}
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template <class T, typename R>
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class Visitor : public Private::VisitorImplLeftWrap<T, R>::Result,
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public Private::VisitorImplRightWrap<T, R>::Result
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{
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public:
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typedef R ReturnType;
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};
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////////////////////////////////////////////////////////////////////////////////
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// class template BaseVisitorImpl
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// Implements non-strict visitation (you can implement only part of the Visit
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// functions)
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////////////////////////////////////////////////////////////////////////////////
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template <class TList, typename R = int /* = void */ > class BaseVisitorImpl;
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// class for the void-case
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template <class TList> class BaseVisitorImplVoid;
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namespace Private
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{
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template <unsigned int ListTag>
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struct BaseVisitorImplHelper
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{
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template <typename T, typename R>
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struct In
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{
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typedef typename T::ERROR_WRONG_SPECIALIZATION_SELECTED Result;
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};
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};
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template<>
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struct BaseVisitorImplHelper<TL::Private::Typelist_ID>
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{
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template <typename TList, typename R>
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struct In
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{
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typedef typename Loki::Select<
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IsVoid<R>::value,
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BaseVisitorImplVoid<TList>,
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BaseVisitorImpl<TList, R>
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>::Result Result;
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//typedef BaseVisitorImpl<TList, R> Result;
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};
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};
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template<>
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struct BaseVisitorImplHelper<TL::Private::NullType_ID>
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{
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template <typename TList, typename R>
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struct In
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{
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struct Result {};
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};
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};
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template <class T, class R>
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struct BaseVisitorImplWrap
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{
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struct Dummy {};
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typedef typename BaseVisitorImplHelper
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<
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TL::Private::IsTypelist<typename T::Tail>::
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type_id == TL::Private::AtomList_ID ?
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TL::Private::Typelist_ID :
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TL::Private::IsTypelist<typename T::Tail>::type_id
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>::template In<typename T::Tail, R>::Result TempType;
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typedef VC_Base_Workaround<TempType, Dummy> Workaround;
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typedef Workaround::LeftBase Result;
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};
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}
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template <class TList, typename R>
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class BaseVisitorImpl : public Visitor<typename TList::Head, R>,
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public Private::BaseVisitorImplWrap<TList, R>::Result
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{
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ASSERT_TYPELIST(TList);
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public:
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// using BaseVisitorImpl<Tail, R>::Visit;
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virtual R Visit(typename TList::Head&)
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{ return R(); }
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};
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// class for the void-case
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template <class TList>
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class BaseVisitorImplVoid : public Visitor<typename TList::Head, void>,
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public Private::BaseVisitorImplWrap<TList, void>::Result
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{
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ASSERT_TYPELIST(TList);
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public:
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// using BaseVisitorImpl<Tail, R>::Visit;
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virtual void Visit(typename TList::Head&)
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{}
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};
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////////////////////////////////////////////////////////////////////////////////
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// class template DefaultCatchAll
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////////////////////////////////////////////////////////////////////////////////
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template <typename R, typename Visited>
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struct DefaultCatchAll
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{
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static R OnUnknownVisitor(Visited&, BaseVisitor&)
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{ return R(); }
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};
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// template template parameter workaround.
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// use Wrapper-Classes like this to instantiate BaseVisitable
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struct DefaultCatchAllWrapper
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{
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template <class R, class Visited>
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struct In
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{
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typedef DefaultCatchAll<R, Visited> type;
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};
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};
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template <typename R, typename Visited>
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struct DefaultCatchAllVoid
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{
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static R OnUnknownVisitor(Visited&, BaseVisitor&)
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{}
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};
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struct DefaultCatchAllVoidWrapper
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{
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template <class R, class Visited>
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struct In
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{
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typedef DefaultCatchAllVoid<R, Visited> type;
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};
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};
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////////////////////////////////////////////////////////////////////////////////
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// class template NonStrictVisitor
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// Implements non-strict visitation (you can implement only part of the Visit
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// functions)
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////////////////////////////////////////////////////////////////////////////////
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template <class T, class Base>
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struct NonStrictVisitorUnit : public Base
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{
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typedef typename Base::ReturnType ReturnType;
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ReturnType Visit(T&)
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{
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return ReturnType();
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}
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};
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struct NonStrictVisitorUnitWrapper
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{
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template <class T, class B>
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struct In
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{
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typedef NonStrictVisitorUnit<T, B> type;
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};
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};
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template <class TList, typename R = int /* = void */>
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class NonStrictVisitor
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: public GenLinearHierarchy<
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TList,
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NonStrictVisitorUnitWrapper,
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Visitor<TList, R> >
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{
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};
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template <class T, class Base>
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struct NonStrictVisitorUnitVoid : public Base
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{
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typedef void ReturnType;
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ReturnType Visit(T&)
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{
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}
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};
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struct NonStrictVisitorUnitVoidWrapper
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{
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template <class T, class B>
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struct In
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{
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typedef NonStrictVisitorUnitVoid<T, B> type;
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};
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};
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template <class TList>
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class NonStrictVisitorVoid
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: public GenLinearHierarchy<
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TList,
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NonStrictVisitorUnitVoidWrapper,
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Visitor<TList, void> >
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{
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};
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////////////////////////////////////////////////////////////////////////////////
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// class template BaseVisitable
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////////////////////////////////////////////////////////////////////////////////
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template
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<
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typename R = int/* = void */,
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class CatchAll = DefaultCatchAllWrapper
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>
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class BaseVisitable
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{
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public:
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typedef R ReturnType;
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virtual ~BaseVisitable() {}
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virtual ReturnType Accept(BaseVisitor&) = 0;
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protected: // give access only to the hierarchy
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template <class T>
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static ReturnType AcceptImpl(T& visited, BaseVisitor& guest)
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{
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typedef ApplyInnerType2<CatchAll, R, T>::type CatchA;
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// Apply the Acyclic Visitor
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if (Visitor<T>* p = dynamic_cast<Visitor<T>*>(&guest))
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{
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return p->Visit(visited);
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}
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return CatchA::OnUnknownVisitor(visited, guest);
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}
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};
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// class for the void-case
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template
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<
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class CatchAll = DefaultCatchAllVoidWrapper
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>
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class BaseVisitableVoid
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{
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public:
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typedef void ReturnType;
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virtual ~BaseVisitableVoid() {}
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virtual ReturnType Accept(BaseVisitor&) = 0;
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protected: // give access only to the hierarchy
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template <class T>
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static ReturnType AcceptImpl(T& visited, BaseVisitor& guest)
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{
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typedef ApplyInnerType2<CatchAll, void, T>::type CatchA;
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// Apply the Acyclic Visitor
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if (Visitor<T, void>* p = dynamic_cast<Visitor<T, void>*>(&guest))
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{
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p->Visit(visited);
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}
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CatchA::OnUnknownVisitor(visited, guest);
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}
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};
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////////////////////////////////////////////////////////////////////////////////
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// macro DEFINE_VISITABLE
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// Put it in every class that you want to make visitable (in addition to
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// deriving it from BaseVisitable<R>
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////////////////////////////////////////////////////////////////////////////////
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#define DEFINE_VISITABLE() \
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virtual ReturnType Accept(Loki::BaseVisitor& guest) \
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{ return AcceptImpl(*this, guest); }
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#define DEFINE_VISITABLE_VOID() \
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virtual void Accept(Loki::BaseVisitor& guest) \
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{ AcceptImpl(*this, guest); }
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////////////////////////////////////////////////////////////////////////////////
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// class template CyclicVisitor
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// Put it in every class that you want to make visitable (in addition to
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// deriving it from BaseVisitable<R>
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////////////////////////////////////////////////////////////////////////////////
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template <typename R, class TList>
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class CyclicVisitor : public Visitor<TList, R>
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{
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public:
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typedef R ReturnType;
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// using Visitor<TList, R>::Visit;
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template <class Visited>
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ReturnType GenericVisit(Visited& host)
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{
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Visitor<Visited, ReturnType>& subObj = *this;
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return subObj.Visit(host);
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}
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};
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template <class TList>
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class CyclicVisitorVoid : public Visitor<TList, void>
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{
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public:
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typedef void ReturnType;
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// using Visitor<TList, R>::Visit;
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template <class Visited>
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ReturnType GenericVisit(Visited& host)
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{
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Visitor<Visited, ReturnType>& subObj = *this;
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subObj.Visit(host);
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}
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};
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////////////////////////////////////////////////////////////////////////////////
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// macro DEFINE_CYCLIC_VISITABLE
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// Put it in every class that you want to make visitable by a cyclic visitor
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////////////////////////////////////////////////////////////////////////////////
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#define DEFINE_CYCLIC_VISITABLE(SomeVisitor) \
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virtual SomeVisitor::ReturnType Accept(SomeVisitor& guest) \
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{ return guest.GenericVisit(*this); }
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#define DEFINE_CYCLIC_VISITABLE_VOID(SomeVisitor) \
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virtual void Accept(SomeVisitor& guest) \
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{ guest.GenericVisit(*this); }
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} // namespace Loki
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////////////////////////////////////////////////////////////////////////////////
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// Change log:
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// March 20: add default argument DefaultCatchAll to BaseVisitable
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// June 20, 2001: ported by Nick Thurn to gcc 2.95.3. Kudos, Nick!!!
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// Oct 27, 2002: ported by Benjamin Kaufmann to MSVC 6.0
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// Feb 23, 2003: Removed superfluous implementation classes and added Loki::
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// qualification to Accept's Paramter (in the macro) B.K.
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////////////////////////////////////////////////////////////////////////////////
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#endif // VISITOR_INC_
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