122 lines
3.4 KiB
C++
122 lines
3.4 KiB
C++
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/*
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VISITOR.hpp - Acyclic Visitor library
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Copyright (C) CinelerraCV
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2007, Hermann Vosseler <Ichthyostega@web.de>
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This program is free software; you can redistribute it and/or
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modify it under the terms of the GNU General Public License as
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published by the Free Software Foundation; either version 2 of the
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License, or (at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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====================================================================
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This code is heavily inspired by
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The Loki Library (loki-lib/trunk/include/loki/Visitor.h)
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Copyright (c) 2001 by Andrei Alexandrescu
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This Loki code accompanies the book:
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Alexandrescu, Andrei. "Modern C++ Design: Generic Programming
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and Design Patterns Applied".
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Copyright (c) 2001. Addison-Wesley. ISBN 0201704315
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*/
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#ifndef CINELERRA_VISITOR_H
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#define CINELERRA_VISITOR_H
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namespace cinelerra
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{
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namespace visitor
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{
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/** Marker interface / base class for all "visiting tools".
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* When applying such a tool to some concrete instance
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* derived from Visitable, a special function treating
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* this concrete subclass can be selected on the visiting
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* tool instance.
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*/
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class Tool
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{
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public:
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virtual ~Tool () { }; ///< use RTTI for all visiting tools
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};
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/** mixin template to declare that some "visiting tool"
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* wants to treat a concrete subclass of Visitable
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*/
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template
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< class TAR,
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typename RET = void
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>
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class Applicable
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{
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public:
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typedef RET ReturnType;
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/** to be implemented by concrete tools
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* wanting to visit type TAR */
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virtual RET treat (TAR& visitable) = 0;
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};
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/** Marker interface / base class for all types
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* to be treated by a "visiting tool" or visitor.
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*/
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template <typename RET = void>
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class Visitable
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{
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public:
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typedef RET ReturnType;
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protected:
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virtual ~Visitable () { };
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/** @internal used by the DEFINE_VISITABLE macro.
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* Dispatches to the actual operation on the
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* "visiting tool" (acyclic visitor implementation)
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*/
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template <class TAR>
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static RET dispatchOp(TAR& target, Tool& tool)
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{
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if (Applicable<TAR,RET>* concreteTool
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= dynamic_cast<Applicable<TAR,RET>*> (&tool))
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return concreteTool->treat (target);
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else
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return ReturnType();
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}
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};
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/** mark a Visitable subclass as actually treatable
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* by some "visiting tool". Defines the apply-function,
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* which is the actual access point to invoke the visiting
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*/
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#define DEFINE_VISITABLE() \
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virtual ReturnType apply (Tool& tool) \
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{ return dispatchOp (*this, tool); }
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} // namespace visitor
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} // namespace cinelerra
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#endif
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