Ichthyostega
5f0c9e209e
this resolves some long standing problems with ambiguous placeholders closes Ticket #161
74 lines
1.9 KiB
C++
74 lines
1.9 KiB
C++
/*
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VISITOR-POLICIES.hpp - Acyclic Visitor library
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Copyright (C) Lumiera.org
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2008, 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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/** @file visitor-policies.hpp
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** Policies usable for configuring the lumiera::visitor::Tool for different kinds of error handling.
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** @see buildertool.hpp for another flavour (calling an catch-all-function there)
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**
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*/
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#ifndef LUMIERA_VISITOR_POLICIES_H
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#define LUMIERA_VISITOR_POLICIES_H
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#include "lib/error.hpp"
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namespace lumiera {
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namespace visitor {
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/**
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* Policy returning just the default return value in case
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* of encountering an unknown Visitor (typically caused by
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* adding a new class to the visitable hierarchy)
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*/
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template<class RET>
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struct UseDefault
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{
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template<class TAR>
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RET
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onUnknown (TAR&)
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{
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return RET();
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}
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};
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/**
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* Policy to throw when encountering an unknown visiting tool
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*/
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template<class RET>
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struct ThrowException
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{
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template<class TAR>
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RET
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onUnknown (TAR&)
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{
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throw lumiera::error::Config("unable to decide what tool operation to call");
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}
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};
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}} // namespace lumiera::visitor
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#endif
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