131 lines
3.4 KiB
C++
131 lines
3.4 KiB
C++
/*
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SINGLETON-REF.hpp - helper template providing singleton-like access for implementation code
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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 singleton-ref.hpp
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** Helper for singleton-kind access without managing object creation and lifecycle.
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** A typical usage scenario is when implementing C Language Interfaces without any
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** canonical access to some "this" pointer.
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**
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** @see gui::NotificationService usage example
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*/
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#ifndef LIB_SINGLETON_REF_H
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#define LIB_SINGLETON_REF_H
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#include "lib/error.hpp"
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#include <boost/noncopyable.hpp>
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namespace lib {
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namespace singleton {
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/***************************************
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* Detail/Policy class specifying
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* how the SingletonRef can be accessed
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*/
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template<class TY>
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class AccessAsReference
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: boost::noncopyable
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{
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TY* obj_;
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typedef AccessAsReference<TY> _ThisType;
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public:
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void
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open (TY* instance)
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{
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ASSERT (!obj_, "Lifecycle error");
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obj_ = instance;
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}
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void
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close ()
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{
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ASSERT (obj_, "Lifecycle error");
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obj_ = 0;
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}
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TY*
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operator-> () const
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{
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if (!obj_)
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throw lumiera::error::State("Target currently not available.");
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return obj_;
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}
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typedef TY* _ThisType::*unspecified_bool_type;
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/** implicit conversion to "bool" */
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operator unspecified_bool_type() const // never throws
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{
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return obj_? &_ThisType::obj_ : 0;
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}
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bool operator! () const { return !obj_; }
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};
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} // namespace Singleton
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/*************************************************************
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* Helper template providing singleton access without managing
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* object creation and lifecycle.
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* @param TY the actual type to be made accessible
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* @param B a base class to inherit from; defaults to noncopyable
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* @param Accessor how to implement the static instance access
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*/
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template< class TY
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, class B = boost::noncopyable
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, template<class> class Access = singleton::AccessAsReference
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>
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struct SingletonRef
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: public B
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{
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typedef Access<TY> Accessor;
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Accessor& accessor_;
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SingletonRef(TY * instance, Accessor& acc)
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: accessor_(acc)
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{
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accessor_.open (instance);
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}
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~SingletonRef()
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{
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accessor_.close ();
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}
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};
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} // namespace lib
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#endif
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