144 lines
4.3 KiB
C++
144 lines
4.3 KiB
C++
/*
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FACTORY.hpp - template for object/smart-pointer factories
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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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#ifndef LIB_FACTORY_H
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#define LIB_FACTORY_H
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#include <tr1/memory>
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namespace lib {
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namespace factory {
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/**
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* Wrapping any object created by the Factory into some smart ptr class.
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* The Factory class inherits this functionality, so it can be exchanged
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* independently from the actual object creation behaviour. For example,
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* an Factory implementing some elaborate subclass creation scheme could
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* be instantiated to either produce auto-ptrs or shared-ptrs.
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*/
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template
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< class T, // the product to be created
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class SMP =std::auto_ptr<T> // smart-pointer actually returned
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>
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class Wrapper
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{
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protected:
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SMP wrap (T* product) { return SMP (product); }
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public:
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typedef SMP PType;
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};
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/**
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* Basic Factory Template, for defining flexible Factory classes.
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* These encapsulate the logic for creating of new objects, maybe
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* delegating the memory allocation to the backend layer. Usually,
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* the clients get just a smart-pointer or similar handle to the
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* created object, which will manage the ownership.
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*
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* The provided default implementation uses just std::auto_ptr.
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*/
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template
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< class T, // the product to be created
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class WR = Wrapper<T> // used for fabricating the wrapper
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>
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class Factory : public WR
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{
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public:
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/** Object creating facility.
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* Intended to be over/written/ with a variant taking
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* the appropriate number of parameters and maybe
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* using some special custom allocator.
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* Note: non-virtual.
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*/
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typename WR::PType operator() () { return wrap (new T ); }
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};
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/* -- some example and default instantiations -- */
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using std::tr1::shared_ptr;
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/**
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* a frequently used instantiation of the Wrapper,
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* Utilising the refcounting tr1::shared_ptr.
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*/
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template<class T>
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class Wrapper<T, shared_ptr<T> >
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{
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protected:
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shared_ptr<T> wrap (T* product) { return shared_ptr<T> (product); }
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public:
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typedef shared_ptr<T> PType;
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};
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/**
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* Shortcut: commonly used (partial) instantiation of the Factory,
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* generating refcounting shared_ptr wrapped Objects. Built upon
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* the corresponding special instantiation of the Wrapper template.
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*/
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template<class T>
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class RefcountFac : public Factory<T, Wrapper<T,shared_ptr<T> > >
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{
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public:
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typedef shared_ptr<T> PType;
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};
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/**
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* another convenience instantiation: auto_ptr-to-Impl-Factory.
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* Creating an implementation subclass and wraps into auto_ptr.
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* @warning the TImpl object will typically be destroyed by the
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* smart ptr using an T*, so ~T() needs to be virtual.
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*/
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template
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< class T, // Interface class
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class TImpl // Implementation class to be created
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>
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class PImplFac : public Factory<T, Wrapper<T> >
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{
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public:
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typedef std::auto_ptr<T> PType;
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PType operator() (){ return wrap (static_cast<T*> (new TImpl)); };
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};
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} // namespace factory
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/// @note Factory can be usable as-is (wraps into std::auto_ptr)
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using factory::Factory;
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} // namespace lib
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#endif
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