refcounted.h

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/***********************************************************************
 Copyright (c) 2007 by Educational Technology Resources, Inc. and
 (c) 2007 by Jonathan Wakely.  Others may also hold copyrights on
 code in this file.  See the CREDITS.txt file in the top directory
 of the distribution for details.

 This file is part of MySQL++.

 MySQL++ is free software; you can redistribute it and/or modify it
 under the terms of the GNU Lesser General Public License as published
 by the Free Software Foundation; either version 2.1 of the License, or
 (at your option) any later version.

 MySQL++ is distributed in the hope that it will be useful, but WITHOUT
 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
 License for more details.

 You should have received a copy of the GNU Lesser General Public
 License along with MySQL++; if not, write to the Free Software
 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
 USA
***********************************************************************/

#if !defined(MYSQLPP_REFCOUNTED_H)
#define MYSQLPP_REFCOUNTED_H

#include <memory>

namespace mysqlpp {

template <class T>
struct RefCountedPointerDestroyer
{
        void operator()(T* doomed) const { delete doomed; }
};



template <class T, class Destroyer = RefCountedPointerDestroyer<T> >
class RefCountedPointer
{
public:
        typedef RefCountedPointer<T> ThisType;  

        RefCountedPointer() :
        counted_(0),
        refs_(0)
        {
        }
        
        explicit RefCountedPointer(T* c) :
        counted_(c),
        refs_(0)
        {
                std::auto_ptr<T> exception_guard(counted_);
                if (counted_) {
                        refs_ = new size_t(1);
                }
                exception_guard.release();      // previous new didn't throw
        }

        RefCountedPointer(const ThisType& other) :
        counted_(other.counted_),
        refs_(other.counted_ ? other.refs_ : 0)
        {
                if (counted_) {
                        ++(*refs_);
                }
        }

        ~RefCountedPointer()
        {
                if (refs_ && (--(*refs_) == 0)) {
                        Destroyer()(counted_);
                        delete refs_;
                }
        }

        ThisType& assign(T* c)
        {
                // The create-temporary-and-swap idiom lets us keep memory
                // allocation in the ctor and deallocation in the dtor so
                // we don't leak in the face of an exception.
                ThisType(c).swap(*this);
                return *this;
        }

        ThisType& assign(const ThisType& other)
        {
                // The create-temporary-and-swap idiom lets us keep memory
                // allocation in the ctor and deallocation in the dtor so
                // we don't leak in the face of an exception.
                ThisType(other).swap(*this);
                return *this;
        }

        ThisType& operator =(T* c)
        {
                return assign(c);
        }

        ThisType& operator =(const ThisType& rhs)
        {
                return assign(rhs);
        }

        T* operator ->() const
        {
                return counted_;
        }       

        T& operator *() const
        {
                return *counted_;
        }       

        operator void*()
        {
                return counted_;
        }

        operator const void*() const
        {
                return counted_;
        }

        T* raw()
        {
                return counted_;
        }

        const T* raw() const
        {
                return counted_;
        }

        void swap(ThisType& other)
        {
                std::swap(counted_, other.counted_);
                std::swap(refs_, other.refs_);
        }       

private:
        T* counted_;

        size_t* refs_;
};


} // end namespace mysqlpp

#endif // !defined(MYSQLPP_REFCOUNTED_H)

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