RageUtil_AutoPtr.h

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#ifndef RAGE_UTIL_AUTO_PTR_H
#define RAGE_UTIL_AUTO_PTR_H

/*
 * This is a simple copy-on-write refcounted smart pointer.  Once constructed, all read-only
 * access to the object is made without extra copying.  If you need read-write access, you
 * can get a pointer with Get(), which will cause the object to deep-copy.  (Don't free
 * the resulting pointer.)
 *
 * Note that there are no non-const operator* or operator-> overloads, because that would
 * cause all const access by code with non-const permissions to deep-copy.  For example,
 *
 *   AutoPtrCopyOnWrite<int> a( new int(1) );
 *   AutoPtrCopyOnWrite<int> b( a );
 *   printf( "%i\n", *a );
 *
 * If we have a non-const operator*, this *a will use it (even though it only needs const
 * access), and will copy the underlying object wastefully.  g++ std::string has this behavior,
 * which is why it's important to qualify strings as "const" when const access is desired,
 * but that's brittle, so let's make all potential deep-copying explicit.
 */

template<class T>
class AutoPtrCopyOnWrite
{
public:
        /* This constructor only exists to make us work with STL containers. */
        inline AutoPtrCopyOnWrite()
        {
                m_pPtr = NULL;
                m_iRefCount = new int(1);
        }

        explicit inline AutoPtrCopyOnWrite( T *p )
        {
                m_pPtr = p;
                m_iRefCount = new int(1);
        }

        inline AutoPtrCopyOnWrite( const AutoPtrCopyOnWrite &rhs )
        {
                m_pPtr = rhs.m_pPtr;
                m_iRefCount = rhs.m_iRefCount;
                ++(*m_iRefCount);
        }

        void Swap( AutoPtrCopyOnWrite<T> &rhs )
        {
                swap( m_pPtr, rhs.m_pPtr );
                swap( m_iRefCount, rhs.m_iRefCount );
        }

        inline AutoPtrCopyOnWrite<T> &operator=( const AutoPtrCopyOnWrite &rhs )
        {
                AutoPtrCopyOnWrite<T> obj( rhs );
                this->Swap( obj );
                return *this;
        }

        ~AutoPtrCopyOnWrite()
        {
                --(*m_iRefCount);
                if( *m_iRefCount == 0 )
                {
                        delete m_pPtr;
                        delete m_iRefCount;
                }
        }

        /* Get a non-const pointer.  This will deep-copy the object if necessary. */
        T *Get()
        {
                if( *m_iRefCount > 1 )
                {
                        --*m_iRefCount;
                        m_pPtr = new T(*m_pPtr);
                        m_iRefCount = new int(1);
                }

                return m_pPtr;
        }

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

private:
        T *m_pPtr;
        int *m_iRefCount;
};

template<class T>
inline void swap( AutoPtrCopyOnWrite<T> &a, AutoPtrCopyOnWrite<T> &b )
{
        a.Swap(b);
}

#endif

/*
 * (c) 2005 Glenn Maynard
 * All rights reserved.
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, and/or sell copies of the Software, and to permit persons to
 * whom the Software is furnished to do so, provided that the above
 * copyright notice(s) and this permission notice appear in all copies of
 * the Software and that both the above copyright notice(s) and this
 * permission notice appear in supporting documentation.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT OF
 * THIRD PARTY RIGHTS. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR HOLDERS
 * INCLUDED IN THIS NOTICE BE LIABLE FOR ANY CLAIM, OR ANY SPECIAL INDIRECT
 * OR CONSEQUENTIAL DAMAGES, OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
 * OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
 * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
 * PERFORMANCE OF THIS SOFTWARE.
 */

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