OW_COWReference.hpp

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#ifndef OW_COWREFERENCE_HPP_INCLUDE_GUARD_
#define OW_COWREFERENCE_HPP_INCLUDE_GUARD_
#include "OW_config.h"
#include "OW_COWReferenceBase.hpp"

namespace OW_NAMESPACE
{

template<class T>
class COWReference : private COWReferenceBase
{
   public:
      typedef T element_type;

      COWReference();
      explicit COWReference(T* ptr);
      COWReference(const COWReference<T>& arg);
      
      /* construct out of a reference to a derived type.  U should be
      derived from T */
      template <class U>
      COWReference(const COWReference<U>& arg);
      ~COWReference();
      COWReference<T>& operator= (const COWReference<T>& arg);
      COWReference<T>& operator= (T* newObj);
      void swap(COWReference<T>& arg);
      T* operator->();
      T& operator*();
      const T* operator->() const;
      const T& operator*() const;
      const T* getPtr() const;
      bool isNull() const OW_DEPRECATED; // in 3.1.0

      typedef T* volatile COWReference::*safe_bool;
      operator safe_bool () const
         {  return m_pObj ? &COWReference::m_pObj : 0; }
      bool operator!() const
         {  return !m_pObj; }
      
      template <class U>
      COWReference<U> cast_to() const;

        template <class U>
        void useRefCountOf(const COWReference<U>&); 

#if !defined(__GNUC__) || __GNUC__ > 2 // causes gcc 2.95 to ICE
      /* This is so the templated constructor will work */
      template <class U> friend class COWReference;
   private:
#endif
      T* volatile m_pObj;
      void decRef();
      void getWriteLock();
};
template<class T>
inline COWReference<T>::COWReference()
   : COWReferenceBase(), m_pObj(0)
{
}
template<class T>
inline COWReference<T>::COWReference(T* ptr)
   : COWReferenceBase(), m_pObj(ptr)
{
}
template<class T>
inline COWReference<T>::COWReference(const COWReference<T>& arg)
   : COWReferenceBase(arg), m_pObj(arg.m_pObj)
{
}
template<class T>
template<class U>
inline COWReference<T>::COWReference(const COWReference<U>& arg)
   : COWReferenceBase(arg), m_pObj(arg.m_pObj)
{
}
template<class T>
inline COWReference<T>::~COWReference()
{
   try
   {
      decRef();
   }
   catch (...)
   {
      // don't let exceptions escape
   }
}
template<class T>
inline void COWReference<T>::decRef()
{
   typedef char type_must_be_complete[sizeof(T)];
   if (COWReferenceBase::decRef())
   {
      delete m_pObj;
      m_pObj = 0;
   }
}

template<class T>
inline void COWReference<T>::getWriteLock()
{
   if (COWReferenceBase::refCountGreaterThanOne())
   {
      // this needs to happen first to avoid a race condition between 
      // another thread deleting the object and this one making a copy.
      T* tmp = COWReferenceClone(m_pObj);
      // this will decrement the count and then make a new one if we're making a copy.
      if (COWReferenceBase::getWriteLock())
      {
         delete tmp;
      }
      else
      {
         m_pObj = tmp;
      }
   }
}
template<class T>
inline COWReference<T>& COWReference<T>::operator= (const COWReference<T>& arg)
{
   COWReference<T>(arg).swap(*this);
   return *this;
}
template<class T>
inline COWReference<T>& COWReference<T>::operator= (T* newObj)
{
   COWReference<T>(newObj).swap(*this);
   return *this;
}
template <class T>
inline void COWReference<T>::swap(COWReference<T>& arg)
{
   COWReferenceBase::swap(arg);
   COWRefSwap(m_pObj, arg.m_pObj);
}
template<class T>
inline T* COWReference<T>::operator->()
{
#ifdef OW_CHECK_NULL_REFERENCES
   checkNull(this);
   checkNull(m_pObj);
#endif
   getWriteLock();
   
   return m_pObj;
}
template<class T>
inline T& COWReference<T>::operator*()
{
#ifdef OW_CHECK_NULL_REFERENCES
   checkNull(this);
   checkNull(m_pObj);
#endif
   getWriteLock();
   
   return *(m_pObj);
}
template<class T>
inline const T* COWReference<T>::operator->() const
{
#ifdef OW_CHECK_NULL_REFERENCES
   checkNull(this);
   checkNull(m_pObj);
#endif
   
   return m_pObj;
}
template<class T>
inline const T& COWReference<T>::operator*() const
{
#ifdef OW_CHECK_NULL_REFERENCES
   checkNull(this);
   checkNull(m_pObj);
#endif
   
   return *(m_pObj);
}
template<class T>
inline const T* COWReference<T>::getPtr() const
{
   return m_pObj;
}
template<class T>
inline bool COWReference<T>::isNull() const
{
   return (m_pObj == 0);
}
template <class T>
template <class U>
inline COWReference<U>
COWReference<T>::cast_to() const
{
   COWReference<U> rval;
   rval.m_pObj = dynamic_cast<U*>(m_pObj);
   if (rval.m_pObj)
   {
      rval.useRefCountOf(*this);
   }
   return rval;
}
template <class T>
template <class U>
inline void
COWReference<T>::useRefCountOf(const COWReference<U>& arg)
{
    COWReferenceBase::useRefCountOf(arg); 
}
// Comparisons
template <class T, class U>
inline bool operator==(const COWReference<T>& a, const COWReference<U>& b)
{
   return a.getPtr() == b.getPtr();
}
template <class T, class U>
inline bool operator!=(const COWReference<T>& a, const COWReference<U>& b)
{
   return a.getPtr() != b.getPtr();
}
template <class T, class U>
inline bool operator<(const COWReference<T>& a, const COWReference<U>& b)
{
   return a.getPtr() < b.getPtr();
}

template <class T>
inline T* COWReferenceClone(T* obj)
{
   // default implementation.  If a certain class doesn't have clone()
   // (like std::vector), then they can overload this function
   return obj->clone();
}

} // end namespace OW_NAMESPACE

#endif   // OW_COWREFERENCE_HPP_

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