COWReference.hpp

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#ifndef BLOCXX_COWREFERENCE_HPP_INCLUDE_GUARD_
#define BLOCXX_COWREFERENCE_HPP_INCLUDE_GUARD_
#include "blocxx/BLOCXX_config.h"
#include "blocxx/COWReferenceBase.hpp"

namespace BLOCXX_NAMESPACE
{

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

   COWReference();

   explicit COWReference(T* ptr);

   COWReference(const COWReference<T>& arg);

   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->();
   
   const T* operator->() const;

   T& operator*();

   const T& operator*() const;

   const T* getPtr() const;

   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;

#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 BLOCXX_CHECK_NULL_REFERENCES
   checkNull(this);
   checkNull(m_pObj);
#endif
   getWriteLock();

   return m_pObj;
}
template<class T>
inline T& COWReference<T>::operator*()
{
#ifdef BLOCXX_CHECK_NULL_REFERENCES
   checkNull(this);
   checkNull(m_pObj);
#endif
   getWriteLock();

   return *(m_pObj);
}
template<class T>
inline const T* COWReference<T>::operator->() const
{
#ifdef BLOCXX_CHECK_NULL_REFERENCES
   checkNull(this);
   checkNull(m_pObj);
#endif

   return m_pObj;
}
template<class T>
inline const T& COWReference<T>::operator*() const
{
#ifdef BLOCXX_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>
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);
      rval.incRef();
   }
   return rval;
}
// 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 BLOCXX_NAMESPACE

#endif   // BLOCXX_COWREFERENCE_HPP_

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