[vtkusers] A template to avoid calling vtkObjectBase->Delete()

[de Boer Ingo]

Hi,

I did a similar approach based on M$ CAutoPtr class
shipped with the Visual Studio.
I guess, it is better to make it a bit more safe...
Maybe this could be a suggestion for making 
vtkSmartPointer a bit safer ?

The usage is like:

CVtkPtr<vtkAxes> pvtkAxes;
pvtkAxes.Create();
pvtkAxes->SetOrigin(0, 0, 0);

and you can ask for result of create to do something
when the creation fails...

greets
  Ingo

---
Dr.-Ing. Ingo H. de Boer

Polytec GmbH
Polytec-Platz 1-7, 76337 Waldbronn, Germany
phone: ++49 7243 604 106
fax  : ++49 7243 604 255
  
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#ifndef __CVTKPTR__
#define __CVTKPTR__

template< typename T > class CVtkPtr
{
public:
	CVtkPtr() throw() : m_p( NULL )
	{
	}
	
	template< typename TSrc > CVtkPtr( CVtkPtr< TSrc >& p ) throw()
	{
		m_p = p.Detach();  // Transfer ownership
	}
	
	template<> CVtkPtr( CVtkPtr< T >& p ) throw()
	{
		m_p = p.Detach();  // Transfer ownership
	}
	
	explicit CVtkPtr( T* p ) throw() : m_p( p )
	{
	}
	
	~CVtkPtr() throw()
	{
		Free();
	}

	long Create() throw()
	{
		try 
		{
			T *p = T::New();

			if (p == NULL)
				return -1; // E_OUTOFMEMORY;

			Free();
			m_p = p;
			return S_OK;
		}
		catch(...)
		{
			return -1; // E_OUTOFMEMORY;
		};
	}

	// Templated version to allow pBase = pDerived
	template< typename TSrc > CVtkPtr< T >& operator=( CVtkPtr< TSrc >& p ) throw()
	{
		Free();
		Attach( p.Detach() );  // Transfer ownership

		return( *this );
	}
	
	template<> CVtkPtr< T >& operator=( CVtkPtr< T >& p ) throw()
	{
		Free();
		Attach( p.Detach() );  // Transfer ownership

		return( *this );
	}

	operator T*() const throw()
	{
		return( m_p );
	}
	
	T* operator->() const throw()
	{
		ASSERT( m_p != NULL );
		return( m_p );
	}

	// Attach to an existing pointer (takes ownership)
	void Attach( T* p ) throw()
	{
		ASSERT( m_p == NULL );
		m_p = p;
	}
	
	// Detach the pointer (releases ownership)
	T* Detach() throw()
	{
		T* p;

		p = m_p;
		m_p = NULL;

		return( p );
	}
	
	// Delete the object pointed to, and set the pointer to NULL
	void Free() throw()
	{
		if (m_p) m_p->Delete();
		m_p = NULL;
	}

private:
	T* m_p;
};

#endif // __CVTKPTR__