wxObjectDataPtr< T > Class Template Reference

#include <wx/object.h>

Detailed Description

template<class T>
class wxObjectDataPtr< T >

This is an helper template class primarily written to avoid memory leaks because of missing calls to wxRefCounter::DecRef() and wxObjectRefData::DecRef().

Despite the name this template can actually be used as a smart pointer for any class implementing the reference counting interface which only consists of the two methods T::IncRef() and T::DecRef().

The difference to wxSharedPtr<T> is that wxObjectDataPtr<T> relies on the reference counting to be in the class pointed to, where instead wxSharedPtr<T> implements the reference counting itself.

Below is an example illustrating how to implement reference counted data using wxRefCounter and wxObjectDataPtr<T> with copy-on-write semantics.

Example

class MyCarRefData: public wxRefCounter
{
public:
    MyCarRefData( int price = 0 ) : m_price(price) { }
    MyCarRefData( const MyCarRefData& data ) : m_price(data.m_price) { }

    void SetPrice( int price )  { m_price = price; }
    int GetPrice() const        { return m_price; }

protected:
    int m_price;
};

class MyCar
{
public:
    // initializes this MyCar assigning to the
    // internal data pointer a new instance of MyCarRefData
    MyCar( int price = 0 ) : m_data( new MyCarRefData(price) )
    {
    }

    MyCar& operator =( const MyCar& tocopy )
    {
        // shallow copy: this is just a fast copy of pointers; the real
        // memory-consuming data which typically is stored inside
        // MyCarRefData is not copied here!
        m_data = tocopy.m_data;
        return *this;
    }

    bool operator == ( const MyCar& other ) const
    {
        if (m_data.get() == other.m_data.get())
            return true; // this instance and the 'other' one share the
                         // same MyCarRefData data...

        return (m_data.GetPrice() == other.m_data.GetPrice());
    }

    void SetPrice( int price )
    {
        // make sure changes to this class do not affect other instances
        // currently sharing our same refcounted data:
        UnShare();

        m_data->SetPrice( price );
    }

    int GetPrice() const
    {
       return m_data->GetPrice();
    }

    wxObjectDataPtr<MyCarRefData> m_data;

protected:
    void UnShare()
    {
        if (m_data->GetRefCount() == 1)
            return;

        m_data.reset( new MyCarRefData( *m_data ) );
    }
};

Library:  wxBase

Category:  Runtime Type Information (RTTI), Smart Pointers

See Also

wxObject, wxObjectRefData, Reference Counting, wxSharedPtr<T>, wxScopedPtr<T>, wxWeakRef<T>

Public Member Functions
	wxObjectDataPtr (T *ptr=NULL)
	Constructor.
	wxObjectDataPtr (const wxObjectDataPtr< T > &tocopy)
	This copy constructor increases the count of the reference counted object to which tocopy points and then this class will point to, as well.
	~wxObjectDataPtr ()
	Decreases the reference count of the object to which this class points.
T *	get () const
	Gets a pointer to the reference counted object to which this class points.
void	reset (T *ptr)
	Reset this class to ptr which points to a reference counted object and calls T::DecRef() on the previously owned object.
	operator unspecified_bool_type () const
	Conversion to a boolean expression (in a variant which is not convertable to anything but a boolean expression).
T &	operator* () const
	Returns a reference to the object.
T *	operator-> () const
	Returns a pointer to the reference counted object to which this class points.
wxObjectDataPtr< T > &	operator= (const wxObjectDataPtr< T > &tocopy)
	Assignment operator.
wxObjectDataPtr< T > &	operator= (T *ptr)
	Assignment operator.

Constructor & Destructor Documentation

template<class T >

wxObjectDataPtr< T >::wxObjectDataPtr

(

T *

ptr = NULL

)

Constructor.

ptr is a pointer to the reference counted object to which this class points. If ptr is not NULL T::IncRef() will be called on the object.

template<class T >

wxObjectDataPtr< T >::wxObjectDataPtr

(

const wxObjectDataPtr< T > &

tocopy

)

This copy constructor increases the count of the reference counted object to which tocopy points and then this class will point to, as well.

template<class T >

wxObjectDataPtr< T >::~wxObjectDataPtr

(

)

Decreases the reference count of the object to which this class points.

Member Function Documentation

template<class T >

T* wxObjectDataPtr< T >::get

(

)

const

Gets a pointer to the reference counted object to which this class points.

template<class T >

wxObjectDataPtr< T >::operator unspecified_bool_type

(

)

const

Conversion to a boolean expression (in a variant which is not convertable to anything but a boolean expression).

If this class contains a valid pointer it will return true, if it contains a NULL pointer it will return false.

template<class T >

T& wxObjectDataPtr< T >::operator*

(

)

const

Returns a reference to the object.

If the internal pointer is NULL this method will cause an assert in debug mode.

template<class T >

T* wxObjectDataPtr< T >::operator->

(

)

const

Returns a pointer to the reference counted object to which this class points.

If this the internal pointer is NULL, this method will assert in debug mode.

template<class T >

wxObjectDataPtr<T>& wxObjectDataPtr< T >::operator=

(

const wxObjectDataPtr< T > &

tocopy

)

Assignment operator.

template<class T >

wxObjectDataPtr<T>& wxObjectDataPtr< T >::operator=

(

T *

ptr

)

Assignment operator.

template<class T >

void wxObjectDataPtr< T >::reset

(

T *

ptr

)

Reset this class to ptr which points to a reference counted object and calls T::DecRef() on the previously owned object.