wxObjectDataPtr< T > Class Template Reference

#include <wx/object.h>

Detailed Description

template<class T>
class wxObjectDataPtr< T >

This is a 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=nullptr)
	Constructor. More...
	~wxObjectDataPtr ()
	Decreases the reference count of the object to which this class points. More...
T *	get () const
	Gets a pointer to the reference counted object to which this class points. More...
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. More...
T *	release ()
	Release the owned pointer, making caller responsible for decrementing its reference count. More...
	operator unspecified_bool_type () const
	Conversion to a boolean expression (in a variant which is not convertible to anything but a boolean expression). More...
T &	operator* () const
	Returns a reference to the object. More...
T *	operator-> () const
	Returns a pointer to the reference counted object to which this class points. More...
template<typename U >
	wxObjectDataPtr (const wxObjectDataPtr< U > &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. More...
	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. More...
template<typename U >
wxObjectDataPtr< T > &	operator= (const wxObjectDataPtr< U > &tocopy)
	Assignment operator. More...
wxObjectDataPtr< T > &	operator= (const wxObjectDataPtr< T > &tocopy)
	Assignment operator. More...
wxObjectDataPtr< T > &	operator= (T *ptr)
	Assignment operator. More...

Constructor & Destructor Documentation

wxObjectDataPtr() [1/3]

template<class T >

wxObjectDataPtr< T >::wxObjectDataPtr

(

T *

ptr = nullptr

)

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.

wxObjectDataPtr() [2/3]

template<class T >

template<typename U >

wxObjectDataPtr< T >::wxObjectDataPtr

(

const wxObjectDataPtr< U > &

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.

Using U different from T is only supported since wxWidgets 3.1.5.

wxObjectDataPtr() [3/3]

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.

Using U different from T is only supported since wxWidgets 3.1.5.

~wxObjectDataPtr()

template<class T >

wxObjectDataPtr< T >::~wxObjectDataPtr

(

)

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

Member Function Documentation

get()

template<class T >

T* wxObjectDataPtr< T >::get

(

)

const

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

operator unspecified_bool_type()

template<class T >

wxObjectDataPtr< T >::operator unspecified_bool_type

(

)

const

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

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

operator*()

template<class T >

T& wxObjectDataPtr< T >::operator*

(

)

const

Returns a reference to the object.

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

operator->()

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 nullptr, this method will assert in debug mode.

operator=() [1/3]

template<class T >

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

(

const wxObjectDataPtr< T > &

tocopy

)

Assignment operator.

Using U different from T is only supported since wxWidgets 3.1.5.

operator=() [2/3]

template<class T >

template<typename U >

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

(

const wxObjectDataPtr< U > &

tocopy

)

Assignment operator.

Using U different from T is only supported since wxWidgets 3.1.5.

operator=() [3/3]

template<class T >

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

(

T *

ptr

)

Assignment operator.

Using U different from T is only supported since wxWidgets 3.1.5.

release()

template<class T >

T* wxObjectDataPtr< T >::release

(

)

Release the owned pointer, making caller responsible for decrementing its reference count.

This method should be used only for interoperating with the existing code working with raw pointers, typically when returning a raw pointer from a function.

After calling this function, this object becomes invalid, i.e. it doesn't hold any valid pointer value any more.

Since

3.1.4

reset()

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.