[Interest] correct d_ptr implementation

[Constantin Makshin]

Right, but:
1) classes derived from DisplayWidget may want to derive their *Private
counterparts from DisplayWidgetPrivate — in this case private section
will make DisplayWidgetPrivate's internals accessible only to this class
itself and its friend DisplayWidget;
2) since not all compilers support "= delete" from C++11, placing an
intentionally-unimplemented constructor[s] and/or assignment operator
into the private section is the most common way to mark them as unavailable.

On 11/11/2013 10:22 PM, andre at familiesomers.nl wrote:
> Constantin Makshin schreef op 11.11.2013 18:33:
>> 1) put your 'd_ptr' into a smart pointer of some kind (usually
>> QScopedPointer), your example leaks memory;
>> 2) placing 'q_ptr' in the public section doesn't make much sense 
>> because
>> it's supposed to be used only by the DisplayWidgetPrivate instance to
>> access its "owner" (DisplayWidget doesn't need any external information
>> to access itself :) );
>> 3) I guess the second "public" section in DisplayWidgetPrivate was
>> supposed to be "private" :) .
>>
>> Other than that, your example looks OK to me.
>>
> How much sense does it make to have a private section in the private 
> DisplayWidgetPrivate class at all? Everything in there is private for 
> DisplayWidgets use anyway, right?
> 
> André
> 
> 
>> On 11/11/2013 06:40 PM, Graham Labdon wrote:
>>> Hi
>>> I am developing a library and in Qt Tradition I want to use the d_ptr
>>> pattern.
>>> I have no previous experience of using this pattern and have a simple
>>> example working but wanted to check that my implementation is correct.
>>> To that end I have set out my classes below and would be grateful if
>>> anyone could confirm that my approach is correct(or not)
>>>
>>> Thanks
>>>
>>> Header file
>>>
>>> #ifndef DISPLAYWIDGET_H
>>> #define DISPLAYWIDGET_H
>>> #include "DisplayWidgetsGlobal.h"
>>> #include <QWidget>
>>>
>>> class DisplayWidgetPrivate;
>>>
>>> class DISPLAYWIDGETS_EXPORT DisplayWidget : public QWidget
>>> {
>>>         Q_OBJECT
>>>
>>> public:
>>>         DisplayWidget(QWidget *parent);
>>>         ~DisplayWidget();
>>>
>>> private:
>>>         DisplayWidgetPrivate* d_ptr;
>>>         Q_DECLARE_PRIVATE(DisplayWidget)
>>> };
>>>
>>> #endif // DISPLAYWIDGET_H
>>>
>>>
>>> Private Header file
>>>
>>> #include "DisplayWidget.h"
>>>
>>> class QLabel;
>>> class DisplayWidgetPrivate
>>> {
>>> public:
>>>         DisplayWidgetPrivate (DisplayWidget* parent);
>>>         void init();
>>>
>>>         QLabel* m_label;
>>>         DisplayWidget* const q_ptr;
>>>         Q_DECLARE_PUBLIC(DisplayWidget)
>>>
>>> public:
>>>         DisplayWidgetPrivate();
>>> };
>>>
>>>
>>> Implementation file
>>>
>>> #include <QLabel>
>>> #include "DisplayWidget.h"
>>> #include "DisplayWidget_p.h"
>>>
>>> DisplayWidgetPrivate::DisplayWidgetPrivate(DisplayWidget* parent)
>>>         : q_ptr(parent)
>>> {
>>>
>>> }
>>>
>>> void DisplayWidgetPrivate::init()
>>> {
>>>         m_label = new QLabel("This is a label",q_ptr);
>>> }
>>>
>>> DisplayWidget::DisplayWidget(QWidget *parent)
>>>         : QWidget(parent),
>>>           d_ptr(new DisplayWidgetPrivate(this))
>>> {
>>>         Q_D(DisplayWidget);
>>>         d->init();
>>> }
>>>
>>> DisplayWidget::~DisplayWidget()
>>> {
>>>
>>> }

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 836 bytes
Desc: OpenPGP digital signature
URL: <http://lists.qt-project.org/pipermail/interest/attachments/20131111/47e859ed/attachment.sig>