[Development] Why does QLabel::pixmap() return `const QPixmap*`?

[Knoll Lars]

On 30/11/14 09:35, "Olivier Goffart" <olivier at woboq.com> wrote:

>On Sunday 30 November 2014 06:37:11 Kevin Kofler wrote:
>> Sze Howe Koh wrote:
>> > I'm curious about the rationale behind this API design. I can't think
>> > of any other Qt function that returns an implicitly-shared object by
>> > pointer, so this seems inconsistent. e.g. QWidget::font() returns a
>> > QFont by const-ref.
>> 
>> Probably because the pointer can be null. C++ does not allow null
>> references. (The compiler might let you get away with it, but in
>>principle,
>> it is not allowed.)
>
>That's not the reason because you can return a null pixmap
>(QPixmap::isNull).
>
>I don't know the reason. It was probably always like that
>( http://doc.qt.digia.com/2.3/qlabel.html#a1bd68 )

Exactly that. It’s been like that since Qt 1 times, where QPixmap was a
non shared class you had to instantiate on the heap. We never changed this
accessor for source compatibility reasons (I remember discussing this with
Matthias when we moved from Qt 3 to Qt 4 ;-) ), but I agree it feels very
wrong these days to return a pointer to a pixmap.

Cheers,
Lars


>
>I know that moc has work around for that kind of property so if the
>getter 
>returns a pointer, it can deference it
> 
>
>
>-- 
>Olivier 
>
>Woboq - Qt services and support - http://woboq.com - http://code.woboq.org
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