20.04.2017 8:47, Ch'Gans пишет:
On 20 April 2017 at 17:03, Igor Mironchik <igor.mironc...@gmail.com> wrote:
Hi,
20.04.2017 7:52, Ch'Gans пишет:
On 20 April 2017 at 16:38, Igor Mironchik <igor.mironc...@gmail.com>
wrote:
Hi,
What the benefits of qobject_cast<> on simple static_cast<>? Or there is
no
qobject_cast
- works only on QObject (obviously)
- returns nullptr if the object cannot be casted to the required type
And it can fail if QObject derived pointer was returned from plugin.
Is this a statement or a question?
if I'm not wrong, qobject_cast relies on QMetaObject
(object->metaObject() and Class::staticMetaObject()).
Actually, i've just checked the sources and qobject_cast<T*>(object)
returns "static_cast<T*>(T::staticMetaObject().cast(object))" and
QMetaObject::cast(obj) returns "(obj &&
obj->metaObject()->inherits(this)) ? obj : nullptr"
QMetaObject allows you to walk the class inheritance hierarchy, and
inherits() does exactly this.
I don't think that the fact that the object comes from a plugin can
make inherits() fail.
If you are able to load the plugin successfully, it means that you
have no unresolved symbols.
Exactly! qobject_cast<> will fail.
Look in application you have:
class Channel
: public QObject
{};
In plugin you have:
class MyChannel
: public Channel
{};
Channel * create();
In application you call:
Channel * ch = create();
And use this object in your application.
Then in one slot in application you can have:
void mySlot()
{
Channel * ch = qobject_cast< Channel* > ( sender() );
// You are 100% sure that sender() is Channel!!!
// And this cast will fail!!!
}
AFAIK, the only problems with plugins is meta-type registration that
has to be done explicitly by calling qRegisterMataType(...);
I don't think that QMetaObject suffers from this. Maybe someone can
confirm this.
- doesn't relies on RTTI, and is way faster than dynamic cast
This is understandable. But with comparison with static cast there are no
benefits?
My point was: dynamic_cast is safer than static_cast, and qobject_cast
is faster than dynamic_cast.
So qobject_cast is a "double win" over static_cast and dynamic_cast.
Chris
Chris
one?
_______________________________________________
Interest mailing list
Interest@qt-project.org
http://lists.qt-project.org/mailman/listinfo/interest
_______________________________________________
Interest mailing list
Interest@qt-project.org
http://lists.qt-project.org/mailman/listinfo/interest
