[Interest] Re: Container members in abstract base class?

Jan Kundr√°t jkt at flaska.net
Thu May 23 19:17:26 CEST 2013


On Thursday, 23 May 2013 19:04:53 CEST, Constantin Makshin wrote:
> There's also qgraphicsitem_cast made specifically for casting to classes
> derived from QGraphicsItem.

It is also of very limited value in real world because it does not support inheritance -- it can only cast to the exact type of the item in question.

Suppose you have a hierarchy -- C derives from B which derives from A. A dynamic_cast of a C to all of B and A will succeed, but a qgraphicsitem_cast will return a null pointer when casting a C* into either B* or C*, only succeeding when casting to A*. Depending on what you're looking for, being able to fully utilize the inheritance tree might or might not be important for you.

(Actually, the bits above are a little bit simplified; the casting is performed based on the target class' Type member, so in cases where you e.g. derive from a QGraphicsItemText but forget to provide your own Type value, a cast to QGraphicsItemText will succeed. Of course, you cannot distinguish between a QGraphicsItemText and your own class via qgraphicsitem_cast in this situation.)

Cheers,
Jan

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