Template deduction in dynamic_cast

Question

I have a class that is defined as the following:

template <class WidgetType>
class CometWidget : public WidgetType;

Inside a function I am doing this:

dynamic_cast<CometWidget *>(iter2->second.second)->changesCommited_();

and it resolves the CometWidget type, complies and run correctly.
The code runs inside the CometWidget class.
How on earth does this happen?
Why is that so? Should it even compile?

Answer 1

Very interesting indeed. It seems to me like an interesting compiler bug.

It is possible to deduce the correct argument of the CometWidget<> template - just the same way you can deduce template parameters of a function from argument list. If it would be static cast, it would be less surprising.

With dynamic cast, there's little expected to be in common between the source and the target type. So, such "guessing" might have occurred, but then it's not a rightful one.

What compiler is this?

Answer 2

If it's inside the declaration of CometWidget then you don't need to explicitly qualify the template (or whatever term you use to say CometWidget<...>).