On 15.03.24 18:31, Christian Kandeler via Development wrote:
> On 3/15/24 18:09, Marc Mutz via Development wrote:
>> I like simple rules. "Overrides should have the same access level as the
>> initial virtual function." is a simple rule.
>
> But it makes no sense in general. The base class is the interface, and
> overrides should have the least possible visibility for their purpose.
Let me turn that around and ask you to explain why the specific static
type should matter when calling a virtual function:
MyWidget *myw = new MyWidget; // ¹
QWidget *id = myw;
QObject *obj = wid;
obj->event(e); // OK
wid->event(e); // ERROR: protected
myw-.event(e); // OK, public again
"Normal" functions never behave that way. Why should virtual functions
behave so erratically? Users look at the QObject docs, see that there's a
public event() function and for some reason decide that's the function
to call. QWidget is-a QObject, so by the Liskov Substitution Principle,
you should be able to do anything to a QWidget than you can do to a
QObject. So why can't I call event() on it?
¹ from src/corelib/doc/snippets/events/events.cpp (iow: our docs)
Thanks,
Marc
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Marc Mutz <marc.m...@qt.io>
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