reimplementing an interface in a derived class

Alex sascha.orlov at
Fri Jan 4 22:41:08 UTC 2019

On Friday, 4 January 2019 at 21:08:24 UTC, Ali Çehreli wrote:
> [...]
> In this case, casting is using the B object through it's A 
> interface. The overridden behavior does not change.

Yeah... This was my mistake.

> (Actually, that is possible in languages that support multiple 
> inheritance through multiple virtual function pointer tables 
> (vtbl) but D does not support that.)
> Although I'm getting into implementation details here, I think 
> it helps with understanding the semantics. There is only one 
> vtbl per class object in D and the function entries are all 
> filled in during construction. So, a B object's 'foo' slot in 
> that table is filled with So, such an object can foo() 
> only as a B.

Nice :)

> [...]

> By the way, do you have a use case in mind? Perhaps there are 
> other ways to achieve that.

Well, not really. I was just astonished that casting is not _the_ 
forge tool. Then, I checked, that the type indeed changes and 
wondered why the behavior was still from the object before 

But I assume, as in an A-type an A object, as well as a B object, 
can be stored, and the creation is under my own control - a use 
case would be some corner case... And the default virtual 
definition explains the behavior very well...

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