Why is the constructor of B called?

[Nicholas Wilson via Digitalmars-d-learn]

On Thursday, 24 September 2015 at 11:26:12 UTC, Marc Schütz wrote:
> On Thursday, 24 September 2015 at 01:01:09 UTC, Nicholas Wilson 
> wrote:
>> On Wednesday, 23 September 2015 at 21:25:15 UTC, tcak wrote:
>>> On Wednesday, 23 September 2015 at 21:14:17 UTC, Adam D. 
>>> Ruppe wrote:
>>>> [...]
>>>
>>> Is there any way to prevent this behaviour?
>>>
>>> Quickly checked whether Java acts in the same way. Answer is 
>>> yes.
>>
>> You might be able to swap out the vtbl entry  for a stub call 
>> it and trick the compiler and swap it back, but...
>
> Urgh...
>
> If you can modify the base class, and you really need it, you 
> can check the dynamic type:
>
> class Base {
>     this() {
>         if(!cast(Base) this) return;
>         // do the initialization
>     }
> }
doesn't upcasting always work? iirc only down casting can return 
null.