Stroustrup is disappointed with D :(

[Brad Roberts via Digitalmars-d]

On 9/22/15 12:38 PM, Ali Çehreli via Digitalmars-d wrote:
> On 09/22/2015 11:58 AM, Tourist wrote:
>> "D disappointed me so much when it went the Java way".
>> https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#to-do-unclassified-proto-rules
>>
>>
>>
>> It's something about virtual calls, but I didn't understand what he
>> means. What does he mean?
>
> It is about virtual calls in ctors and dtors. Here is the problem:

snip for length

> Although we are in the middle of consructing a D, the call foo() inside B's ctor is dispatched to
> D's virtual foo() even though the D part of the object has not been constructed yet. This is in
> contrast to C++, where the object goes through multiple personalities during its construction: First
> B, then D, etc.
>
> The program above prints
>
> derived
> derived is only now complete
>
> As can be seen, D.foo is called before D is ready for use.
>
> The output of the C++ program:
>
> base
> derived is only now complete
>
> C++'s approach is better from the point of view of correctness. However, it is slower because the
> object's vtbl pointer must be stamped several times during construction. (I am not aware of
> available compiler optimizations there.)
>
> Ali

Keep in mind there's another core difference between c++ and d here and that is: when member 
variables are set their initial values.  In D, it's before any ctors are called for the full object. 
  In c++ they're split into the parts associated with each step in the hierarchy and set as 
effectively line 0 of the ctor (even though syntactically outside the body of the ctor).  These 
differences are subtle, but can be critical for code that's doing what many would say is too much in 
the ctor.