DIP 45 - approval discussion

[Andrei Alexandrescu]

On 11/11/13 10:59 PM, deadalnix wrote:
> On Tuesday, 12 November 2013 at 05:46:19 UTC, Andrei Alexandrescu wrote:
>> On 11/11/13 2:36 PM, Timon Gehr wrote:
>>> On 11/11/2013 11:02 PM, deadalnix wrote:
>>>> On Sunday, 10 November 2013 at 12:39:35 UTC, Timon Gehr wrote:
>>>>> What about Object.factory?
>>>>
>>>> I always though of it as a misfeature.
>>>
>>> Me too.
>>
>> ... well time to substantiate.
>>
>> Andrei
>
> OK, but first, it has to be noted that this is putting the burden of
> proof on the wrong side of the argument.

Well I'm not "burdening", just trying to figure how to do it better.

> So I ran `grep -r * -e 'Object.factory'` on my d folder. I have various
> D project there. The only uses of Object.factory are the test suite of
> dmd, ldc and GDC.

That really proves nothing.

> I have bunch of D code in there, not simply mine. So first thing : it is
> unused.
> Secondly, the only useful things you can do with that require to upcast
> (and break basic OOP principle, which is kind of ironic for a feature
> that produce objects). The design of the feature is unsound.

I think you're wrong here (even after one discounts for 
s/upcast/downcast/). There's no breakage of any basic OOP principle. 
There's no irony. Polymorphic creation aka the factory pattern is a 
classic in object-oriented design. You'd have a bad time arguing against 
it with anyone.

> It is not that surprising as different possible uses case are better
> solved with compile time reflection and metaprograming.

These don't take care of the dynamic case, which is sometimes needed 
(wherever factories are useful: serialization, scripting, ...).

> Implementationwise, this feature require to pull into the application
> some unoptimizable bloat.

This is a good point. But I presume the dedicated code is small in size.

> It is also a tedious constraint for shared objects as we see in this
> thread.

My reading of the thread is that there are concerns about DIP 45 beyond 
support of factories for shared objects.


Andrei