Re: basic basic ada question

[Maciej Sobczak <no.spam@no.spam.com>]

Dmitry A. Kazakov wrote:

>>> 1. T's components
>>> 2. S's components
>>> 3. T (Initialize)
>>> 4. S (Initialize)
>>> 5. T'Class
>>>     -- here a class-wide constructor defined for T can safely dispatch to a
>>>     -- some primitive operation overridden by S
>>> 6. S'Class
>>>
>>> [I am not sure about ordering 5 and 6]
>> And I am not sure why do you need 5 and 6 at all - you've already done 
>> the whole job in 3 and 4.
> 
> You cannot dispatch to the procedures of S from Initialize of T, i.e. from
> 3 before 4 is done. S might be unusable. The step 5 is for this purpose.

But why would you need to dispatch to S after step 4?

>> For me 4 should 
>> be the last step and 5,6 should not exist at all.
> 
> Which is indeed a maintenance disaster. Consider GUI interfaces built in
> C++. Note that practically all of them have procedures like OnInit, because
> it is eventually impossible to construct widgets fully functional. Ada
> suffers this as well. For example, it is impossible to embed task
> components. You need special Start/Stop entries in the tasks.

But then, the construction process will involve the interaction with 
other objects and that's why automating all 6 steps above for a single 
object will not necessarily solve the problem. In the case of GUI, you 
might want to construct widgets somewhere between 4 and 5. The 
OnInit-like procedures provide explicit hooks for this.
I any case, if there is a way to get rid of OnInit, I think it should be 
possible without 5 and 6 anyway - possibly with additional objects 
involved instead, but I'd prefer more elaborate collaboration pattern 
(which is explicit in the design) in place of more elaborate 
construction mechanism (which is implicit).


-- 
Maciej Sobczak : http://www.msobczak.com/
Programming    : http://www.msobczak.com/prog/